US20140302532A1

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Publication number: US20140302532A1
Application number: US14/111,326
Authority: US
Inventors: David Wilson; John Henrik Zetterber; Kaj Blennow; Jeffrey D. Randall
Original assignee: Quanterix Corp
Current assignee: Quanterix Corp
Priority date: 2011-04-12
Filing date: 2012-04-12
Publication date: 2014-10-09
Also published as: US11275092B2; US20250208150A1; US20220229074A1; US20220244276A1; US20200124620A1; US20170160292A1; US10393759B2; WO2012142301A3; WO2012142301A2

Abstract

The present invention, in some embodiments, generally relates to methods of determining a treatment protocol for and/or a prognosis of a patient's recovery from a brain injury. In some embodiments, the brain injury results from a hypoxic event. In some embodiments, methods are provided for determining a measure of the concentration of tau protein in a patient sample containing or suspected of containing tau protein.

Description

FIELD OF THE INVENTION

The present invention generally relates, in some embodiments, to methods of determining a treatment protocol for and/or a prognosis of a patient's recovery from a brain injury. In some embodiments, the brain injury results from a hypoxic event. In some embodiments, methods are provided for determining a measure of the concentration of tau protein in a patient sample containing or suspected of containing tau protein.

BACKGROUND OF THE INVENTION

A brain injury in a human may be caused by any number of events or conditions. In some cases, a brain injury may be caused by external mechanical force, such as rapid acceleration or deceleration, impact, blast waves, or penetration by a projectile. This type of acquired brain injury is generally known as traumatic brain injury. Another type of acquired brain injury involves biochemical forces, such as oxygen deprivation (hypoxia). Hypoxia generally refers to a deficiency in the amount of oxygen reaching body tissues or a condition of insufficient levels of oxygen in tissue or blood. Oxygen deprivation to the brain results in neuronal damage and death, which is in turn related to the extent of long term brain dysfunction. The concentration of certain biomarkers may become elevated as a result of neuronal damage and death. For example, tau proteins are associated with microtubules and localized in the axonal compartment of neurons. Tau is known to be elevated in the cerebrospinal fluid (CSF) of patients with neurodegenerative disease and head injuries. However, since such biomarkers must diffuse across the blood brain barrier, they may be present in the blood in proportion in extremely low concentrations that are not reliably measurable by typical conventional immunoassays. While the concentration of some biomarkers in the brain and central nervous system are known to increase with hypoxic events, the increased concentration has not been correlated with specific diagnostic indications and/or methods of treatment. In addition, while some methods exist for determining a brain injury in a patient and/or determining a course of treatment following a brain injury, many of the known methods are costly (e.g., magnetic resonance imaging) and/or provide unclear results and/or predictors. Accordingly, improved methods are needed.

SUMMARY OF THE INVENTION

In some embodiments, a method for determining a measure of the concentration of tau protein in a patient sample containing or suspected of containing tau protein is provided comprising performing an assay to determine a measure of the concentration of tau protein in the sample, wherein the limit of detection of tau protein of the assay is less than about 0.2 pg/mL.

In some embodiments, a method of determining a treatment protocol for and/or a prognosis of a patient's recovery from a brain injury is provided comprising performing an assay on a blood sample from the patient and/or plasma and/or serum derived from the blood sample to determine a measure of the concentration of tau protein in the sample; and determining a prognosis of the patient's recovery from the brain injury and/or a method of treatment based at least in part on the measured concentration of tau protein present in the sample.

In some embodiments, a method of determining a treatment protocol for and/or a prognosis of a patient's recovery from a brain injury is provided comprising determining a prognosis of the patient's recovery from the brain injury and/or a method of treatment based at least in part on a measured concentration of tau protein present in a patient sample, wherein the measured concentration has been determined by performing an assay on the patient sample, which comprises a blood sample from the patient and/or plasma and/or serum derived from the blood sample, to determine the measure of the concentration of tau protein in the sample.

In some embodiments, a method for performing an assay and providing data for determining a treatment protocol for and/or a prognosis of a patient's recovery from a brain injury is provided comprising performing an assay on a blood sample from the patient and/or plasma and/or serum derived from the blood sample to determine a measure of the concentration of tau protein in the sample; and providing data from the assay to enable determining a prognosis of the patient's recovery from the brain injury and/or a method of treatment based at least in part on the measured concentration of tau protein present in the sample.

In some embodiments, a method of determining a treatment protocol for and/or a prognosis of a patient's recovery from a brain injury is provided comprising determining a measure of the concentration of tau protein in each of a plurality of samples obtained from the patient following the brain injury; and determining a prognostic of the patient's recovery from the brain injury and/or a method of treatment based at least in part on the measured concentration tau protein present in the sample.

In some embodiments, a method of determining a method of treatment for and/or a prognosis of a patient's recovery from a brain injury is provided comprising (a) performing an assay on each of a plurality of samples obtained from the patient following the brain injury to determine the measured concentration of tau protein in each of the samples, wherein the plurality of samples are obtained from the patient over a period of time of at least about 48 hours; (b) determining the area under the curve of a graph of the tau protein concentration in the plurality of samples versus time, wherein the area is determined for the entire time period and/or for a second peak in the tau protein concentration; and (c) determining a prognosis of the patient's recovery from the brain injury and/or a method of treatment based at least in part on the area under the curve for the entire time period and/or the second peak in the tau protein concentration determined in step (b).

In some embodiments, a method of determining a method of treatment for and/or a prognosis of a patient's recovery from a brain injury is provided comprising determining a prognosis of the patient's recovery from the brain injury and/or a method of treatment based at least in part on the area under the curve of a graph of the tau protein concentration in the plurality of samples versus time, wherein the area is determined for the entire time period and/or for a second peak in the tau protein concentration, which has been determined by (a) performing an assay on each of a plurality of samples obtained from the patient following the brain injury to determine the measured concentration of tau protein in each of the samples, wherein the plurality of samples have been obtained from the patient over a period of time of at least about 48 hours; and (b) determining the area under the curve of a graph of the tau protein concentration in the plurality of samples versus time for the entire time period and/or for a second peak in the tau protein.

In some embodiments, a method for performing an assay and providing data for determining a method of treatment for and/or a prognosis of a patient's recovery from a brain injury is provided comprising (a) performing an assay on each of a plurality of samples obtained from the patient following the brain injury to determine the measured concentration of tau protein in each of the samples, wherein the plurality of samples are obtained from the patient over a period of time of at least about 48 hours; (b) determining the area under the curve of a graph of the tau protein concentration in the plurality of samples versus time, wherein the area under the curve is determined for the entire time period and/or for a second peak in the tau protein concentration; and (c) providing data derived in steps (a) and (b) to enable determining a prognosis of the patient's recovery from the brain injury and/or a method of treatment based at least in part on the area under the curve determined for the entire time period and/or for a second peak in the tau protein concentration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1ais a schematic flow diagram depicting one embodiment of steps (A-D) for performing an exemplary method of the present invention;

FIG. 1bis a schematic flow diagram depicting one embodiment of steps (A-D) for performing an exemplary method of the present invention;

FIG. 2 show plots of serum tau concentrations for numerous patients following resuscitation from cardiac arrest having a-c) a poor outcome and d) a good outcome;

FIG. 3 shows plots of receiver operating characteristics (ROC) curves and areas under the curve values of tau protein concentration versus time for a) the first 24 hours, b) all serial samplings, and c) the secondary tau peak only;

FIG. 4 illustrates six naturally occurring isoforms of tau proteins.

Other aspects, embodiments, and features of the invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings. The accompanying figures are schematic and are not intended to be drawn to scale. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention. All patent applications and patents incorporated herein by reference are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control.

DETAILED DESCRIPTION

The present invention generally relates to methods of determining a treatment protocol for and/or a prognosis of a patient's recovery from a brain injury. In some embodiments, the brain injury may result from a hypoxic event. In some embodiments, methods are provided for determining a measure of the concentration of tau protein in a patient sample containing or suspected of containing tau protein. The subject matter of the present invention involves, in some cases, interrelated products, alternative solutions to a particular problem, and/or a plurality of different uses of one or more systems and/or articles.

In some embodiments, a method of the present invention comprises determining a measure of the concentration of at least one biomarker in one or more samples obtained from a patient following a brain injury. In some embodiments, a method of the present invention comprises determining a measure of the concentration of at least one biomarker in one or more samples obtained from a patient following the brain injury (e.g., optionally resulting from a hypoxic event). A prognostic indication of the patient's recovery and/or determining a course of treatment (e.g., from the brain injury, optionally resulting from a hypoxic event) may be based at least in part on the measure of the concentration of the at least one biomarker present in the one or more samples. It should be understood, that while much of the discussion below is directed to methods involving the analysis of more than one sample, this is by way of example only, and similar methods may be employed wherein only a single sample is employed.

As will be known to those of ordinary skill in the art, the term “hypoxia” generally refers to a deficiency in the amount of oxygen reaching body tissues or a condition of insufficient levels of oxygen in tissue or blood. Hypoxia at a cellular level develops when delivery of oxygen to cell mitochondria slows as the partial pressure gradient from capillaries to tissues decreases. As the delivery of oxygen decreases, aerobic metabolism stops and less efficient anaerobic pathways of glycolysis become responsible for the production of cellular energy. The end result is an increase in cellular concentrations of sodium, calcium, and hydrogen ions which may lead to cell death.

Oxygen deprivation to the brain results in neuronal damage and death. The extent of neuronal damage and death in turn relates to the extent of long term brain dysfunction, as can be assessed using standard criteria (such as Cerebral Performance Category, CPC rating, or like criteria). Severe hypoxia can result in a patient's death and/or an irreversible brain injury (e.g., resulting in the patient being in a vegetative state). Hypoxic events may be global (e.g., due to low oxygen content in the blood) or focused (e.g., affecting only an area of the brain). Causes of hypoxia include, but are not limited to, local asphyxia (e.g., caused by smoke inhalation), carbon monoxide poisoning and/or toxicity, cardiac arrest, choking, drowning, high altitudes, strangulation, an ischemic event, thrombosis, arterial embolism, hemorrhage, swelling of the brain, stroke, physical trauma and/or physical injury (e.g., blunt trauma to the head), arteriosclerosis, and/or atherosclerosis. In some cases, the event may be myocardial infarction, myocardial ischemia, and/or transient ischemic attack.

Hypoxic conditions can lead to the production and/or change in the concentration of certain biomarkers. That is, the concentration of certain biomarkers increase or decrease following the hypoxic event. For example, the production of the proteolytic products of β-amyloid precursor protein has been found to become elevated in the brain and central nervous system under hypoxic condition. The increased concentration is theorized to be due to a hypoxia-inducible factor (HIF-1) that promotes the production of beta-amyloid peptides from amyloid precursor protein, a membrane protein concentrated in neuronal synapses. A cascade of biomarkers, such as tau proteins, is generated in the brain in proportion to the extent of hypoxia. Such biomarkers could in turn diffuse across the blood brain barrier and into the blood in proportion to the extent of hypoxia, and may be generally found in low abundance. The ability to determine a change in the concentration of a biomarker in a plurality of samples (or a single sample) obtained from a patient following a hypoxic event can, in some embodiments, be correlated with a prognostic indication of the patient's recovery from a brain injury and/or used to determine a method of treatment. In some cases, sample(s) of the patient's cerebrospinal fluid (CSF) may be obtained and analyzed to determine the concentration and/or a change in the concentration of the biomarker. In some cases, however, it is advantageous to determine the level of a biomarker in the blood of a patient as compared to CSF, as blood sampling is generally less invasive and may result in fewer complications as compared to CSF sampling. However, many of the biomarkers that are present in the CSF have a slow rate of transmission across and/or a high barrier of transportation across the blood-brain barrier (BBB) and thus, the concentration of the biomarker in the patient's blood may be sufficient lowered as compared to the concentration in CSF to make it difficult or impossible to accurately determine using typically employed conventional immunoassays. Accordingly, assay methods which have very low limits of quantification (LOQ) and/or limits of detection (LOD) are generally necessary to determine a measure of the concentration of a biomarker in the patient's blood to provide statistically significant and/or meaningful results. In some embodiments, the methods of the present invention make use of methods having very low LODs and/or LOQs (e.g., in the low pg/mL range) to determine a measure of the concentration of a biomarker in a sample(s) obtained from a patient following a hypoxic event. Various parameters related to the changes in the concentration of the biomarker in the samples (e.g., blood samples) may be correlated with a prognostic indication and/or a method of treatment following a hypoxic event. Correlations (e.g., between the concentration and prognostic indication(s) and/or between the concentration and method(s) of treatment) have been discovered and/or are now discoverable due to recent advancements in technology which allow for the determination of the low concentrations of biomarkers in bodily fluids with sufficient accuracy and precision, thus allowing for the variations in concentration to be statistically significant and therefore, diagnostic.

It should be noted, that while many of the embodiments described herein focus on brain injuries caused by hypoxic events, this is by no way limiting, and in some embodiments, the brain injury may be caused by other events, for example, traumatic brain injuries wherein the force is such that the skull fractures causing mechanical damage to the brain. In some cases, a traumatic brain injury may be caused by external mechanical force, such as rapid acceleration or deceleration, impact, blast waves, or penetration by a projectile.

In embodiments where a plurality of samples are obtained from a patient, the samples may be obtained from a patient over any suitable period of time. Generally, the period of time may be selected such that the concentration of a biomarker in the samples becomes statistically significant and/or a trend is observable (e.g., an increase and/or decrease in the concentration). For biomarkers which are analyzed in blood samples, the period of time over which a plurality of samples are obtained from the patient may account for any lag time required for the biomarker to cross the BBB. Non-limiting examples of suitable periods of time in which the samples may be obtained from the patient include 1 hour, 2 hours, 3 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 18 hours, 24 hours, 36 hours, 48 hours, 60 hours, 72 hours, 4 days, 5 days, 6 days, 7 days, or more. In some cases, the duration of time of sample collection time is at least 60 hours, or at least 72 hours. In some cases, the duration of time of sample collection is between 12 hours and 7 days, or between 24 hours and 4 days, or between 2 days and 4 days, or between 3 days and 4 days. The first sample may be obtained from the patient without a short timeframe following the brain injury. For example, the first sample may be obtained from the patient within 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 8 hours, 10 hours, or 12 hours of the brain injury. In some cases, the first sample is obtained within 6 hours of the brain injury. In some embodiments, a first sample is obtained from the patient within 6 hours of the suspected brain injury, and at about 1, about 2, about 6, about 12, about 24, about 48, and about 72 hours, following the first sampling. In some embodiments, additional samples are obtained at about 96 and/or at about 108 hours following the first sampling.

Any number of samples (e.g., one or more) may be obtained from the patient over the time period of sample collection. Generally, the minimum number of samples obtained is such that a trend (e.g., an increase or decrease) in the concentration of the biomarker is observable. Non-limiting examples of the number of samples that are obtained from the patient (e.g., during the prescribed collection time) is at least aboutbout 1, about 2, at least about 3, at least about 4, at least abut 5, at least about 6, at least about 7, at least about 8, at least about 9, at least about 10, at least about 12, at least about 15 or more. In some cases, the number of samples obtained from the patient is between 2 and 20, between 5 and 15, or between 5 and 10.

The sample(s) obtained from the patient may be from any suitable bodily source. In some cases, the samples are CSF fluid samples. In some cases, the samples are not CSF fluid samples. In some cases, the samples are blood or blood products (e.g., whole blood, plasma, serum, etc.). In other cases, the samples may be urine or saliva samples. In some embodiments, the samples may be analyzed directly (e.g., without the need for extraction of the biomarker from the fluid sample) and/or with dilution (e.g., addition of a buffer or agent to the sample). Generally, each of the samples obtained from the patient is collected using substantially similar procedures (e.g., to ensure minimal variation between samples based on sample collection methods). Those of ordinary skill in the art will be aware of suitable systems and methods for obtaining a sample from a patient.

Each of or substantially all of the samples may be analyzed using an assay method (e.g., as described herein) to determine a measure of the concentration of at least one biomarker in each, a subset of or substantially all of the samples. In some cases, the methods comprise determining a measure of the concentration of a single biomarker in the samples. In other cases, a method comprises determining a measure of the concentration of more than one biomarker in each, a subset of or substantially all of the samples. For example, a measure of the concentration of 2, 3, 4, 5, 6, 7, 8, 9, 10, or more, biomarkers may be determined in the samples.

In some embodiments, the methods of the present invention comprise determining a prognostic indication based at least in part on the measured concentration of the at least one biomarker in the samples. In some cases, the prognostic indication may be correlated with standard criteria employed to define long-term brain dysfunction and/or injury. Those of ordinary skill in the art will be aware of such criteria, for example, cerebral performance category ratings (“CPC rating”), or more specifically, Glasgow-Pittsburgh cerebral performance category ratings (or scale) (e.g., see Teasdale G, Jennett B (1974);Assessment of coma and impaired consciousness; Lancet 2 (7872): 81-84). The CPC scale ranges from 1 to 5, with 1 representing a slight possibility of neurological deficit and 5 representing severe deficit and/or death. In some methods of the present invention, the prognostic indication of the patient's recovery from the brain injury is classified as either “good” (e.g., correlating to a CPC score of 1 or 2) corresponding to a high likelihood of recovery and/or returning to independent living, or “poor” (e.g., correlating to a CPC score of 3, 4, or 5) corresponding to little possibility of a full recovery and resulting in assisted living and/or death.

In the CPC scale, a rating of 1 is generally classified as good cerebral performance. The patient is conscious and alert, is able to work, but may have mild neurological or psychological deficit. A rating of 2 is generally classified as having moderate cerebral disability. The patient is conscious and has sufficient cerebral function for independent activities of daily life, and is generally able to work in sheltered environment. A rating of 3 corresponds to severe cerebral disability. While the patient is conscious, they generally depend on others for daily support because of impaired brain function. The patient may have abilities ranging from ambulatory state to severe dementia or paralysis. A rating of 4 corresponds to a coma or vegetative state. The patient is generally unaware, even if they appear awake (e.g., the patient is in a vegetative state) without interaction with environment and is cerebral unresponsive. A rating of 5 refers to brain death, associated with apnea, areflexia, and/or EEG silence. The CPC scale is summarized in Table 1.

TABLE 1

CPC Scale Summary

CPC
Score	Description


1	Conscious and alert with normal function or onlyslight disability
2	Conscious and alert withmoderate disability
3	Conscious withsevere disability
4	Comatose or persistentvegetative state
5	Brain dead or death from other causes

Other non-limiting examples of suitable criteria include the “scale g” criteria (e.g., see Dekaban A S, Robinson C E.; Application of a new rating scale of brain dysfunction to monitoring rehabilitation in 65 patients with severe head injury, Bull Clin Neurosci., 1984; 49, 82-92), the “Rancho Los Amigos Scale,” and the “Disabilities Rating Scale.”

In addition to the biomarkers specifically mentioned herein, those of ordinary skill will be aware of other suitable biomarkers to use in connection with the methods described herein. As described herein, the biomarker generally undergoes a change in concentration as a result of a hypoxic event. For example, the concentration of the biomarker may increase or decrease as a result of the brain injury. Non-limiting examples of biomarkers include neuron specific neuronal enolase (NSE), β-site aPP-cleaving enzyme 1 (BACe1), S100B, myelin basic protein (MBP), growth associated protein 43, glutamine synthetase, glial fibrillary acid protein (GFAP), glycine transporter (e.g., GLYT1, GLYT2), neuron specific glycoprotein (e.g., GP50), calpain, neurofibrillary protein, heat shock protein 72, beta-amyloid precursor proteins, calbindin D-28K, proteolipid protein, myeline associated glycoprotein, neurofilament H, creatine kinase protein (e.g., CK-BB), tau proteins (including phosphorylated taus such as p-tau-81 or p-tau-231), and endothelium membrane proteins (e.g., thrombomodulin).

In some cases, the biomarker is a tau protein. Various forms and/or combinations of tau proteins may be contemplated for use as a target biomarker with the methods described herein, include isoforms and short isoforms, for example, ranging from tau 23 (352a.a, “0N3R”, wherein R indicates the number of repeats and N indicates the number or amino terminal inserts, as will be understood by those of ordinary skill in the art) to tau 40 (441a.a, “2N4R”). There are six known naturally-occurring tau proteins, the sequences of which are well known in the art. The six tau proteins include tau 23 (352, 0N3R), tau 24 (383, 0N4R), tau 37 (381, 1N3R), tau 34 (412, 1N4R), tau 39 (410, 2N3R), tau 40 (441, 2N4R), and/or combinations thereof (e.g., seeFIG. 4). In some cases, at least some of the tau proteins may be phosphorylated.

Those of ordinary skill in the art will understand that determination of a biomarker in a sample may comprise determining the concentration a single isoform of a biomarker, or alternatively, may comprise determining the concentration of a plurality of isoforms of the biomarker. For example, with respect to tau proteins, in some cases, the concentration of tau protein employed in the algorithms and methods described herein may be the concentration of a single isoform of tau protein in the sample, or alternatively, the concentration of tau protein employed in the algorithms and methods described herein may be the concentration of a plurality of forms of tau proteins in the sample.

The plurality of samples obtained from the patient may be analyzed (e.g., using an assay method as described herein) to determine a measure of the concentration of the at least one biomarker in each of the samples (or a single sample). A prognostic indication and/or a method of treatment may be determined based at least in part on the measure of the concentration of the biomarker in each of the plurality of samples. The data may be analyzed using a variety of techniques, as described herein, and a prognostic indication for recovery from a brain injury (e.g., a “good” outcome or a “poor” outcome), or a specific method of treatment may be determined based on the results.

In some embodiments, the measure of the concentration of the at least one biomarker for each of the plurality of samples obtained from the patient may be plotted on a graph of concentration versus time (e.g., in hours), and one or more parameters can be obtained from the graph and used to determine the method of treatment and/or the prognostic indication. Non-limiting examples of parameters that may be determined and/or employed include baseline biomarker concentration, increase in biomarker concentration, duration of rise of biomarker concentration, maximum slope of increasing biomarker concentration, rate of change of biomarker concentration, area under the curve and/or magnitude of the fold increase of biomarker concentration. Each of the parameters and their determination will now be described in detail, followed by a description of possible data analysis and methods useful or potentially useful to determine suitable correlations between the measure of the concentration determined in the samples and a treatment/prognostic indication. The measure of the concentration of the biomarker may be determined/displayed in any suitable unit. In some cases, the measure of the concentration is determined/displayed in pg/mL.

The term “baseline biomarker concentration” refers to the concentration of the biomarker generally present in a fluid sample from a normal patient (e.g., prior to or unexposed to a hypoxic event). The baseline biomarker concentration can be determined using a variety of methods which will be commonly known and understood by those of ordinary skill in the art. In some cases, the baseline biomarker concentration can be determined by averaging the value of a biomarker present in a population of control patients (e.g., patients who have not experienced a hypoxic event). This may be useful in embodiments where the baseline concentration of the biomarker is substantially the same for a given population of individuals (e.g., based on age, gender, medical condition, etc.). However, many of the methods described herein require accurate determination of extremely low concentrations of the at least one biomarker in samples obtained from a patient, and accordingly, a general baseline concentration of a biomarker (e.g., based on a sampling of a population) may not provide enough accuracy and/or precision to give useful results. Accordingly, a measure of the baseline biomarker concentration, in some embodiments, may be determined for each individual patient. In some embodiments, the baseline biomarker concentration may be set to zero, e.g., in embodiments where the concentration of the biomarker is zero or essentially zero in normal patients.

In some cases, the baseline biomarker concentration for each individual is equal to the measure of the concentration of the biomarker in the first sample obtained from the patient following the hypoxic event. In other cases, if available, a baseline biomarker concentration is the measure of the concentration of the biomarker present in a sample obtained from the patient prior to the hypoxic event. In yet other cases, the baseline biomarker concentration is the average concentration of the biomarker determined in a plurality of samples taken from the patient immediately or substantially immediately following the hypoxic event (e.g., prior to the concentration of the biomarker increasing due to the hypoxic event). That is, the concentration of the biomarker in the plurality of samples obtained from the patient in a selected time period following the hypoxic event may be averaged to determine the baseline biomarker concentration for that patient. As will be understood by those of ordinary skill in the art, in such cases, any sample which has a concentration level that significantly differs from the other concentration levels during that period of time (e.g., a data point/outlier having a concentration which deviates significantly from the other concentrations measured during the time frame) may be excluded from the averaging calculation. In some cases, if a sample has a concentration which differs by greater than about 50% from the calculated average, that sample may be excluded from the averaging calculation. In some cases, if a sample has a concentration which differs by more than about 0.5 pg/mL, about 1 pg/mL, about 2 pg/mL, about 5 pg/mL, or about 10 pg/mL from the calculated average, that sample may be excluded from the averaging calculation. An anomalous data point may be observed and/or caused by administration of drugs to the patient. The baseline biomarker concentration may be determined by averaging the concentration of the biomarker in the samples obtained from the patient between the first sample (e.g., obtained within 6 hours of the hypoxic event) and 24 hours following the first collection of a sample, or between the first sample and 18 hours following the first collection of a sample, or between the first sample, and 12 hours following the first collection of a sample, or between the first sample, and 6 hours following the first collection of a sample (e.g., not including any outliers).

The term “area under the curve,” (or AUC) is a common parameter used to analyze data, and such calculations will be well known and understood by those of ordinary skill in the art. In context with the methods of this disclosure, the AUC refers to the area under the biomarker concentration versus time curve. Generally the calculation takes into account the baseline biomarker concentration. Those of ordinary skill it the art will be aware of suitable algorithms and/or computer programs capable of determining the area under the curve for a selected set of data. In some cases, the area under the curve may be determined for more than one portion of the data. For example, a first area under the curve value may be determined for a first range of data, and a second area under the curve value may be determined for a second range of data. The first and the second ranges of data may or may not be overlapping (e.g., may comprise some overlapping data points or may comprise different data points). It should be understood, that determining the area under the curve can be accomplished using a variety of techniques which will be known to those of ordinary skill in the art, including but not limited to, plotting the concentration versus time on a graph and determining the area under the line/curve (e.g., optionally with use of a computer program) and/or determining a functional relationship between the concentration and time and integrating the data without requiring physically plotting or drawing of a graph. As used herein, the phrase “determining the area under the curve of a graph of a biomarker concentration versus time” covers all of the above techniques and others applicable for determining the area or equivalent, and is not limited to physically or electronically plotting the concentration versus time on a graph and determining the area under the line/curve.

The term “magnitude of the fold increase of biomarker concentration” refers to the magnitude of the fold-increase in concentration over the duration of sample collection, and may be calculated by dividing the maximum biomarker concentration (e.g., as described herein) by the baseline biomarker concentration (e.g., as described herein).

The term “duration of rise of biomarker concentration” refers to the time over which the concentration of the biomarker is increasing during the time period over which the samples are collected. In some cases, the duration of rise of biomarker concentration can be determined by subtracting the time at which the last sample was collected at approximately the baseline biomarker concentration (e.g., starting time of the rise) from the time at which the maximum biomarker concentration was observed (e.g., ending time of the rise). That is, the duration of the rise may be equal to the ending time of the rise minus the starting time of the rise. The duration of rise is generally provided in hours.

The term “maximum slope of increasing biomarker concentration” refers to the slope at which the maximum increase in concentration occurred over the time period in which the samples were collected. Those of ordinary skill will be aware of methods to calculate this value using common graphical analysis methods. For example, a plot may be prepared showing concentration versus time, and the maximum slope may be calculated based on this plot. In some cases, the maximum slope is equal to the slope between two data points, whereas in other cases, the maximum slope may be determined based on the average slope between a plurality of data points.

The above parameters, alone or in combination, may be correlated to a prognostic indication and/or a method of treatment for a patient following a brain injury (e.g., caused by a hypoxic event). Following determination of a correlation between biomarker concentrations and a prognostic indication and/or a method of treatment (e.g., using a plurality of samples obtained from a plurality of test patients with known outcomes), the correlation can be used in connection with methods to determine prognosis (e.g., prognostic indications) and/or methods of treatment for patients with unknown outcomes. That is, an algorithm can be developed relating changes in a biomarker concentration and specific methods of treatment and/or prognostic indications using samples from test patients having been subject to known methods of treatment and/or having a known prognosis. Once the algorithm has been developed, it can be used to determine methods of treatment and/or prognostic indications for patients with unknown outcomes.

To determine a correlation between a biomarker and a prognostic indication and/or a method of treatment (e.g., to develop an algorithm relating the measured biomarker concentration to preferred methods of treatment and/or prognostic indications), a plurality of samples from a plurality of test patients may be obtained. A “test patient” is a patient who has a known outcome (e.g., a good or a poor CPC score) and/or has received a certain treatment. The plurality of the samples obtained from each of the test patients may be analyzed to determine the measure of the concentration of at least one biomarker in the each of the samples. Some or all of the parameters described herein may be determined for each patient, and the data may be analyzed to determine correlations between the parameters and the patient outcomes and/or treatments, which can in turn be used to develop an algorithm. The algorithm may then be applied to the concentration of the at least one biomarker in samples obtained from a patient having an unknown outcome to determine a method of treatment and/or a prognostic indication for that patient. A specific example of such an analysis is described below, and further details are provided in Example 1.

A therapeutic agent is generally administered in an amount effective to provide a medically desirable result. The effective amount will vary with the particular condition being treated, the age and physical condition of the subject being treated, the severity of the condition, the duration of the treatment, the nature of the concurrent therapy (if any), the specific route of administration and the like factors within the knowledge and expertise of the health care practitioner. In some cases, a therapeutic agent may reduce brain injuries resulting from the hypoxic event. In some cases, the method of treatment may involve a change in treatment, such as an increase or decrease in the dose of a therapeutic agent, a switch from one therapeutic agent to another therapeutic agent, an addition of another therapeutic agent to the existing therapeutic agent, or a combination thereof. A switch from one therapeutic agent to another may involve a switch to a therapeutic agent with a high risk profile but where the likelihood of expected benefit is increased.

In one embodiment, a correlation was determined between certain parameters (e.g., area under the curve of a plot of tau protein concentration versus time) and a good (e.g.,CPC rating 1 or 2) or a poor (e.g., CPC rating of 3, 4, or 5) prognostic indication. To determine the correlation, an assay was carried out on each of the samples obtained from a plurality of test patients having undergone a brain injury (e.g., resulting from a hypoxic event) (e.g., patients having a known outcome and/or having undergone a certain method of treatment following a brain injury). The first sample was taken within 6 hours of the brain injury (e.g., resulting from a hypoxic event), and additional samples were generally obtained at about 1, 2, 6, 12, 24, 48, and 72 hours following the first sample (and optionally, at 96 and/or 108 hours). Each of the test patients had a known prognostic outcome according to the CPC scale. For each test patient, a plot of the measured concentration of tau protein in pg/mL time in hours was prepared. The data was analyzed and the area under the curve of the tau protein concentration (in pg/mL) versus time (in hours) was determined for a variety of time ranges, and was determined to correlate with a “good” or “poor” prognosis for the patients. In some embodiments, the plot of the concentration of the tau protein versus time showed two peaks, one occurring mostly in the first 24 hours following the hypoxic event, and one occurring at some point following the first 24 hours following the hypoxic event. Thus, the area under the curve was determined for each patient for three ranges of time: 1) for the entire duration of the data collection, 2) for the first 24 hours, and 3) for the second peak in tau protein concentration (if present). Generally, the baseline used to determine the area under the curve for 1) and 2) was set to zero, whereas the baseline used to determine the area under the curve for 3) was set as the concentration of tau protein determined at the beginning of the rise of the second peak. For the total area under the curve, a value of greater than about 800 correlated with a poor prognosis (e.g., a CPC score of 3, 4, or 5) and a value of less than about 800 correlated with a good prognosis (e.g., a CPC score of 1 or 2). For the area under the curve of the second peak, a value of greater than about 500 correlated with a poor prognosis (e.g., a CPC score of 3, 4, or 5) and a value of less than about 500 correlated with a good prognosis (e.g., a CPC score of 1 or 2). Accordingly, a correlation/algorithm was established between the varying parameters relating to concentration and a prognostic indication.

The developed correlation/algorithm can be applied to patients with unknown outcomes. That is, samples may be obtained from a patient and the concentration of tau protein in each of the samples can be determined. The data may be analyzed to determine the total area under the curve and/or the area under the curve of the second tau protein peak. If the sum of the total area under the curve and/or the area under the curve of the second peak is greater than 800 or 500, respectively, the prognostic indication for that patient is “poor,” and if the sum is less than 800 or 500, respectively, the prognostic indication is “good.” Using similar techniques, a variety of correlations may be determined for this tau protein (e.g., increase in tau protein concentration, duration of the increase of tau protein concentration, and/or the magnitude of the fold increase of tau protein) and/or other biomarkers.

Exemplary Assay Methods and Systems

Those of ordinary skill in the art will be aware of a variety of assay methods and systems that may be used in connection with the methods of the present invention. Generally, the methods employed have low limits of detection and/or limits of quantification as compared to bulk analysis techniques (e.g., ELISA methods). The use of assay methods that have low limits of detection and/or limits of quantification allows for correlations to be made between the various parameters discussed above and a method of treatment and/or diagnostic indication that may otherwise not be determinable and/or apparent. For example, in the method described above which correlates the total area under the curve and/or the area under the curve of a second peak of tau protein concentration to a prognostic indication of brain injury, the limits of detection, and/or limits of quantification needs to be substantially lower than the LOD and/or LOQ provided by common ELISA techniques.

The terms “limit of detection” (or LOD) and “limit of quantification” (or LOQ) are given their ordinary meaning in the art. The LOD refers to the lowest analyte concentration likely to be reliably distinguished from background noise and at which detection is feasible. The LOD as used herein is defined as three standard deviations (SD) above background noise. The LOQ refers to the lowest concentration at which the analyte can not only be reliably detected but at which some predefined goals for bias and imprecision are met. Generally, as is used herein, the LOQ refers to the lowest concentration above the LOD wherein the coefficient of variation (CV) of the measured concentrations less than about 20%.

In some embodiments, an assay method employs a step of spatially segregating biomarker molecules into a plurality of locations to facilitate detection/quantification, such that each location comprises/contains either zero or one or more biomarker molecules. Additionally, in some embodiments, the locations may be configured in a manner such that each location can be individually addressed. In some embodiments, a measure of the concentration of biomarker molecules in a fluid sample may be determined by detecting biomarker molecules immobilized with respect to a binding surface having affinity for at least one type of biomarker molecule. In certain embodiments the binding surface may form (e.g., a surface of a well/reaction vessel on a substrate) or be contained within (e.g., a surface of a capture object, such as a bead, contained within a well) one of a plurality of locations (e.g., a plurality of wells/reaction vessels) on a substrate (e.g., plate, dish, chip, optical fiber end, etc.). At least a portion of the locations may be addressed and a measure indicative of the number/percentage/fraction of the locations containing at least one biomarker molecule may be made. In some cases, based upon the number/percentage/fraction, a measure of the concentration of biomarker molecules in the fluid sample may be determined. The measure of the concentration of biomarker molecules in the fluid sample may be determined by a digital analysis method/system optionally employing Poisson distribution adjustment and/or based at least in part on a measured intensity of a signal, as will be known to those of ordinary skill in the art. In some cases, the assay methods and/or systems may be automated.

Certain methods and systems which employ spatially segregating analyte molecules (e.g., biomarkers) are known in the art, and are described in U.S. Patent Application Publication No. US-2007-0259448 (Ser. No. 11/707,385), filed Feb. 16, 2007, entitled “METHODS AND ARRAYS FOR TARGET ANALYTE DETECTION AND DETERMINATION OF TARGET ANALYTE CONCENTRATION IN SOLUTION,” by Walt et al.; U.S. Patent Application Publication No. US-2007-0259385 (Ser. No. 11/707,383), filed Feb. 16, 2007, entitled “METHODS AND ARRAYS FOR DETECTING CELLS AND CELLULAR COMPONENTS IN SMALL DEFINED VOLUMES,” by Walt et al.; U.S. Patent Application Publication No. US-2007-0259381 (Ser. No. 11/707,384), filed Feb. 16, 2007, entitled “METHODS AND ARRAYS FOR TARGET ANALYTE DETECTION AND DETERMINATION OF REACTION COMPONENTS THAT AFFECT A REACTION,” by Walt et al.; International Patent Publication No. WO 2009/029073 (International Patent Application No. PCT/US2007/019184), filed Aug. 30, 2007, entitled “METHODS OF DETERMINING THE CONCENTRATION OF AN ANALYTE IN SOLUTION,” by Walt et al.; U.S. Patent Application Publication No. US-2010-0075862 (Ser. No. 12/236,484), filed Sep. 23, 2008, entitled “HIGH SENSITIVITY DETERMINATION OF THE CONCENTRATION OF ANALYTE MOLECULES OR PARTICLES IN A FLUID SAMPLE,” by Duffy et al.; U.S. Patent Application Publication No. US-2010-00754072 (Ser. No. 12/236,486), filed Sep. 23, 2008, entitled “ULTRA-SENSITIVE DETECTION OF MOLECULES ON SINGLE MOLECULE ARRAYS,” by Duffy et al.; U.S. Patent Application Publication No. US-2010-0075439 (Ser. No. 12/236,488), filed Sep. 23, 2008, entitled “ULTRA-SENSITIVE DETECTION OF MOLECULES BY CAPTURE-AND-RELEASE USING REDUCING AGENTS FOLLOWED BY QUANTIFICATION,” by Duffy et al.; International Patent Publication No. WO2010/039179 (International Patent Application No. PCT/US2009/005248), filed Sep. 22, 2009, entitled “ULTRA-SENSITIVE DETECTION OF MOLECULES OR ENZYMES,” by Duffy et al.; U.S. Patent Application Publication No. US-2010-0075355 (Ser. No. 12/236,490), filed Sep. 23, 2008, entitled “ULTRA-SENSITIVE DETECTION OF ENZYMES BY CAPTURE-AND-RELEASE FOLLOWED BY QUANTIFICATION,” by Duffy et al.; U.S. patent application Ser. No. 12/731,130, filed Mar. 24, 2010, published as US-2011-0212848 on Sep. 1, 2011, entitled “ULTRA-SENSITIVE DETECTION OF MOLECULES OR PARTICLES USING BEADS OR OTHER CAPTURE OBJECTS,” by Duffy et al.; International Patent Application No. PCT/US2011/026645, filed Mar. 1, 2011, published as WO 2011/109364 on Sep. 9, 2011, entitled “ULTRA-SENSITIVE DETECTION OF MOLECULES OR PARTICLES USING BEADS OR OTHER CAPTURE OBJECTS,” by Duffy et al.; International Patent Application No. PCT/US2011/026657, filed Mar. 1, 2011, published as WO 2011/109372 on Sep. 9, 2011, entitled “ULTRA-SENSITIVE DETECTION OF MOLECULES USING DUAL DETECTION METHODS,” by Duffy et al.; U.S. patent application Ser. No. 12/731,135, filed Mar. 24, 2010, published as US-2011-0212462 on Sep. 1, 2011, entitled “ULTRA-SENSITIVE DETECTION OF MOLECULES USING DUAL DETECTION METHODS,” by Duffy et al.; International Patent Application No. PCT/US2011/026665, filed Mar. 1, 2011, published as WO 2011/109379 on Sep. 9, 2011, entitled “METHODS AND SYSTEMS FOR EXTENDING DYNAMIC RANGE IN ASSAYS FOR THE DETECTION OF MOLECULES OR PARTICLES,” by Rissin et al.; U.S. patent application Ser. No. 12/731,136, filed Mar. 24, 2010, published as US-2011-0212537 on Sep. 1, 2011, entitled “METHODS AND SYSTEMS FOR EXTENDING DYNAMIC RANGE IN ASSAYS FOR THE DETECTION OF MOLECULES OR PARTICLES,” by Duffy et al.; U.S. patent application Ser. No. 13/035,472, filed Feb. 25, 2011, entitled “SYSTEMS, DEVICES, AND METHODS FOR ULTRA-SENSITIVE DETECTION OF MOLECULES OR PARTICLES,” by Fournier et al.; U.S. patent application Ser. No. 13/037,987, filed Mar. 1, 2011, published as US-2011-0245097 on Oct. 6, 2011, entitled “METHODS AND SYSTEMS FOR EXTENDING DYNAMIC RANGE IN ASSAYS FOR THE DETECTION OF MOLECULES OR PARTICLES,” by Rissin et al.; each herein incorporated by reference.

Additional details of exemplary, non-limiting assay methods which comprise one or more steps of spatially segregating biomarker molecules will now be described. In certain embodiments, a method for detection and/or quantifying biomarker molecules in a sample comprises immobilizing a plurality of biomarker molecules with respect to a plurality of capture objects (e.g., beads) that each include a binding surface having affinity for at least one type of biomarker. For example, the capture objects may comprise a plurality of beads comprising a plurality of capture components (e.g., an antibody having specific affinity for a biomarker of interest, etc.). At least some of the capture objects (e.g., at least some associated with at least one biomarker molecule) may be spatially separated/segregated into a plurality of locations, and at least some of the locations may be addressed/interrogated (e.g., using an imaging system). A measure of the concentration of biomarker molecules in the fluid sample may be determined based on the information received when addressing the locations (e.g., using the information received from the imaging system and/or processed using a computer implemented control system). In some cases, a measure of the concentration may be based at least in part on the number of locations determined to contain a capture object that is or was associated with at least one biomarker molecule. In other cases and/or under differing conditions, a measure of the concentration may be based at least in part on an intensity level of at least one signal indicative of the presence of a plurality of biomarker molecules and/or capture objects associated with a biomarker molecule at one or more of the addressed locations.

In some embodiments, the number/percentage/fraction of locations containing a capture object but not containing a biomarker molecule may also be determined and/or the number/percentage/fraction of locations not containing any capture object may also be determined. In such embodiments, a measure of the concentration of biomarker molecules in the fluid sample may be based at least in part on the ratio of the number of locations determined to contain a capture object associated with a biomarker molecule to the total number of locations determined to contain a capture object not associated with a biomarker molecule, and/or a measure of the concentration of biomarker molecule in the fluid sample may be based at least in part on the ratio of the number of locations determined to contain a capture object associated with a biomarker molecule to the number of locations determined to not contain any capture objects, and/or a measure of the concentration of biomarker molecule in the fluid sample may be based at least in part on the ratio of the number of locations determined to contain a capture object associated with a biomarker molecule to the number of locations determined to contain a capture object. In yet other embodiments, a measure of the concentration of biomarker molecules in a fluid sample may be based at least in part on the ratio of the number of locations determined to contain a capture object and a biomarker molecule to the total number of locations addressed and/or analyzed.

In certain embodiments, at least some of the plurality of capture objects (e.g., at least some associated with at least one biomarker molecule) are spatially separated into a plurality of locations, for example, a plurality of reaction vessels in an array format. The plurality of reaction vessels may be formed in, on and/or of any suitable material, and in some cases, the reaction vessels can be sealed or may be formed upon the mating of a substrate with a sealing component, as discussed in more detail below. In certain embodiments, especially where quantization of the capture objects associated with at least one biomarker molecule is desired, the partitioning of the capture objects can be performed such that at least some (e.g., a statistically significant fraction; e.g., as described in International Patent Application No. PCT/US2011/026645, filed Mar. 1, 2011, published as WO 2011/109364 on Sep. 9, 2011, entitled “ULTRA-SENSITIVE DETECTION OF MOLECULES OR PARTICLES USING BEADS OR OTHER CAPTURE OBJECTS,” by Duffy et al) of the reaction vessels comprise at least one or, in certain cases, only one capture object associated with at least one biomarker molecule and at least some (e.g., a statistically significant fraction) of the reaction vessels comprise an capture object not associated with any biomarker molecules. The capture objects associated with at least one biomarker molecule may be quantified in certain embodiments, thereby allowing for the detection and/or quantification of biomarker molecules in the fluid sample by techniques described in more detail herein.

An exemplary assay method may proceed as follows. A sample fluid containing or suspected of containing biomarker molecules is provided. An assay consumable comprising a plurality of assay sites is exposed to the sample fluid. In some cases, the biomarker molecules are provided in a manner (e.g., at a concentration) such that a statistically significant fraction of the assay sites contain a single biomarker molecule and a statistically significant fraction of the assay sites do not contain any biomarker molecules. The assay sites may optionally be exposed to a variety of reagents (e.g., using a reagent loader) and or rinsed. The assay sites may then optionally be sealed and imaged (see, for example, U.S. patent application Ser. No. 13/035,472, filed Feb. 25, 2011, entitled “SYSTEMS, DEVICES, AND METHODS FOR ULTRA-SENSITIVE DETECTION OF MOLECULES OR PARTICLES,” by Fournier et al.). The images are then analyzed (e.g., using a computer implemented control system) such that a measure of the concentration of the biomarker molecules in the fluid sample may be obtained, based at least in part, by determination of the number/fraction/percentage of assay sites which contain a biomarker molecule and/or the number/fraction/percentage of sites which do not contain any biomarkers molecules. In some cases, the biomarker molecules are provided in a manner (e.g., at a concentration) such that at least some assay sites comprise more than one biomarker molecule. In such embodiments, a measure of the concentration of biomarker molecules in the fluid sample may be obtained at least in part on an intensity level of at least one signal indicative of the presence of a plurality of biomarkers molecules at one or more of the assay sites

In some cases, the methods optionally comprise exposing the fluid sample to a plurality of capture objects, for example, beads. At least some of the biomarker molecules are immobilized with respect to a bead. In some cases, the biomarker molecules are provided in a manner (e.g., at a concentration) such that a statistically significant fraction of the beads associate with a single biomarker molecule and a statistically significant fraction of the beads do not associate with any biomarker molecules. At least some of the plurality of beads (e.g., those associated with a single biomarker molecule or not associated with any biomarker molecules) may then be spatially separated/segregated into a plurality of assay sites (e.g., of an assay consumable). The assay sites may optionally be exposed to a variety of reagents and/or rinsed. At least some of the assay sites may then be addressed to determine the number of assay sites containing a biomarker molecule. In some cases, the number of assay sites containing a bead not associated with a biomarker molecule, the number of assay sites not containing a bead and/or the total number of assay sites addressed may also be determined. Such determination(s) may then be used to determine a measure of the concentration of biomarker molecules in the fluid sample. In some cases, more than one biomarker molecule may associate with a bead and/or more than one bead may be present in an assay site. In some cases, the plurality biomarker molecules may be exposed to at least one additional reaction component prior to, concurrent with, and/or following spatially separating at least some of the biomarker molecules into a plurality of locations.

The biomarker molecules may be directly detected or indirectly detected. In the case of direct detection, a biomarker molecule may comprise a molecule or moiety that may be directly interrogated and/or detected (e.g., a fluorescent entity). In the case of indirect detection, an additional component is used for determining the presence of the biomarker molecule. For example, the biomarker molecules (e.g., optionally associated with a bead) may be exposed to at least one type of binding ligand. A “binding ligand,” is any molecule, particle, or the like which specifically binds to or otherwise specifically associates with a biomarker molecule to aid in the detection of the biomarker molecule. In certain embodiments, a binding ligand may be adapted to be directly detected (e.g., the binding ligand comprises a detectable molecule or moiety) or may be adapted to be indirectly detected (e.g., including a component that can convert a precursor labeling agent into a labeling agent). A component of a binding ligand may be adapted to be directly detected in embodiments where the component comprises a measurable property (e.g., a fluorescence emission, a color, etc.). A component of a binding ligand may facilitate indirect detection, for example, by converting a precursor labeling agent into a labeling agent (e.g., an agent that is detected in an assay). A “precursor labeling agent” is any molecule, particle, or the like, that can be converted to a labeling agent upon exposure to a suitable converting agent (e.g., an enzymatic component). A “labeling agent” is any molecule, particle, or the like, that facilitates detection, by acting as the detected entity, using a chosen detection technique. In some embodiments, the binding ligand may comprise an enzymatic component (e.g., horseradish peroxidase, beta-galactosidase, alkaline phosphatase, etc.). A first type of binding ligand may or may not be used in conjunction with additional binding ligands (e.g., second type, etc.).

More than one type of binding may be employed in any given assay method, for example, a first type of binding ligand and a second type of binding ligand. In one example, the first type of binding ligand is able to associate with a first type of biomarker molecule and the second type of binding ligand is able to associate with the first binding ligand. In another example, both a first type of binding ligand and a second type of binding ligand may associate with the same or different epitopes of a single biomarker molecule, as described herein. In some embodiments, at least one binding ligand comprises an enzymatic component.

In some embodiments, a binding ligand and/or a biomarker may comprise an enzymatic component. The enzymatic component may convert a precursor labeling agent (e.g., an enzymatic substrate) into a labeling agent (e.g., a detectable product). A measure of the concentration of biomarker molecules in the fluid sample can then be determined based at least in part by determining the number of locations containing a labeling agent (e.g., by relating the number of locations containing a labeling agent to the number of locations containing a biomarker molecule (or number of capture objects associated with at least one biomarker molecule to total number of capture objects)). Non-limiting examples of enzymes or enzymatic components include horseradish peroxidase, beta-galactosidase, and alkaline phosphatase. Other non-limiting examples of systems or methods for detection include embodiments where nucleic acid precursors are replicated into multiple copies or converted to a nucleic acid that can be detected readily, such as the polymerase chain reaction (PCR), rolling circle amplification (RCA), ligation, Loop-Mediated Isothermal Amplification (LAMP), etc. Such systems and methods will be known to those of ordinary skill in the art, for example, as described in “DNA Amplification: Current Technologies and Applications,” Vadim Demidov et al., 2004.

Another exemplary embodiment of indirect detection is as follows. In some cases, the biomarker molecules may be exposed to a precursor labeling agent (e.g., enzymatic substrate) and the enzymatic substrate may be converted to a detectable product (e.g., fluorescent molecule) upon exposure to a biomarker molecule.

The assay methods and systems may employ a variety of different components, steps, and/or other aspects that will be known and understood by those of ordinary skill in the art. For example, a method may further comprise determining at least one background signal determination (e.g., and further comprising subtracting the background signal from other determinations), wash steps, and the like. In some cases, the assays or systems may include the use of at least one binding ligand, as described herein. In some cases, the measure of the concentration of biomarker molecules in a fluid sample is based at least in part on comparison of a measured parameter to a calibration curve. In some instances, the calibration curve is formed at least in part by determination at least one calibration factor, as described above.

As will be understood by those of ordinary skill in the art, a system and/or method may be calibrated using natural and/or synthetic forms of the target biomarker, and/or analogues thereof. In embodiments where the target analyte is a tau protein, the system and/or method may be calibrated using one or more natural and/or synthetic isoforms of tau protein. Naturally occurring tau proteins are described herein. Synthetic isoforms of tau proteins include two nearest neighbor antibody epitope synthetic peptides (<20 amino acids) to long synthetic peptides (80-100 amino acids in length. In some cases, short isoforms of the naturally occurring tau proteins may be employed. For example, tau protein isoforms can have varying lengths of amino acids selected from thetau 441 sequence. Non-limiting examples of short forms of tau proteins include tau 50-mers (e.g., comprising residues 187-237, 190-240, or 155-205 of tau 441) and tau 64-mers (e.g., comprising residues 155-235 oftau 441, RGAAP PGQKG QTPPA PKpTPP SSKSG DRSGY SSPGS PGTSR TPSLP TPPTR EPKKV AVVRT PPKS-NH₂(SEQ ID NO.: 1)). In some cases, at least a portion of the tau protein(s) used may be phosphorylated (e.g., RGAAP PGQKG QTPPA PKpTPP SSKSG DRSGY SSPGS PGTSR TPSLP TPPTR EPKKV AVVRpT PPKS-NH2 (SEQ ID NO.: 2)).

In certain embodiments, solubilized, or suspended precursor labeling agents may be employed, wherein the precursor labeling agents are converted to labeling agents which are insoluble in the liquid and/or which become immobilized within/near the location (e.g., within the reaction vessel in which the labeling agent is formed). Such precursor labeling agents and labeling agents and their use is described in commonly owned U.S. Patent Application Publication No. US-2010-0075862 (Ser. No. 12/236,484), filed Sep. 23, 2008, entitled “HIGH SENSITIVITY DETERMINATION OF THE CONCENTRATION OF ANALYTE MOLECULES OR PARTICLES IN A FLUID SAMPLE,” by Duffy et al., incorporated herein by reference.

A non-limiting example of an embodiment where a capture object is associated with more than one biomarker molecule is illustrated inFIG. 1b. A plurality of capture objects20 are provided (step (A)). In this example, the plurality of capture objects comprises a plurality of beads. The plurality of beads is exposed to a fluid sample containing plurality of biomarker molecules21 (e.g.,beads20 are incubated with biomarker molecules21). At least some of the biomarker molecules are immobilized with respect to a bead. For example, as shown in step (B), biomarker molecule22 is immobilized with respect to bead24, thereby formingcomplex26. Also illustrated is complex30 comprising a bead immobilized with respect to three biomarker molecules and complex32 comprising a bead immobilized with respect to two biomarker molecules. Additionally, in some cases, some of the beads may not associate with any biomarker molecules (e.g., bead28). The plurality of beads from step (B) is exposed to a plurality of bindingligands31. As shown in step (C), a binding ligand associates with some of the biomarker molecules immobilized with respect to a bead. For example, complex40 comprisesbead34,biomarker molecule36, and bindingligand38. The binding ligands are provided in a manner such that a statistically significant fraction of the beads comprising at least one biomarker molecule become associated with at least one binding ligand (e.g., one, two, three, etc.) and a statistically significant fraction of the beads comprising at least one biomarker molecule do not become associated with any binding ligands. At least a portion of the plurality of beads from step (C) are then spatially separated into a plurality of locations. As shown in step (D), in this example, the locations comprise a plurality ofreaction vessels41 on a substrate42. The plurality of reaction vessels may be exposed to the plurality of beads from step (C) such at each reaction vessel contains zero or one beads. The substrate may then be analyzed to determine the number of reaction vessels containing a binding ligand (e.g., reaction vessels43), wherein in the number may be related to a measure of the concentration of biomarker molecules in the fluid sample. In some cases, the number of reaction vessels containing a bead and not containing a binding ligand (e.g., reaction vessel44), the number of reaction vessels not containing a bead (e.g., reaction vessel45), and/or the total number of reaction vessels addressed/analyzed may also be determined. Such determination(s) may then be used to determine a measure of the concentration of biomarker molecules in the fluid sample.

In some embodiments, the locations are optically interrogated. The locations exhibiting changes in their optical signature may be identified by a conventional optical train and optical detection system. Depending on the detected species (e.g., type of fluorescence entity, etc.) and the operative wavelengths, optical filters designed for a particular wavelength may be employed for optical interrogation of the locations. In embodiments where optical interrogation is used, the system may comprise more than one light source and/or a plurality of filters to adjust the wavelength and/or intensity of the light source. In some embodiments, the optical signal from a plurality of locations is captured using a CCD camera.

In some embodiments of the present invention, the plurality of reaction vessels may be sealed (e.g., after the introduction of the biomarker molecules, binding ligands, and/or precursor labeling agent), for example, through the mating of the second substrate and a sealing component. The sealing of the reaction vessels may be such that the contents of each reaction vessel cannot escape the reaction vessel during the remainder of the assay. In some cases, the reaction vessels may be sealed after the addition of the biomarker molecules and, optionally, at least one type of precursor labeling agent to facilitate detection of the biomarker molecules. For embodiments employing precursor labeling agents, by sealing the contents in some or each reaction vessel, a reaction to produce the detectable labeling agents can proceed within the sealed reaction vessels, thereby producing a detectable amount of labeling agents that is retained in the reaction vessel for detection purposes.

The plurality of locations may be formed may be formed using a variety of methods and/or materials. In some embodiments, the plurality of locations comprises a plurality of reaction vessels/wells on a substrate. In some cases, the plurality of reaction vessels is formed as an array of depressions on a first surface. In other cases, however, the plurality of reaction vessels may be formed by mating a sealing component comprising a plurality of depressions with a substrate that may either have a featureless surface or include depressions aligned with those on the sealing component. Any of the device components, for example, the substrate or sealing component, may be fabricated from a compliant material, e.g., an elastomeric polymer material, to aid in sealing. The surfaces may be or made to be hydrophobic or contain hydrophobic regions to minimize leakage of aqueous samples from the microwells. The reactions vessels, in certain embodiments, may be configured to receive and contain only a single capture object.

In some embodiments, the reaction vessels may all have approximately the same volume. In other embodiments, the reaction vessels may have differing volumes. The volume of each individual reaction vessel may be selected to be appropriate to facilitate any particular assay protocol. For example, in one set of embodiments where it is desirable to limit the number of capture objects used for biomarker capture contained in each vessel to a small number, the volume of the reaction vessels may range from attoliters or smaller to nanoliters or larger depending upon the nature of the capture objects, the detection technique and equipment employed, the number and density of the wells on the substrate and the expected concentration of capture objects in the fluid applied to the substrate containing the wells. In one embodiment, the size of the reaction vessel may be selected such only a single capture object used for biomarker capture can be fully contained within the reaction vessel (see, for example, U.S. patent application Ser. No. 12/731,130, filed Mar. 24, 2010, published as US-2011-0212848 on Sep. 1, 2011, entitled “ULTRA-SENSITIVE DETECTION OF MOLECULES OR PARTICLES USING BEADS OR OTHER CAPTURE OBJECTS,” by Duffy et al.; International Patent Application No. PCT/US2011/026645, filed Mar. 1, 2011, published as WO 2011/109364 on Sep. 9, 2011, entitled “ULTRA-SENSITIVE DETECTION OF MOLECULES OR PARTICLES USING BEADS OR OTHER CAPTURE OBJECTS ,” by Duffy et al., each herein incorporated by reference).

In some embodiments, the reaction vessels may have a volume between about 1 femtoliter and about 1 picoliter, between about 1 femtoliters and about 100 femtoliters, between about 10 attoliters and about 100 picoliters, between about 1 picoliter and about 100 picoliters, between about 1 femtoliter and about 1 picoliter, or between about 30 femtoliters and about 60 femtoliters. In some cases, the reaction vessels have a volume of less than about 1 picoliter, less than about 500 femtoliters, less than about 100 femtoliters, less than about 50 femtoliters, or less than about 1 femtoliter. In some cases, the reaction vessels have a volume of about 10 femtoliters, about 20 femtoliters, about 30 femtoliters, about 40 femtoliters, about 50 femtoliters, about 60 femtoliters, about 70 femtoliters, about 80 femtoliters, about 90 femtoliters, or about 100 femtoliters.

The total number of locations and/or density of the locations employed in an assay (e.g., the number/density of reaction vessels in an array) can depend on the composition and end use of the array. For example, the number of reaction vessels employed may depend on the number of types of biomarker molecule and/or binding ligand employed, the suspected concentration range of the assay, the method of detection, the size of the capture objects, the type of detection entity (e.g., free labeling agent in solution, precipitating labeling agent, etc.). Arrays containing from about 2 to many billions of reaction vessels (or total number of reaction vessels) can be made by utilizing a variety of techniques and materials. Increasing the number of reaction vessels in the array can be used to increase the dynamic range of an assay or to allow multiple samples or multiple types of biomarker molecules to be assayed in parallel. The array may comprise between one thousand and one million reaction vessels per sample to be analyzed. In some cases, the array comprises greater than one million reaction vessels. In some embodiments, the array comprises between about 1,000 and about 50,000, between about 1,000 and about 1,000,000, between about 1,000 and about 10,000, between about 10,000 and about 100,000, between about 100,000 and about 1,000,000, between about 100,000 and about 500,000, between about 1,000 and about 100,000, between about 50,000 and about 100,000, between about 20,000 and about 80,000, between about 30,000 and about 70,000, between about 40,000 and about 60,000 reaction vessels. In some embodiments, the array comprises about 10,000, about 20,000, about 50,000, about 100,000, about 150,000, about 200,000, about 300,000, about 500,000, about 1,000,000, or more, reaction vessels.

The array of reaction vessels may be arranged on a substantially planar surface or in a non-planar three-dimensional arrangement. The reaction vessels may be arrayed in a regular pattern or may be randomly distributed. In a specific embodiment, the array is a regular pattern of sites on a substantially planar surface permitting the sites to be addressed in the X-Y coordinate plane.

In some embodiments, the reaction vessels are formed in a solid material. As will be appreciated by those in the art, the number of potentially suitable materials in which the reaction vessels can be formed is very large, and includes, but is not limited to, glass (including modified and/or functionalized glass), plastics (including acrylics, polystyrene and copolymers of styrene and other materials, polypropylene, polyethylene, polybutylene, polyurethanes, cyclic olefin copolymer (COC), cyclic olefin polymer (COP), Teflon®, polysaccharides, nylon or nitrocellulose, etc.), elastomers (such as poly(dimethyl siloxane) and poly urethanes), composite materials, ceramics, silica or silica-based materials (including silicon and modified silicon), carbon, metals, optical fiber bundles, or the like. In general, the substrate material may be selected to allow for optical detection without appreciable autofluorescence. In certain embodiments, the reaction vessels may be formed in a flexible material.

A reaction vessel in a surface (e.g., substrate or sealing component) may be formed using a variety of techniques known in the art, including, but not limited to, photolithography, stamping techniques, molding techniques, etching techniques, or the like. As will be appreciated by those of the ordinary skill in the art, the technique used can depend on the composition and shape of the supporting material and the size and number of reaction vessels.

In a particular embodiment, an array of reaction vessels is formed by creating microwells on one end of a fiber optic bundle and utilizing a planar compliant surface as a sealing component. In certain such embodiments, an array of reaction vessels in the end of a fiber optic bundle may be formed as follows. First, an array of microwells is etched into the end of a polished fiber optic bundle. Techniques and materials for forming and etching a fiber optic bundle are known to those of ordinary skill in the art. For example, the diameter of the optical fibers, the presence, size and composition of core and cladding regions of the fiber, and the depth and specificity of the etch may be varied by the etching technique chosen so that microwells of the desired volume may be formed. In certain embodiments, the etching process creates microwells by preferentially etching the core material of the individual glass fibers in the bundle such that each well is approximately aligned with a single fiber and isolated from adjacent wells by the cladding material. Potential advantages of the fiber optic array format is that it can produce thousands to millions of reaction vessels without complicated microfabrication procedures and that it can provide the ability to observe and optically address many reaction vessels simultaneously.

Each microwell may be aligned with an optical fiber in the bundle so that the fiber optic bundle can carry both excitation and emission light to and from the wells, enabling remote interrogation of the well contents. Further, an array of optical fibers may provide the capability for simultaneous or non-simultaneous excitation of molecules in adjacent vessels, without signal “cross-talk” between fibers. That is, excitation light transmitted in one fiber does not escape to a neighboring fiber.

Alternatively, the equivalent structures of a plurality of reaction vessels may be fabricated using other methods and materials that do not utilize the ends of an optical fiber bundle as a substrate. For example, the array may be a spotted, printed or photolithographically fabricated substrate produced by techniques known in the art; see for example WO95/25116; WO95/35505; PCT US98/09163; U.S. Pat. Nos. 5,700,637, 5,807,522, 5,445,934, 6,406,845, and 6,482,593. In some cases, the array may be produced using molding, embossing, and/or etching techniques as will be known to those of ordinary skill in the art.

In some embodiments, the plurality of locations may not comprise a plurality of reaction vessels/wells. For example, in embodiments where capture objects are employed, a patterned substantially planar surface may be employed and the patterned areas form a plurality of locations. In some cases, the patterned areas may comprise substantially hydrophilic surfaces which are substantially surrounded by substantially hydrophobic surfaces. In certain embodiments, a plurality of capture objects (e.g., beads) may be substantially surrounded by a substantially hydrophilic medium (e.g., comprising water), and the beads may be exposed to the patterned surface such that the beads associate in the patterned areas (e.g., the hydrophilic locations on the surface), thereby spatially segregating the plurality of beads. For example, in one such embodiment, a substrate may be or include a gel or other material able to provide a sufficient barrier to mass transport (e.g., convective and/or diffusional barrier) to prevent capture objects used for biomarker capture and/or precursor labeling agent and/or labeling agent from moving from one location on or in the material to another location so as to cause interference or cross-talk between spatial locations containing different capture objects during the time frame required to address the locations and complete the assay. For example, in one embodiment, a plurality of capture objects is spatially separated by dispersing the capture objects on and/or in a hydrogel material. In some cases, a precursor labeling agent may be already present in the hydrogel, thereby facilitating development of a local concentration of the labeling agent (e.g., upon exposure to a binding ligand or biomarker molecule carrying an enzymatic component). As still yet another embodiment, the capture objects may be confined in one or more capillaries. In some cases, the plurality of capture objects may be absorbed or localized on a porous or fibrous substrate, for example, filter paper. In some embodiments, the capture objects may be spatially segregated on a uniform surface (e.g., a planar surface), and the capture objects may be detected using precursor labeling agents which are converted to substantially insoluble or precipitating labeling agents that remain localized at or near the location of where the corresponding capture object is localized. The use of such substantially insoluble or precipitating labeling agents is described herein. In some cases, single biomarker molecules may be spatially segregated into a plurality of droplets. That is, single biomarker molecules may be substantially contained in a droplet containing a first fluid. The droplet may be substantially surrounded by a second fluid, wherein the second fluid is substantially immiscible with the first fluid.

In some embodiments, during the assay, at least one washing step may be carried out. In certain embodiments, the wash solution is selected so that it does not cause appreciable change to the configuration of the capture objects and/or biomarker molecules and/or does not disrupt any specific binding interaction between at least two components of the assay (e.g., a capture component and a biomarker molecule). In other cases, the wash solution may be a solution that is selected to chemically interact with one or more assay components. As will be understood by those of ordinary skill in the art, a wash step may be performed at any appropriate time point during the inventive methods. For example, a plurality of capture objects may be washed after exposing the capture objects to one or more solutions comprising biomarker molecules, binding ligands, precursor labeling agents, or the like. As another example, following immobilization of the biomarker molecules with respect to a plurality of capture objects, the plurality of capture objects may be subjected to a washing step thereby removing any biomarker molecules not specifically immobilized with respect to a capture object.

Other assay methods in addition to those described herein are known in the art and may be used in connection with the inventive methods. For example, various analyzers are commercially available for the determination of the concentration of biomarkers. The assay methods employed should meet the algorithm requirements for LOD and LOQ.

The following examples are included to demonstrate various features of the invention. Those of ordinary skill in the art should, in light of the present disclosure, will appreciate that many changes can be made in the specific embodiments which are disclosed while still obtaining a like or similar result without departing from the scope of the invention as defined by the appended claims. Accordingly, the following examples are intended only to illustrate certain features of the present invention, but do not necessarily exemplify the full scope of the invention.

Example 1

The following example provides experimental details relating to prognostication of neurological outcome in comatose survivors of oxygen deprivation, using tau proteins

Objective:

Use of peripheral tau protein measurements as an indicator of the presence of brain injury has remained elusive, in large part due to the lack of adequate sensitivity for reliable measurement of the protein in serum or plasma using common technologies. Additionally, little was known about the time-dependence of tau protein release from the central nervous system into peripheral circulation. Using methods described herein, which, in certain embodiments are capable of ultra sensitive tau protein measurement, serial serum samples from 25 resuscitated cardiac arrest patients were analyzed to longitudinally study tau protein release into serum and determine prognostic significance of tau protein elevation for prediction of long-term cognitive impairment from hypoxic insult.

Summary of Methods:

25 unconscious patients with cardiac arrest were resuscitated with restoration of spontaneous circulation and admitted to a hospital intensive care unit (ICU). Patients were treated with hypothermia and repeated blood samplings were obtained during the first five days in the ICU. Serum levels of total tau protein were measured with a digital immunoassay described in Example 2. Cognitive assessments were made using Cerebral Performance Categorization (CPC) at discharge from the ICU and six months later. Tau protein data were analyzed in the context of six-month cognitive outcome.

Summary of Results:

Tau protein elevations ranged from modest to very high, and exhibited unexpected bi-modal kinetic profiles in many patients. Total area-under-the-curve (AUC) was highly prognostic for six-month cognitive outcome. AUC of the secondary tau protein peak exhibited 100% sensitivity and 91% specificity for predicting 6-month outcome.

Summary of Conclusions:

The data indicate that sufficiently sensitive peripheral tau protein measurements in conjunction with an understanding of tau protein release kinetics have clinical utility for brain injury assessment and prognostication of cognitive outcome.

Additional Background:

Tau proteins, with a molecular mass of 48 to 67 kd depending on isoform, are associated with microtubules and localized in the axonal compartment of neurons. Tau proteins plays a structural role in the assembly of tubulin monomers into axonal microtubule bundles, which are important for maintaining the cytoskeleton and axonal transport. Tau protein is generally elevated in the cerebrospinal fluid (CSF) of patients with neurodegenerative disease and severe head injuries, making it a candidate for peripheral measurement as a biomarker of acquired or traumatic brain injury (ABI, TBI). However, studies on peripheral tau protein have been hampered by its low abundance in serum and plasma (typically low pg/mL), making its measurement difficult.

While CSF tau protein elevation is known to correlate with 1-year outcome in severe TBI patients, no such correlation has been made to serum tau protein, in part because most common assays cannot accurately detect the low levels of tau protein in serum. In addition, the clinical value of serum tau protein for assessment of minor head injury has been questioned. A previous study looked at serum tau protein elevation measured in 24 ischemic stroke patients studied using an immunoassay with a limit of detection of 60 pg/mL, but no correlation was made or found between tau protein appearance to stroke severity. A recent rat TBI model indicated serum tau protein elevation peaked rapidly and declined after six hours, with no significant additional tau protein elevation over 7 days. Little else has been reported about the kinetics of tau protein movement across the blood brain barrier (BBB), nor the potential prognostic significance of peripheral tau protein appearance with ABI or TBI.

Methods:

This example employed the protocol described in Example 2 below, which is capable in certain embodiments of three logs greater sensitivity than typical conventional methods. The assay was utilized to examine serial serum samples from 25 resuscitated cardiac arrest patients to longitudinally study tau protein release into serum and probe for prognostic significance of tau protein elevation for prediction of long-term cognitive impairment due to hypoxic insult.

The study was performed at the general intensive care unit at Uppsala University Hospital, Sweden, and approved by the Human Ethics Committee of Uppsala, Sweden. Twenty-five unconscious patients with cardiac arrest were resuscitated with restoration of spontaneous circulation (ROSC). Patients were >18 yrs old, exhibited systolic blood pressure>80 mmHg after ROSC, and a Glasgow Coma Scale≦7.

Upon admission, hypothermia treatment was started immediately after resuscitation. Ventilation was administered during the coma period, with a target PaO₂of ≧12 kPa (90 mmHg) and PaCO₂between 5.0 and 5.5 kPa (38-41 mmHg). Targeted mean arterial pressure was 65-100 mmHg, with application of inotropic/vasopressor support, if required, using dobutamine as the first line medication, followed by noradrenaline (norepinephrine) or adrenaline (epinephrine), if necessary. If the patient was considered euvolaemic but had a diuresis of less than 0.5 ml/kg/h, furosemide was administered. Furosemide was also given if the intensive care physician considered that the patient had a fluid overload. All patients received an arterial line in the radial or femoral artery for blood sampling. Serial blood samples were collected, starting as soon as possible in the emergency phase (within 6 h after cardiac arrest), and continuing at 1, 2, 6, 12, 24, 48, 72, 96, and 108 h after cardiac arrest. Serum aliquots were frozen at −70° C. until analysis.

Patient outcome was assessed in accordance with the Glasgow-Pittsburgh cerebral performance category (CPC) scale at discharge from the intensive care unit and 6 months later. The CPC scale ranges from 1 to 5, with 1 representing mildest possible neurological deficit (patient is able to return to work), and 4-5 representing the most severe deficit (vegetative) and death. A CPC of 1 or 2 was considered a “good” outcome and a CPC score of 3-5 a “poor” outcome. For patients who died after ICU discharge, the better of the two scores was used, as recommended by the Utstein templates.

Patient serum samples were measured in triplicate by a single molecule digital immunoassay for tau protein (see Example 2 for more details). The technique involves performing a paramagnetic bead-based ELISA using beta-galactosidase as a reporter, followed by isolation of individual capture beads within femtoliter-sized reaction wells in a microarray. Isolation of individual beads permits the buildup of fluorescent substrate in the presence of tau protein, such that wells containing a single immunocomplex can be detected. The limit of detection of the assay is 0.02 pg/mL, making it approximately 1000-fold more sensitive than typical conventional immunoassays. The assay was calibrated from 0 pg/mL to 100 pg/mL total tau protein and was able to precisely measure serum tau protein in the patient samples. The extreme sensitivity of the method permits pre-dilution of the samples prior to assay, reducing potential endogenous interferences. All samples were pre-diluted 1:4 with a PBS-tween diluent prior to assay.

Tau protein elevation profiles were analyzed for area-under-the-curve (AUC) with GraphPad Prism 5.0d (GraphPad Software, La Jolla, Calif.). Four of the 25 patients died 24-48 hours after admission, and these patients were excluded from AUC analysis. AUC was evaluated during the first 24-hour period as well as over the full time course of samples (to 108 hours) using a baseline of zero. In addition, the AUC of secondary tau protein elevation peaks were estimated assuming a baseline corresponding to the tau protein concentration measured at the initial time point of the secondary peak. Statistical significance between ‘good’ and ‘poor’ 6-month outcome was determined by student t-test, with significance taken as p<0.05.

Results:

Representative elevation profiles for patients with good and poor 6-month outcomes are depicted inFIG. 2.FIG. 2 shows serum tau following resuscitation from cardiac arrest. CPC scores are listing for each patient in the legends. The first two numbers correspond to the CPC assessments upon discharge from the ICU and six months later. The third number represents overall 6-month outcome assessment (1=poor, 0=good).FIGS. 2a-2cdepict representative groupings of patients exhibiting different profiles of tau elevations: a) initial 24-hour peaks; b) delayed peaks, and c) both initial 24-hour and delayed peaks.FIG. 2ddepicts representative profiles from patients with good outcomes. Note the difference in scales. Error bars depict SD of triplicate measurements.

Tau protein expression ranged from almost undetectable to large elevations approaching 700 pg/mL. There was a strong general association between tau protein elevation and patient outcome: the more tau protein expressed, the greater the likelihood for poor 6-month outcome. Tau protein elevation also showed clear bi-modal tendencies, with the appearance of one or both peaks varying with patient. The initial peak was generally fully expressed during the first 24 hours following cardiac arrest, while the secondary peak generally expressed after 24-48 hours. Some patients exhibited only the first peak (FIG. 2a), some exhibited only the second peak (FIG. 2b), and some exhibited both peaks (FIG. 2c).

TABLE 2

AUC </= 24 hr	AUC all	AUC 2nd peak only

Patient	Good	Poor	Good	Poor	Good	Poor

2		1590		4759		1440
3	708.9		2145		0
4	748.3		2861		154.2
5		525.2		3007		1690
6		179.9		1232		897.5
7	4.72		92.86		54.5
8		11.19		1646		1545
9	59		1141		0
10		109.7		9336		8206
11	14.63		84.56		0
12		52.15		848.2		567.8
13	26.01		288.5		215.8
14	12.93		431.5		393
15	12.31		184.4		168.2
17	0.02		30.66		30.9
18	15.78		46.62		0
20		334.6		6827		5511
21		580.8		19876		18051
23		1039		26150		23935
24		12.92		72.9		35.94
25		9.37		8987		8842
AVG	160.26	413.17	730.61	7521.83	101.66	6447.39

t-test (p)	0.090609467	0.011726946	0.01197362

To compare the significance of the primary and secondary elevation profiles for 6-month outcome, AUCs were calculated for the first 24 hours (referred to as the “first peak”), the full time course, and the secondary peak only. Table 2 exhibits AUCs for each patient, which are plotted inFIG. 3. More specifically, Table 2 tabulates characteristics of serum tau elevation profiles from resuscitated survivors of cardiac arrest during the first 96-108 hours following admission to the ICD. Parameters were sorted on the basis of good or poor 6-month cerebral outcome and compared by student t-test. Four patients (all with good outcome) exhibited no discernable secondary peaks.FIG. 3 plots AUC results a) across the first 24 hours, b) for all serial samplings, and c) the secondary tau peak only. Error bars depict standard error of the means.

Weak correlation was observed between the initial 24 hours and 6-month outcome (p>0.05). Notably, there was a strong correlation between the secondary peak and 6-month outcome (p=0.01). The weak correlation between initial tau protein appearance and outcome reflects inter-patient differences in primary peak expression rather than lack of significance between tau protein elevation and outcome. Calculation of overall AUC gave similar statistical significance with outcome as the AUC of the second peak only. Patients with good outcome generally had very low serum tau protein, and secondary peaks where either absent or weak (FIG. 2d).

The appearance and magnitude of the secondary tau protein peak was highly prognostic for 6-month outcome. Bifurcating the data with an AUC cut point of 500 resulted in 100% sensitivity (10/10 patients) and 91% specificity (10/11 patients) for predicting good and poor 6-month outcomes respectively.

Discussion:

These data represent a high-resolution longitudinal examination of serum tau protein elevation following an acute ABI event. The bimodal profile elevation kinetics are consistent with two modes of neuronal damage: initially upon acute oxygen deprivation, followed by delayed cell death due to apoptosis and/or cerebral swelling. With ROSC as an inclusion criterion, the elevation kinetics should be unrelated to reperfusion differences between patients. Patients were all treated with hypothermia, and were not treated with drugs known to significantly affect BBB permeability. It seems likely the bimodal profiles are related to neuronal damage rather than BBB or reperfusion variables.

Inter-patient differences in expression one or both elevation peaks could be related to the extent and duration of the hypoxia. Global cerebral ischemia could trigger rapid necrosis in addition to longer-term apoptosis cascades. Sub lethal hypoxic encephalopathy can set a series of toxic reactions in motion that finish off injured neurons and kill additional ones over hours or days following the insult. While early tau protein peaks were less prognostics for 6-month outcome than the secondary elevation, they are nonetheless deadly when high levels of tau protein are measured. Among the four patients who did not survive the first 48 hours, two patients had prominent initial tau protein peaks of well over 200 pg/mL that had dropped 10-fold by 24 hours (not shown). In these patients, it may have been that the acute initial necrosis was sufficiently lethal, and it might be anticipated that survival would have witnessed prominent secondary peaks.

It is noted that the serial sampling in this study was concluded at 108 hours. It may be that additional tau protein elevation occurs beyond 108 hours. Studies of tau protein elevation in CSF following severe TBI have revealed temporal elevations well beyond five days. It is possible that patients in the present study exhibiting tau protein peaks in the first 24 hours with minimal secondary elevation could go on to express significant additional tau protein beyond 108 hours.

Since the magnitude of cognitive impairment should reflect the magnitude of hypoxia, correlation of serum tau protein elevation with cognitive outcome indicates released tau protein reflects the extent of hypoxia and associated neuronal damage. Serum tau protein appearance as measured by digital immunoassay exhibited considerable prognostic significance for 6-month cognitive outcome, with a sensitivity and specificity of 100% using an AUC cut point of 500. This example demonstrates that serial blood measurements of tau protein in the ICU following resuscitation from cardiac arrest has a clinical value for stratifying likely cognitive outcome.

Example 2

The following example describes the tau protein ultra-sensitive digital immunoassay for plasma tau using single molecule arrays that was employed in Example 1.

Reagents were developed for a paramagnetic bead-based ELISA. Tau protein molecules in plasma were captured on antibody-coated paramagnetic capture beads and labeled with an enzyme conjugate. The beads were loaded into arrays of 50,000, 50-femtoliter reaction wells etched into bundles of optical fibers. Single capture beads trapped in each well were sealed in the presence of enzyme substrate and imaged using a fluorescence microscope fitted with a CCD camera. At low concentrations, the images were analyzed for the presence or absence of single immunocomplexes of labeled tau protein, resulting in a digital signal. At high concentrations, the analog intensity of the beads was normalized to the digital signals, extending the dynamic range of the assay to over four logs. Analytical performance of the assay was evaluated, and serum samples from hypoxia patients were tested for tau protein.

The assay described in this example has a detection limit LOD) of 0.02 pg/mL and was linear to 100 pg/mL tau protein (R2>0.996, Patient I.J cal curve). Results using serum samples from hypoxia patients showed a bi-phasic response across the time course post hypoxic insult.

Concentrations of tau protein in serum and plasma are believed to be over 100-fold lower than in cerebrospinal fluid.

This example describes the development and validation of a digital immunoassay using single molecule array technology that is capable of measuring tau protein in hypoxia induced serum without biomarker enrichment or sample pretreatment procedures. The assay exhibits over 1000-fold greater sensitivity than validated commercially available ELISAs. The assay can be used for directly measuring and monitoring serum tau protein in therapeutic trials aimed at altering and lowering levels of this protein, down to sub-femtomolar levels.

The single molecule array technology employed two primary steps: an initial analyte capture step conducted with paramagnetic beads, followed by isolation of individual beads in arrays of femtoliter-sized reaction wells for digital imaging. Isolation of the individual beads in microwells permits the buildup of fluorescent product from the enzyme label such that signal from a single immunocomplex is readily detected using a CCD camera. This approach permits counting of single molecules when tau protein concentrations are low enough that the ratio of bound labeled peptide per bead is much less than one. In this concentration realm, Poisson statistics predict that bead-containing microwells in the array will contain either a single labeled tau protein molecule or no labeled tau protein molecules, resulting in a binary signal. Due to the amplified sensitivity for detecting label molecules afforded by confining fluorescent product buildup to the microwells, concentrations of label (detector anti-Tau antibody and enzyme label) can be reduced relative to standard ELISAs. Lowered concentrations of labeling reagents reduces their interaction with capture beads, resulting in reduced nonspecific binding enabling high signal to background ratios, even at extremely low concentrations of biomarker. For higher biomarker concentrations where all beads contain one or more labeled immunocomplexes, digital signals from the Poisson realm are used to calibrate analog intensity measurements, extending the dynamic range to over four logs.

Three reagents were developed for this tau protein immunoassay: capture beads, biotinylated detector, and a conjugate of streptavidin:beta-galactosidase The capture bead reagent comprised of a commercially available monoclonal anti-tau antibody (Covance) directed to an epitope (amino acids 210-230). The antibody was covalently attached by standard coupling chemistry to 2.7 μm carboxy paramagnetic microbeads (Varian). Because individual beads were captured in array wells 4.5 μm wide×3.25 μm deep, it was advantageous that the capture beads remain monomeric. The antibody-coated beads were diluted to a working concentration of 6×106 beads/mL in Tris buffer with a surfactant and BSA. The biotinylated detector reagent was comprised of two commercially available monoclonal anti-tau antibodys (Pierce) directed to the N-terminus of the Capture Detector (amino acids 159-163 and 194-198). The antibodies were biotinylated using standard methods (Solulink), and the biotinylation level was confirmed spectrophotometrically per manufacturer's instructions. The monomeric state of the detector antibody before and after biotinylation was confirmed by size exclusion HPLC. The biotinylated detector antibodies were diluted to individual concentration of 0.2 μg/ml for assay in a PBS diluent containing a surfactant and newborn calf serum, NCS (PBS/NCS), The enzyme conjugate streptavidin: β-galactosidase (SPG) was prepared by covalent conjugation of purified streptavidin (Thermo Scientific) and β-galactosidase (Sigma) using standard coupling chemistry (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, Thermo Scientific). Aliquots of a concentrated stock solution of SβG were prepared in PBS with 50% glycerol and transferred to −20° C. for storage, Prior to assay, an aliquot was thawed and diluted to 25 μM in PBS/NCS with MgCl2.Purified Tau 381 antigen for calibrators and for specificity testing were from Millipore.

Assay calibrators and controls were prepared by dilution ofTau 381 stock in PBS diluent containing a surfactant and BSA (PBS/BSA). In some cases, a stock solution prepared by dilution to 1000 ng/mL in PBS/10G. For dynamic range/linearity characterization, a series of calibrators were prepared by serial 3-fold dilution to give a calibration range of 0-100 pg/mL. To evaluate assay day-to-day reproducibility at low concentrations, three low controls were prepared at 0.1, 5.0, and 50.0 pg/mL in PBS/BSA.

50,000 well optical fiber microarrays were prepared as previously described. In brief, optical fiber bundles (Schott North America) were cut into 5 cm lengths and sequentially polished with 30, 9, and 1 um-sized diamond lapping films. One end of each bundle was etched in a 0.025 N HCl solution for 2 minutes and then submerged into water. The differential etch rate of the core and cladding glass of the fiber bundles caused an array of 4.5 um diameter wells to be formed in the core fibers.

Bead-plasma incubations and labeling of immunocomplexes in conical 96 well plates (Axygen) were conducted using a robotic liquid handling system (Tecan EVO 150). Conical wells are used to facilitate magnetic attraction of the beads to the sides of the wells for efficient removal of reaction mixtures and bead washing. For magnetic attraction, a microplate bar magnet (Invitrogen) was used. Incubation periods were conducted with shaking on a microplate shaker (VWR) to keep beads suspended in the wells. The assays were initiated by mixing 100 of sample with 600,000 capture beads, and the mixtures were incubated with shaking for two hours, Serum samples were pre-diluted 1:4 prior to assay with PBS/BSA as a precaution for sample quality and interference effects, Following serum incubation in the presence of biotinylated detector antibody, the beads were washed 3 times with a wash buffer of 5-fold concentrated PBS with a surfactant (5×PBS). After a the wash step, 100 μL of streptavidin-β-galactosidase was incubated with the beads for 30 minutes to form the final enzyme-labeled immunocomplex. The beads were then washed eight times per above, and concentrated to 2×107 beads/ml with the addition of a reduced volume (30 μL) of array loading buffer comprised of PBS with a surfactant. Beads were then loaded onto the arrays. 10 μL of the concentrated bead solution (2×106 beads) were pipetted onto the arrays and the arrays were centrifuged at 1,300 g for 10 minutes, Excess beads were removed by a PBS rinse and swabbing with deionized water. With this technique, array filling by the beads was generally 50-60%, which was adequate for minimizing contributions to imprecision from Poisson noise. Wells containing tau protein-labeled beads were detected utilizing beta-galactosidase catalyzed hydrolysis of resorufin β-D-galactopyranoside (RGP, Invitrogen) into fluorescent product (resorufin, excitation 558 nm, emission 577 nm). To introduce RGP substrate to the array wells, droplets of substrate were placed on a silicone gasket and introduced into the array wells with a mechanical platform. This step resulted in an array of sealed femtoliter wells in which enzyme-containing beads developed a concentrated fluorescence signal.

Imaging was accomplished via a custom-built fluorescence imaging system containing a light source, objectives, filter cubes and a CCD camera. For each sample, five fluorescent images of one second each were acquired (to identify wells containing an enzyme) and one white light image was acquired (to identify wells containing a bead). Background fluorescence and any contaminating artifacts were discriminated from true ‘positive’ wells by analyzing for signal growth over the multiple images. These images were analyzed to determine the average number of enzymes per bead (AEB) across the concentration range. In some cases, at <50% active beads, the system was determined to be in the digital realm, so AEB was be determined from the fraction of beads that contain at least one enzyme and the Poisson distribution; and at >50% active beads, the average fluorescence intensity of the beads was normalized to the average fluorescence intensity of beads containing a single enzyme to yield AEB. In other cases, at <70% active beads relative to total beads, AEB was determined as a count of active beads corrected for a low statistical probability of multiple enzymes per bead; and at >70% active beads, the probability of multiple enzymes/bead increases such that all wells contain multiple enzymes and all are growing in signal and in this realm, the signal is was no longer digital, and average fluorescence intensities of the wells were converted to AEB based on the average intensities of wells containing single enzymes as determined at lower A1342 concentrations. The AEB unit worked continuously across the digital and analog realms.

For description of various details associate with this assay, see, for example, U.S. patent application Ser. No. 12/731,130, filed Mar. 24, 2010, published as US-2011-0212848 on Sep. 1, 2011, entitled “ULTRA-SENSITIVE DETECTION OF MOLECULES OR PARTICLES USING BEADS OR OTHER CAPTURE OBJECTS,” by Duffy et al.; International Patent Application No. PCT/US2011/026645, filed Mar. 1, 2011, published as WO 2011/109364 on Sep. 9, 2011, entitled “ULTRA-SENSITIVE DETECTION OF MOLECULES OR PARTICLES USING BEADS OR OTHER CAPTURE OBJECTS,” by Duffy et al.; International Patent Application No. PCT/US2011/026657, filed Mar. 1, 2011, published as WO 2011/109372 on Sep. 9, 2011, entitled “ULTRA-SENSITIVE DETECTION OF MOLECULES USING DUAL DETECTION METHODS,” by Duffy et al.; U.S. patent application Ser. No. 12/731,135, filed Mar. 24, 2010, published as US-2011-0212462 on Sep. 1, 2011, entitled “ULTRA-SENSITIVE DETECTION OF MOLECULES USING DUAL DETECTION METHODS,” by Duffy et al.; International Patent Application No. PCT/US2011/026665, filed Mar. 1, 2011, published as WO 2011/109379 on Sep. 9, 2011, entitled “METHODS AND SYSTEMS FOR EXTENDING DYNAMIC RANGE IN ASSAYS FOR THE DETECTION OF MOLECULES OR PARTICLES,” by Rissin et al.; U.S. patent application Ser. No. 12/731,136, filed Mar. 24, 2010, published as US-2011-0212537 on Sep. 1, 2011, entitled “METHODS AND SYSTEMS FOR EXTENDING DYNAMIC RANGE IN ASSAYS FOR THE DETECTION OF MOLECULES OR PARTICLES,” by Duffy et al.; U.S. patent application Ser. No. 13/035,472, filed Feb. 25, 2011, entitled “SYSTEMS, DEVICES, AND METHODS FOR ULTRA-SENSITIVE DETECTION OF MOLECULES OR PARTICLES,” by Fournier et al.; U.S. patent application Ser. No. 13/037,987, filed Mar. 1, 2011, published as US-2011-0245097 on Oct. 6, 2011, entitled “METHODS AND SYSTEMS FOR EXTENDING DYNAMIC RANGE IN ASSAYS FOR THE DETECTION OF MOLECULES OR PARTICLES,” by Rissin et al.; each herein incorporated by reference. While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the functions and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the scope of the present invention.

The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to “A and/or B,” when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.