CN110499287B - Method for simply preparing placenta mesenchymal stem cell exosome - Google Patents

Abstract

The invention relates to a method for simply preparing a cytokine from placenta mesenchymal stem cells. A method for simply preparing the placenta mesenchymal stem cell exosome. In particular to a method for separating and extracting exosome from placenta mesenchymal stem cells, which comprises the following steps: culturing the placenta mesenchymal stem cells to obtain a culture supernatant; performing sephadex column chromatography on the culture supernatant to obtain a chromatographic solution; concentrating the chromatographic solution by using a tangential flow ultrafiltration system to obtain an exosome concentrated solution; and (4) freezing and storing or freezing and drying the exosome concentrated solution. The process of the invention exhibits advantageous properties as described in the description.

Description

Method for simply preparing placenta mesenchymal stem cell exosome

Technical Field

The invention belongs to the technical field of biology, relates to a method for obtaining membrane vesicles participating in cell biological activities, and particularly relates to a method for separating and obtaining Exosomes (Exosomes) from human placenta Mesenchymal Stem Cells (MSC), and an application of the Exosomes in cell repair. In particular, the invention relates to a method for isolating exosomes from human placental mesenchymal stem cell sources.

Background

Mesenchymal Stem Cells (MSCs) are a type of non-hematopoietic pluripotent stem cells derived from mesoderm, and it has been confirmed that MSCs have strong anti-inflammatory and multiple immune cell-suppressing abilities in addition to self-renewal and multipotentiality, and are capable of inducing peripheral immune tolerance. Studies have shown that MSCs inhibit their function by secreting various immunomodulatory factors, such as IFN- γ, PGE2, etc. (see: Polchert D, Sobinsky J, Douglas G, Kidd M, Moadsiri A, Reina E, et al. IFN-gamma activation of sensory stem cells for treatment and preservation of graft summary host disease. European great deal of immunity.2008; 38(6):1745-55. and Spagiari GM, deletion H, Becchetti F, Moretta L. MSCs inhibition of monoclonal-derived DC activation and preservation by selection of immune cells with the same expression of the same cell of the same expression of cell culture of the same expression of cell and the same expression of cell of the same expression of the same M, Carlo Stella C, Magni M, Milanesi M, Longoni PD, Matteucci P, et al human bone random structural cells supress T-lymphocyte promotion induced by cell or nonpecific biological stimulation. blood.2002; 99(10):3838-43.).

Exosomes (exosomes) are membrane-like microvesicles secreted by cells with a diameter of about 30 to 100nm and a density ranging from 1.13 to 1.19 g/ml. Exosomes can carry a variety of proteins, mrnas, mirnas similar to the source cell, and are involved in immune regulation, cellular communication, cell migration, angiogenesis, etc. (see: Yanez-Mo M, siljar PR, Andreu Z, Zavec AB, Borras FE, Buzas EI, et al, biological properties of extracellular fluids and the same physiological functions. journal of extracellular fluids. 2015; 4: 27066.). Lai et al found that MSCs-derived exosomes reduced myocardial ischemia reperfusion injury and demonstrated that miRNA of exosomes could promote angiogenesis, and thus exosomes could be a new approach to the treatment of cardiovascular disease (see: Lai RC, Arslan F, Lee MM, Sze NS, Choo A, Chen TS, et al. Xin et al found that MSCs-derived exosomes can promote growth of neural axons by transferring miR-133B to neural cells (see: Xin H, Li Y, Buller B, Katakowski M, Zhang Y, Wang X, et al. exosome medium transfer of miR-133B from multi-potential media structural cells to neural cells compositions to neural cells outer growth. Stem cells.2012; 30(7): 1556-64.). Filipazzi et al found that tumor cell-derived exosomes could inhibit cytotoxicity of T-cells and NK-cells through the NK cell activating receptor NKG2D (natural killer group 2, member D), thereby affecting the host's immune system (see: Filipazzi P, Burdek M, Villa A, Rivolltini L, Huber V.Recent Advances on the roll of tumor exosomes in immune suppression and disease progression. Secondary in cancer biology.2012; 22(4): 342-9.).

Exosomes (exosomes), membrane vesicles secreted by living cells, were first discovered in 1983. With the progress of research, it is continuously paid attention to find that it has the functions of carrying out protein and nucleic acid transport, specifically targeting receptor cells, exchanging proteins and lipids or triggering downstream signaling events, and participating in intercellular communication. The exosome-carrying protein includes two types of protein molecules, source cell non-specific and source cell specific. The former may be associated with biogenesis and biological actions of exosomes, mainly including: cytosolic proteins, proteins involved in intracellular signal transduction, various metabolic enzymes, heat shock proteins, and tetraspanin; the other is a special protein, which exists only in an exosome secreted by a special cell, and the exosome of the special cell source is closely related to the biological function, such as: the exosomes of molecular origin contain mhc class ii molecules. Therefore, exosomes from different cell sources carry different signaling molecules and exert different functions. For example: exosomes secreted by tumor cells can mediate angiogenesis tumor cell proliferation and immune escape, while dendritic cell-derived exosomes can cause an effective anti-tumor immune response of an organism. At present, research finds that the exosome contains protein rRNA and microRNA related to cell sources, and the exosome can transmit functional nucleic acid molecules among cells through a biological barrier, so that various biological functions are exerted, and the exosome is expected to become a novel administration route and a gene therapy vector.

Research shows that mesenchymal stem cells such as umbilical cord or placenta-derived exosomes carry various effective cytokines, proteins and small molecule nucleic acid substances, and can effectively mediate cell proliferation, apoptosis and function regulation. Research shows that the exosome contains vascular endothelial growth factor, fibroblast growth factor, platelet proliferation factor, tumor necrosis factor, tumor growth factor and the like, and has the functions of inhibiting apoptosis and the fibrosis degree of cells, promoting angiogenesis mitosis, mediating immunoreaction and the like. Experiments prove that insulin-like growth factors and vascular endothelial cell growth factors carried by exosomes secreted by using mesenchymal stem cells are key leading factors for treating acute kidney injury. In immunology, the surface of the exosome lipid membrane secreted by the mesenchymal stem cell expresses various membrane proteins, such as: coagulation factors, tumor necrosis factors, MHC I/II molecules, and CCR5 chemokine receptors, among others, which are important for their role in resisting inflammation.

The current methods and approaches for exosome extraction are also diverse, such as: bone marrow extraction, peripheral blood extraction, etc., and all these exosome acquisition pathways require traumatic cell or tissue sources. The exosome extraction method mainly adopts an ultracentrifugation method or an expensive kit column-passing method, but the ultracentrifugation method has the defects of uneven exosome mass, incapability of ensuring the obtained amount of exosomes, long step-by-step centrifugation time, and time and cost waste because the exosomes cannot be finally separated due to the centrifugation time or the centrifugation speed. The cartridge-over-column method is generally only suitable for obtaining relatively small amounts of exosomes and is expensive.

The prior art has reported some methods for the isolation and extraction of exosomes. For example, CN106282107A (chinese patent application No. 201610779165.2) discloses a method for isolating exosomes from human placental mesenchymal stem cells, when the confluence rate of P2-P3 placental mesenchymal stem cells reaches 85% -90%, collecting a culture medium, obtaining cell culture supernatant, performing membrane filtration, and collecting filtrate; and then centrifuging the filtrate, collecting the supernatant fluid, adding 10 w/v% -12 w/v% of polyethylene glycol culture medium supernatant fluid solution according to the volume ratio of the supernatant fluid to 1: 1, fully and uniformly mixing, then centrifuging for the second time, and finally obtaining the precipitate, namely the exosome. The method is convenient in material obtaining and easy in enrichment, amplification and culture, and the exosome is obtained by recycling the supernatant of the culture medium of the P2-P3 generation placenta mesenchymal stem cells without involving the medical ethical problem. In the exosome separation process, the exosome enrichment is effectively increased by adopting the means of membrane filtration, centrifugation, polyethylene glycol solution addition and the like, the time consumption is short, and the cost is low.

CN105708861A (chinese patent application No. 201610149852.6) discloses the use of exosomes derived from mesenchymal stem cells in the preparation of a medicament for treating ankylosing spondylitis, wherein the extraction method of exosomes comprises: culturing sufficient bone marrow mesenchymal stem cells, washing the cells with PBS 48h before extracting the stem cell exosomes, replacing a serum-free culture medium, and continuously culturing for 48 h; collecting serum-free culture medium, centrifuging at 300 × g for 10min, and collecting supernatant; centrifuging at 2000 Xg for 10min, and collecting supernatant; centrifuging at 10000 Xg for 30min, and collecting supernatant; centrifuging at 100000 × g for 70min, and collecting precipitate; and (4) resuspending the precipitate with PBS, centrifuging at 100000 Xg for 70min, and collecting the precipitate to obtain the exosome.

CN105267240A (chinese patent application No. 201410781765.3) discloses the use of exosomes derived from mesenchymal stem cells, wherein the exosomes are prepared by a method comprising the following steps: (1) and (3) isolated culture of mesenchymal stem cells: according to different sources of the mesenchymal stem cells, different isolated culture modes are adopted, and the method specifically comprises the following steps: separating and culturing human umbilical cord mesenchymal stem cells: taking a sterile fresh umbilical cord of a newborn, repeatedly washing the umbilical cord by Phosphate Buffer Solution (PBS), and cutting the umbilical cord into tissue blocks with the diameter of about 1-2 mm; digesting with collagenase type 2 and pancreatin in sequence, centrifuging the supernatant, taking cell precipitate, placing the cell precipitate into a culture bottle, and culturing with DMEM/F12 culture medium containing 10% fetal calf serum, 5% CO2 and saturated humidity at 37 ℃; removing non-adherent cells, and performing subculture by digestion with 0.25% trypsin after 80% fusion of adherent cells; separating and culturing human placenta mesenchymal stem cells: shearing a tissue with the thickness of 1-2cm on the surface of a placental villus membrane, shearing the tissue into 1-2mm fragments, rinsing the fragments to be colorless by using a phosphate buffer solution, digesting the fragments by using dispaseII type enzyme and 4 type collagenase in a water bath at 37 ℃ for 1 hour, shaking and standing the fragments, naturally dividing the liquid into three layers, absorbing the suspension of the middle layer into a centrifugal tube, adding the phosphate buffer solution into the centrifugal tube, uniformly mixing the suspension, centrifuging the mixture, removing the supernatant, taking cell precipitates, putting the cell precipitates into a culture bottle, and culturing the cell precipitates by using a DMEM culture medium containing 10% fetal calf serum, 5% CO2 and the saturated humidity at 37 ℃; removing non-adherent cells, and performing subculture by digestion with 0.25% trypsin after 80% fusion of adherent cells; ③ separating and culturing the human adipose-derived mesenchymal stem cells: the fat extract was aseptically aspirated and washed several times with phosphate buffer. Removing medicine and blood cells used in liposuction surgery, digesting for 1 hour at 37 ℃ by using collagenase 1, and stirring at intervals; centrifuging, removing upper fat, mixing, filtering with 200 mesh sieve, centrifuging the obtained cell suspension, washing cell precipitate with phosphate buffer solution, suspending with 10% fetal calf serum alpha-MEM culture solution, transferring into culture flask, and culturing with 5% CO2 and 37 deg.C saturated humidity; subculture was performed with 0.25% trypsin digestion after 80% fusion of adherent cells. (2) Collecting the mesenchymal stem cell conditioned medium: taking 3-5 generation mesenchymal stem cells to culture for 48h in a serum-free manner; collecting culture supernatant; filtering with 0.22 μm sterile membrane to obtain mesenchymal stem cell conditioned medium. (3) The exosome separation and purification comprises the following steps: collecting the filtered mesenchymal stem cell conditioned medium, centrifuging at 4 ℃ for 10min at 1000g, and collecting the supernatant; centrifuging the collected supernatant at 4 ℃ for 20min at 2000g, and collecting the supernatant; centrifuging the collected supernatant at 4 ℃ for 30min at 10000g, and collecting the supernatant; centrifuging the collected supernatant at 110000g for 70min, discarding the supernatant, and resuspending the precipitate by using a phosphate buffer solution; and centrifuging the mixture for 70min at 110000g again, discarding the supernatant, resuspending the precipitate by using a small amount of phosphate buffer solution, and filtering and sterilizing the precipitate by using a 0.22-micrometer filter membrane to obtain the exosome derived from the mesenchymal stem cells.

CN104382827A (Chinese patent application No. 201410705462.3) discloses the use of human amniotic mesenchymal stem cell exosomes, wherein the exosomes are prepared by the following steps: 1. culturing the human amniotic mesenchymal stem cells: taking well-grown human amniotic mesenchymal stem cells, culturing the well-grown human amniotic mesenchymal stem cells by using a serum-free culture medium, digesting and passaging the well-grown human amniotic mesenchymal stem cells by 0.25% pancreatin, transferring the well-grown human amniotic mesenchymal stem cells to P2 generation, removing culture supernatant after the well-grown human amniotic mesenchymal stem cells grow to 80%, washing the culture supernatant for three times by using PBS (phosphate buffer solution), adding a 1640 basic culture medium, collecting the culture supernatant every day, replacing a fresh 1640 culture medium, continuously collecting and culturing for 3-5 days, and collecting the culture supernatant for extracting exosomes. 2. The exosomes are extracted (the whole extraction process is carried out at 4 ℃ unless otherwise specified): centrifuging 300g of all collected culture supernatants for 10min, reserving the supernatants, discarding the precipitates, and removing cells in the culture solution; centrifuging the supernatant fluid for 20-30 min at 2000-3000 g, keeping the supernatant fluid, discarding the precipitate, and removing cell debris; centrifuging the supernatant fluid at 10000g for 60-100 min, reserving the supernatant fluid, discarding the precipitate, and removing cell debris again; centrifuging 100000g of supernatant for 60-120 min, discarding the supernatant, and retaining the precipitate; adding PBS into the precipitate for resuspension, centrifuging at 100000g for 60-120 min, discarding the supernatant, retaining the precipitate, removing the protein in the culture medium to obtain the exosome of the purified human amniotic mesenchymal stem cells, resuspending with PBS buffer solution, and measuring the protein concentration with BCA kit.

CN103767985A (chinese patent application No. 201210402915.6) discloses preparation and application of exosome secreted by human blood or mesenchymal stem cells, wherein the exosome is prepared by the following method: 1) collecting blood → differential centrifugal separation → low-temperature ultra-speed purification → obtaining the exosome contained in the high-purity serum; 2) extracting mesenchymal stem cells → culturing in vitro, amplifying → collecting cell culture supernatant → melting the culture supernatant and mixing → differential centrifugation separation → low-temperature ultra-speed purification → obtaining exosome secreted by high-purity stem cells; 3) extracting mesenchymal stem cells → culturing in vitro, amplifying → collecting cell culture supernatant → melting the culture supernatant and mixing → centrifuging at low temperature and purifying by immunoadsorption → obtaining exosome secreted by high-purity mesenchymal stem cells.

CN105861430A (chinese patent application No. 201610279473.9) discloses an exosome prepared by the following method: (1) separating and culturing human umbilical cord mesenchymal stem cells; (2) optimally treating human umbilical cord mesenchymal stem cells by using IL-1 beta; (3) collecting the culture medium supernatant in the step (2), and collecting the exosome by using a differential centrifugation method to obtain the exosome derived from the human umbilical cord mesenchymal stem cell optimized by the IL-1 beta.

However, in the prior art, when mesenchymal stem cells are cultured from placenta, umbilical cord blood, bone marrow and fat, the culture medium supernatant of the MSCs is mostly adopted to extract exosomes, and the methods all have the defects of low yield, complex process and the like. Therefore, there is still a need in the art for a new method for isolating and extracting exosomes, particularly for extracting exosomes secreted by mesenchymal stem cells in a simple, easily available and high-yield manner.

Disclosure of Invention

The invention aims to provide a novel method for separating and extracting exosome, and particularly the method can extract exosome through mesenchymal stem cell secretion in a simple and easily-obtained and high-yield manner. It has surprisingly been found that the above object can be achieved advantageously by the process according to the invention. The present invention has been completed based on this finding.

To this end, the present invention provides in a first aspect a method for isolating exosomes from placental mesenchymal stem cells, comprising the steps of:

1) providing 2 nd to 5 th generation human placenta mesenchymal stem cells in logarithmic growth phase at the rate of 5000 to 15000/cm²Inoculating to DMEM/F12 medium containing 2mM L-glutamine, culturing for 3-4 days, collecting supernatant, centrifuging at 20000g centrifugal force for 20min to remove cells and debris, and filtering with 0.22 μm filter membrane to obtain culture supernatant;

2) guiding a Pudex sephadex filtration medium Pudex G-25 into a chromatographic column by using a glass rod for drainage, and stirring by using the glass rod while installing;

3) after the column is filled, sucking water on the upper surface of the column by using a pipette, and loading the culture supernatant collected in the step 1) into a chromatographic column;

4) covering an upper cover of the chromatographic column, inserting a thin tube of the upper cover into a beaker filled with double distilled water, opening a constant flow pump and a collector device, adjusting the speed of the constant flow pump and the time of the collector, and beginning to elute and collect an eluted fraction containing cell secretion to serve as a chromatographic solution;

5) concentrating the filtrate with a tangential flow ultrafiltration system (such as Shibi pure KR2i type tangential flow ultrafiltration system), flushing the pipeline with ultra-pure water, and installing 100kD 100cm²The MidiKros filter is used for filtering and concentrating 5L of the chromatographic solution obtained in the step 4) to obtain 100ml of reflux liquid which is concentrated by 50 times and is an exosome concentrated solution; optional 6) exosomesSubpackaging the concentrated solution, and freezing and storing at-80 deg.C; or adding a freeze-drying excipient into the exosome concentrated solution and then freeze-drying.

In the present invention, the tangential flow ultrafiltration system used is a Shibi pure KR2i type tangential flow ultrafiltration system, as not otherwise specified. Of course other brands of tangential flow ultrafiltration systems may be used.

The Pudex series of sephadex filter media, which is a gel filter media developed based on sephadex microspheres, is readily commercially available, e.g., from kyropoulos, and is believed to have good chemical stability and high resolution, with a wide range of separation ranges and particle sizes available, and is widely used for protein isolation and protein desalting.

The method according to the first aspect of the present invention, wherein in step 1), the concentration is at 10000/cm²The density of (a) to seed the cells.

The method according to the first aspect of the present invention, wherein in the step 1), the method further comprises adding sodium mannose phosphate to the filtrate obtained by filtration through a 0.22 μm filter to dissolve the filtrate, thereby obtaining a culture supernatant; in one embodiment, the sodium mannose phosphate is added at a concentration of 0.05 to 0.1% mass/volume, for example 0.08%.

The method according to the first aspect of the present invention, wherein in step 1), the 2 nd to 5 th generation human placental mesenchymal stem cells in logarithmic growth phase are prepared according to methods known in the art. Such as chinese patent application No. 201210044648.X, 201710653583.1, 201811568552.7, etc. of the present applicant.

The method according to the first aspect of the present invention, wherein in step 1), the 2 nd to 5 th generation human placental mesenchymal stem cells in logarithmic growth phase are obtained according to a method comprising the steps of:

(1) treatment of placental tissue

Removing amnion from human placenta, cutting placenta lobular epidermis membrane sample tissue, and cleaning with normal saline;

shearing the placental lobule epidermis membrane-like tissue into tissue fragments with a volume size of about 0.2cm 3;

placing the tissue fragments in a centrifuge tube, adding a proper amount of 0.9% physiological saline, filtering by using a 300-mesh filter screen, and cleaning twice by using a proper amount of 0.9% physiological saline until filtrate is clear;

adding the cleaned tissue into HBSS digestive juice containing 0.005% Liberase MNP-S enzyme and 0.05% DNA I type enzyme, mixing well, and shaking and digesting in shaker for 30min (37 deg.C, 100 rpm);

(2) obtaining placental progenitor cells

After digestion is finished, adding fetal calf serum into a centrifuge tube to stop digestion, uniformly mixing, diluting with 50ml of normal saline containing 5% dextran, 2.5% human serum albumin and 200U of DNase I, filtering by using a 300-mesh filter screen, washing tissues for multiple times by using 100ml of normal saline, and collecting filtrate;

centrifuging the filtrate at 1400rpm for 5min (e.g. acceleration 9 and deceleration 7), removing supernatant, collecting precipitate, resuspending with physiological saline, centrifuging again, and collecting precipitate;

suspending the precipitated cells by DMEM/F12, sampling and counting to obtain P0 generation cells;

(3) purification culture

The culture conditions are as follows: DMEM/F12 medium containing 10% fetal bovine serum, 2mM L-glutamine at 37 deg.C and 5% CO₂Culturing in a constant-temperature wet incubator;

digestion conditions are as follows: 0.25% pancreatin, digested at 37 ℃ for 2 minutes;

harvesting conditions are as follows: after termination of digestion with complete medium (i.e., 10% fetal bovine serum, 2mM DMEM/F12 medium with L-glutamine) and centrifugation at 1400rpm for 5 minutes, the pellet was collected;

at a rate of 5000 to 15000/cm²The placenta P0 generation cells are inoculated in a T75 culture bottle, and the liquid is changed all the day 3 to 4; a plurality of cell clones appear on days 6-7, and flaky fusiform cells growing in a vortex shape on days 10-11, namely P1 generation placental mesenchymal stem cells, can be collected and then passed;

at a rate of 5000 to 15000/cm²The inoculation density culture is carried out, the culture medium components and the culture conditions are the same as those of the culture medium components and the culture conditions of the culture medium components of the P0-P1, and the culture medium components and the culture conditions are harvested after 3-4 days to obtain P2 generation cells; by analogy, culturing for 3-4 days at the same inoculation density and the same culture condition, and harvesting to obtain P3,P4, P5 generation placental mesenchymal stem cells; and optionally (4) detecting the obtained placenta mesenchymal stem cells.

The method according to the first aspect of the present invention, wherein in step 2), the chromatography column is a sephadex G-25 column.

The process according to the first aspect of the present invention, wherein in the step 4), the elution fraction obtained is dissolved by adding magnesium chloride as a chromatographic solution; in one embodiment, the magnesium chloride is added in an amount of 0.02 to 0.05%, for example 0.04%, mass/volume% of the elution fraction.

The method according to the first aspect of the invention, wherein in step 6) the freeze-drying of the exosome concentrate is performed as follows:

7.1) taking the exosome concentrated solution or taking the exosome concentrated solution frozen at minus 80 ℃ to be completely melted in water bath at 37 ℃, and adding 5-15% of freeze-dried excipient to dissolve the excipient;

7.2) filtering the solution added with the excipient by using a 70-micron filter, then subpackaging the filtered solution into glass bottles with 2-5 ml of each bottle, covering a forked rubber plug, putting the glass bottles into a freeze dryer, and starting the following freeze-drying procedure:

pre-freezing for 3.5 hours at the normal pressure, wherein the temperature is-30 to-40 ℃;

starting a vacuum pump to ensure that the vacuum value is 0.04mbar, and freezing for 1-3 hours at the temperature of-38 to-40 ℃;

keeping the vacuum degree unchanged, and raising the temperature to-20 to-25 ℃ for freeze drying for 10 to 15 hours;

keeping the vacuum degree unchanged, and raising the temperature to-2 ℃ for freeze drying for 1-3 hours;

keeping the vacuum degree unchanged, and heating to 33-37 ℃ for drying for 2-5 hours;

and (5) after the program is finished, covering the cover under vacuum to obtain the exosome freeze-dried powder.

The present invention is further described below. The documents cited in the present application, and the documents cited in the documents, are incorporated herein by reference in their entirety.

In the present invention, any of the technical features in any of the technical aspects of the present invention are equally applicable to any of the embodiments of any of the technical aspects of the present invention, as long as they do not cause contradiction, and such mutual application may be appropriately modified as necessary.

In the present invention, the term "placental mesenchymal stem cells" refers to mesenchymal stem cells derived from the placenta. Thus in the present invention, and in particular in the context relating to the present invention, the term "placental mesenchymal stem cells" may be used interchangeably with "placental stem cells", "mesenchymal stem cells", unless otherwise specifically indicated.

Exosomes (exosomes) are vesicular corpuscles secreted extracellularly by cells, have a diameter of about 30-150 nm, have a typical lipid bilayer membrane structure, and can be present in cell culture supernatants, plasma, serum, saliva, urine, amniotic fluid and malignant ascites, as well as other biological fluids; it carries important information of various proteins, lipids, DNA and RNA of the mother cell, and plays an important role in substance and information transmission between cells. Exosomes of diverse cellular origin are involved in important physiological and pathological processes such as antigen presentation, genetic material exchange, immune response, angiogenesis, inflammation, tumor metastasis and processing, pathogen or oncogene transmission. These functions are dependent on the content of the exosomes, in particular proteins and RNA.

The existing research proves that the exosome secreted by the mesenchymal stem cell plays an important role in the aspects of promoting skin injury repair, relieving inflammatory reaction, promoting blood vessel regeneration and the like. Related studies demonstrate that stem cells act through exosomes for skin repair. The mesenchyma stem cell is pretreated by endotoxin to enhance the paracrine action of the mesenchyma stem cell, and the nutrition support and regeneration repair performance of the stem cell are improved. Research shows that the mesenchymal stem cells construct a steady-state tissue repair microenvironment by releasing a large amount of exosomes, so that inflammatory reaction is eliminated, and wound healing is promoted. If the exosome can act on human skin to promote angiogenesis, nutrition is delivered to the skin, and metabolic waste is transported, so that the skin is younger. Research by korean scientists has shown that adipose-derived stem cells and their secreted factors have a wrinkle-removing effect on ultraviolet-induced wrinkles, and the wrinkle-removing effect is mainly achieved by reducing mid-wave ultraviolet B-induced apoptosis and promoting collagen synthesis by human fibroblasts.

With the recent pursuit of skin whitening, more and more people use whitening skin care products. Melanin in the skin is synthesized by melanocytes, and melanin diffuses to adjacent cells by osmosis, forming color on the skin. The shade of the color is mainly determined by the content of melanin in the skin. Biochemical reaction processes occurring within melanocytes: fatty acid tyrosine generates dopaquinone under the action of tyrosinase, and the dopaquinone is converted into melanin through haematochrome and leuco pigment under the action of enzyme or non-enzyme oxidation, and the process is the main cause of the melanin. Therefore, retarding or inhibiting the action of tyrosinase in the first stage of the reaction, i.e., inhibiting melanogenesis, and finding drugs that can retard or inhibit the action of tyrosinase, is extremely important for retarding or inhibiting melanogenesis due to the action of tyrosinase.

The invention provides a simple and easily-obtained and high-yield method for extracting exosomes through mesenchymal stem cell secretion.

Drawings

FIG. 1: and (3) a morphological observation picture of the partial generation placenta mesenchymal stem cells.

FIG. 2: and (3) detecting the result of the cell flow type of the P3 generation placenta mesenchymal stem cells.

FIG. 3: and (3) osteogenic differentiation of the placenta mesenchymal stem cells.

FIG. 4: western Blotting identified exosomes.

Detailed Description

The present invention will be further described by the following examples, however, the scope of the present invention is not limited to the following examples. It will be understood by those skilled in the art that various changes and modifications may be made to the invention without departing from the spirit and scope of the invention. The present invention has been described generally and/or specifically with respect to materials used in testing and testing methods. Although many materials and methods of operation are known in the art for the purpose of carrying out the invention, the invention is nevertheless described herein in as detail as possible.

Example 1: preparation of placental mesenchymal Stem cells

(1) Treatment of placental tissue

Removing amnion from a fresh human placenta, shearing placental lobule surface membrane sample tissue, and cleaning with normal saline;

shearing the placental lobule epidermis membrane-like tissue into tissue fragments with a volume size of about 0.2cm 3;

placing the tissue fragments in a centrifuge tube, adding a proper amount (100ml) of 0.9% physiological saline, filtering by using a 300-mesh filter screen, and cleaning twice by using a proper amount (100ml) of 0.9% physiological saline until filtrate is clear;

adding the cleaned tissue into HBSS digestive juice (100ml) containing 0.005% Liberase MNP-S enzyme and 0.05% DNA I enzyme, mixing well, and shaking and digesting in shaker for 30min (37 deg.C, 100 rpm);

(2) obtaining placental progenitor cells

After digestion, adding fetal bovine serum (2ml) into a centrifuge tube to terminate digestion, uniformly mixing, diluting with 50ml of normal saline containing 5% dextran, 2.5% human serum albumin and 200U of DNase I, filtering with a 300-mesh filter screen, washing tissues for multiple times with 100ml of normal saline, and collecting filtrate;

centrifuging the filtrate at 1400rpm for 5min (acceleration 9, deceleration 7), removing supernatant, collecting precipitate, resuspending with physiological saline (100ml), centrifuging again, and collecting precipitate;

suspending the precipitated cells by DMEM/F12(100ml), sampling and counting to obtain P0 generation cells;

(3) purification culture

The culture conditions are as follows: DMEM/F12 medium containing 10% fetal bovine serum, 2mM L-glutamine at 37 deg.C and 5% CO₂Culturing in a constant-temperature wet incubator;

digestion conditions are as follows: 0.25% pancreatin, digested at 37 ℃ for 2 minutes;

harvesting conditions are as follows: after termination of digestion with complete medium (i.e., 10% fetal bovine serum, 2mM DMEM/F12 medium with L-glutamine) and centrifugation at 1400rpm for 5 minutes, the pellet was collected;

at a rate of 5000 to 15000/cm²The placenta P0 generation cells were inoculated into a T75 flask (actual inoculation density: 10000 cells/cm)²) Changing the liquid completely on the 3 rd to 4 th days; a plurality of cell clones appear on days 6-7, and flaky fusiform cells growing in a vortex shape on days 10-11, namely P1 generation placental mesenchymal stem cells, can be collected and then passed;

at a rate of 5000 to 15000/cm²The inoculation density culture is carried out, the culture medium components and the culture conditions are the same as those of the culture medium components and the culture conditions of the culture medium components of the P0-P1, and the culture medium components and the culture conditions are harvested after 3-4 days to obtain P2 generation cells; by analogy, culturing for 3-4 days under the same inoculation density and the same culture condition, and harvesting to obtain P3, P4 and P5 generation placenta mesenchymal stem cells;

(4) detecting the obtained placenta mesenchymal stem cells:

and (4.1) observing the cell morphology through an optical inverted microscope, and obtaining cells with better consistency and activity according to the operation procedures of standardized separation, purification, culture and amplification of the placenta mesenchymal stem cells. The cells of the partial passage are arranged in a long spindle vortex (see FIG. 1).

(4.2) detecting the placenta tissue-derived MSCs by adopting a flow cytometry analysis technology, wherein the result shows that: the placenta MSCs are positive to CD73, CD90 and CDl05, and the positive rate is not lower than 95%; CD11b, CD19, CD34, CD45 and HLA-DR are negative, and the positive rate is not higher than 2%. By analyzing the phenotype of primary P0 cells isolated from placenta to the phenotype of P3 cells, it was found that fewer and fewer cells expressing negative markers were present, while more and more cells expressing positive markers were present. The MSCs were enriched and purified after three subcultures (see fig. 2 for exemplary P3 generation results).

And (4.3) adopting a conventional osteogenesis induction culture medium to perform differentiation induction on the placenta mesenchymal stem cells, and then determining the differentiation potential of the placenta mesenchymal stem cells by alizarin red staining. Following in vitro subculture, placental MSCs retained the osteogenic differentiation potential (results for partially passage cells are shown in figure 3).

Example 2: exosome separated and extracted from placenta mesenchymal stem cells

1) Providing in logarithmic growthThe 2 nd to 5 th generation of human placental mesenchymal stem cells (in this example, the 3 rd generation obtained in example 1) are 5000 to 15000/cm²Inoculating the cells (inoculation density of this example: 10000/cm2) to DMEM/F12 medium containing 2mM L-glutamine, culturing for 3 to 4 days (culture for 4 days in this example), collecting the supernatant, centrifuging at 20000g for 20min to remove cells and debris, filtering through a 0.22 μm filter, and adding sodium mannose phosphate thereto to dissolve the cells and debris to obtain a culture supernatant; in this example, the addition amount of mannose sodium phosphate was 0.08% by mass/volume of the filtrate]

2) The Pudex Sephadex G-25 filter medium is drained and guided into a chromatographic column (in the embodiment, Sephadex G-25 column) by a glass rod, and the mixture is stirred by the glass rod while being filled;

3) after the column is filled, sucking water on the upper surface of the column by using a pipette, and loading the culture supernatant collected in the step 1) into a chromatographic column;

4) covering an upper cover of the chromatographic column, inserting a thin tube of the upper cover into a beaker filled with double distilled water, opening a constant flow pump and a collector device, adjusting the speed of the constant flow pump and the time of the collector, starting elution and collecting elution fractions containing cell secretions, and adding magnesium chloride into the elution fractions to dissolve the elution fractions to obtain a chromatographic solution; [ in this example, the amount of magnesium chloride added was 0.04% based on the mass/volume percentage of the eluted fractions ]

5) Concentrating the filtrate with tangential flow ultrafiltration system (Shibi pure KR2i type tangential flow ultrafiltration system in this example), flushing the pipeline with ultra-pure water, and installing 100kD 100cm²The MidiKros filter is used for filtering and concentrating 5L of the chromatographic solution obtained in the step 4) to obtain 100ml of reflux liquid which is concentrated by 50 times (the filtered filtrate is removed of exosome and can be used for extracting cell factors), and the reflux liquid is exosome concentrated solution; through determination, mannose phosphate sodium and magnesium chloride can not be detected in the obtained exosome concentrated solution, and the mannose phosphate sodium and the magnesium chloride are easily understood, wherein the mannose phosphate sodium and the magnesium chloride are removed through column chromatography, and the mannose phosphate sodium and the magnesium chloride are removed through tangential flow ultrafiltration; carrying out freeze drying treatment or low-temperature cryopreservation treatment on the exosome concentrated solution according to actual requirements, or directly using the exosome concentrated solution;

6) subpackaging the exosome concentrated solution, and freezing and storing at-80 ℃; or adding a freeze-drying excipient into the exosome concentrated solution and then freeze-drying.

The exosome concentrate is freeze-dried by adding a freeze-drying excipient, which is well known in the art, and may be selected from: lactose, trehalose, mannitol, chitosan, dextran, glycine, arginine, glycine and the like. The freeze drying of the present invention can be carried out in the following manner:

7.1) taking the exosome concentrated solution or taking the exosome concentrated solution frozen at minus 80 ℃ to be completely melted in water bath at 37 ℃, and adding 5-15% of freeze-dried excipient to dissolve the excipient;

7.2) filtering the solution added with the excipient by using a 70-micron filter, then subpackaging the filtered solution into glass bottles with 2-5 ml of each bottle, covering a forked rubber plug, putting the glass bottles into a freeze dryer, and starting the following freeze-drying procedure:

pre-freezing for 3.5 hours at the normal pressure, wherein the temperature is-30 to-40 ℃;

starting a vacuum pump to ensure that the vacuum value is 0.04mbar, and freezing for 1-3 hours at the temperature of-38 to-40 ℃;

keeping the vacuum degree unchanged, and raising the temperature to-20 to-25 ℃ for freeze drying for 10 to 15 hours;

keeping the vacuum degree unchanged, and raising the temperature to-2 ℃ for freeze drying for 1-3 hours;

keeping the vacuum degree unchanged, and heating to 33-37 ℃ for drying for 2-5 hours;

and (5) after the program is finished, covering the cover under vacuum to obtain the exosome freeze-dried powder.

Various materials were tested in this example 2:

(a) detecting the exosome concentrated solution obtained in the two liquids obtained in the implementation step (step 5) and the culture supernatant obtained in the step 1) by using a Western Blotting method]Exosome positive markers in (1) CD63 and CD81, and determining exosome yield; the results of Western Blotting to identify exosome positive markers CD63 and CD81 are shown in FIG. 4; the results show that the exosome concentrate obtained in this example has excellent purity and shows a great purification rate; in addition, the same procedure was used for the measurementStep 5), filtering the obtained filtrate without the exosomes, and displaying that the exosomes are not present in the filtering solution (not detected); the exosome yield refers to the number of the placenta mesenchymal stem cells inoculated in the step 1) of the embodiment 2 is 10⁶Cytometric analysis, the mass of exosomes contained in the exosome concentrate obtained in step 5; the exosome yield reflects the comprehensive result of the amount of exosome produced by the cells after culture and the exosome yield of the extraction process;

(b) calculating the process recovery rate of the exosome according to the content of the exosome in the exosome concentrated solution obtained in the step 5) and the content of the exosome in the two kinds of liquid of the culture supernatant obtained in the step 1), wherein the result shows that the method has excellent process recovery rate in the whole process from the obtained culture supernatant to the exosome concentrated solution; the algorithm of the process recovery rate is as follows: the percentage obtained by multiplying the amount of the exosome in the exosome concentrated solution obtained in the step 5) by the amount of the exosome in the culture supernatant by 100 percent;

(c) in addition, the content of exosomes in the three liquids of the chromatographic liquid in the step 4), the exosome concentrated liquid in the step 5) and the filtrate in the step 5) is measured, the volume of the three liquids is combined, and the percentage of the amount of exosomes in the concentrated liquid to the amount of exosomes in the chromatographic liquid (referred to as concentrated liquid exosome proportion) and the percentage of the amount of exosomes in the filtrate to the amount of exosomes in the chromatographic liquid (referred to as filtrate exosome proportion) are calculated, and theoretically, the sum of the two percentages is 100%; the results indicate that there are essentially no exosomes in the filtrate and that a slightly greater or slightly less than 100% sum of the two results may be due to assay error.

Example 3: exosome separated and extracted from placenta mesenchymal stem cells

Reference is made to example 2.

1) Providing 2 nd generation human placental mesenchymal stem cells in logarithmic growth phase at 5000/cm²Inoculating to DMEM/F12 medium containing 2mM L-glutamine, culturing for 3 days, collecting the supernatant, centrifuging at 20000g for 20min to remove cells and debris, filtering with 0.22 μm filter membrane, and dissolving with 0.1% sodium mannose phosphate to obtain culture supernatant;

2) guiding a Pudex sephadex filter medium Pudex G-25 into a chromatographic column (sephadex G-25 column) by using a glass rod for drainage, and stirring by using the glass rod while installing;

3) after the column is filled, sucking water on the upper surface of the column by using a pipette, and loading the culture supernatant collected in the step 1) into a chromatographic column;

4) covering an upper cover of the chromatographic column, inserting a thin tube of the upper cover into a beaker filled with double distilled water, opening a constant flow pump and a collector device, adjusting the speed of the constant flow pump and the time of the collector, starting elution and collecting elution fractions containing cell secretions, and adding 0.02% magnesium chloride into the elution fractions to dissolve the elution fractions to obtain a chromatographic solution;

5) concentrating the chromatography liquid by using a tangential flow ultrafiltration system, washing the pipeline by using ultrapure water, and installing 100kD 100cm²The MidiKros filter is used for filtering and concentrating 5L of the chromatographic solution obtained in the step 4) to obtain 100ml of reflux liquid which is concentrated by 50 times and is an exosome concentrated solution;

6) subpackaging the exosome concentrated solution, and freezing and storing at-80 ℃; or adding a freeze-drying excipient into the exosome concentrated solution and then freeze-drying. Various materials were tested according to the method of example 2.

Example 4: exosome separated and extracted from placenta mesenchymal stem cells

Reference is made to example 2.

1) Providing 5 th generation human placental mesenchymal stem cells in logarithmic growth phase at 15000/cm²Inoculating to DMEM/F12 medium containing 2mM L-glutamine, culturing for 4 days, collecting the supernatant, centrifuging at 20000g for 20min to remove cells and debris, filtering with 0.22 μm filter membrane, and dissolving with 0.05% sodium mannose phosphate to obtain culture supernatant;

2) guiding a Pudex sephadex filter medium Pudex G-25 into a chromatographic column (sephadex G-25 column) by using a glass rod for drainage, and stirring by using the glass rod while installing;

3) after the column is filled, sucking water on the upper surface of the column by using a pipette, and loading the culture supernatant collected in the step 1) into a chromatographic column;

4) covering an upper cover of the chromatographic column, inserting a thin tube of the upper cover into a beaker filled with double distilled water, opening a constant flow pump and a collector device, adjusting the speed of the constant flow pump and the time of the collector, starting elution and collecting elution fractions containing cell secretions, and adding 0.05% magnesium chloride into the elution fractions to dissolve the elution fractions to obtain a chromatographic solution;

5) concentrating the chromatography liquid by using a tangential flow ultrafiltration system, washing the pipeline by using ultrapure water, and installing 100kD 100cm²The MidiKros filter is used for filtering and concentrating 5L of the chromatographic solution obtained in the step 4) to obtain 100ml of reflux liquid which is concentrated by 50 times and is an exosome concentrated solution;

6) subpackaging the exosome concentrated solution, and freezing and storing at-80 ℃; or adding a freeze-drying excipient into the exosome concentrated solution and then freeze-drying. Various materials were tested according to the method of example 2.

Example 5:the procedure is as in example 2, except that no sodium mannose phosphate is added in step 1).

Example 6:the procedure is as in example 2, except that no magnesium chloride is added in step 4).

Example 7:the procedure is as in example 2, except that no sodium mannose phosphate is added in step 1) and no magnesium chloride is added in step 4).

The results of the tests (n-5) of examples 2-7 are shown in the following table:

according to the results, the following results are found: tangential flow ultrafiltration was able to recover more than 99% of the exosomes with the addition of magnesium chloride and about 1% of the exosomes were filtered into the filtrate, but tangential flow ultrafiltration was only able to recover about 64% of the exosomes with no addition of magnesium chloride and about 36% of the exosomes were filtered into the filtrate, indicating that the addition of magnesium chloride helped to recover the exosomes when tangential flow ultrafiltration was performed; when the mannose phosphate sodium is added, exosomes can enter elution fractions, but the exosomes entering the elution fractions are greatly reduced when the mannose phosphate sodium is not added, so that the mannose phosphate sodium is beneficial to the recovery of the exosomes through chromatography. Although the method of the present invention can obtain a large amount of exosomes by a simple operation, it is necessary to add sodium mannose phosphate to the culture supernatant and magnesium chloride to the elution fraction at the same time.

All references cited in this specification, including without limitation all papers, publications, patents, patent applications, presentations, texts, reports, manuscripts, brochures, books, internet articles, journal articles, periodicals, and the like, are hereby incorporated by reference into this specification in their entirety. The discussion of the references herein is intended merely to summarize the assertions made by their authors and no admission is made that any reference constitutes prior art. Applicants reserve the right to challenge the accuracy and pertinency of the cited references.

Although embodiments of the present disclosure have been described using specific terms, devices, and methods, such description is for illustrative purposes only. The words used are words of description rather than limitation. It is to be understood that variations and modifications may be effected by one of ordinary skill in the art without departing from the spirit and scope of the disclosure as set forth in the appended claims. Additionally, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained therein.

Claims (9)

1. A method for separating and extracting exosome from placenta mesenchymal stem cells comprises the following steps:

1) providing 2 nd-5 th generation human placenta mesenchymal stem cells in logarithmic growth phase at the rate of 5000-15000 cells/cm²Is inoculated into DMEM/F12 medium containing 2mM L-glutamine, cultured for 3-4 days, the supernatant is collected and centrifuged at 20000g for 20min to remove cellsAnd the fragments are filtered by a filter membrane of 0.22 mu m, and mannose sodium phosphate is added into the obtained filtrate to dissolve the filtrate, so that culture supernatant is obtained; the mass/volume percentage concentration of the added mannose sodium phosphate is 0.05-0.1%;

2) guiding a Pudex sephadex filtration medium Pudex G-25 into a chromatographic column by using a glass rod for drainage, and stirring by using the glass rod while installing;

3) after the column is filled, sucking water on the upper surface of the column by using a pipette, and loading the culture supernatant collected in the step 1) into a chromatographic column;

4) covering an upper cover of the chromatographic column, inserting a thin tube of the upper cover into a beaker filled with double distilled water, opening a constant flow pump and a collector device, adjusting the speed of the constant flow pump and the time of the collector, starting elution and collecting elution fractions containing cell secretions, and adding magnesium chloride into the obtained elution fractions to dissolve the elution fractions to obtain a chromatographic solution; the addition amount of magnesium chloride accounts for 0.02-0.05% of the mass/volume percentage concentration of the elution fraction;

5) concentrating the chromatography liquid by using a tangential flow ultrafiltration system, washing the pipeline by using ultrapure water, and installing 100kD 100cm²The MidiKros filter is used for filtering and concentrating 5L of the chromatographic solution obtained in the step 4) to obtain 100ml of reflux liquid which is concentrated by 50 times and is an exosome concentrated solution;

6) subpackaging the exosome concentrated solution, and freezing and storing at-80 ℃; or adding a freeze-drying excipient into the exosome concentrated solution and then freeze-drying.

2. The method according to claim 1, step 1), at 10000 pieces/cm²The density of (a) to seed the cells.

3. The process according to claim 1, said tangential flow ultrafiltration system is a Shilby pure KR2i type tangential flow ultrafiltration system.

4. The method according to claim 1, wherein the sodium mannose phosphate is added at a concentration of 0.08% w/v.

5. The method according to claim 1, wherein in step 1), the 2 nd to 5 th generation of human placental mesenchymal stem cells in logarithmic growth phase are obtained by the following method:

(1) treatment of placental tissue

Removing amnion from human placenta, cutting placenta lobular epidermis membrane sample tissue, and cleaning with normal saline;

cutting the membrane sample tissue of placenta lobule surface to 0.2cm³The tissue fragment of (a);

placing the tissue fragments in a centrifuge tube, adding a proper amount of 0.9% physiological saline, filtering by using a 300-mesh filter screen, and cleaning twice by using a proper amount of 0.9% physiological saline until filtrate is clear;

adding the cleaned tissue into HBSS digestive juice containing 0.005% Liberase MNP-S enzyme and 0.05% DNA I type enzyme, mixing well, and digesting in shaking table at 37 deg.C and 100rpm for 30 min;

(2) obtaining placental progenitor cells

After digestion is finished, adding fetal calf serum into a centrifuge tube to stop digestion, uniformly mixing, diluting with 50ml of normal saline containing 5% dextran, 2.5% human serum albumin and 200U of DNase I, filtering by using a 300-mesh filter screen, washing tissues for multiple times by using 100ml of normal saline, and collecting filtrate;

centrifuging the obtained filtrate at 1400rpm for 5min, removing supernatant, collecting precipitate, resuspending with physiological saline, centrifuging again, and collecting precipitate;

suspending the precipitated cells by DMEM/F12, sampling and counting to obtain P0 generation cells;

(3) purification culture

The culture conditions are as follows: DMEM/F12 medium containing 10% fetal bovine serum and 2mM L-glutamine at 37 deg.C with 5% CO₂Culturing in a constant-temperature wet incubator;

digestion conditions are as follows: 0.25% pancreatin, digested at 37 ℃ for 2 minutes;

harvesting conditions are as follows: terminating digestion with complete medium, centrifuging at 1400rpm for 5min, and collecting precipitate;

at a rate of 5000 to 15000 pieces/cm²The placenta P0 generation cells are inoculated in a T75 culture bottle, and the liquid is changed all the day 3 to 4; cell clone appeared on 6-7 days, and cell growing in spindle-shaped vortex shape on 10-11 days, i.e. P1The placenta mesenchymal stem cells can be collected and then can be subjected to passage;

at a rate of 5000 to 15000 pieces/cm²The inoculation density culture is carried out, the culture medium components and the culture conditions are the same as those of the culture medium components and the culture conditions of the culture medium components of the P0-P1, and the culture medium components and the culture conditions are harvested after 3-4 days to obtain P2 generation cells; by analogy, culturing for 3-4 days under the same inoculation density and the same culture condition, and harvesting to obtain P3, P4 and P5 generation placenta mesenchymal stem cells; and

(4) and detecting the obtained placenta mesenchymal stem cells.

6. The method according to claim 1, wherein in step 2) the chromatography column is a sephadex G-25 column.

7. The method according to claim 5, wherein the complete medium of step (3) is DMEM/F12 medium containing 10% fetal bovine serum and 2mM L-glutamine.

8. The process according to claim 1, wherein the amount of magnesium chloride added is 0.04% w/v of the eluted fractions.

9. The method according to claim 1, wherein in step 6) the freeze-drying of the exosome concentrate is performed as follows:

6.1) taking the exosome concentrated solution or taking the exosome concentrated solution frozen at minus 80 ℃ to be completely melted in water bath at 37 ℃, and adding 5-15% of freeze-dried excipient to dissolve the excipient;

6.2) filtering the solution added with the excipient by using a 70 mu m filter, then subpackaging the filtered solution into glass bottles, covering 2-5 ml of branched rubber plugs in each bottle, putting the bottles into a freeze dryer, and starting the following freeze-drying procedures:

pre-freezing for 3.5 hours under normal pressure, wherein the temperature is minus 30 to minus 40 ℃;

starting a vacuum pump, enabling the vacuum value to be 0.04mbar, and freezing for 1-3 hours at the temperature of-38 to-40 ℃;

keeping the vacuum degree unchanged, heating to the temperature of minus 20 to minus 25 ℃, and freeze-drying for 10 to 15 hours;

keeping the vacuum degree unchanged, and raising the temperature to-2 ℃ for freeze drying for 1-3 hours;

keeping the vacuum degree unchanged, and heating to 33-37 ℃ for drying for 2-5 hours;

and (5) after the program is finished, covering the cover under vacuum to obtain the exosome freeze-dried powder.

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