To explore the therapeutic effects of intravenous injection of small extracellular vesicles (sEVs) derived from human umbilical cord mesenchymal stem cells (MSCs) on experimental autoimmune uveitis (EAU) in mice.

MSCs from human umbilical cord were cultured and the supernatant was collected.The sEVs were isolated by ultracentrifugation method and a NanoSight instrument was used to analyze the particle size.The expression of surface markers sEVs, CD9, CD81 and CD63 was determined via Western blot.The morphology of sEVs was observed with a transmission electron microscope.Forty-eight 7-week-old female C57BL/6 mice were seclected to establish the EAU model through immunization with interphotoreceptor retinoid-binding protein peptide 651-670 (IRBP_651-670). The mice were divided into sEVs treatment group and phosphate buffer solution (PBS) control group using a random number table, with 24 mice in each group.The mice in the sEVs treatment group were injected with 50 μg of MSCs-derived sEVs via tail vein on the 11th day after modeling.In the PBS control group, the mice were injected with the same volume of PBS.Six mice in each group were randomly selected to observe the inflammation of the retina after mydriasis with an ophthalmoscope every other day from 8th day following modeling and the inflammation scores were evaluated.Six mice were randomly selected and sacrificed on the 14th day and 6 on the 18th day following modeling in each group, and both eyeballs of the mice were enucleated.Retinal tissue sections of the 6 mice sacrificed on the 18th day were stained with hematoxylin-eosin and the pathological scores were evaluated.The infiltration of helper T 1 (Th1) cells and Th17 cells in the eyeballs of the 6 mice sacrificed on the 18th day following modeling was detected by flow cytometry.T cells were isolated from spleen and lymph nodes of the 6 mice sacrificed on the 14th day, and the proliferation of T cells under different concentrations of IRBP_651-670 (0, 1, 10 and 20 μg/ml) was detected using a 5-bromodeoxyuridine (BrdU) method.To further study the effects of MSCs-derived sEVs on Th1/Th17 cells differentiation, naive T cells of spleen from another 3 normal mice were isolated by magnetic bead negative sorting and incubated with 10 μg/ml MSCs-derived sEVs or 10 μg/ml PBS, and then were cultured under Th1/Th17 cell differentiation conditions, respectively.Flow cytometry was used to measure the differentiation of naive T cells into Th1/Th17 cells.This study protocol complied with the regulations of the care and use of laboratory animals in China and was approved by an Ethics Committee of Tianjin Medical University (No.TJYY2019103022).

The isolated human MSCs-derived sEVs was with an average diameter of (102.4±33.6) nm and showed a double-layer membrane vesicle structure under the transmission electron microscope.The CD9, CD63 and CD81 proteins were highly expressed in sEVs.The inflammation scores of the sEVs treatment group were significantly lower than those in the control group on day 14, 16, 18, 20 and 22 after modeling (all at P<0.05). The pathological score of mice in the sEVs treatment group was significantly lower than that of PBS control group on the 18th day following modeling (P<0.05). The flow cytometry results showed that on day 18 after modeling, the proportions of Th1 and Th17 cells in eyeballs in the sEVs treatment group were (15.55±2.03)% and (15.67±2.15)%, respectively, which were significantly lower than (21.35±0.72)% and (20.90±1.10)% in the PBS control group (t=6.58, 5.31; both at P<0.01). BrdU results showed that when the IRBP_651-670 concentration was 20 μg/ml, the T cell proliferation ability in the sEVs treatment group was inhibited obviously compared with the control group (P<0.05). The proportions of naive T cells differentiated into Th1 cells and Th17 cells in the sEVs treatment group were (28.15±1.32)% and (11.60±2.23)% respectively, which were significantly lower than (31.58±1.75)% and (23.52±1.76)% of the PBS control group, and the differences were statistically significant (t=3.93, 10.26; both at P<0.05).

Intravenous injection of human umbilical cord MSCs-derived sEVs can reduce the inflammation in EAU mice.The mechanism may be related to inhibiting the differentiation of naive T cells to Th1 and Th17 cells, and reducing the infiltration of Th1 and Th17 cells in the eyeballs.

Mesenchymal stem cells; Small extracellular vesicles; Exosome; Autoimmune uveitis