Specifically Enhanced Immunosuppression of B Cells with Chimeric Antigen Receptors Modify Mesenchymal Stem Cells

Recently, cell therapies, including chimeric antigen receptor (CAR) modified T cell therapy and mesenchymal stem cell (MSC) therapy, have demonstrated considerable potential for systemic lupus erythematosus (SLE). In this study, a CAR-MSC model was constructed, combining two cell therapies. The structural domains of the CAR were designed by using the anti-CD19 scFv, targeting the CD19 antigen on the surface of B cells and the intracellular region of the interferon-gamma receptor, activating the JAK-STAT1 signaling pathway. Then we screened and identified the most effective structural domain of CAR as CAR1, as it facilitates MSCs to maintain significantly higher levels of JAK2 phosphorylation and IDO expression, as shown by western blot analysis. We also demonstrated CAR1 could be consistently and stably expressed at high levels in MSCs, and CAR1 transduction did not significantly affect the surface antigenic phenotypic criteria of MSCs via flow analysis. Furthermore, immunofluorescence results showed CAR1-MSCs could stably bind CD19 antigen, and they were activated by human CD19 antigen resulting in significantly high JAK2 phosphorylation and IDO expression via western blot analysis following co-culture. Besides, when activated peripheral blood mononuclear cells (PBMCs) were co-cultured with untransduced MSCs (UTD-MSCs) and CAR1-MSCs in vitro, respectively, the results showed that the percentage of activated CD3⁺ T cells and CD19⁺ B cells was both significantly lower after co-culturing. The percentage of activated CD19⁺ B cells was lower in the CAR1-MSCs co-culture group than in the UTD-MSCs co-culture group, whereas the percentage of activated CD3⁺ T cells was similar in the two co-culture groups. This suggests that CAR1 increased the inhibitory ability of MSCs on activated CD19⁺ B cells and had no significant effect on the ability of MSCs to inhibit activated CD3⁺ T cells. In conclusion, CAR1-MSCs were successfully constructed and demonstrated the ability to enhance the inhibitory effect of MSCs on activated human CD19⁺ B cells, facilitating SLE therapy.