[Preliminary study of the fourth-generation CAR-T cells targeting CS1 in the treatment of refractory and recurrent multiple myeloma].

Objective: To design the fourth-generation chimeric antigen receptor-T (CAR-T) cells that secrete interleukin-7 (IL7) and chemokine C legend 19 (CCL19) on the basis of the second-generation CAR, and to analyze and compare the differences in proliferation, chemotaxis, tumor cell clearance and persistence in the microenvironment of multiple myeloma (MM) between them. Methods: The fourth-generation CAR vector plasmid was constructed by using 2A self-cleaving peptide technology. The third-generation lentiviral packaging system was used to prepare high-titer lentivirus. Flow cytometry was used to monitor the transduction efficiency of lentivirus and the subtype changes of CAR-T cells. The enzyme-linked immunosorbent assay (ELISA) was used to quantify the IL7 and CCL19 secreted by CAR-T cells.The calculation of absolute number of CAR-T cells during culture was used to analysis cell proliferation activity. Transwell migration assay was used to verify the chemotactic ability of CAR-T cells. The specific killing activity of CAR-T cells was detected by using the luciferase bioluminescence method. The NOD-Prkdcem26Cd52Il2rgem26Cd22/Nju (NOD) mouse xenograft model was used to verify the anti-myeloma activity and safety of CAR-T cells in vivo. Results: Flow cytometry results showed that the stable CAR expression rates of the second-generation anti-CS1 CAR-T and fourth-generation anti-CS1-IL7-CCL19 CAR-T cells were (91.50±0.29)% and (46.7±0.12)%, respectively. CAR-T cells were successfully constructed. Subtype analysis demonstrated that the ratio of stem memory T cell (TSCM) in anti-CS1-IL7-CCL19 CAR-T cells was (67.58±0.59)%, which was significantly higher than (50.74 ± 1.01)% of anti-CS1 CAR-T (P=0.000 1), with more strong immune memory function and better durability. Anti-CS1-IL7-CCL19 CAR-T cells can continuously secrete IL7 and CCL19 compared to MOCK-T and anti-CS1 CAR-T (P<0.000 1). The number of anti-CS1-IL7-CCL19 CAR-T cells reached (22.77±0.79)×10(6) on the 9th day after lentivirus transduction, which was significantly higher than (9.40±0.79)×10(6) of anti-CS1 CAR-T cells (P=0.000 1), with stronger proliferation ability. The number of chemotaxis cells of anti-CS1-IL7-CCL19 CAR-T cells to reactive T cells was (109.0±4.04), which was significantly higher than (9.33±1.20) of MOCK-T (P<0.000 1) and (7.33±0.88) of anti-CS1 CAR-T (P<0.000 1), with stronger chemotactic ability. The specific killing activity showed that both anti-CS1-IL7-CCL19 CAR-T and anti-CS1 CAR-T cells had specific killing efficacies when compared with the MOCK-T cells (P<0.000 1). Animal experiment indicated that anti-CS1-IL7-CCL19 CAR-T cells significantly reduced the tumor burden (P<0.000 1) and extended the overall survival time (P=0.006 1) of tumor-bearing mice. Conclusions: The anti-CS1-IL7-CCL19 CAR-T cells designed in this study show stronger proliferative activity, chemotactic ability, and durability without affecting the anti-myeloma activity in vivo and in vivo, which provides strategies for overcoming the defects of low survival rate, poor durability and inhibition by tumor microenvironment of traditional CAR-T cells, and offers preliminary experimental basis for the clinical application of the fourth-generation CAR-T cells.