P827: study on the percentage and function of tscm cells and the antitumor effect in vitro amplification in patients with multiple myeloma

Topic: 13. Myeloma and other monoclonal gammopathies - Biology & Translational Research Background: Immune dysfunction play a vital role in Multiple myeloma(MM) progression. Although myeloma-targeted and immunomodulatory agents improve the survival of MM it still remains incurable, the majority of patients eventually end in progressive disease. Further studies to prolong survival time and improve quality of life deserved more exploration. Recently, a rare subset of memory lymphocytes which is termed “T memory stem cells” (Tscm) has been thought a more potential Immunotherapy as its characteristics of Long-lived, self-renewing, and antitumor effects of strong immune-mediated. Tscm cells may improve the survival of MM patients. Aims: To explore the percentage and function of Tscm cells in MM. Furthermore, the amplification system of TSCM cells was constructed in vitro and co-cultured with myeloma cells to detect the antitumor ability, thus providing a practical basis to search a new treatment strategy for MM. Methods: Based on previous study, 3 markers were used to define the gating strategy. CD45RA+CCR7+CD95+cells was defined TSCM cells in CD3+/CD8+T cells. The expression of Tscm cells in BM samples from MM patients including 31 newly diagnosed MM (NDMM), and 20 healthy controls (HC) were detected by flow cytometry. Simultaneously, the expression of PD-1 and TIGIT and perforin and granzyme B on T cells was also detected. Furthermore, the amplification system of Tscm cells in vitro was constructed and the anti-tumor effect of TSCM cells was detected after Tscm cells and MM cell line were co-cultured. Results: The percentage of CD3+TSCM cells in NDMM group (0.51±0.31%) were significantly decreased than HC group (0.98±0.39%) (P<0.05), the percentage of CD3+CD8+TSCM cells in NDMM group (0.41±0.28%) were significantly decreased than HC group (0.97±0.40%) (P<0.05). The expression of PD-1 on CD3+TSCM cells increased significantly than CD3+T cells (35.04±5.11%) (P<0.0001), the expression of TIGIT on CD3+TSCM cells increased significantly than CD3+T cells (64.84±7.46%) (P<0.0001). And the expression of Perforin on CD3+TSCM cells (42.26±3.685%) was significantly increased than CD3+T cells (15.32±2.75%) (P<0.0001); CD3+CD8+TSCM cells (42.26±3.685%) was significantly increased than CD8+T cells (18.37±3.89%) (P<0.0001). The expression of Granzyme B in CD3+TSCM cells (57.18±6.381%) was significantly increased than CD3+T cells (21.56±3.38%) (P<0.0001), CD3+CD8+TSCM cells (57.18±6.381%) was significantly increased than CD8+T cells (28.84 ±3.49%) (P<0.0001). The amplification system of Tscm cells was divided into 4 groups (Group A: cultured for 2 days with IL-2; Group B: culture for 2 days with IL-2+MEKI; Group C: culture for 7 days with IL-2; Group D: cultured for 7 days with IL-2+IL-15). Results show that the percentage of CD3+TSCM cells in group B (6.04±1.02%) increased significantly than group A (2.77±0.48%) (P<0.0001), and Group B increased significantly than group D (P=0.0002). The apoptosis of RPMI-8226 cells in group B (30.55 ±6.92%) increased significantly than group A (16.06 ±6.82%) (P<0.05), group D (26.10 ±6.56%) increased significantly than group C (13.43 ±4.30%) (P<0.05). Summary/Conclusion: The dramatically increased effective function of Tscm but low level may be amplified by IL-2+MEKI and enhance the anti-tumor ability, which prolongs the survival of MM patients. FigureKeywords: Multiple myeloma, T cell, T cell expansion