Effect and changes in PD-1 expression of CD19 CAR-T cells from T cells highly expressing PD-1 combined with reduced-dose PD-1 inhibitor

CD19 chimeric antigen receptor (CAR) T cell therapy has changed the outcomes of relapsed/refractory B-cell leukemia and lymphoma. However, its efficacy in patients with relapsed/refractory non-Hodgkin lymphoma (NHL) has been less impressive compared with that in patients with acute lymphoid leukemia. Furthermore, immune checkpoints have a critical role in the immune system. Several clinical trials have confirmed the dramatic effects of programmed death-1/programmed death-ligand 1 (PD-1/PD-L1) inhibitors in numerous malignancies, but the immune-associated adverse events of PD-1/PD-L1 inhibitors may occur in a number of systems. The aim of the present study was to investigate the combination of CD19 CAR-T cells with a reduced dose of PD-1 inhibitor. This method is expected to overcome the side-effects of PD-1 inhibitors, while maintaining therapeutic efficacy. The findings demonstrated that a reduced dose of PD-1 inhibitor did not affect the transfection rate, proliferation rate or cytokine secretion of CD19 CAR-T cells. An interesting finding of the present study was that the number of PD-1-positive cells CAR-T cells, measured by flow cytometry, declined when they were cultured in vitro, but returned to high levels with gradual prolongation of the co-culture time of CD19 CAR-T cells with lymphoma cells; however, there was no change in the mRNA expression of T cells and CAR-T cells during this process. This phenomenon may be one of the reasons why the curative effect of CAR-T cells on B-cell lymphoma is unsatisfactory compared with B-cell leukemia. The synergistic effect of a reduced-dose PD-1 inhibitor combined with CD19 CAR-T cells from T cells highly expressing PD-1 was confirmed in a mouse trial. Mice in the combined treatment group achieved the longest survival time. In this group, the proportion of CAR-T cells and the level of interleukin-6 were higher compared with those in the CAR-T cell group. In conclusion, a reduced dose of a PD-1 inhibitor combined with CD19 CAR-T cells appears to be a promising treatment option for relapsed/refractory B-NHL exhibiting high PD-1 expression by T cells. This method may achieve good clinical efficacy while reducing the side-effects of PD-1 inhibitors.