Association of CAR-T cell secreting CD47 blocking protein with an enhanced antitumor activity in small cell lung cancer.

Abstract

e20512 Background: Notch ligand family DLL3 has been considered a therapeutic target for small cell lung cancer. CD47/SIRPa is an important immunosuppressive factor in the tumor microenvironment and is considered to be a "checkpoint" of innate immune cells. Here, we described an DLL3 targeting CAR-T cells secreting CD47/SIRPa signal blocking protein. We hypothesized that the armored CAR-T cells, by blocking the CD47/SIRPa signal with specific antibodies may promote macrophages to engulf tumor cells and induce anti-tumor immune response, thus addressing a clinical need of cell therapy in SCLC. Methods: Bioinformatics analysis of immune cell composition in the microenvironment of small cell lung cancer, focusing on macrophage content and phenotypic characteristics. The CAR genes were cloned into the lentiviral vector pWPXLd, the expression, phenotype, activation, proliferation, killing and cytokine release of CAR-T cells were detected by flow cytometry, Western blot, RTCA and ELISA; NSG mice were injected subcutaneously with H446-DLL3 cells or H446-DLL3(+/-) combined with CAR-T cells or armored CAR-T cells. Tumor size was measured every 3rd day. The number and phenotype of macrophages in tumors were detected by FCM. Results: Bioinformatics analysis showed that tumors with high expression of DLL3 were often accompanied by downregulation of antigen presentation-related genes; there is a large amount of macrophage infiltration in SCLC, and the later the stage, the more the infiltration. CAR-T cells co-cultured with target cells could effectively activate T cells, promote CAR-T cell proliferation, secrete IL-2, IFN-γ and TNF-α cytokines, and specifically kill DLL3 positive tumor cells. We have established a solid tumor model with heterogeneous antigen expression. CAR-T cells can effectively inhibit the growth of tumors with positive DLL3 expression in vivo, but the inhibition on tumors with heterogeneous antigens is not obvious. Blocking CD47 can promote phagocytosis of tumor cells by macrophages. Western blot analysis revealed the presence of CD47 blocking protein CV1-Fc in the supernatant of secreted CAR-T cells, which can effectively promote the phagocytic effect of macrophages; Armored CAR-T cells have a better anti-tumor effect in antigen heterogeneous tumor model in vivo, delays tumor progression, and promotes the aggregation of M1 type macrophages. Conclusions: CAR-T cells that specifically target DLL3 can effectively kill antigen-positive tumor cells in vivo and in vitro. Blocking CD47 can promote the non-specific anti-tumor effect of macrophages. CAR-T cells secreting CD47 blocking protein have dual anti-tumor effects, not only killing antigen-positive tumor cells, but also recruit and activate macrophages to exert phagocytosis, and have better anti-tumor effects in antigenic heterogeneous solid tumors.