DOSE INTENSIFIED TEMOZOLOMIDE IMPROVES INFILTRATION OF CD70 CAR T CELLS INTO THE GBM TUMOR MICROENVIRONMENT

Abstract CD70 CAR T cells developed by our group have anti-tumor efficacy in syngeneic murine GBM model and are currently being developed for first-in-human testing. The objective of this study was to evaluate the impact of temozolomide (TMZ) in various dosing strategies on the expansion, persistence and function of the CD70 CAR T cells after infusion. C57BL/6 mice underwent intracranial implantation of KR-158 overexpressing CD70 tumor cells. Tumor bearing animals were treated with standard dose (SD) (50 mg/kg x 5 days), metronomic dose (MD) (25mg/kg x 10 days), or dose intensified (DI) (75mg/kg x 5 days) of TMZ, followed by 10×106 CAR T cells infusion. Peripheral blood was collected to monitor the persistence of CAR T cells in the systemic blood circulation. Six weeks post treatments, spleens and tumors were collected and CAR T cells abundance and function were measured. TMZ preconditioning resulted in the expected lymphopenia in animals by generation of dose dependent lymphopenia. Circulating CD70 CAR T cells peaked in the systemic blood 2 weeks after infusion (3-fold, p< 0.0001). Markers of T cell exhaustion including PD-1 and TOX expression on CAR T cells were not different between the three TMZ treatment groups compared to control. Six weeks post treatment, CD70 CAR T cells were found to be highly infiltrated within the tumor microenvironment in the DI TMZ group compared to the other groups (4-fold,p < 0.0001). Tumor infiltrating CD70 CAR T cells in the DI TMZ group did not have an increase in PD-1 and TOX expression which was seen in the MD and SD TMZ groups. DI TMZ preconditioning results in greater CD70 CAR T cell trafficking to the tumor without T cell exhaustion compared to lower doses of TMZ. The affects of TMZ on the immune microenvironment to enhance CAR T cell regimens warrants further study.