Preclinical Analyses Support Clinical Investigation of Combined PD-L1 Blockade and Anti-CD19 CAR T Cell Therapy for the Treatment of NHL

In clinical studies, CD19-targeted CAR T cells have demonstrated encouraging clinical activity in adult and pediatric subjects with relapsed or refractory (R/R) B-cell acute lymphoblastic leukemia (ALL) and B-cell non-Hodgkin lymphoma (NHL). In general, the anti-tumor activity of CAR T cells in NHL is less than that observed in ALL patients. Immunosuppressive aspects of the NHL tumor microenvironment may inhibit CAR T cell expansion, effector function and tumor killing capacity. One mechanism of suppression may be PD-L1 expression on tumor cells and on cells within the tumor microenvironment. PD-L1 may interact with the inhibitory receptor PD-1 expressed by T cells infiltrating the tumor and limit anti-tumor activity. Reported antitumor activity by nivolumab, an anti-PD-1 inhibitor, in patients with B-cell NHL supports this hypothesis. The data to be presented suggest that the PD-1/PD-L1 pathway could limit CAR T cell efficacy in patients with NHL.

Presented data will show that PD-L1 is expressed on tumor cells and in the tumor microenvironment of a subset of NHL patients. In addition, CAR T cells upregulate PD-1 and, to a more limited extent, PD-L1 under certain manufacturing conditions. Co-culture of anti-CD19 CAR T cells with CD19-expressing target cells results in a rapid increase in expression of both PD-1 and PD-L1 on CAR T cells and expression levels are dependent upon the amount of available CAR target antigen. The upregulation of PD-1 and PD-L1 occurs on T cells transduced with CAR constructs containing either a CD28 or 4-1BB costimulatory signaling domain. Thus, the expression pattern of PD-1 on CAR T cells together with the presence of PD-L1 in NHL tumors suggests that this axis could play a role in the modulation of CAR T cell function in NHL.

A series of in vitro studies were carried out to characterize the effects of PD-L1 blockade on the activity of anti-CD19 CAR T cells. Tumor B cell lines expressing CD19 and PD-L1 were cultured with anti-CD19 CAR T cells in the presence or absence of anti-PD-L1 blocking antibody. Dose-dependent effects of the blocking antibody on CAR T cell effector function, including cytokine production, proliferation, and cytotoxicity, will be discussed. Collectively, these results provide justification for clinical evaluation of combining therapeutic blockade of PD-L1 with anti-CD19 CAR T cells for the treatment of NHL. A Phase 1b study of anti-CD19 CAR T cells in combination with durvalumab (MEDI4736) for R/R B Cell NHL is planned.