Agonistic CD40 mAb-Driven IL12 Reverses Resistance to Anti-PD1 in a T-cell–Rich Tumor

Shin Foong Ngiow, Arabella Young, Stephen J. Blake, Geoffrey R. Hill, Hideo Yagita, Michele W. L. Teng, Alan J. Korman, Mark J. Smyth

The durability and efficacy of anti-human PD1 monoclonal antibodies (PD1 mAb) vary across different malignancies. Although an absence of tumor-infiltrating cytotoxic T lymphocytes has been identified as a cause for resistance to PD1 mAb, the presence of intratumor exhausted PD1hi T cells also contributes to insensitivity to this immune checkpoint therapy. In this study, we used mouse tumor models of PD1 mAb resistance that harbored PD1hi T cells and flow cytometry analysis of tumor-infiltrating leukocytes immediately post-therapy as a screening platform to identify agents that could resensitize T cells to PD1 blockade. We showed that an agonistic anti-CD40 mAb converted PD1hi T cells into PD1lo T cells, reversing phenotypic T cell exhaustion and allowing the anti-PD1 refractory tumors to respond to anti-PD1 therapy. PD1 down-modulation by anti-CD40 mAb relied upon IL-12 but not IL-23, CD80/CD86/CD28 or CD70/CD27. Consistent with a role for regulatory T cells (Treg) in promoting T cell exhaustion, we also showed that intratumor Treg presented with a less activated and attenuated suppressive phenotype, marked by reductions in CTLA4 and PD1. Similar to anti-CD40 mAb, anti-CTLA4 mAb also lowered intratumor T cell PD1 expression. Our study provides a proof-of-principle framework to systematically identify immune conditioning agents able to convert PD1hi T cells to PD1lo T cells, with clinical implications in the management of anti-PD1 refractory patients.