Tregs constrain CD8+ T cell priming required for curative intratumorally anchored anti-4-1BB immunotherapy

Costimulation of T cells with agonist antibodies targeting 4-1BB (CD137) improves antitumor immune responses in preclinical studies, but clinical development has been hampered by on-target, off-tumor toxicity. Here, we report the development of a tumor-anchored ?4-1BB agonist, termed ?4-1BB-LAIR, which consists of an ?4-1BB antibody fused to the collagen binding protein mLAIR1. Combination treatment with an antitumor antibody (TA99) displayed only modest efficacy, but surprisingly cured >90% of mice upon depletion of CD4+ cells. We elucidated two mechanisms of action for this synergy: ?CD4 increased priming and activation in the tumor draining lymph node , and TA99 + ?4-1BB-LAIR supported the cytotoxic program of these newly primed CD8+ T cells within the tumor microenvironment. Replacement of ?CD4 with ?CTLA-4, a more clinically relevant agent to enhance T cell priming, produces equivalently high cure rates while generating significantly more robust immunological memory against secondary tumor rechallenge. Overall design: RNA-sequencing was performed on CD45+ cells isolated from tumors (B16F10) and tumor draining lymph node samples from mice treated with various immmunotherapy combinations at two different time points