Selective targeting of GARP-LTGFb axis in the tumor microenvironment augments PD-1 blockade via enhancing CD8+ T cell anti-tumor immunity

Immune checkpoint blockade (ICB) has revolutionized cancer immunotherapy. However, the majority of cancer patients fail to respond clinically. One potential reason is the accumulation of transforming growth factor-beta (TGFb) in the tumor microenvironment (TME). TGFb drives cancer immune evasion in part by inducing regulatory T cells (Tregs) and limiting CD8+ T cell function. Glycoprotein-A repetitions predominant (GARP) is a cell surface docking receptor for activating latent TGF?1, TGFb2 and TGFb3, with its expression restricted in effector Tregs, cancer cells as well as platelets. Herein we demonstrate that GARP overexpression in human cancers correlates with unfavorable TME and poor clinical response to ICB, raising a possibility of GARP blockade to improve cancer immunotherapy. However, it is unclear if targeting GARP in the TME is feasible without affecting platelets. We report an anti-human GARP antibody (named PIIO-1) specific for its ligand-interacting domain, effectively blocking activation of latent TGFb1. PIIO-1 lacks recognition of GARP-TGF? complex on platelets. Using human GARP knock-in mice, we demonstrate that PIIO-1 does not cause thrombocytopenia, and is preferentially distributed in the TME and effective for treating both GARP+ and GARP- cancers, alone or in combination with anti-PD-1 antibody. PIIO-1 treatment reduces canonical TGFb signaling in tumor-infiltrating immune cells, prevents T cell exhaustion, and enhances CD8+ T cell migration into the TME in a CXCR3-dependent manner. Collectively, we conclude that GARP contributes to multiple aspects of immune resistance in cancer; anti-GARP antibody PIIO-1 is an efficacious and safe strategy to overcome ICB resistance, therefore warranting clinical development. Overall design: 1x10^5 MB-49 Bladder Cancer cells were injected s.c. on the right flank of hLrrc32KI mice. PIIO-1 (200 ug/mouse, i.p.) were delivered on day 6 and 9 for 2 doses. Tumors were collected on day 10. Single cell suspension and RNA isolation were prepared, and then subjected to bulk RNA sequencing.