TY - JOUR T1 - Selective targeting of GARP-LTGFβ axis in the tumor microenvironment augments PD-1 blockade via enhancing CD8<sup>+</sup> T cell antitumor immunity JF - Journal for ImmunoTherapy of Cancer JO - J Immunother Cancer DO - 10.1136/jitc-2022-005433 VL - 10 IS - 9 SP - e005433 AU - Anqi Li AU - Yuzhou Chang AU - No-Joon Song AU - Xingjun Wu AU - Dongjun Chung AU - Brian P Riesenberg AU - Maria Velegraki AU - Giuseppe D Giuliani AU - Komal Das AU - Tamio Okimoto AU - Hyunwoo Kwon AU - Karthik B Chakravarthy AU - Chelsea Bolyard AU - Yi Wang AU - Kai He AU - Margaret Gatti-Mays AU - Jayajit Das AU - Yiping Yang AU - Daniel T Gewirth AU - Qin Ma AU - David Carbone AU - Zihai Li Y1 - 2022/09/01 UR - http://jitc.bmj.com/content/10/9/e005433.abstract N2 - Background Immune checkpoint blockade (ICB) has revolutionized cancer immunotherapy. However, most patients with cancer fail to respond clinically. One potential reason is the accumulation of immunosuppressive transforming growth factor β (TGFβ) in the tumor microenvironment (TME). TGFβ 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 TGFβ1, TGFβ2 and TGFβ3, with its expression restricted predominantly to effector Tregs, cancer cells, and platelets.Methods We investigated the role of GARP in human patients with cancer by analyzing existing large databases. In addition, we generated and humanized an anti-GARP monoclonal antibody and evaluated its antitumor efficacy and underlying mechanisms of action in murine models of cancer.Results We demonstrate that GARP overexpression in human cancers correlates with a tolerogenic TME and poor clinical response to ICB, suggesting GARP blockade may improve cancer immunotherapy. We report on a unique anti-human GARP antibody (named PIIO-1) that specifically binds the ligand-interacting domain of all latent TGFβ isoforms. PIIO-1 lacks recognition of GARP-TGFβ complex on platelets. Using human LRRC32 (encoding GARP) knock-in mice, we find that PIIO-1 does not cause thrombocytopenia; is preferentially distributed in the TME; and exhibits therapeutic efficacy against GARP+ and GARP- cancers, alone or in combination with anti-PD-1 antibody. Mechanistically, PIIO-1 treatment reduces canonical TGFβ signaling in tumor-infiltrating immune cells, prevents T cell exhaustion, and enhances CD8+ T cell migration into the TME in a C-X-C motif chemokine receptor 3 (CXCR3)-dependent manner.Conclusion GARP contributes to multiple aspects of immune resistance in cancer. Anti-human GARP antibody PIIO-1 is an efficacious and safe strategy to block GARP-mediated LTGFβ activation, enhance CD8+ T cell trafficking and functionality in the tumor, and overcome primary resistance to anti-PD-1 ICB. PIIO-1 therefore warrants clinical development as a novel cancer immunotherapeutic.Data are available in a public, open access repository. Data are available on reasonable request. The sequencing data and processed expression matrix have been deposited at the Gene Expression Omnibus with access number GSE202153. ER -