Ha et al. studied the potential complementary or opposing outcomes of anti-CTLA-4 antibody (mAb) treatment on CTLA-4+ suppressive CD4+ Tregs and newly antigen-activated CD8+ T cells using ADCC/ADCP-active, FcR affinity-enhanced or -silent mAbs in vitro with human PBMCs and in a mouse model. Concurrent FcR-enhanced mAb and tumor vaccine treatment effectively reduced CD45RA-FoxP3+ Tregs but also reduced activated CD8+ T cells, while delayed antibody treatment spared CD8+ T cell generation, translating to improved tumor control in mice. Timing of interventions may also be relevant to other Treg-depleting approaches.

Anti-CTLA-4 mAb is efficacious in enhancing tumor immunity in humans. CTLA-4 is expressed by conventional T cells upon activation and by naturally occurring FOXP3(+)CD4(+) Treg cells constitutively, raising a question of how anti-CTLA-4 mAb can differentially control these functionally opposing T cell populations in tumor immunity. Here we show that FOXP3(high) potently suppressive effector Treg cells were abundant in melanoma tissues, expressing CTLA-4 at higher levels than tumor-infiltrating CD8(+) T cells. Upon in vitro tumor-antigen stimulation of peripheral blood mononuclear cells from healthy individuals or melanoma patients, Fc-region-modified anti-CTLA-4 mAb with high antibody-dependent cell-mediated cytotoxicity (ADCC) and cellular phagocytosis (ADCP) activity selectively depleted CTLA-4(+)FOXP3(+) Treg cells and consequently expanded tumor-antigen-specific CD8(+)T cells. Importantly, the expansion occurred only when antigen stimulation was delayed several days from the antibody treatment to spare CTLA-4(+) activated effector CD8(+)T cells from mAb-mediated killing. Similarly, in tumor-bearing mice, high-ADCC/ADCP anti-CTLA-4 mAb treatment with delayed tumor-antigen vaccination significantly prolonged their survival and markedly elevated cytokine production by tumor-infiltrating CD8(+) T cells, whereas antibody treatment concurrent with vaccination did not. Anti-CTLA-4 mAb modified to exhibit a lesser or no Fc-binding activity failed to show such timing-dependent in vitro and in vivo immune enhancement. Thus, high ADCC anti-CTLA-4 mAb is able to selectively deplete effector Treg cells and evoke tumor immunity depending on the CTLA-4-expressing status of effector CD8(+) T cells. These findings are instrumental in designing cancer immunotherapy with mAbs targeting the molecules commonly expressed by FOXP3(+) Treg cells and tumor-reactive effector T cells.

Author Info: (1) Experimental Immunology, Immunology Frontier Research Center, Osaka University, 565-0871 Osaka, Japan. Laboratory of Experimental Immunology, Department of Regeneration Science and Engineering, Institute for Frontier

Author Info: (1) Experimental Immunology, Immunology Frontier Research Center, Osaka University, 565-0871 Osaka, Japan. Laboratory of Experimental Immunology, Department of Regeneration Science and Engineering, Institute for Frontier Life and Medical Sciences, Kyoto University, 606-8507 Kyoto, Japan. (2) Experimental Immunology, Immunology Frontier Research Center, Osaka University, 565-0871 Osaka, Japan. (3) Experimental Immunology, Immunology Frontier Research Center, Osaka University, 565-0871 Osaka, Japan. Research Division, Chugai Pharmaceutical Co., Ltd., 247-8530 Kanagawa, Japan. (4) Department of Dermatology, Graduate School of Medicine, Osaka University, 565-0871 Osaka, Japan. (5) Experimental Immunology, Immunology Frontier Research Center, Osaka University, 565-0871 Osaka, Japan. (6) Experimental Immunology, Immunology Frontier Research Center, Osaka University, 565-0871 Osaka, Japan. (7) Experimental Immunology, Immunology Frontier Research Center, Osaka University, 565-0871 Osaka, Japan. (8) Agency for Science, Technology and Research, Singapore Immunology Network, 138632 Singapore. (9) Experimental Immunology, Immunology Frontier Research Center, Osaka University, 565-0871 Osaka, Japan. (10) Agency for Science, Technology and Research, Singapore Immunology Network, 138632 Singapore. (11) Department of Dermatology, Graduate School of Medicine, Osaka University, 565-0871 Osaka, Japan. (12) Experimental Immunology, Immunology Frontier Research Center, Osaka University, 565-0871 Osaka, Japan. (13) Experimental Immunology, Immunology Frontier Research Center, Osaka University, 565-0871 Osaka, Japan; shimon@ifrec.osaka-u.ac.jp. Laboratory of Experimental Immunology, Department of Regeneration Science and Engineering, Institute for Frontier Life and Medical Sciences, Kyoto University, 606-8507 Kyoto, Japan.

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