Abstract 2794: Blocking histamine receptor H1 on macrophages with anti-allergy drugs restores T-cell anti-tumor immunity

CD8+ T lymphocytes in tumors often become dysfunctional, prompting cancer immune escape and immunotherapy resistance. Restoring T-cell anti-tumor immunity remains an unmet challenge. Here, we show that histamine receptor H1 (HRH1) is highly expressed and tightly associated with T-cell dysfunction in human cancers. Histamine, the HRH1 ligand, is also increased in human and mouse tumors. HRH1 is predominantly expressed on tumor-associated macrophages (TAMs) and is activated by cancer cell-secreted histamine. The histamine/HRH1 axis in TAMs confers CD8+ T-cell dysfunction via increasing membrane localization of V-domain Ig suppressor of T cell activation (VISTA), an inhibitory immune checkpoint that promotes immunotherapy resistance. Blocking HRH1, genetically, or by anti-allergy drugs, reversed immunosuppressive TAMs, activated T-cells, and inhibited tumor growth in vivo. HRH1-targeting anti-allergy drugs more efficaciously enhanced immunotherapy response than anti-VISTA antibodies. Markedly, allergy-induced histamine also activates HRH1 on macrophages to induce T-cell dysfunction and immunotherapy resistance, which were reversed by the over-the-counter anti-allergy drug. Taken together, tumor cell-derived and allergy-released histamines activate HRH1 on TAMs to concede immunosuppression, pro-tumor function, and immunotherapy resistance, which can be negated by inexpensive and safer anti-allergy drugs. Citation Format: Hongzhong Li, Yi Xiao, Jun Yao, Xiangliang Yuan, Xuedong Yin, Yuan Zhang, Yohei Saito, Hideo Yagita, Don Gibbons, Dihua Yu. Blocking histamine receptor H1 on macrophages with anti-allergy drugs restores T-cell anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2794.