Anti-4CB1: A Novel Selective HVEM-Blocking Antibody Enhancing T-Cell and Macrophage Immunity Against Solid Tumors.

Immune checkpoint inhibitors (ICIs) have improved cancer outcomes; however, many patients fail to respond, highlighting the need for novel targets. HVEM (Herpes Virus Entry Mediator) is an immune regulator with both inhibitory and stimulatory functions, making it a promising therapeutic candidate. We have developed Anti-4CB1, a fully human monoclonal antibody (mAb) that selectively blocks HVEM interactions with BTLA and CD160. Its activity was evaluated in-vitro using human tumor-infiltrating lymphocytes (TILs), peripheral blood mononuclear cells (PBMCs), and M1 macrophages, as well as in ex-vivo patient-derived tumor samples and in-vivo transgenic and humanized mouse models. HVEM expression was also assessed in serum and tumor tissues. Anti-4CB1 enhanced T-cell activation and cytotoxicity, evidenced by increased tumor cell killing, upregulation of activation markers (41BB, CD107a), and elevated IFNγ and TNFα secretion. It also promoted macrophage-mediated phagocytosis. In ex-vivo analyses of 49 patient-derived tumor samples, Anti-4CB1 increased cytotoxicity in 28.5% of cases, including samples unresponsive to anti-PD1. In-vivo, Anti-4CB1 demonstrated significant anti-tumor activity as monotherapy and showed enhanced efficacy in combination with anti-PD1. Additionally, higher tumor HVEM expression correlated with improved response to checkpoint blockade, while elevated soluble HVEM levels were associated with reduced responsiveness to Anti-HVEM. Anti-4CB1 enhances both adaptive and innate anti-tumor immunity and shows activity in anti-PD1 resistant settings. These findings support its potential as a novel therapeutic agent and suggest HVEM as a predictive biomarker for immunotherapy response.