HM-266

**HM-266** is a monoclonal antibody agonist of programmed cell death protein 1 (**PD-1**), originally developed from a hybridoma clone established by researchers at Japan's National Institutes of Biomedical Innovation, Health, and Nutrition. Unlike standard antagonistic anti-PD-1 antibodies used in cancer immunotherapy, HM-266 activates PD-1 signaling to suppress T cell responses, particularly inhibiting Th2 differentiation and cytokine production (IL-4, IL-5, IL-13) while having lesser effects on Th1 responses. Its activity requires binding to the membrane-proximal region of human PD-1 (segment 38-48) and engagement with FcγRIIB on antigen-presenting cells, enabling immunosuppressive effects additive to PD-L1. It demonstrates efficacy in preclinical models of allergic asthma (preventing eosinophil infiltration, mucus production, and IgE elevation), colitis (reducing effector T cell expansion and pathology), graft-versus-host disease, and humoral responses, positioning it as a potential therapy for Th2-driven inflammatory and autoimmune disorders.[1][3][5][7]