BTN1A1 (butyrophilin 1A1)

Class

Humanized anti-BTN1A1 monoclonal antibody (immune checkpoint inhibitor)

Pathway

Blocks formation of the BTN1A1-galectin-9-PD-1 complex, reactivating anti-tumor T-cell immunity, including in PD-L1-low/refractory tumors (BTN1A1 is expressed largely mutually exclusive of PD-L1)

BTN1A1 (butyrophilin 1A1) is a cell-surface protein of the butyrophilin family, a group of immunoglobulin-superfamily molecules involved in regulating immune responses. On certain tumor cells, BTN1A1 partners with a secreted lectin called galectin-9 to form a complex that engages the PD-1 receptor on T cells. This engagement delivers an inhibitory signal that dampens T-cell activity, allowing the tumor to evade immune attack in a manner distinct from, but functionally parallel to, the well-known PD-L1/PD-1 checkpoint. Notably, BTN1A1 tends to be expressed on tumors that express little PD-L1, meaning tumors resistant or non-responsive to conventional PD-1/PD-L1-blocking therapies may still suppress T cells through this alternate route. An antibody designed to block formation of the BTN1A1-galectin-9-PD-1 complex aims to interrupt this inhibitory signal, restoring the capacity of T cells to recognize and attack tumor cells. This mechanism is relevant broadly across solid tumor immunotherapy, particularly as a strategy to extend checkpoint blockade benefit to patients whose cancers do not rely primarily on the PD-L1 pathway for immune evasion.