BC31M4 binds to CD47 and blocks the CD47-SIRPα interaction with higher efficiency at acidic-pH than at physiological-pH; accordingly, BC31M4 more potently promotes macrophage phagocytosis of tumor cells at acidic-pH than at physiological-pH in vitro, which still requires the Fc-mediated effector functions. The gene discussed is SIRPA; the disease is neoplasm.