Effector CD8+ T cells are important mediators of adaptive immunity, and receptor-ligand interactions that regulate their survival may have therapeutic potential. Here, we identified a subset of effector CD8+ T cells that expressed the inhibitory fragment crystallizable (Fc) receptor FcãRIIB following activation and multiple rounds of division. CD8+ T cell-intrinsic genetic deletion of Fcgr2b increased CD8+ effector T cell accumulation, resulting in accelerated graft rejection and decreased tumor volume in mouse models. Immunoglobulin G (IgG) antibody was not required for FcãRIIB-mediated control of CD8+ T cell immunity, and instead, the immunosuppressive cytokine fibrinogen-like 2 (Fgl2) was a functional ligand for FcãRIIB on CD8+ T cells. Fgl2 induced caspase-3/7-mediated apoptosis in Fcgr2b+, but not Fcgr2b-/-, CD8+ T cells. Increased expression of FcãRIIB correlated with freedom from rejection following withdrawal from immunosuppression in a clinical trial of kidney transplant recipients. Together, these findings demonstrate a cell-intrinsic coinhibitory function of FcãRIIB in regulating CD8+ T cell immunity.
Adult Aged