Antibody-dependent anti-cytomegalovirus activity of human γδ T cells expressing CD16 (FcγRIIIa)

Human cytomegalovirus (HCMV) infection is an important cause of morbidity and mortality in transplant recipients. Long-term protective immunity against HCMV requires both sustained specific T-cell response and neutralizing IgG production, but the interplay between these effector arms remains poorly defined. We demonstrated previously that γδ T cells play a substantial role as anti-HCMV T-cell effectors. The observation that CD16 (FcγRIIIA) was specifically expressed by the vast majority of HCMV-induced γδ T cells prompted us to investigate their cooperation with anti-HCMV IgG. We found that CD16 could stimulate γδ T cells independently of TCR engagement and provide them with an intrinsic antibody-dependent cell-mediated cytotoxic (ADCC) potential. Although CD16+ γδ T cells did not mediate ADCC against HCMV-infected cells, in accordance with the low level of anti-HCMV IgGs recognizing infected cells, they produced IFNγ when incubated with IgG-opsonized virions. This CD16-induced IFNγ production was greatly enhanced by IL12 and IFNα, two cytokines produced during HCMV infection, and conferred to γδ T cells the ability to inhibit HCMV multiplication in vitro . Taken together, these data identify a new antiviral function for γδ T cells through cooperation with anti-HCMV IgG that could contribute to surveillance of HCMV reactivation in transplant recipients.