In utero human cytomegalovirus infection expands NK cell-like FcγRIII-expressing CD8+ T cells that mediate antibody-dependent functions.

Human cytomegalovirus (HCMV) profoundly modulates host T and natural killer (NK) cells across the lifespan, expanding unique effector cells bridging innate and adaptive immunity. Though HCMV is the most common congenital infection worldwide, how this ubiquitous herpesvirus impacts developing fetal T and NK cells remains unclear. Using computational flow cytometry and transcriptome profiling of cord blood from neonates with and without congenital HCMV (cCMV) infection, we identify major shifts in fetal cellular immunity marked by an expansion of Fcγ receptor III (FcγRIII)-expressing CD8+ T cells (FcRT) following HCMV exposure in utero. FcRT cells from cCMV-infected neonates express a cytotoxic NK cell-like transcriptome and mediate antigen-specific antibody-dependent functions including degranulation and IFNγ production, the hallmarks of NK cell antibody-dependent cellular cytotoxicity (ADCC). FcRT cells may represent a previously unappreciated effector population with innate-like functions that could be harnessed for maternal-infant vaccination strategies and antibody-based therapeutics in early life.