Congenital cytomegalovirus infection drives oligoclonal expansion of cytotoxic γδ T cells from early fetal progenitors.

Gamma delta (γδ) T cells emerge early during human gestation and are uniquely equipped to protect the fetus and infant following infection, due to their innate-like recognition of conserved molecular ligands. Following congenital cytomegalovirus infection (cCMV), Vδ1 T cells have been shown to expand, differentiate, and upregulate cytotoxic mediators, but display markedly restricted γδTCR diversity compared to CMV-infected adults. Early fetal γδ T cells are biased toward rapid effector function and comprise a distinct ontological "layer" that can be distinguished from late gestation γδ T cells based on TCR characteristics. To better understand the contribution of fetal γδ T cells to antiviral defense in utero, we analyzed γδ T cells from cCMV+ and uninfected neonates in Uganda using flow cytometry and paired single-cell RNA and TCR sequencing. We observed that in cCMV+ neonates, γδ T cells clonally proliferate and differentiate into a uniform population of cytotoxic effectors. The expanded Vδ1 population is comprised of diverse clonotypes with broad Vγ chain usage, with a striking correlation between expansion and publicity. Overall, γδTCR repertoires of cCMV+ infants have shorter CDR3 lengths and fewer N additions, suggesting they derive from early fetal progenitor cells. In cCMV+ infants, most cells with fetal γδTCR characteristics are effector-differentiated, whereas in uninfected infants, such cells are rare and predominantly naïve. Together, these findings demonstrate that cCMV infection drives an oligoclonal expansion of highly cytotoxic effector γδ T cells with fetal-like TCR features, illustrating how the developing immune system prioritizes broad reactivity and rapid effector function over specificity.