Limited protection against early-life cytomegalovirus infection results from deficiency of cytotoxic CD8 T cells

Differential antiviral T cell immunity in early life impacts the clinical outcome of Cytomegalovirus (CMV) infection, but the underlying mechanisms are not well understood. Here, we found delayed enrichment of early-life murine CMV-specific CD8 T cells due to a general deficiency of αβ T cells. Adoptive transfer of naïve adult T cells into neonates did not protect due to a blockade of CD8 but not of CD4 effector T cell differentiation. Early-life deficiency of critical signal 3 cytokines during T cell priming resulted in the appearance of non-cytotoxic CD8 effector T cells whereas the effector phase of adult-primed T cells was not disrupted in neonates. Accordingly, we found an overall low number of antiviral human CD8 T cells in newborns with congenital CMV. Together, this study suggests defective CD8 T cell immunity as an important factor explaining the higher risk for CMV disease in the early-life phase.