Infant CD4 T-Cell Response to SARS-CoV-2 mRNA Vaccination Is Restricted in Cytokine Production and Modified by Vaccine Manufacturer.

Background: Safe and effective vaccines are a key preventative measure to protect infants from SARS-CoV-2 infection and disease. Although mRNA vaccines induce robust antibody titers in infants, little is known about the quality of CD4 T-cell responses induced by vaccination. CD4 T-cell responses are important in orchestrating coordinated immune responses during infection and may help to limit disease severity. Methods: To characterize the CD4 T-cell response to SARS-CoV-2 mRNA vaccination in infants, we sampled blood from 13 infants before and after primary SARS-CoV-2 mRNA vaccine series; samples from 12 historical vaccinated adults were used for comparisons. Peripheral blood mononuclear cells were stimulated with spike peptide pools, and the ability of CD4 T-cells to secrete Th1, Th2, and Th17 cytokines was quantified. Measures of polyfunctionality were generated with the COMPASS algorithm. Results: We observed a significant increase in CD4 T-cells producing IL-2 (0.01% vs 0.08%, P = .04) and TNF-α (0.007% vs 0.07%, P = .007) following vaccination in infants but a more muted induction of IFN-γ production (0.01% vs 0.04%, P = .08). This contrasted with adults, in whom vaccination induced robust production of IFN-γ, IL-2, and TNF-α. Th2 and Th17 responses were limited in both infants and adults. In infants, CD4 T-cell responses post vaccination were greater in those who received mRNA-1273 vs BNT162b. In contrast to CD4 T-cell responses, spike-specific IgG titers were similar in infants and adults. Conclusions: These data suggest that infants have restricted induction of cytokine-producing CD4 T-cells following SARS-CoV-2 mRNA vaccination relative to adults.