Neonatal T cell maternal microchimerism is common and associates with early pregnancy SARS2 vaccination

The fetus acquires a graft of maternal cells in utero, known as maternal microchimerism (MMc), which may be enriched for T cells. However, little is known regarding the determinants of T cell trafficking into the fetus or regarding the prevalence of T cell MMc in healthy neonates. Using a closely followed cohort, we determined the association between maternal vaccination and acute infection and the detection of T cell MMc in cord blood, as measured using polymorphism-specific qPCR. We identified an association between early pregnancy SARS2 mRNA vaccination, a potent T cell stimulus, and increased detection of T cell MMc.