Myeloid-derived suppressor cells and their association with vaccine immunogenicity in South African infants

The role of Myeloid-Derived Suppressor Cells (MDSC) in infant immune ontogeny is unknown. Here, we evaluated MDSC frequency and relationship with infant vaccine responses throughout the first year of life in a prospective cohort study. Ninety-one South African infant-mother pairs were enrolled at delivery, and blood samples were collected at 0, 6, 10, and 14 weeks, 6 months, 9 months, and 1 year. MDSC frequencies were quantified, and immune responses to the childhood vaccines Bacillus Calmette-Guérin (BCG), hepatitis B (HepB), and combination diphtheria, tetanus, and pertussis (dTaP) were measured by Ag-specific CD4⁺ T cell proliferation and interferon gamma (IFN-γ) production. Vaccine-specific Ab responses to HepB, dTaP, and Haemophilus influenzae type b (Hib) were quantified via Enzyme-Linked Immunosorbent assay (ELISA). MDSC frequency in mother-infant pairs was strongly correlated; the frequency of MDSC decreased in both mothers and infants during the months after delivery/birth; and by 1 year, infant MDSC frequencies rebounded to birth levels. Higher MDSC frequency at vaccination was associated with a lack of subsequent IFN-γ release in response to vaccine Ags, with the exception of BCG. With the exception of a weak, positive correlation between MDSC frequency at 6 weeks (time of initial vaccination) and peak Hepatitis B surface antigen Ab titer, Polymorphonuclear Myeloid-Derived Suppressor Cells (PMN-MDSC) was not correlated with T cell proliferation or Ab responses in this study. The potential for MDSC-mediated suppression of vaccine Ag-specific IFN-γ responses should be explored further, and considered when evaluating candidate infant vaccines.