Myeloid derived suppressor cells are present at high frequency in neonates and suppress in vitro T cell responses.

Over 4 million infants die each year from infections, many of which are vaccine-preventable. Young infants respond relatively poorly to many infections and vaccines, but the basis of reduced immunity in infants is ill defined. We sought to investigate whether myeloid-derived suppressor cells (MDSC) represent one potential impediment to protective immunity in early life, which may help inform strategies for effective vaccination prior to pathogen exposure. We enrolled healthy neonates and children in the first 2 years of life along with healthy adult controls to examine the frequency and function of MDSC, a cell population able to potently suppress T cell responses. We found that MDSC, which are rarely seen in healthy adults, are present in high numbers in neonates and their frequency rapidly decreases during the first months of life. We determined that these neonatal MDSC are of granulocytic origin (G-MDSC), and suppress both CD4+ and CD8+ T cell proliferative responses in a contact-dependent manner and gamma interferon production. Understanding the role G-MDSC play in infant immunity could improve vaccine responsiveness in newborns and reduce mortality due to early-life infections.

Natural killer cell and T-cell subset distributions and activation influence susceptibility to perinatal HIV-1 infection.

OBJECTIVE: To determine neonatal immunologic factors that correlate with mother-to-child-transmission of HIV-1. DESIGN: This case-control study compared cord blood natural killer (NK) and T-cell populations of HIV-1 exposed infants who subsequently acquired infection by 1 month (cases) to those who remained uninfected by 1 year of life (controls). Control specimens were selected by proportional match on maternal viral load. METHODS: Cryopreserved cord blood mononuclear cells (CBMCs) were thawed and stained for multiparameter flow cytometry to detect NK and T-cell subsets and activation status. CBMCs were also used in a viral suppression assay to evaluate NK cell inhibition of HIV-1 replication in autologous CD4 T cells. RESULTS: Cord blood from cases contained a skewed NK cell repertoire characterized by an increased proportion of CD16CD56 NK cells. In addition, cases displayed less-activated CD16CD56 NK cells and CD8 T cells, based on HLA-DRCD38 costaining. NK cell suppression of HIV-1 replication ex vivo correlated with the proportion of acutely activated CD68CD16CD56 NK cells. Finally, we detected a higher proportion of CD27CD45RA effector memory CD4 and CD8 T cells in cord blood from cases compared with controls. CONCLUSION: When controlled for maternal viral load, cord blood from infants who acquired HIV-1 had a higher proportion of CD16CD56 NK cells, lower NK cell activation and higher levels of mature T cells (potential HIV-1 targets) than control infants who remained uninfected. Our data provide evidence that infant HIV-1 acquisition may be influenced by both innate and adaptive immune cell phenotypes and activation status.