The Protective Role of Maternal Immunization in Early Life

Abstract

With birth, the newborn is transferred from a quasi-sterile environment to the outside world. At this time, the neonatal immune system is inexperienced and continuously subject to a process of development as it encounters different antigenic stimuli after birth. It is initially characterized by a bias toward T helper 2 phenotype, reduced T helper 1, and cytotoxic responses to microbial stimuli, low levels of memory, and effector T and B cells and a high production of suppressive T regulatory cells. The aim of this setting, during fetal life, is to maintain an anti-inflammatory state and immune-tolerance. Maternal antibodies are transferred during pregnancy through the placenta and, in the first weeks of life of the newborn, they represent a powerful tool for protection. Thus, optimization of vaccination in pregnancy represents an important strategy to reduce the burden of neonatal infections and sepsis. Beneficial effects of maternal immunization are universally recognized, although the optimal timing of vaccination in pregnancy remains to be defined. Interestingly, the dynamic exchange that takes place at the fetal-maternal interface allows the transfer not only of antibodies, but also of maternal antigen presenting cells, probably in order to stimulate the developing fetal immune system in a harmless way. There are still controversial effects related to maternal immunization including the so called “immunology blunting,” i.e., a dampened antibody production following infant's vaccination in those infants who received placentally transferred maternal immunity. However, clinical relevance of this phenomenon is still not clear. This review will provide an overview of the evolution of the immune system in early life and discuss the benefits of maternal vaccination. Current maternal vaccination policies and their rationale will be summarized on the road to promising approaches to enhance immunity in the neonate.

LAMP-1 Chimeric to HIV-1 p55Gag in the Immunization of Neonate Mice Induces an Early Germinal Center Formation and AID Expression

“…Neonate vaccination could be affected by maternal antibodies [6], whereas neonatal DNA vaccination seems to overcome the inhibitory effect of maternal immunization, favoring neonatal antigen priming. At the site of injection, DNA vaccines delivered to cells mainly induce a CD8+ T-cell response [7].…”

Immune Response of Neonates Born to Mothers Infected With SARS-CoV-2

“…7 During the first weeks after birth, the infant is therefore passively protected by maternal immunoglobulins transferred via the placenta during the last trimester of pregnancy. 8 Passive protection continues after birth, with breastmilk containing maternal secretory immunoglobulin A (sIgA) antibodies mostly derived from the respiratory and intestinal maternal mucosal immune system. 9 Specific SARS-CoV-2 maternal antibodies are transferred through the placenta during the last months of pregnancy and can be detected in the serum of the neonates born to naturally infected or vaccinated mothers.…”

Knowledge gaps in late-onset neonatal sepsis in preterm neonates: a roadmap for future research

“…Several studies on the protective role of breastmilk in women vaccinated during pregnancy identified a high amount of vaccine-specific sIgA in the breastmilk samples up to several weeks postpartum. [27][28][29] Consequently, a lower incidence of respiratory illness with fever episodes in young infants of influenza-vaccinated mothers was reported. 28,29 The potential of neonatal immunization against Gram-negative bacteria has also been described, either a maternal vaccination to pregnant woman, via breastmilk and directly to the neonate.…”

“…[27][28][29] Consequently, a lower incidence of respiratory illness with fever episodes in young infants of influenza-vaccinated mothers was reported. 28,29 The potential of neonatal immunization against Gram-negative bacteria has also been described, either a maternal vaccination to pregnant woman, via breastmilk and directly to the neonate. 30 Knowledge gaps and opportunities for future research.…”