# Maternal Immunization with Adjuvanted Recombinant Receptor-Binding Domain Protein Provides Immune Protection against SARS-CoV-2 in Infant Monkeys

## TL;DR

Maternal vaccination with a protein-based SARS-CoV-2 vaccine in monkeys transferred protective antibodies to infants, showing potential for human maternal immunization.

## Contribution

Demonstrates placental transfer of SARS-CoV-2 antibodies in monkeys after maternal immunization with adjuvanted RBD-Fc vaccines.

## Key findings

- Infant monkeys had high levels of spike-specific IgG, correlated with maternal antibody titers.
- Infant IgG showed antigen specificity matching the maternal vaccine variant (Wuhan or Gamma).
- Sera showed stronger ACE2-RBD inhibition against vaccine-matched variants than divergent ones like Delta and Omicron.

## Abstract

Maternal vaccinations administered prior to conception or during pregnancy enhance the immune protection of newborn infants against many pathogens. A feasibility experiment was conducted to determine if monkeys can be used to model the placental transfer of maternal antibody against SARS-CoV-2. Six adult rhesus monkeys were immunized with adjuvanted recombinant-protein antigens comprised of receptor-binding domain human IgG1-Fc fusion proteins (RBD-Fc) containing protein sequences from the ancestral-Wuhan or Gamma variants. The female monkeys mounted robust and sustained anti-SARS-CoV-2 antibody responses. Blood samples collected from their infants after delivery verified prenatal transfer of high levels of spike-specific IgG, which were positively correlated with maternal IgG titers at term. In addition, an in vitro test of ACE2 neutralization indicated that the infants’ IgG demonstrated antigen specificity, reflecting prior maternal immunization with either Wuhan or Gamma-variant antigens. All sera showed stronger ACE2-RBD binding inhibition when variants in the assay more closely resembled the vaccine RBD sequence than with more distantly related variants (i.e., Delta and Omicron). Monkeys are a valuable animal model for evaluating new vaccines that can promote maternal and infant health. Further, the findings highlight the enduring nature and safety of the immune protection elicited by an adjuvanted recombinant RBD-Fc vaccine.