Maternal immunization with a recombinant adenovirus-expressing fusion protein protects neonatal cotton rats from respiratory syncytia virus infection by transferring antibodies via breast milk and placenta

We evaluated the efficacy of a recombinant adenovirus that expresses a membrane-truncated respiratory syncytial virus (RSV) fusion protein (Ad-F0ΔTM) in newborns via maternal immunization (MI) of pregnant cotton rats. Intranasal Ad-F0ΔTM immunization was given to pregnant female rats, and MI-newborn rats were then challenged intranasally with RSV. Anti-RSV IgGs were observed in the serum of MI-newborn rats after birth. The pulmonary viral loads in Ad-F0ΔTM vs. control vector, Ad-LacZ, and MI-newborns on day 3 post-challenge were reduced by 4 log10/g lung. The neutralizing antibody remained for up to 3 weeks in the serum of MI-newborns, which is when weaning began. Ad-F0ΔTM protected MI-newborns from RSV challenge for 1 week. Vertical-transferred protective antibodies were examined in the breast milk and placenta as well. Finally, anti-RSV immunity was not boosted but was only primed during the next RSV exposure in Ad-F0ΔTM-MI-newborns. Maternal Ad-F0ΔTM immunization provides acute protection against RSV infection in neonates.