Comparison of systemic and mucosal vaccination: impact on intravenous and rectal SIV challenge

Mucosal tissues are the primary route of transmission for most respiratory and sexually transmitted diseases, including human immunodeficiency virus. We aimed to generate strong mucosal immune responses to simian immunodeficiency virus (SIV) in rhesus macaques by targeting recombinant adenovirus serotype 5 (rAd5) to the lung. The immunogenicity and efficacy of aerosol (AE) vaccination was compared with intramuscular (IM) delivery in either an intravenous (IV) or intrarectal (IR) SIV mac251 challenge model. Aerosolized rAd5 induced strong cellular responses in the lung and systemic humoral responses equivalent to IM. Strikingly, all immunization groups controlled acute viremia in the IV challenge model by 1–2 logs. By contrast, after IR challenge, only peak viremia was reduced by immunization, with no significant effect on SIV infection acquisition rate or mucosal CD4 + T-cell preservation. Improved disease outcome was associated with pre-challenge cellular and humoral responses, while post-challenge T-cell responses were highly correlated with viremia control. The similar outcomes achieved by systemic and airway mucosal immunization support AE delivery as a safe, effective, and less invasive alternative to parenteral vaccination.