Decrease in circulating CD25hiFoxp3+ regulatory T cells following vaccination with the candidate malaria vaccine RTS,S

We found that the frequency of CD25hiFoxp3+ Treg cells decreased following administration of RTS,S (p = 0.0195), with no differences based on vaccine regimen. There was a concomitant decrease in CTLA-4 expression on CD25hiFoxp3+ Treg cells (p = 0.0093) and PD-1 levels on CD8+ T cells (p = 0.0002). Additionally, the frequency of anergic CTLA-4+CCR7+ T cells decreased following vaccination. An inverse correlation was observed between the frequency of Plasmodium falciparum circumsporozoite protein (PfCSP)-specific IFN-γ and PfCSP-specific IL-10, as well as an inverse correlation between IL-10 induced by Hepatitis B surface antigen, the carrier of RTS,S, and PfCSP-specific IFN-γ, suggesting that immunity against the vaccine backbone could impact vaccine immunogenicity. These results have implications for future malaria vaccine design.