Rapid and robust immune response boosting with potent, next-generation adjuvant in viral vector-primed primates

To identify strategies for augmenting vaccine immunogenicity, we compared a pox-protein prime-boost regimen comprising recombinant modified vaccinia virus Ankara and multimeric HIV-1 Env gp145, adjuvanted with Army Liposomal Formulation (ALF) either adsorbed to aluminum salt (ALFA) or formulated with the QS-21 saponin (ALFQ), in rhesus macaques. ALFQ promoted greater magnitude and more durable humoral and cellular immune responses than ALFA, which exhibits similar immunogenicity to aluminum-based adjuvants. Peak Env-specific CD4⁺ T cell responses assessed by intracellular cytokine staining were 10-fold greater with ALFQ, and CD8⁺ T cell responses were unexpectedly robust, averaging greater than 1%. ALFQ induced higher levels of several immunostimulatory cytokines in plasma, which correlated with adaptive immune responses. However, vaccination did not protect against heterologous intrarectal challenge with transmitted/founder SHIV-CH505. We provide evidence that CH505 Env may maintain a relatively closed conformation, rendering it less susceptible to targeting by Fc-mediated antibody functions. Overall, ALFQ is a promising adjuvant to improve antibody and T cell response magnitude.IMPORTANCEAn effective and durable vaccine preventing HIV-1 acquisition is urgently needed to end the HIV-1 pandemic. To date, of the nine vaccine efficacy trials conducted in humans, only the RV144 vaccine trial demonstrated efficacy in reducing infections, although immune responses waned rapidly. We evaluated a modified HIV-1 vaccine regimen incorporating next-generation adjuvants to improve immune responses and vaccine efficacy in a gold standard, pre-clinical primate model. Adjuvanted protein boosting markedly increased antibody, T cell, and pro-inflammatory response magnitude. These data, combined with the adjuvant's strong safety and immunogenicity track record in clinical trials, indicate that novel adjuvants represent a promising strategy for improving immune responses to protein immunogens. Future vaccine regimens against HIV-1 and other pathogens for which eliciting robust immunity has been difficult may benefit from incorporating these or related next-generation adjuvants.