Primate immune responses to HIV-1 Env formulated in the saponin-based adjuvant AbISCO-100 in the presence or absence of TLR9 co-stimulation

Protein-based vaccines require adjuvants to achieve optimal responses. Toll-like receptor (TLR) 9 agonists were previously shown to improve responses to protein-based vaccines, such as the Hepatitis B virus vaccine formulated in alum. Here, we used CpG-C together with the clinically relevant saponin-based adjuvant AbISCO-100/Matrix-M (AbISCO), to assess if TLR9 co-stimulation would quantitatively or qualitatively modulate HIV-1 envelope glycoprotein (Env)-specific B and T cell responses in rhesus macaques. The macaques were inoculated with soluble Env trimers in AbISCO, with or without the addition of CpG-C, using an interval similar to the Hepatitis B virus vaccine. Following a comprehensive evaluation of antigen-specific responses in multiple immune compartments, we show that the Env-specific circulating IgG, memory B cells and plasma cells displayed similar kinetics and magnitude in the presence or absence of CpG-C and that there was no apparent difference between the two groups in the elicited HIV-1 neutralizing antibody titers or antigen-specific CD4+ T cell responses. Importantly, the control of SHIV viremia was significantly improved in animals from both Env-immunized groups relative to adjuvant alone controls, demonstrating the potential of AbISCO to act as a stand-alone adjuvant for Env-based vaccines.