ALVAC-HIV B/C candidate HIV vaccine efficacy dependent on neutralization profile of challenge virus and adjuvant dose and type

The ALVAC-HIV clade B/AE and equivalent SIV-based/gp120 + Alum vaccines successfully decreased the risk of virus acquisition in humans and macaques. Here, we tested the efficacy of HIV clade B/C ALVAC/gp120 vaccine candidates + MF59 or different doses of Aluminum hydroxide (Alum) against SHIV-Cs of varying neutralization sensitivity in macaques. Low doses of Alum induced higher mucosal V2-specific IgA that increased the risk of Tier 2 SHIV-C acquisition. High Alum dosage, in contrast, elicited serum IgG to V2 that correlated with a decreased risk of Tier 1 SHIV-C acquisition. MF59 induced negligible mucosal antibodies to V2 and an inflammatory profile with blood C-reactive Protein (CRP) levels correlating with neutralizing antibody titers. MF59 decreased the risk of Tier 1 SHIV-C acquisition. The relationship between vaccine efficacy and the neutralization profile of the challenge virus appear to be linked to the different immunological spaces created by MF59 and Alum via CXCL10 and IL-1 beta, respectively. Author summary The ALVAC-based clade C /gp120 combination is currently being tested for efficacy and licensures in South Africa in the HVTN702 HIV vaccine trial using the MF59 adjuvant rather than Alum with the intent of inducing higher neutralizing antibodies and T cell responses. Here, we present studies in 71 macaques that evaluated the relative efficacy of identical ALVAC-HIV B/C HIV vaccines with Alum or MF59 following challenge exposure to SHIV-clade C viral stocks that differed in their neutralization profiles. Our results demonstrated that use of the proprietary Novartis Alum at lower doses affects the proportion of mucosal V2-specific IgG and IgA, and that IgAs and IgGs were respectively associated with an increased or decreased risk of virus acquisition. In contrast, animals immunized with the MF59 regimen had no V2 mucosal responses, and a high level of serum neutralizing antibodies (Tier 1) to easy to neutralize viruses that were associated with a decreased risk of Tier 1 SHIV-C acquisition. In vitro studies suggest the hypothesis that the low doses of proprietary Novartis Alum used in our studies may be the underlying reason for the decreased vaccine efficacy, via lower inflammasome activation and IL-1 beta production.