With the HIV-1 epidemic in southern Africa still rising, a prophylactic
vaccine against the region's most prolific subtype (subtype C) would be a significant step forward. In this paper we report on the effect of 2 different adjuvants,
AddaVax and
AlhydroGel, formulated with HIV-1 subtype C
gp140, on the development of binding and neutralising antibody titres in rabbits.
AddaVax is a
squalene-based oil-in-water nano-
emulsion (similar to
MF59) which can enhance both cellular and humoral immune responses, whilst
AlhydroGel (
aluminium hydroxide gel) mainly drives a Th2 response. The
gp140 gene tested was derived from the superinfecting virus (SU) from participant CAP256 in the CAPRISA 002 Acute
infection cohort. The
furin cleavage site of the
Env protein was replaced with a flexible linker and an I559P mutation introduced.
Lectin affinity purified soluble
Env protein was mainly trimeric as judged by molecular weight using BN-PAGE and contained intact broadly neutralising
epitopes for the V3-glycan supersite (
monoclonal antibodies PGT128 and PGT135), the CD4 binding site (VRC01) and the V2-glycan (PG9) but not for the trimer-specific
monoclonal antibodies PG16, PGT145 and CAP256-VRC26_08. When this soluble
Env protein was tested in rabbits,
AlhydroGel significantly enhanced soluble Env and V1V2 binding
antibodies when compared to
AddaVax. Finally,
AlhydroGel resulted in significantly higher neutralization titres for a subtype C Tier 1A virus (MW965.26) and increased neutralization breadth to Tier 1A and 1B viruses. However, no autologous Tier 2 neutralisation was observed. These data suggest that adjuvant selection is critical for developing a successful
vaccine and
AlhydroGel should be further investigated. Additional purification of trimeric native-like CAP256 Env and/or priming with
DNA or MVA might enhance the induction of
neutralizing antibodies and possible Tier 2 HIV-1 neutralisation.