Analysis of the ability of five adjuvants to enhance immune responses to a chimeric plant virus displaying an HIV-1 peptide

The ability of five different adjuvants (alum, complete Freund's adjuvant, Quil A, AdjuPrime and Ribi) to stimulate humoral and T-cell mediated immune responses against a purified chimeric virus particle was investigated. Each adjuvant was administered subcutaneously to adult mice together with 10 μg of wildtype ( wt) cowpea mosaic virus (CPMV) or a chimeric CPMV displaying the HIV-1 gp41 peptide, residues 731–752. All preparations elicited strong antibody responses to CPMV, but Quil A elicited the highest and most consistent responses to the HIV-1 peptide. This finding was reflected in both ELISA titres with immobilized peptide and in HIV-1-neutralizing antibody. In addition Quil A was also the only adjuvant to stimulate an in vitro proliferative T-cell response. Surprisingly with all adjuvant formulations a predominately IgG2a anti-gp41 peptide response was observed, indicating a type 1 T-helper cell-like response. Furthermore, the efficiency of the CPMV display system was demonstrated by its ability to induce good levels of peptide specific antibody in the absence of any adjuvant.