The recombinant canarypox vector, ALVAC-HIV, together with human immunodeficiency virus (HIV) gp120 envelope glycoprotein, has protected 31.2% of Thai individuals from HIV acquisition in the RV144 HIV vaccine trial. This outcome was unexpected, given the limited ability of the vaccine components to induce CD8 ؉ T-cell responses or broadly neutralizing antibodies. We vaccinated macaques with an immunization regimen intended to mimic the RV144 trial and exposed them intrarectally to a dose of the simian immunodeficiency virus SIV mac251 that transmits few virus variants, similar to HIV transmission to humans. Vaccination induced anti-envelope antibodies in all vaccinees and CD4؉ and CD8 ؉ T-cell responses. Three of the 11 macaques vaccinated with ALVAC-SIV/gp120 were protected from SIV mac251 acquisition, but the result was not significant. The remaining vaccinees were infected and progressed to disease. The magnitudes of vaccine-induced SIV mac251 -specific T-cell responses and binding antibodies were not significantly different between protected and infected animals. However, sera from protected animals had higher avidity antibodies to gp120, recognized the variable envelope regions V1/V2, and reduced SIV mac251 infectivity in cells that express high levels of ␣ 4 ␤ 7 integrins, suggesting a functional role of antibodies to V2. The current results emphasize the utility of determining the titer of repeated mucosal challenge in the preclinical evaluation of HIV vaccines.

The immunogenicity of a poylvalent HIV-1 vaccine comprised of Env antigens from primary R5 isolates was evaluated in rhesus macaques. DNA vaccines encoding four Env antigens from multiple HIV-1 subtypes and HIV-1 Gag antigen from a single subtype elicited a persistent level of binding antibodies to gp120 from multiple HIV-1 isolates that were markedly enhanced following boosting with homologous gp120 proteins in QS-21 adjuvant irrespective of the route of DNA immunization. These sera neutralized homologous and, to a lesser degree, heterologous HIV-1 isolates. Four of the six immunized animals were completely protected following rectal challenge with a SHIV encoding Env from HIV-1(Ba-L), whereas the virus load was reduced in the remaining animals compared to naïve controls. Hence priming with DNA encoding Env antigens from multiple HIV-1 clades followed by boosting with homologous Env proteins elicits anti-HIV-1 immune responses capable of protecting macaques against mucosal transmission of R5 tropic SHIV isolate.

As sexual transmission of human immunodeficiency virus-1 (HIV-1) occurs via the mucosa, an ideal HIV-1 vaccine should induce both mucosal and systemic immunity. We therefore sought to evaluate the induction of mucosal responses using a DNA env prime–gp120 protein boost approach in which sequential nasal and parenteral protein administration was performed with two novel carbohydrate-based adjuvants. These adjuvants, Advax-M and Advax-P, were specifically designed for mucosal and systemic immune enhancement, respectively. Murine intranasal immunization with gp120/Advax-M adjuvant elicited gp120-specific IgA in serum and mucosal secretions that was markedly enhanced by DNA priming. Boosting of DNA-primed mice with gp120/Advax-M and gp120/Advax-P by sequential intranasal and intramuscular immunization, or vice versa, elicited persistent mucosal gp120-specific IgA, systemic IgG and memory T- and B-cell responses. Induction of homologous, but not heterologous, neutralizing activity was noted in the sera of all immunized groups. While confirmation of efficacy is required in challenge studies using non-human primates, these results suggest that the combination of DNA priming with sequential nasal and parenteral protein boosting, with appropriate mucosal and systemic adjuvants, could generate strong mucosal and systemic immunity and may block HIV-1 mucosal transmission and infection.

Immunization of macaques with multivalent DNA encoding gp120 genes from HIV-1 subtypes A, B, C and E and a gag gene followed by boosting with homologous gp120 proteins elicited strong anti-gp120 antibodies capable of neutralizing homologous and to a lesser degree heterologous HIV-1 isolates. Both Env-and Gag-specific cell mediated immune (CMI) responses were detected in the immunized animals. Following rectal challenge with an SHIV isolate encoding HIV-1 Ba-L env, plasma viremia in the infected immunized animals was significantly lower than that observed in the naïve animals. Further, one of six immunized animals was completely protected whereas all six naïve animals were infected. These results demonstrate that a vaccine based on priming with a polyvalent DNA vaccine from multiple HIV-1 subtypes followed by boosting with homologous Env proteins elicits anti-HIV-1 immune responses capable of controlling rectal transmission of SHIV Ba-L .