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A major challenge for HIV vaccine development is to raise anti-envelope antibodies capable of recognizing and neutralizing diverse strains of HIV-1. Accordingly, a full length single chain (FLSC) of gp120-CD4 chimeric vaccine construct was designed to present a highly conserved CD4-induced (CD4i) HIV-1 envelope structure that elicits cross-reactive anti-envelope humoral responses and protective immunity in animal models of HIV infection. IHV01 is the FLSC formulated in aluminum phosphate adjuvant. We enrolled 65 healthy adult volunteers in this first-in-human phase 1a randomized, double-blind, placebo-controlled study with three dose-escalating cohorts (75 µg, 150 µg, and 300 µg doses). Intramuscular injections were given on weeks 0, 4, 8, and 24. Participants were followed for an additional 24 weeks after the last immunization. The overall incidence of adverse events (AEs) was not significantly different between vaccinees and controls. The majority (89%) of vaccine-related AE were mild. The most common vaccine-related adverse event was injection site pain. There were no vaccine-related serious AE, discontinuation due to AE, intercurrent HIV infection, or significant decreases in CD4 count. By the final vaccination, all vaccine recipients developed antibodies against IHV01 and demonstrated anti-CD4i epitope antibodies. The elicited antibodies reacted with CD4 non-liganded Env antigens from diverse HIV-1 strains. Antibody-dependent cell-mediated cytotoxicity against heterologous infected cells or gp120 bound to CD4+ cells was evident in all cohorts as were anti-gp120 T-cell responses. IHV01 vaccine was safe, well tolerated, and immunogenic at all doses tested. The vaccine raised broadly reactive humoral responses against conserved CD4i epitopes on gp120 that mediates antiviral functions.

Background A primary challenge for HIV vaccine development is to raise antiviral antibodies capable of recognizing highly variable viral antigens. The full-length single chain (FLSC) gp120-CD4 chimeric protein was designed to present a highly conserved CD4-induced HIV-1 envelope structure that evokes cross-reactive humoral responses (Figure 1). IHV01 is an FLSC subunit vaccine formulated in alum adjuvant. The safety and immunogenicity of IHV01 was evaluated in this first-in-human phase 1a trial. Methods This randomized, double-blind placebo-controlled study involved three dose-escalating cohorts (75 µg, 150 µg, and 300 µg doses). Eligible participants were HIV-1 uninfected healthy volunteers aged 18 to 45 years. Participants in each cohort were block randomized in groups of four in a 3:1 ratio to receive either vaccine or placebo. Intramuscular injections were given on weeks 0, 4, 8, and 24. Participants were followed for an additional 24 weeks after the last immunization. Crossreactive antibody binding titers against diverse HIV envelopes and antigens and specific CD4i epitopes on gp120 were assessed. Results Sixty-five volunteers were enrolled—49 vaccine and 16 placebo. Majority (81%) of vaccinations with IHV01 produced no localized or systemic reactions; no different from the control group. The overall incidence of adverse events (AEs) was not significantly different between groups. Majority (89%) of vaccine-related AEs were mild in severity. The most common vaccine-related AEs were injection site pain (31%), pruritus (10%), and headache (10%). There were no vaccine-related serious AE, discontinuation due to AE, or intercurrent HIV infection. By the final vaccination, all subjects in all cohorts had developed antibodies against IHV01; all placebo recipients were negative. The antibodies induced by IHV01 reacted with envelope antigens from diverse HIV-1 strains (Figure 2). Conclusion IHV01 vaccine was safe, well tolerated, and immunogenic in all doses tested. The vaccine raised broadly reactive humoral responses against multiple gp120 domains, transition state structures, and CD4i epitopes. Disclosures All Authors: No reported Disclosures.