Safety of and Immune Response to an HIV-1 Subtype C Vaccine (AVX101) in HIV Uninfected Adults

• Grade IV adverse events [ Time Frame: 1 year ] [ Designated as safety issue: Yes ]
  The sample size at each vaccine dose level was selected such that the stopping rule for not escalating the dose (2 or more vaccine-related Grade IV adverse experiences) would be met with high probability if the true toxicity rate was above 15-20%, and such that dose escalation would occur with high probability if the true toxicity rate was less than 5%.
  
  

• Local and systemic adverse events [ Time Frame: 7 days after each dose ] [ Designated as safety issue: Yes ]
  Reactogenicity assessments were performed for all participants before and after each injection, beginning 25 to 45 minutes post injection and continuing daily for 7 days. Assessments performed included systemic reactogenicity (body temperature, malaise and/or fatigue, myalgia, headache, chills, arthralgia, nausea, vomiting) and local reactogenicity (injection site pain, tenderness, erythema or induration, and axillary lymph node tenderness or enlargement).
  
  
• Binding antibodies by ELISA [ Time Frame: 1 year ] [ Designated as safety issue: No ]
  Binding antibodies to commercially available Gag protein (P55 Gag; Quality Biologicals) were assessed by ELISA using single serum dilutions (1/50 or 1/100) on samples taken at baseline, two weeks after the second and third vaccinations and at the final visit. Samples that were positive in the initial ELISA were tested by endpoint titration ELISA using six 2- to 7-fold serial dilutions of serum beginning at a 1/50 or 1/100 dilution. Magnitude of responses is reported as the difference in optical density (OD) in antigen-containing and non-antigen containing wells at the 1:50 dilution.
  
  
• Chromium release CTL assay [ Time Frame: 3 months ] [ Designated as safety issue: No ]
  A standard 51Cr-release CTL assay was performed on fresh peripheral blood mononuclear cells (PBMC) at baseline and 2 weeks after the second and third vaccinations, using a 50:1 effector to target (E:T) ratio.
  
  
• IFN-gamma ELISpot assay [ Time Frame: 3 months ] [ Designated as safety issue: No ]
  Bulk T cell responses were assessed by IFN-γ ELISpot, using cryopreserved PBMC collected at baseline and 2 weeks after the second and third vaccinations, and stimulated overnight with Gag peptide pools at 200,000 cells per well.
  
  
• Antibodies to VEE virus [ Time Frame: 1 year ] [ Designated as safety issue: No ]
  Neutralizing antibodies to VEE virus were measured in serum obtained at baseline, 2 weeks after the second and third vaccinations and at the final visit.
  
  
• Replication-competent viral vector viremia [ Time Frame: 2 weeks after each vaccine dose ] [ Designated as safety issue: Yes ]
  Any participant who reported a fever greater than 38oC, or other moderate symptoms consistent with a viral illness (e.g. headache or malaise) during the 7 days following vaccination, or neurological symptoms (e.g. nuchal rigidity, ataxia, convulsions, coma, paralysis) within the window of the 2-week post vaccination visit, provided a serum sample to confirm the absence of replication-competent VEE viremia.
  
  
• Intracellular cytokine staining (ICS) assay [ Time Frame: 3 months ] [ Designated as safety issue: No ]
  Flow cytometry was used to examine HIV-specific CD4+ and CD8+ T cell responses using ICS, following stimulation with Gag peptides that span the protein sequence encoded by the vaccine construct. ICS assays were performed at baseline and 2 weeks after the second and third vaccinations.
  
  

HIV-1 subtype C is the prevailing subtype of HIV found in sub-Saharan Africa and is primarily responsible for the HIV/AIDS epidemic in southern Africa. Thus, development of a preventive subtype C vaccine is critically important in controlling the spread of HIV in this part of the world. This study will determine the safety and immunogenicity of an alphavirus replicon HIV-1 subtype C gag vaccine, AVX101, in HIV uninfected adults. This vaccine utilizes a propagation-defective replicon vector system derived from an attenuated strain of Venezuelan Equine Encephalitis (VEE) virus. The vaccine replicon expresses the gag gene from a South African subtype C isolate of HIV-1. Participants will be recruited in the United States, South Africa, and Botswana.

The study will last for 1 year. Participants will be enrolled sequentially, from lowest to highest dose of vaccine, into one of four groups. Groups will begin enrollment only following safety review of the previous group. Participants will be randomly assigned to receive active vaccine or placebo. During the study, participants will receive either 3 injections of one of four possible doses of the vaccine or 3 injections of placebo. Injections will be given at study entry and at Days 28 and 84. At screening, participants will undergo medical history assessment, a complete physical, HIV testing and counseling, and blood and urine collection; they will also be interviewed and asked to complete a questionnaire. After screening, there will be 8 study visits; the visits will occur at Days 14, 28, 42, 84, 98, 168, 273, and 364. Participants will be interviewed and asked to fill out a questionnaire at each study visit; participants will undergo a physical, additional HIV testing and counseling, and blood and urine collection at selected visits.