There is evidence in both simian immunodeficiency virus and human immunodeficiency virus (HIV) type 1 infection that class I major histocompatibility complex-restricted CD8 + cytotoxic T lymphocytes play a pivotal role in controlling infection and, potentially, in protecting by immunization. Progress has been made in designing strategies to elicit these responses with HIV-1 vaccines, but methods to reproducibly quantify them have posed difficulties. An interferon-g enzyme-linked immunospot assay, using peptide pools spanning the HIV-1 genes, was developed and standardized. This method is rapid (2 days), sensitive (threshold of detection, у0.005%), quantitative, feasible using cryopreserved cells, and able to define epitope specificities. When this assay was applied to 36 HIV-1-seropositive and 10 HIV-1-seronegative subjects, it proved to be robust (specificity, 100%). When responses in natural infection were compared with vaccine-induced responses, vaccine recipient responses were у1 log lower, which confirms the importance of using this sensitive assay as an initial screen in vaccine protocols.

Overall, the HIV-specific CD8 cytotoxic T lymphocyte (CTL) response was not sufficient to qualify the regimen for a subsequent trial designed to detect an immune correlate of protection requiring a minimum CD8 CTL frequency of 30%.

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BackgroundIndividuals without prior immunity to a vaccine vector may be more sensitive to reactions following injection, but may also show optimal immune responses to vaccine antigens. To assess safety and maximal tolerated dose of an adenoviral vaccine vector in volunteers without prior immunity, we evaluated a recombinant replication-defective adenovirus type 5 (rAd5) vaccine expressing HIV-1 Gag, Pol, and multiclade Env proteins, VRC-HIVADV014-00-VP, in a randomized, double-blind, dose-escalation, multicenter trial (HVTN study 054) in HIV-1-seronegative participants without detectable neutralizing antibodies (nAb) to the vector. As secondary outcomes, we also assessed T-cell and antibody responses.Methodology/Principal FindingsVolunteers received one dose of vaccine at either 1010 or 1011 adenovector particle units, or placebo. T-cell responses were measured against pools of global potential T-cell epitope peptides. HIV-1 binding and neutralizing antibodies were assessed. Systemic reactogenicity was greater at the higher dose, but the vaccine was well tolerated at both doses. Although no HIV infections occurred, commercial diagnostic assays were positive in 87% of vaccinees one year after vaccination. More than 85% of vaccinees developed HIV-1-specific T-cell responses detected by IFN-γ ELISpot and ICS assays at day 28. T-cell responses were: CD8-biased; evenly distributed across the three HIV-1 antigens; not substantially increased at the higher dose; and detected at similar frequencies one year following injection. The vaccine induced binding antibodies against at least one HIV-1 Env antigen in all recipients.Conclusions/SignificanceThis vaccine appeared safe and was highly immunogenic following a single dose in human volunteers without prior nAb against the vector.Trial RegistrationClinicalTrials.gov NCT00119873

e On the basis of positive preclinical data, we evaluated the safety and immunogenicity of an alphavirus replicon HIV-1 subtype C gag vaccine (AVX101), expressing a nonmyristoylated form of Gag, in two double-blind, randomized, placebo-controlled clinical trials in healthy HIV-1-uninfected adults. Escalating doses of AVX101 or placebo were administered subcutaneously to participants in the United States and Southern Africa. Because of vaccine stability issues, the first trial was halted prior to completion of all dose levels and a second trial was implemented. The second trial was also stopped prematurely due to documentation issues with the contract manufacturer. Safety and immunogenicity were evaluated through assessments of reactogenicity, reports of adverse events, and assessment of replication-competent and Venezuelan equine encephalitis (VEE) viremia. Immunogenicity was measured using the following assays: enzyme-linked immunosorbent assay (ELISA), chromium 51 ( 51 Cr)-release cytotoxic T lymphocyte (CTL), gamma interferon (IFN-␥) ELISpot, intracellular cytokine staining (ICS), and lymphoproliferation assay (LPA). Anti-vector antibodies were also measured. AVX101 was well tolerated and exhibited only modest local reactogenicity. There were 5 serious adverse events reported during the trials; none were considered related to the study vaccine. In contrast to the preclinical data, immune responses in humans were limited. Only low levels of binding antibodies and T-cell responses were seen at the highest doses. This trial also highlighted the difficulties in developing a novel vector for HIV.