The immunogenicities of candidate DNA-and modified vaccinia virus Ankara (MVA)-vectored human immunodeficiency virus (HIV) vaccines were evaluated on their own and in a prime-boost regimen in phase I clinical trials in healthy uninfected individuals in the United Kingdom. Given the current lack of approaches capable of inducing broad HIV-neutralizing antibodies, the pTHr.HIVA DNA and MVA.HIVA vaccines focus solely on the induction of cell-mediated immunity. The vaccines expressed a common immunogen, HIVA, which consists of consensus HIV-1 clade A Gag p24/p17 proteins fused to a string of clade A-derived epitopes recognized by cytotoxic T lymphocytes (CTLs). Volunteers' fresh peripheral blood mononuclear cells were tested for HIV-specific responses in a validated gamma interferon enzyme-linked immunospot (ELISPOT) assay using four overlapping peptide pools across the Gag domain and three pools of known CTL epitopes present in all of the HIVA protein. Both the DNA and the MVA vaccines alone and in a DNA prime-MVA boost combination were safe and induced HIV-specific responses in 14 out of 18, seven out of eight and eight out of nine volunteers, respectively. These results are very encouraging and justify further vaccine development.
DNA priming has previously been shown to elicit augmented immune responses when administered by electroporation (EP) or codelivered with a plasmid encoding interleukin-12 (pIL-12). We hypothesized that the efficacy of a DNA prime and recombinant adenovirus 5 boost vaccination regimen (DNA/rAd5) would be improved when incorporating these vaccination strategies into the DNA priming phase, as determined by pathogenic simian immunodeficiency virus SIVmac239 challenge outcome. The whole SIVmac239 proteome was delivered in 5 separate DNA plasmids (pDNA-SIV) by EP with or without pIL-12, followed by boosting 4 months later with corresponding rAd5-SIV vaccine vectors. Remarkably, after repeated low-dose SIVmac239 mucosal challenge, we demonstrate 2.6 and 4.4 log reductions of the median SIV peak and set point viral loads in rhesus macaques (RMs) that received pDNA-SIV by EP with pIL-12 compared to the median peak and set point viral loads in mock-immunized controls (P < 0.01). In 5 out of 6 infected RMs, strong suppression of viremia was observed, with intermittent "blips" in virus replication. In 2 RMs, we could not detect the presence of SIV RNA in tissue and lymph nodes, even after 13 viral challenges. RMs immunized without pIL-12 demonstrated a typical maximum of 1.5 log reduction in virus load. There was no significant difference in the overall magnitude of SIV-specific antibodies or CD8 T-cell responses between groups; however, pDNA delivery by EP with pIL-12 induced a greater magnitude of SIV-specific CD4 T cells that produced multiple cytokines. This vaccine strategy is relevant for existing vaccine candidates entering clinical evaluation, and this model may provide insights into control of retrovirus replication.
Ex vivo functional immunoassays such as ELISpot and intracellular cytokine staining (ICS) by flow cytometry are crucial tools in vaccine development both in the identification of novel immunogenic targets and in the immunological assessment of samples from clinical trials. Cryopreservation and subsequent thawing of PBMCs via validated processes has become a mainstay of clinical trials due to processing restrictions inherent in the disparate location and capacity of trial centres, and also in the need to standardize biological assays at central testing facilities. Logistical and financial requirement to batch process samples from multiple study timepoints are also key. We used ELISpot and ICS assays to assess antigen-specific immunogenicity in blood samples taken from subjects enrolled in a phase II malaria heterologous prime-boost vaccine trial and showed that the freeze thaw process can result in a 3–5-fold reduction of malaria antigen-specific IFNγ-producing CD3+CD4+ effector populations from PBMC samples taken post vaccination. We have also demonstrated that peptide responsive CD8+ T cells are relatively unaffected, as well as CD4+ T cell populations that do not produce IFNγ. These findings contribute to a growing body of data that could be consolidated and synthesised as guidelines for clinical trials with the aim of increasing the efficiency of vaccine development pipelines.
During chronic HIV-1 infection, continuing viral replication is associated with impaired proliferative capacity of virus-specific CD8+ T cells and with the expansion and persistence of oligoclonal T cell populations. TCR usage may significantly influence CD8+ T cell-mediated control of AIDS viruses; however, the potential to modulate the repertoire of functional virus-specific T cells by immunotherapy has not been explored. To investigate this, we analyzed the TCR Vβ usage of CD8+ T cells populations which were expanded following vaccination with modified vaccinia virus Ankara expressing a HIV-1 gag/multiepitope immunogen (MVA.HIVA) in HIV-1-infected patients receiving highly active antiretroviral therapy. Vaccinations induced the re-expansion of HIV-1-specific CD8+ T cells and these showed broad TCR Vβ usage which was maintained for at least 1 year in some individuals. By contrast, virus-specific CD8+ T cell populations in the same donors which failed to expand after vaccination and in unvaccinated controls were oligoclonal. Simultaneously, we observed that CD8+ T cells recognizing vaccine-derived HIV-1 epitopes displayed enhanced capacity to proliferate and to inhibit HIV-1 replication in vitro, following MVA.HIVA immunizations. Taken together, these data indicate that an attenuated viral-vectored vaccine can modulate adaptive CD8+ T cell responses to HIV-1 and improve their antiviral functional capacity. The potential therapeutic benefit of this vaccination approach warrants further investigation.
Induction of a long-term immunological memory, which can expand and defend the host upon pathogen encounter, is the ''holy grail'' of vaccinology. Here, using a sensitive cultured IFN-c ELISPOT assay, we show that 50% (15 out of 30) of healthy, HIV-1/2-uninfected volunteers who received pTHr.HIVA DNA prime-modified vaccinia virus Ankara. HIVA boost vaccine regimen 1 to 3 1/2 years ago had detectable HIV-1-specific T-cell responses. These T cells, predominantly of the CD4 1 subtype, could proliferate and produce multiple cytokines in response to in vitro peptide stimulation. Peptide mapping studies showed that the vaccine-induced CD4 1 T cells were mostly directed toward epitopes targeted in HIV-1-infected individuals. In addition, we used the same assay to re-evaluate 51 volunteers from past vaccine trial IAVI-006 and corrected the previously reported 10% of vaccine responders to 50%. Thus, we confirmed that cultured assays are a valuable tool for studying T-cell memory. These results are discussed in the context of the current state-of-affairs of the HIV-1 vaccine field.Key words: Clinical trial . DNA-MVA vaccines . HIV-1 . Memory T cells
IntroductionDespite proven methods of prevention and/or decrease of transmission, all efforts to slow the rate of new HIV-1 infections are failing in most countries around the world, including the USA (http://www.unaids.org/). The best solution to control of the HIV-1 epidemic remains the development of a safe, effective and accessible preventive vaccine [1]. The aim of vaccination is induction of long-lived, pathogen-specific circulating antibodies and cellular immunological memory, which together provide a faster and more efficient defense of the host following exposure to the pathogen. A central role in both the T-and B-cell memory development is played by CD4 1 T cells [2,3], the functionality of which is tuned by the non-adaptive innate response [4]. It is the CD4 1 T-cell population that is decimated by HIV-1-infection, which eventually leads to opportunistic infections [5,6].The long-term aim of our effort is development of an effective HIV-1 vaccine. In particular, we explore strategies for eliciting HIV-1-specific T-cell responses, which could on their own, or together with vaccine-induced anti-HIV-1 antibodies, limit tissue damage during HIV-1 infection. Our first vaccine platform was designed as a heterologous DNA prime-modified vaccinia virus Ankara (MVA) boost regimen delivering a common immunogen HIVA, which consists of consensus African clade A Gag p24 and The most sensitive assay employed and validated by the IAVI-016 trial was the IFN-g ELISPOT assay combined with a prior 10-day-culture expansion of PBMC using immunogen-derived peptides and externally supplemented cytokines. This so called cultured IFN-g ELISPOT assay increased the frequencies of specific T cells more than 24-fold compared with the ex vivo assay and detected vaccine-induced HIV-1-specific responses in all (8 out of 8) IAVI-016 subjects who received the pTHr.HIVA DNA-MVA.HIVA regimen [14]. Thes...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.