Novel Conserved-region T-cell Mosaic Vaccine With High Global HIV-1 Coverage Is Recognized by Protective Responses in Untreated Infection

An effective human immunodeficiency virus type 1 (HIV-1) vaccine is the best solution for halting the acquired immune deficiency syndrome epidemic. Here, we describe the design and preclinical immunogenicity of T-cell vaccine expressing novel immunogens tHIVconsvX, vectored by DNA, simian (chimpanzee) adenovirus, and poxvirus modified vaccinia virus Ankara (MVA), a combination highly immunogenic in humans. The tHIVconsvX immunogens combine the three leading strategies for elicitation of effective CD8(+) T cells: use of regions of HIV-1 proteins functionally conserved across all M group viruses (to make HIV-1 escape costly on viral fitness), inclusion of bivalent complementary mosaic immunogens (to maximize global epitope matching and breadth of responses, and block common escape paths), and inclusion of epitopes known to be associated with low viral load in infected untreated people (to induce field-proven protective responses). tHIVconsvX was highly immunogenic in two strains of mice. Furthermore, the magnitude and breadth of CD8(+) T-cell responses to tHIVconsvX-derived peptides in treatment-naive HIV-1(+) patients significantly correlated with high CD4(+) T-cell count and low viral load. Overall, the tHIVconsvX design, combining the mosaic and conserved-region approaches, provides an indisputably better coverage of global HIV-1 variants than previous T-cell vaccines. These immunogens delivered in a highly immunogenic framework of adenovirus prime and MVA boost are ready for clinical development.

Modified vaccinia Ankara expressing HIVA antigen stimulates HIV-1-specific CD8 T cells in ELISpot assays of HIV-1 exposed infants

Recombinant modified vaccinia virus Ankara expressing HIV-1 antigens (MVA.HIVA) was used in ELISpot assays to monitor HIV-1-specific T cell responses in infants. Responses to MVA.HIVA and HIV-1 peptides were examined in 13 infected and 81 exposed uninfected infants in Nairobi, Kenya. Responses to MVA.HIVA (38%) and peptide stimulation (38%) were similar in frequency (p=1.0) and magnitude (mean 176 versus 385 HIVSFU/10(6), p=0.96) in HIV-1 infected infants. In exposed uninfected infants, MVA.HIVA detected more positive responses and higher magnitude responses as compared to peptide. MVA.HIVA ELISpot is a sensitive method for quantification of HIV-1-specific CD8+ T cell responses in HIV-1 exposed infants. These results demonstrate the relevance of HIV-1 clade A consensus-derived immunogen HIVA for the viruses currently circulating in Nairobi.

A human immunodeficiency virus 1 (HIV-1) clade A vaccine in clinical trials: stimulation of HIV-specific T-cell responses by DNA and recombinant modified vaccinia virus Ankara (MVA) vaccines in humans

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.

Construction and immunogenicity in a prime-boost regimen of a Semliki Forest virus-vectored experimental HIV clade A vaccine

A novel, experimental subunit human immunodeficiency virus (HIV) vaccine, SFV.HIVA, was constructed. This consists of Semliki Forest virus (SFV), which is a suitable vaccine vector for use in humans, and a passenger gene encoding HIVA, which is an immunogen derived from HIV-1 clade A that is being currently tested in clinical trials of combined DNA- and modified vaccinia virus Ankara (MVA)-vectored vaccines in Oxford (UK) and Nairobi (Kenya). In the mouse, the SFV.HIVA vaccine was highly immunogenic for T cell-mediated immune responses and induced T cell memory that lasted for at least 6 months. SFV.HIVA was also compared to the vaccines currently used in the clinical trials and was shown to be as effective in T cell induction as pTHr.HIVA DNA but less immunogenic than MVA.HIVA. When tested in a prime-boost regimen, SFV.HIVA-induced responses could be boosted by MVA.HIVA. This work is a part of a long-term effort to build a panel of subunit vaccines expressing a common immunogen, which will allow both a direct comparison of various vaccine vectors and combined vaccination regimens in humans and provide more flexibility and/or a potential optimization of vaccinations for individuals based on their pre-existing anti-vector immunity.

Immunogenicity in Mamu-A*01 rhesus macaques of a CCR5-tropic human immunodeficiency virus type 1 envelope from the primary isolate (Bx08) after synthetic DNA prime and recombinant adenovirus 5 boost

Envelopes of primary R5-tropic human immunodeficiency virus type 1 (HIV-1) isolates may be particularly relevant for vaccine purposes and should be evaluated for immunogenicity in animals including macaques before carrying out human vaccine trials. In the present study, the immunogenicities of synthetic HIV-1 env DNA vaccines, which had been derived from the early primary isolate Bx08 and contain humanized codons, were evaluated in mice, guinea pigs and rhesus macaques. Neutralization sensitivity of the HIV-1(Bx08) isolate was found to resemble that of other primary isolate prototypes. Immunogenicity of gp120 delivered as codon-optimized DNA vaccine was comparable to that of recombinant gp120 protein plus adjuvant in mice. Similarly, DNA vaccination of guinea pigs with synthetic gp140(Bx08) and gp150(Bx08) DNA induced a strong antibody response independent of the gene construct and DNA immunization route. Mamu-A*01 rhesus macaques were DNA vaccinated with synthetic gp150(Bx08) or gp140(Bx08) DNA and boosted with a replication-deficient recombinant human adenovirus type 5 expressing a synthetic gp120(Bx08) gene. DNA-vaccinated rhesus macaques developed specific CD8+ T lymphocyte responses and anti-rgp120(IIIb) antibody responses. Both the humoral and cellular responses were significantly improved following intramuscular boosting with the recombinant adenovirus. The demonstrated humoral and cellular immunogenicities of these HIV Bx08 Env vaccines in non-human primates encourages their further development as one component in candidate HIV vaccines for humans.

Development of a DNA-MVA/HIVA vaccine for Kenya

Without going into the details of the devastation that human immunodeficiency virus (HIV) infection causes especially in the developing world, the best hope for changing the course of this epidemic is development of a safe, effective, accessible prophylactic HIV vaccine. While the inaccessibility of potentially neutralising epitopes on primary HIV isolates has hampered the development of envelope-based vaccines, there is a number of new potent technologies capable of inducing high levels of circulating virus-specific CD8(+) cytotoxic T lymphocytes (CTL). Our original finding that a successive immunisation with DNA and modified vaccinia virus Ankara (MVA) vaccines expressing a common immunogen is a potent way of inducing CD8(+) CTL, which has been since reinforced by us and others, prompted us to test this approach in humans. With the view of proceeding into a high-risk cohort in Kenya for the efficacy trial, we designed the immunogen, termed HIVA, to match the HIV strain responsible locally for over 70% infections. It consists of a consensus clade A gag p24/p17 and a string of clade A-derived CTL epitopes. Pre-clinical studies demonstrated high immunogenicities of both the pTHr.HIVA and MVA.HIVA vaccines. In mice, these induced strong T cells-mediated immune responses which lasted at least 155 days. In rhesus macaques, the prime-boost immunisation elicited T cell responses specific for multiple HIV-derived epitopes. Phase I trials in healthy low-risk volunteers have commenced in Oxford and Nairobi, and the preliminary immunogenicity analysis from the Oxford site indicated that both vaccine components alone induced T cell responses in a majority of volunteers. These results have boosted expectations for the prime-boost vaccinations.

A DNA/MVA-based candidate human immunodeficiency virus vaccine for Kenya induces multi-specific T cell responses in rhesus macaques

The minimum requirement for candidate human immunodeficiency virus (HIV) vaccines to enter clinical evaluation in humans should be their demonstrable immunogenicity in non-human primates: induction of antibodies neutralizing primary HIV isolates or elicitation of broad T cell-mediated immune responses. Here, we showed in rhesus macaques that the very same vaccines that had entered clinical trials in Oxford and Nairobi, plasmid pTHr.HIVA DNA and recombinant modified vaccinia virus Ankara MVA.HIVA in a prime-boost protocol (Hanke & McMichael, Nature Medicine 6, 951-955, 2000), induced cellular immune responses specific for multiple HIV-derived epitopes. This was demonstrated by using the intracellular cytokine staining and ELISPOT assays detecting interferon-gamma and pools of peptides employed in the clinical studies. These results have both boosted our expectations for the performance of these vaccines in humans and increased our confidence about the choice of these assays as the primary readouts in the on-going human trials.