SAAVI MVA-C Research Articles

Modifications to the HIV-1 SAAVI MVA-C vaccine improve in vitro expression and in vivo immunogenicity

Two HIV-1 vaccines (SAAVI DNA-C2 and SAAVI MVA-C) were previously developed in South Africa and tested in preclinical studies and Phase 1 clinical trials. Here we report on improvements made to the SAAVI MVA-C vaccine design which include: the use of different promoters for both the Gag and Env genes, replacement of the native Gag gene with an in silico designed subtype C mosaic Gag antigen which forms virus-like particles and the modification of Env by sequence changes to improve stability and transport to the cell surface. A head-to-head comparison of the newly conceived MVAGD5 candidate vaccine with SAAVI MVA-C showed increased in vitro expression of both Env and Gag, and superior immunogenicity in rabbits. MVAGD5 induced high levels of binding antibodies to Env and Tier 1A and 1B neutralizing antibodies, neither of which were induced by SAAVI MVA-C.

Correction: Priming with Recombinant Auxotrophic BCG Expressing HIV-1 Gag, RT and Gp120 and Boosting with Recombinant MVA Induces a Robust T Cell Response in Mice.

[This corrects the article DOI: 10.1371/journal.pone.0071601.].

Priming with recombinant auxotrophic BCG expressing HIV-1 Gag, RT and Gp120 and boosting with recombinant MVA induces a robust T cell response in mice.

In previous studies we have shown that a pantothenate auxotroph of Myocbacterium bovis BCG (BCGΔpanCD) expressing HIV-1 subtype C Gag induced Gag-specific immune responses in mice and Chacma baboons after prime-boost immunization in combination with matched rMVA and VLP vaccines respectively. In this study recombinant BCG (rBCG) expressing HIV-1 subtype C reverse transcriptase and a truncated envelope were constructed using both the wild type BCG Pasteur strain as a vector and the pantothenate auxotroph. Mice were primed with rBCG expressing Gag and RT and boosted with a recombinant MVA, expressing a polyprotein of Gag, RT, Tat and Nef (SAAVI MVA-C). Priming with rBCGΔpanCD expressing Gag or RT rather than the wild type rBCG expressing Gag or RT resulted in higher frequencies of total HIV-specific CD8+ T cells and increased numbers of T cells specific to the subdominant Gag and RT epitopes. Increasing the dose of rBCG from 105 cfu to 107 cfu also led to an increase in the frequency of responses to subdominant HIV epitopes. A mix of the individual rBCGΔpanCD vaccines expressing either Gag, RT or the truncated Env primed the immune system for a boost with SAAVI MVA-C and generated five-fold higher numbers of HIV-specific IFN-γ-spot forming cells than mice primed with rBCGΔpanCD containing an empty vector control. Priming with the individual rBCGΔpanCD vaccines or the mix and boosting with SAAVI MVA-C also resulted in the generation of HIV-specific CD4+ and CD8+ T cells producing IFN-γ and TNF-α and CD4+ cells producing IL-2. The rBCG vaccines tested in this study were able to prime the immune system for a boost with rMVA expressing matching antigens, inducing robust, HIV-specific T cell responses to both dominant and subdominant epitopes in the individual proteins when used as individual vaccines or in a mix.

A single dose of SAAVI MVA-C reboosts rhesus macaques after more than 3 years post DNA-MVA prime-boost vaccination

Background We have previously reported induction of robust immune responses in rhesus macaques following a prime boost immunization with candidate HIV-1 vaccines, SAAVI DNA-C (DNA) and SAAVI MVA-C (MVA). These vaccines are already in clinical evaluation. In the current study, we investigated whether re-boosting these animals with as ingle MVA inoculation after more than 3y ears was sufficient to restore previous magnitudes of HIVspecific immune responses. Methods Seven rhesus macaques which had been vaccinated with three doses of DNA vaccine (4mg DNA/dose) and two doses of MVA (10 9 pfu MVA/dose) in a past study, >3 years previously, were re-boosted with a single dose of MVA. HIV-1-specific responses were quantified in the peripheral blood using an IFN-gamma ELISPOT assay. Results A peak magnitude of response (1146±240 sfu/10 6 PBMC) was reached 1 week after vaccination with the first dose of MVA. The second MVA inoculation did not increase these responses which declined to undetectable levels by 1 year post vaccination. After re-boosting with MVA after 3.5 years post the second MVA, all animals responded, with a peak response (1824±672 sfu/10 6 PBMC) being reached 1 week after vaccination. Although the mean magnitude of the second peak was not significantly higher than the one seen in the first peak, boosting of responses in 3 of 7 animals with an apparent broadening of the breadth of responses was observed. Conclusion These preliminary data suggest a long-term preservation of vaccine memory following a prime-boost vaccination regimen with SAAVI DNA-C and SAAVI MVA-C vaccines.

Screen failure in phase I HIV clinical trials in Soweto, South Africa: an opportunity for care

Background Reasons for screen failures are evaluated for three phase 1 HIV vaccine clinical trials recruiting healthy low-risk participants at the Perinatal HIV Research Unit: SAAVI102/HVTN073 and SAAVI103/HVTN086 (the first trials evaluating a Clade C vaccine, Novartis Subtype C gp140 with MF59 adjuvant boosting SAAVI DNA-C2 and SAAVI MVA-C vaccine) and IAVIB003/HVTN091 (Ad26 and Ad35 ENV vaccines). Recruitment strategies involved a pre-screening programme, clinics and community outreach.

A prime-boost immunization with rBCG expressing HIV-1 Gag, RT and gp120 and SAAVI MVA-C elicits immune responses in blood and MALT of rhesus macaques

Methods Chinese rhesus macaques (n=8) were primed twice with a mixture of rBCG, 12 weeks apart. A control group (n=4) was mock-primed with a control BCG. Both groups were boosted with MVA. Two weeks after the MVA vaccination, two macaques from the rBCG-primed group were euthanased and jejunum, spleen and inguinal, mesenteric, iliac and bronchial lymph nodes were harvested for isolation of mononuclear cells. HIV-1-specific IFN-gamma ELISPOT responses were measured in the blood and these tissues using pools of overlapping HIV-1 peptides.

Construction, Characterization, and Immunogenicity of a Multigene Modified Vaccinia Ankara (MVA) Vaccine Based on HIV Type 1 Subtype C

Candidate vaccines composed of a DNA construct to prime the immune system, followed by modified vaccinia Ankara (MVA) containing matching genes as a booster vaccination, have produced encouraging immune responses in human volunteers. This study presents the detailed construction and characterization of a recombinant MVA that will be tested in combination with a DNA vaccine in Phase I clinical trials in South Africa and the United States. To match recently transmitted viruses in the southern African region and to maximize epitope coverage, the vaccines were constructed to contain five HIV-1 subtype C genes, namely gag, reverse transcriptase, tat, and nef (grttn), expressed as a polyprotein, and a truncated env (gp150). An initial recombinant MVA construct containing wild-type env was found to be genetically unstable, and thus a human codon-optimized gene was used. Grttn and gp150 were inserted into two different sites in MVA yielding a double recombinant, SAAVI MVA-C. The recombinant MVA was shown to be genetically stable and high level expression of the transgenes was observed. Env retained infectivity in a functional infectivity assay despite a point mutation that arose during virus generation. Mice inoculated with SAAVI MVA-C at various doses developed high levels of Gag, RT, and Env-specific CD8(+) and CD4(+) T cells, and some of these responses could be boosted by a second inoculation. An accompanying paper describes the immunogenicity of SAAVI MVA-C when given in combination with SAAVI DNA-C.

A Multigene HIV Type 1 Subtype C Modified Vaccinia Ankara (MVA) Vaccine Efficiently Boosts Immune Responses to a DNA Vaccine in Mice

Heterologous prime-boost vaccine strategies have generated high frequencies of antigen-specific T cells in preclinical and clinical trials of candidate HIV vaccines. We have developed a DNA (SAAVI DNA-C) and MVA (SAAVI MVA-C) vaccine based on HIV-1 subtype C for testing in clinical trials. Both vaccines contain five subtype C genes: gag, reverse transcriptase, tat, and nef, expressed as a polyprotein, and a truncated env (gp150). The individual vaccines induced CD8(+) and CD4(+) T cells specific for the vaccine-expressed antigens in BALB/c mice. Combining the vaccines in a DNA prime and MVA boost regimen increased the cumulative peptide response compared to the DNA vaccine alone 10-fold, to over 6000 SFU/10(6) splenocytes in the IFN-gamma ELISPOT assay. Th1 cytokine IFN-gamma and TNF-alpha levels from HIV-specific CD8(+) and CD4(+) T cells increased 20- and 8-fold, respectively, with a SAAVI MVA-C boost. Effector and effector memory RT- and Env-specific memory CD8(+) T cell subsets were boosted after MVA immunization, and over time the cells returned to an intermediate memory phenotype similar to that prior to the boost. Immunization of guinea pigs with the DNA-MVA combination induced high titers of antibodies to gp120, although neutralizing activity was weak or absent. The demonstration that these vaccines induce potent cellular immune responses merits their testing in clinical trials.