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Volume 9 Supplement 2

AIDS Vaccine 2012

Induction of HIV-1 Gag-specific memory T cells in Chacma baboons by MVA prime and VLP boost vaccine regimen


We previously reported induction of HIV-specific responses in Chacma baboons following immunization with SAAVI MVA-C (MVA) and HIV-1 Pr55 Gag virus-like particles (VLPs) in a prime-boost vaccination strategy. In the current study, we characterised the vaccine specific memory T cells by flow cytometry.


Peripheral blood mononuclear cells (PBMC) from baboons primed with MVA and boosted with VLPs (n=3) or vaccinated with VLPs only controls (n=2) were stimulated with HIV-1 Gag peptide pools. T cell cytokine production (multiplex TNF-a, IFN-y and IL-2) and memory phenotype was determined by flow cytometry. Human anti-CD28 and CD95 antibodies were used to delineate effector memory (Tem) and central memory (Tcm) T cells.


Vaccine specific memory responses were detectable one week after MVA prime. At peak T cell response (four weeks after VLP boost), the frequency of cytokine producing cells in prime-boost animals (mean response: 0.21%±0.012 and 0.242% ±0.049 of CD4+ and CD8+ cells respectively) was higher than in control animals (mean response: 0.066%±0.005 and 0.034%± 0.016 of CD4+ and CD8+ cells respectively). Gag-specific CD4+ cells from the prime-boost animals were significantly skewed towards a Tcm phenotype (>95%) of total cytokine responses compared to the Tem phenotype (<2%). A similar memory distribution profile of Gag-specific CD4+ cells was maintained 20 weeks after the VLP boost. At this time, Gag-specific CD8+ cells were evenly distributed between Tcm (~40%) and Tem (~60%) phenotypes. Vaccine specific memory responses were preserved 20 weeks after the VLPs boost (mean: 0.128%±0.025 and 0.147%± 0.039 of CD4+ and CD8+ cells respectively) in the prime-boost animals.


In conclusion, the MVA prime and VLP boost induced Gag-specific cytokine producing Tcm and Tem defined by expression of CD28 and CD95. These cells were detected up to 20 weeks post vaccination suggesting these vaccines could be potential HIV-1 vaccine candidates.

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This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Singh, V., Chege, G., Shephard, E. et al. Induction of HIV-1 Gag-specific memory T cells in Chacma baboons by MVA prime and VLP boost vaccine regimen. Retrovirology 9 (Suppl 2), P27 (2012).

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  • Peptide Pool
  • Chacma Baboon
  • Cell Cytokine Production
  • Boost Vaccine
  • Memory Distribution