Open Access Research

Heterologous prime-boost-boost immunisation of Chinese cynomolgus macaques using DNA and recombinant poxvirus vectors expressing HIV-1 virus-like particles

Simon H Bridge16, Sally A Sharpe2, Mike J Dennis2, Stuart D Dowall2, Brian Getty3, Donald S Anson4, Michael A Skinner5, James P Stewart3 and Tom J Blanchard17*

Author Affiliations

1 Clinical Research group, Liverpool School of Tropical Medicine, Liverpool, UK

2 Health Protection Agency, Porton Down, Salisbury, UK

3 Department of Clinical Infection, Microbiology and Immunology, University of Liverpool, Liverpool, UK

4 Gene Technology Unit, Department of Genetic Medicine, Women's and Children's Hospital, Adelaide, Australia

5 Vaccine Vector Group, Dept of Virology, Imperial College London, London, UK

6 Institute of Cellular Medicine, Newcastle University, UK

7 Consultant in Infectious Diseases & Tropical Medicine, Department for Infectious Diseases, North Manchester General Hospital, Delaunay's Road, Manchester M8 5RB, UK

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Virology Journal 2011, 8:429  doi:10.1186/1743-422X-8-429

Published: 7 September 2011

Abstract

Background

There is renewed interest in the development of poxvirus vector-based HIV vaccines due to the protective effect observed with repeated recombinant canarypox priming with gp120 boosting in the recent Thai placebo-controlled trial. This study sought to investigate whether a heterologous prime-boost-boost vaccine regimen in Chinese cynomolgus macaques with a DNA vaccine and recombinant poxviral vectors expressing HIV virus-like particles bearing envelopes derived from the most prevalent clades circulating in sub-Saharan Africa, focused the antibody response to shared neutralising epitopes.

Methods

Three Chinese cynomolgus macaques were immunised via intramuscular injections using a regimen composed of a prime with two DNA vaccines expressing clade A Env/clade B Gag followed by boosting with recombinant fowlpox virus expressing HIV-1 clade D Gag, Env and cholera toxin B subunit followed by the final boost with recombinant modified vaccinia virus Ankara expressing HIV-1 clade C Env, Gag and human complement protein C3d. We measured the macaque serum antibody responses by ELISA, enumerated T cell responses by IFN-γ ELISpot and assessed seroneutralisation of HIV-1 using the TZM-bl β-galactosidase assay with primary isolates of HIV-1.

Results

This study shows that large and complex synthetic DNA sequences can be successfully cloned in a single step into two poxvirus vectors: MVA and FPV and the recombinant poxviruses could be grown to high titres. The vaccine candidates showed appropriate expression of recombinant proteins with the formation of authentic HIV virus-like particles seen on transmission electron microscopy. In addition the b12 epitope was shown to be held in common by the vaccine candidates using confocal immunofluorescent microscopy. The vaccine candidates were safely administered to Chinese cynomolgus macaques which elicited modest T cell responses at the end of the study but only one out of the three macaques elicited an HIV-specific antibody response. However, the antibodies did not neutralise primary isolates of HIV-1 or the V3-sensitive isolate SF162 using the TZM-bl β-galactosidase assay.

Conclusions

MVA and FP9 are ideal replication-deficient viral vectors for HIV-1 vaccines due to their excellent safety profile for use in humans. This study shows this novel prime-boost-boost regimen was poorly immunogenic in Chinese cynomolgus macaques.

Keywords:
Prime-boost HIV vaccine; broadly reactive neutralising antibodies; recombinant poxvirus; modified vaccinia virus Ankara; fowlpox virus; cholera toxin B; human complement protein C3d; virus-like particle