Priming with a recombinant pantothenate auxotroph of Mycobacterium bovis BCG and boosting with MVA elicits HIV-1 Gag specific CD8+ T cells.

Rosamund Chapman,Enid Shephard,Anna-Lise Williamson,Helen Stutz,Bernhard Ryffel,William Jacobs,Irene Garcia,Vasan Sambandamurthy,Nicola Douglass

doi:10.1371/journal.pone.0032769

Abstract

A safe and effective HIV vaccine is required to significantly reduce the number of people becoming infected with HIV each year. In this study wild type Mycobacterium bovis BCG Pasteur and an attenuated pantothenate auxotroph strain (BCGΔpanCD) that is safe in SCID mice, have been compared as vaccine vectors for HIV-1 subtype C Gag. Genetically stable vaccines BCG[pHS400] (BCG-Gag) and BCGΔpanCD[pHS400] (BCGpan-Gag) were generated using the Pasteur strain of BCG, and a panothenate auxotroph of Pasteur respectively. Stability was achieved by the use of a codon optimised gag gene and deletion of the hsp60-lysA promoter-gene cassette from the episomal vector pCB119. In this vector expression of gag is driven by the mtrA promoter and the Gag protein is fused to the Mycobacterium tuberculosis 19 kDa signal sequence. Both BCG-Gag and BCGpan-Gag primed the immune system of BALB/c mice for a boost with a recombinant modified vaccinia virus Ankara expressing Gag (MVA-Gag). After the boost high frequencies of predominantly Gag-specific CD8+ T cells were detected when BCGpan-Gag was the prime in contrast to induction of predominantly Gag-specific CD4+ T cells when priming with BCG-Gag. The differing Gag-specific T-cell phenotype elicited by the prime-boost regimens may be related to the reduced inflammation observed with the pantothenate auxotroph strain compared to the parent strain. These features make BCGpan-Gag a more desirable HIV vaccine candidate than BCG-Gag. Although no Gag-specific cells could be detected after vaccination of BALB/c mice with either recombinant BCG vaccine alone, BCGpan-Gag protected mice against a surrogate vaccinia virus challenge.

Highlights

Information in the 2010 UNAIDS Report on the global AIDS epidemic indicates a global decline in human immunodeficiency virus type 1 (HIV) infection, observed as a lower number of infections and deaths from AIDS
We have shown that recombinant BCG (rBCG) expressing HIV-1 subtype C Gag is able to prime the immune system of baboons to a boost with Pr55gag virus-like particles (Gag VLPs) with induction of high magnitudes of Gag-specific CD8+ and CD4+ T cells as well as antiGag antibodies [6]
To determine whether the high levels of LysA were contributing to the instability of the rBCG, the hsp60 promoter and lysA gene were deleted from the shuttle vector to generate the plasmid pHS400, following which bacillus Calmette-Guerin (BCG)[pHS400] (BCG-Gag) and BCGDpanCD[pHS400] (BCGpan-Gag) were generated

Summary

Introduction

Information in the 2010 UNAIDS Report on the global AIDS epidemic indicates a global decline in HIV infection, observed as a lower number of infections and deaths from AIDS. The precise requirements of an HIV vaccine needed for eliciting protection against infection are as yet not known. Immune responses to human immunodeficiency virus type 1 (HIV) that participate in virus replication control, as observed in infected individuals termed long-term non progressors or elite controllers, include specific cellular responses that strongly target Gag [1,2]. Induction of such cellular HIV-specific immune responses is one of the favourable and necessary requirements of a protective vaccination strategy [3]. There is abundant evidence indicating heterologous prime-boost vaccine regimens that combine the use of recombinant bacterial vaccine vectors and recombinant virus vaccine vectors expressing HIV antigens and HIV virus like particle protein vaccines induce robust HIV-specific cellular immune responses [4,5,6]

Methods

Results

Conclusion