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Here, we evaluate the T cell responses raised by our HIV-1 clade B DNA/MVA vaccine for recognition of a HIV-1 circulating recombinant form (CRF) AG Gag sequence (CRF-02). The cross-clade activity for the AG sequence was better conserved for CD8 than CD4 T cells. CD8 T cells exhibited 75% conservation for height and 83% conservation for breadth, whereas CD4 responses exhibited 45% conservation for height and 50% conservation for breadth. Five CD8 epitopes and 8 CD4 epitopes were mapped. Three of the 5 CD8 epitopes and 2 of the 8 CD4 epitopes were conserved across multiple HIV-1 clades. Impressively, all of the CD8 epitopes and half of the CD4 epitopes have been reported for human infections. Our results demonstrate that the clade B DNA/MVA HIV vaccine elicits T cell responses against epitopes that are conserved in multiple clades and recognized by humans and macaques.

Recently, a vaccine consisting of DNA priming followed by boosting with modified vaccinia Ankara (MVA) has provided long-term protection of rhesus macaques against a virulent challenge with a chimera of simian and human immunodeficiency viruses. Here, we report studies on the development of the DNA component for a DNA/MVA HIV vaccine for humans. Specifically, we assess the ability of a codon-optimized Gag-expressing DNA and two noncodon-optimized Gag-Pol-Env-expressing DNAs to prime the MVA booster dose. The codon-optimized DNA expressed virus-like particles (VLPs), whereas one of the noncodon-optimized DNAs expressed VLPs and the other expressed aggregates of HIV proteins. The MVA boost expressed Gag-Pol and Env and produced VLPs. Immunogenicity studies in macaques used one intramuscular prime with 600 microg of DNA and two intramuscular boosts with 1 x 10(8) pfu of MVA at weeks 8 and 30. The codon-optimized and noncodon-optimized DNAs proved similar in their ability to prime anti-Gag T cell responses. The aggregate and VLP-expressing Gag-Pol-Env DNAs also showed no significant differences in their ability to prime anti-Env Ab responses. The second MVA booster dose did not increase the peak CD4 and CD8 T cell responses, but increased anti-Env Ab titers by 40- to 90-fold. MVA-only immunizations elicited 10-100 times lower frequencies of T cells and 2-4 lower titers of anti-Env Ab than the Gag-Pol-Env DNA/MVA immunizations. Based on the breadth of the T cell response and a trend toward higher titers of anti-Env Ab, we are moving forward with human trials of the noncodon-optimized VLP-expressing DNA.

Recently, a simian/human immunodeficiency virus (SHIV) vaccine consisting of priming with a Gag-Pol-Env-expressing DNA and boosting with a Gag-Pol-Env-expressing recombinant modified vaccinia Ankara (rMVA) has successfully controlled a virulent SHIV challenge in a macaque model. In this, and the accompanying paper, we report on the construction and testing of a Gag-Pol-Env DNA/MVA vaccine for HIV-1/AIDS. The DNA vaccine, pGA2/JS2, expresses aggregates of Gag proteins and includes safety mutations that render it integration, reverse transcription, and packaging defective. The rMVA vaccine, MVA/HIV 48, is integration and reverse transcription defective and has a truncated Env to enhance expression on the plasma membrane. In a study in rhesus macaques, priming with pGA2/JS2 and boosting with MVA/HIV 48 raised high frequencies of T cells for Gag and Env and lower frequencies of T cells for PR, RT, and Tat. Stimulations with five peptide pools for Gag and seven peptide pools for Env revealed epitopes for cellular immune responses throughout Gag and Env. On average, CD4 T cells from the vaccinated animals recognized 7.1 peptide pools and CD8 T cells, 3.2 peptide pools. Both the height and the breadth of the elicited cellular response provide hope that this multiprotein DNA/MVA vaccine will successfully control clade B isolates of HIV-1, as well as contribute to the control of other clades and recombinant forms of HIV-1/AIDS.

One of the unknowns faced by an HIV/AIDS vaccine is the ability of a single clade vaccine to protect against the multiple genetic subtypes and recombinant forms of HIV-1 present in the current pandemic. Here, we use a macaque model to investigate the ability of our clade B vaccine that consists of DNA priming and modified vaccinia Ankara (MVA) virus boosting to elicit T cell responses that recognize an A/G recombinant of HIV-1. To test for cross-reactive T cells, intracellular cytokine staining was conducted using five pools of Gag and six pools of Env peptides representing B or A/G sequences. Studies using the peptide pools revealed essentially complete conservation of the CD8 response but only approximately 50% conservation of the CD4 response. Thus, the ability of an HIV vaccine for one clade to protect against other clades may be more limited by the ability to provide CD4 T cell help than the ability to elicit CD8 effector functions.