A Replication Competent Adenovirus 5 Host Range Mutant-Simian Immunodeficiency Virus (SIV) Recombinant Priming/Subunit Protein Boosting Vaccine Regimen Induces Broad, Persistent SIV-Specific Cellular Immunity to Dominant and Subdominant Epitopes in Mamu-A*01 Rhesus Macaques

Abstract

CTL are important in controlling HIV and SIV infection. To quantify cellular immune responses induced by immunization, CD8⁺ T cells specific for the subdominant Env p15m and p54m epitopes and/or the dominant Gag p11C epitope were evaluated by tetramer staining in nine macaques immunized with an adenovirus (Ad) 5 host range mutant (Ad5hr)-SIVenv/rev recombinant and in four of nine which also received an Ad5hr-SIVgag recombinant. Two Ad5hr-SIV recombinant priming immunizations were followed by two boosts with gp120 protein or an envelope polypeptide representing the CD4 binding domain. Two mock-immunized macaques served as controls. IFN-γ-secreting cells were also assessed by ELISPOT assay using p11C, p15m, and p54m peptide stimuli and overlapping pooled Gag and Env peptides. As shown by tetramer staining, Ad-recombinant priming elicited a high frequency of persistent CD8⁺ T cells able to recognize p11C, p15m, and p54m epitopes. The presence of memory cells 38 wk postinitial immunization was confirmed by expansion of tetramer-positive CD8⁺ T cells following in vitro stimulation. The SIV-specific CD8⁺ T cells elicited were functional and secreted IFN-γ in response to SIV peptide stimuli. Although the level and frequency of response of peripheral blood CD8⁺ T cells to the subdominant Env epitopes were not as great as those to the dominant p11C epitope, elevated responses were observed when lymph node CD8⁺ T cells were evaluated. Our data confirm the potency and persistence of functional cellular immune responses elicited by replication competent Ad-recombinant priming. The cellular immunity elicited is broad and extends to subdominant epitopes.