Heteroclitic Peptides Increase Proliferation and Reduce Evidence of Human Immunodeficiency Virus-Specific CD8⁺ T Cell...

Human immunodeficiency virus (HIV)-specific CD8(+) T cell dysfunction parallels disease progression; therefore, restoring potent HIV-specific CD8(+) T cell responses is a key therapeutic goal. Certain CD8(+) T cell peptide epitope variants, termed heteroclitic, enhance cytokine production by the HIV-specific CD8(+) T cells of some individuals. In this study, we investigated whether heteroclitic peptides that enhance cytokine production by HIV-specific CD8(+) T cells also reduce functional and phenotypic evidence of HIV-specific CD8(+) T cell exhaustion in those instances. Twenty-four variant peptides of human histocompatibility-linked leukocyte antigen (HLA)-A2-restricted reference HIV peptide epitopes designated as A2-7; Nef 83→91, A2-8; Nef 135→143, A2-Gag; Gag 77→85 and A2-9; Gag 433→440 were synthesized with conservative and semiconservative amino acid substitutions at positions 3, 5, and 7 or 3, 5, and 8 of Gag 433→440. Variants that enhanced interferon-gamma (IFN-γ) and/or interleukin-2 (IL-2) production in enzyme-linked immunospot assays (29 cases overall) were subsequently tested by 7-day in vitro peptide stimulation for their effects on HIV-specific CD8(+) T cell proliferation and programmed death-1 (PD-1) expression. Heteroclitic variants enhanced HIV-specific CD8(+) T cell proliferation by >20% in 13/29 cases tested, reduced PD-1 expression on proliferating cells by 15-50% in 10 cases, and reduced PD-1 expression on proliferating cells by >50% in 3 cases. In five cases, the same heteroclitic peptide increased proliferation by >20% and reduced PD-1 expression by >15%. These data demonstrate that heteroclitic peptides can alter the magnitude and character of HIV-specific CD8(+) cell responses relative to reference peptides and may have a unique immunotherapeutic value in therapeutic vaccines.