De novo generation of escape variant-specific CD8+ T-cell responses following cytotoxic T-lymphocyte escape in chronic human immunodeficiency virus type 1 infection

Abstract

Human immunodeficiency virus type 1 (HIV-1) evades CD8(+) T-cell responses through mutations within targeted epitopes, but little is known regarding its ability to generate de novo CD8(+) T-cell responses to such mutants. Here we examined gamma interferon-positive, HIV-1-specific CD8(+) T-cell responses and autologous viral sequences in an HIV-1-infected individual for more than 6 years following acute infection. Fourteen optimal HIV-1 T-cell epitopes were targeted by CD8(+) T cells, four of which underwent mutation associated with dramatic loss of the original CD8(+) response. However, following the G(357)S escape in the HLA-A11-restricted Gag(349-359) epitope and the decline of wild-type-specific CD8(+) T-cell responses, a novel CD8(+) T-cell response equal in magnitude to the original response was generated against the variant epitope. CD8(+) T cells targeting the variant epitope did not exhibit cross-reactivity against the wild-type epitope but rather utilized a distinct T-cell receptor Vbeta repertoire. Additional studies of chronically HIV-1-infected individuals expressing HLA-A11 demonstrated that the majority of the subjects targeted the G(357)S escape variant of the Gag(349-359) epitope, while the wild-type consensus sequence was significantly less frequently recognized. These data demonstrate that de novo responses against escape variants of CD8(+) T-cell epitopes can be generated in chronic HIV-1 infection and provide the rationale for developing vaccines to induce CD8(+) T-cell responses directed against both the wild-type and variant forms of CD8 epitopes to prevent the emergence of cytotoxic T-lymphocyte escape variants.

FIG. 1.

Clinical course of HIV-1 infection in study subject AC-04. Viral loads and CD4⁺ T-cell counts in AC-04 are shown, starting at the time of acute HIV-1 infection. Shaded regions denote time under treatment with HAART.

FIG. 2.

Changes in epitope-specific CD8⁺ T-cell responses in relationship to the emergence of viral sequence variations in AC-04. Changes in the magnitude of epitope-specific CD8⁺ T-cell responses measured by IFN-γ ELISPOT assay are shown for the four epitopes targeted by study subject AC-04 that exhibited viral sequence variations over time. Panels: A, HIV-1 Gag_349-359; B, HIV-1 Rev_67-75; C, HIV-1 Vpr_57-63; D, HIV-1 Tat_30-37. Shaded regions denote periods during which the autologous viral sequence reflected wild-type (wt) sequences, escape variant sequences, or a mixture of both, as determined by the sequencing of individual viral clones. Mill, million.

FIG. 3.

Lack of cross-reactivity between A11-AK11-specific and A11-AK11_G357S-specific CD8⁺ T cells. Dot plots showing the flow cytometric analysis of HIV-1-specific CD8⁺ T-cell responses in AC-04 using MHC class I-peptide tetramer complexes specific for the A11-AK11 peptide (PE labeled) or for the A11-AK11_G357S escape variant (APC labeled). Tetramer-positive CD8⁺ T cells were quantified at day 1,427 pp and day 2,323 pp. wt, wild type.

FIG. 4.

Usage of different TCR Vβ repertoires by A11-AK11-specific and A11-AK11_G357S-specific CD8⁺ T cells. A11-AK11- and A11-AK11_G357S-specific CD8⁺ T cells were characterized by intracellular IFN-γ staining following stimulation with the respective peptide at day 1,427 pp (A) and day 2,220 pp (B). TCR Vβ usage was determined using Vβ-specific antibodies. At day 1,427 pp (A), only A11-AK11 (wild type [wt])-specific CD8⁺ T cells were detectable, while at day 2,220 pp (B), only A11-AK11_G357S (escape variant)-specific CD8⁺ T-cell responses were detectable. A11-AK11-specific CD8⁺ T cells utilized TCR Vβ1 (82.4%), while A11-AK11_G357S-specific CD8⁺ T cells did not utilize TCR Vβ1 (1.7%) but rather TCR Vβ9 (30.5%). FITC, fluorescein isothiocyanate.