<i>In vivo</i> persistence of a HIV‐1‐encoded HLA‐B27‐restricted cytotoxic T lymphocyte epitope despite specific <i>in vitro</i> reactivity

146

155

Although the HLA B * 5701 class I allele is highly overrepresented among human immunodeficiency virus (HIV)-infected long-term nonprogressors (LTNPs), it is also present at the expected frequency (11%) in patients with progressive HIV infection. Whether B57؉ progressors lack restriction of viral replication because of escape from recognition of highly immunodominant B57-restricted gag epitopes by CD8 ؉ T cells remains unknown. In this report, we investigate the association between restriction of virus replication and recognition of autologous virus sequences in 27 B * 57 ؉ patients (10 LTNPs and 17 progressors). Amplification and direct sequencing of single molecules of viral cDNA or proviral DNA revealed low frequencies of genetic variations in these regions of gag. Furthermore, CD8؉ T-cell recognition of autologous viral variants was preserved in most cases. In two patients, responses to autologous viral variants were not demonstrable at one epitope. By using a novel technique to isolate primary CD4 ؉ T cells expressing autologous viral gene products, it was found that 1 to 13% of CD8 ؉ T cells were able to respond to these cells by gamma interferon production. In conclusion, escape-conferring mutations occur infrequently within immunodominant B57-restricted gag epitopes and are not the primary mechanism of virus evasion from immune control in B * 5701 ؉ HIV-infected patients. Qualitative features of the virus-specific CD8 ؉ T-cell response not measured by current assays remain the most likely determinants of the differential abilities of HLA B * 5701 ؉ LTNPs and progressors to restrict virus replication.

Section: Discussioncontrasting

confidence: 99%

The Differential Ability of HLA B^*5701⁺Long-Term Nonprogressors and Progressors To Restrict Human Immunodeficiency Virus Replication Is Not Caused by Loss of Recognition of Autologous ViralgagSequences

Migueles

Laborico

Imamichi

et al. 2003

146

155

“…There are limited prior reports examining escape from CTL responses in progressors, examining either a single case or one specific CTL epitope (28,35). Similar conclusions were recently reported in a cohort of chronically infected B57 ϩ subjects (36), limited to analysis of epitopes presented by HLA B57.…”

Section: Discussionsupporting

confidence: 55%

Persistent Recognition of Autologous Virus by High-Avidity CD8 T Cells in Chronic, Progressive Human Immunodeficiency Virus Type 1 Infection

Draenert

Verrill

Tang

et al. 2004

128

115

CD8 T-cell responses are thought to be crucial for control of viremia in human immunodeficiency virus (HIV) infection but ultimately fail to control viremia in most infected persons. Studies in acute infection have demonstrated strong CD8-mediated selection pressure and evolution of mutations conferring escape from recognition, but the ability of CD8 T-cell responses that persist in late-stage infection to recognize viruses present in vivo has not been determined. Therefore, we studied 24 subjects with advanced HIV disease (median viral load ‫؍‬ 142,000 copies/ml; median CD4 count ‫؍‬ 71/l) and determined HIV-1-specific CD8 T-cell responses to all expressed viral proteins using overlapping peptides by gamma interferon Elispot assay. Chronic-stage virus was sequenced to evaluate autologous sequences within Gag epitopes, and functional avidity of detected responses was determined. In these subjects, the median number of epitopic regions targeted was 13 (range, 2 to 39) and the median cumulative magnitude of CD8 T-cell responses was 5,760 spot-forming cells/10 6 peripheral blood mononuclear cells (range, 185 to 24,700). On average six (range, one to 8) proteins were targeted. For 89% of evaluated CD8 T-cell responses, the autologous viral sequence was predicted to be well recognized by these responses and the majority of analyzed optimal epitopes were recognized with medium to high functional avidity by the contemporary CD8 T cells. Withdrawal of antigen by highly active antiretroviral therapy led to a significant decline both in breadth (P ‫؍‬ 0.032) and magnitude (P ‫؍‬ 0.0098) of these CD8 T-cell responses, providing further evidence that these responses had been driven by recognition of autologous virus. These results indicate that strong, broadly directed, and high-avidity gamma-interferonpositive CD8 T-cells directed at autologous virus persist in late disease stages, and the absence of mutations within viral epitopes indicates a lack of strong selection pressure mediated by these responses. These data imply functional impairment of CD8 T-cell responses in late-stage infection that may not be reflected by gamma interferon-based screening techniques.

“…Some CTL epitopes persist within HIV-1 over years of infection despite the maintenance of CTLs that specifically recognize them (10,27,33,48,52,57). Thus, why escape mutations develop in some epitopes and not others remains unclear.…”

Section: Cd8mentioning

confidence: 99%

Evolution of Human Immunodeficiency Virus Type 1 Cytotoxic T-Lymphocyte Epitopes: Fitness-Balanced Escape

Liu

McNevin

Zhao³

et al. 2007

103

CD8؉ cytotoxic T lymphocytes (CTL) are strong mediators of human immunodeficiency virus type 1 (HIV-1) control, yet HIV-1 frequently mutates to escape CTL recognition. In an analysis of sequences in the Los Alamos HIV-1 database, we show that emerging CTL escape mutations were more often present at lower frequencies than the amino acid(s) that they replaced. Furthermore, epitopes that underwent escape contained amino acid sites of high variability, whereas epitopes persisting at high frequencies lacked highly variable sites. We therefore infer that escape mutations are likely to be associated with weak functional constraints on the viral protein. This was supported by an extensive analysis of one subject for whom all escape mutations within defined CTL epitopes were studied and by an analysis of all reported escape mutations of defined CTL epitopes in the HIV Immunology Database. In one of these defined epitopes, escape mutations involving the substitution of amino acids with lower database frequencies occurred, and the epitope soon reverted back to the sensitive form. We further show that this escape mutation substantially diminished viral fitness in in vitro competition assays. Coincident with the reversion in vivo, we observed the fixation of a mutation 3 amino acids C terminal to the epitope, coincident with the ablation of the corresponding CTL response. The C-terminal mutation did not restore replication fitness reduced by the escape mutation in the epitope and by itself had little effect on replication fitness. Therefore, this C-terminal mutation presumably impaired the processing and presentation of the epitope. Finally, for one persistent epitope, CTL cross-reactivity to a mutant form may have suppressed the mutant to undetected levels, whereas for two other persistent epitopes, each of two mutants showed poor cross-reactivity and appeared in the subject at later time points. Thus, a viral dynamic exists between the advantage of immune escape, peptide cross-reactivity, and the disadvantage of lost replication fitness, with the balance playing an important role in determining whether a CTL epitope will persist or decline during infection.