Publications

OBJECTIVES

HIV-infected subjects are at increased risk for myocardial infarction. The mechanism of this increased risk remains unclear. Since cytomegalovirus (CMV) infection has been associated with accelerated atherosclerosis in the transplant population and immune responses against CMV may be altered by HIV disease, we hypothesized that enhanced T-cell responses against CMV would be associated with increased atherosclerosis in subjects with HIV.

METHODS

We measured high-sensitivity C-reactive protein (hs-CRP), T-cell activation, CMV-specific T-cell responses, and carotid artery intima-media thickness (IMT) in 93 HIV-infected subjects and in 37 uninfected controls.

RESULTS

The mean age of the HIV-infected subjects was 48 years and 85 (91%) were male. The median carotid IMT was higher in the HIV-infected group compared to the uninfected group (0.95 mm versus 0.68 mm, P < 0.001). This difference remained significant after controlling for all traditional risk factors. Compared to HIV-negative controls, HIV-infected subjects had higher median levels of hs-CRP (P = 0.05), higher levels of CD4 and CD8 T-cell activation (P < 0.0001) and higher CMV-specific interferon-gamma CD8 T-cell responses (P < 0.0001). CMV-specific T-cell responses, but not hs-CRP and T-cell activation, were independently associated with higher carotid IMT (P = 0.001).

CONCLUSIONS

HIV-infected subjects had thicker carotid IMT compared to controls. While HIV patients also had higher T-cell activation, hs-CRP levels, and CMV-specific T-cell responses, only CMV-specific T-cell responses were independently associated with IMT. Accelerated atherosclerosis in HIV patients may be mediated by heightened CMV-induced immune responses.

The relative contributions of HLA alleles and T-cell receptors (TCRs) to the prevention of mutational viral escape are unclear. Here, we examined human immunodeficiency virus type 1 (HIV-1)-specific CD8(+) T-cell responses restricted by two closely related HLA class I alleles, B*5701 and B*5703, that differ by two amino acids but are both associated with a dominant response to the same HIV-1 Gag epitope KF11 (KAFSPEVIPMF). When this epitope is presented by HLA-B*5701, it induces a TCR repertoire that is highly conserved among individuals, cross-recognizes viral epitope variants, and is rarely associated with mutational escape. In contrast, KF11 presented by HLA-B*5703 induces an entirely different, more heterogeneous TCR beta-chain repertoire that fails to recognize specific KF11 escape variants which frequently arise in clade C-infected HLA-B*5703(+) individuals. These data show the influence of HLA allele subtypes on TCR selection and indicate that extensive TCR diversity is not a prerequisite to prevention of allowable viral mutations.

Although quantitative identification and viable enrichment of natural regulatory T cells (T-regs) in humans are problematic, such steps would greatly facilitate the analysis of these cells in disease states. In an attempt to identify markers that are sensitive and specific for human T-regs, we analyzed the expression of fourteen intracellular and cell surface markers on human CD4(+) cells. Many markers were partially selective for CD25(hi) T-regs, but consistent and specific discrimination of functional T-regs was only made possible by focus on CD127, the alpha chain of the IL-7 receptor. Although most CD4(+) human T cells express CD127, T-regs exhibiting suppressive activity in vitro display distinctly lower surface expression of this marker, irrespective of their level of CD25 expression. Sorted cells with the surface phenotype CD4(+)CD25(+)CD127(low) had higher levels of intracellular FOXP3 and CTLA-4 and, as determined by functional assays, were suppressive, hypoproliferative, and poorly responsive to TCR signaling. The CD4(+)CD25(+)CD127(low) phenotype was also found to be characteristic of T-regs found in mice and in rhesus macaques. This surface phenotype should allow for quantitative studies of regulatory T cells in disease states as well as for enrichment of live regulatory T cells for functional analyses and/or expansion in vitro.

BACKGROUND

Many treatment-experienced, HIV-infected patients who have limited therapeutic options for complete viral suppression continue to receive a partially suppressive treatment regimen pending the availability of at least 2 new antiretroviral drugs. The major risk of this approach is ongoing viral evolution and the loss of future drug options.

METHODS

Antiretroviral-treated subjects with incomplete viral suppression were sampled from a clinic-based cohort. Inclusion criteria were receipt of a stable treatment regimen for > or = 120 days, a plasma HIV RNA load of > 500 copies/mL, and > or = 1 resistance mutation. Phenotypic and genotypic resistance testing was performed every 4 months.

RESULTS

The 106 patients who were eligible for the study had a median of 3 observations during a median of 11.3 months. An estimated 23% and 18% developed at least 1 new nucleoside analogue and 1 new protease inhibitor mutation at 1 year, respectively. An estimated 30% lost the phenotypic equivalent of 1 susceptible drug at 1 year. A lower number of total mutations at baseline was a significant predictor of developing a new nucleoside analogue mutation (P=.01). At 1 year, the probability that an existing mutation would become undetectable using population-based sequencing was 32%. There was a higher rate of change at nonresistance codons than at codons known to be associated with drug resistance.

CONCLUSIONS

Heavily pretreated patients with HIV infection who remain on a partially suppressive regimen have a measurable risk of losing future drug options, particularly those patients who have few baseline mutations. Resistance mutations vary over time, which suggests that the results of any single resistance test may not be representative of all mutations selected by a given treatment regimen.