Increased levels of activated subsets of CD4 T cells add to the prognostic value of low CD4 T cell counts in a cohort of HIV-infected drug users

Can immune markers predict subsequent discordance between immunologic and virologic responses to antiretroviral therapy? Adult AIDS Clinical Trials Group

It is unclear why discordant immunologic and virologic responses occur during therapy for human immunodeficiency virus (HIV) infection. This study examined whether markers of immune activation and naive/memory lymphocyte subsets at study baseline could predict discordance between HIV type 1 (HIV-1) RNA and CD4+ lymphocyte responses at week 24 of antiretroviral therapy. Ten diverse, prospective antiretroviral studies with 1007 evaluable subjects were included. Subsets of subjects at increased risk for discordance were identified by recursive partitioning. The strongest predictor of more-favorable immunologic than virologic responses was a lower baseline CD4+ lymphocyte count. Weaker predictors in small subsets of subjects were fewer activated CD4+ lymphocytes and fewer CD8+ lymphocytes. Conversely, the strongest predictors of more-favorable virologic than immunologic responses were higher baseline CD4+ lymphocyte count and percentage. Additional predictors in some analyses were higher CD8+ lymphocyte count or percentage and lower HIV-1 RNA concentrations. Baseline markers of immune activation and naive/memory lymphocyte subsets had limited ability to predict subsequent discordance.

Correlates of immune activation marker changes in human immunodeficiency virus (HIV)-seropositive and high-risk HIV-seronegative women who use illicit drugs

The majority of natural history studies of human immunodeficiency virus (HIV) infection have immune and viral parameters in men. Data demonstrating that women have lower HIV-1 RNA levels than men at the same CD4 cell counts have raised the question of immunologic differences in HIV-seropositive women. This study describes levels and changes in phenotypic markers of immune maturity, function, and activation in the CD4 and CD8 cell subsets in HIV-seropositive and high-risk HIV-seronegative women. Our primary hypothesis was that activation levels would be significantly higher among illicit drug users. However, results showed that HIV-1 RNA level was the strongest predictor of marker level and that both HIV-1 RNA level and CD4 cell count were independently associated with CD4 activation, but illicit drug use was not. In summary, this study demonstrated that immune activation was a significant pathogenic feature in women and that activation was driven by HIV infection and not illicit drug use.

Human CD38 interferes with HIV-1 fusion through a sequence homologous to the V3 loop of the viral envelope glycoprotein gp120

CD38 is a progression marker in HIV-1 infection, it displays lateral association with CD4, and down-modulates gp120/CD4 binding. The aim of this study was to elucidate the mechanism behind the interplay between CD4, CD38, and HIV-1. We used mouse cell transfectants expressing human CD4 and either CD38 or other CD4-associated molecules to show that CD38 specifically inhibits gp120/CD4 binding. Human cell transfectants expressing truncated forms of CD38 and bioinformatic analysis were used to map the anti-HIV activity and show that it is concentrated in the membrane-proximal region. This region displayed significant sequence-similarity with the V3 loop of the HIV-1 gp120 glycoprotein. In line with this similarity, synthetic soluble peptides derived from this region reproduced the anti-HIV effects of full-length CD38 and inhibited HIV-1 and HIV-2 primary isolates from different subtypes and with different coreceptor use. A multiple-branched peptide construct presenting part of the sequence of the V3-like region potently and selectively inhibited HIV-1 replication in the nanomolar range. Conversely, a deletion in the V3-like region abrogated the anti-HIV-1 activity of CD38 and its lateral association with CD4. These findings may provide new insights into the early events of HIV-1 fusion and strategies to intervene.

Cell turnover and cell tropism in HIV-1 infection

Early infection with HIV-1 is dominated by CCR5-tropic (R5, non-syncytium-inducing) viruses. The evolution of CXCR4-tropic (X4, syncytium-inducing) viruses occurs later in the infection and is associated with rapid disease progression. Here, we propose that the tropism of X4 viruses for naive CD4+ T cells is disadvantageous in early infection owing to the low division rate of these cells. In healthy individuals, the division rate of memory cells is nearly ten times higher than that of naive cells and thus the memory-cell tropism of R5 viruses could account for their dominance early in infection. As the division rate of naive T cells increases with CD4+ depletion, X4 viruses come to dominate in late disease.

Impact of suppression of viral replication by highly active antiretroviral therapy on immune function and phenotype in chronic HIV-1 infection

We compared immune phenotypes, lymphocyte proliferation (LP), and delayed type hypersensitivity (DTH) responses in 28 male antiretroviral treatment-naive and experienced HIV-1-infected patients, matched pair-wise according to age and CD4+ T-lymphocyte count. Median CD4+ T-lymphocyte counts were 441 cells/microL and 483 cells/microL and median CD4+ T-lymphocyte nadirs were 435 cells/microL and 150 cells/microL in both groups, respectively. Absolute numbers of circulating T-lymphocyte subpopulations and proportions of naive and memory T-lymphocytes were comparable in the two groups. Untreated patients had greater proportions of activated CD4+ (p <.05) and CD8+ (p <.01) T-cells expressing human leukocyte antigen (HLA)DR and CD38 and fewer CD8+ cells expressing CD28 (p <.05). DTH and LP responses were comparable in both groups except for HIVp24, LP responses, and mumps DTH responses, which were of greater magnitude in the group treated with highly active antiretroviral therapy (HAART) (p <.05). Thus, HIV-1-infected patients who experienced substantial increases in CD4+ T-lymphocyte counts after suppression of viral replication on HAART had fewer activated lymphocytes and similar immune function when compared with findings in untreated patients with similar CD4+ T-cell counts. HIV replication has minimal real-time effect on CD4+ T-cell function in response to non-HIV antigens but helper T-cell responses to HIV-gag antigen are impaired during ongoing viral replication and may be restored by antiretroviral therapy.