Mark Dybul

HIV preferentially infects HIV-specific CD4+ T cells

HIV infection is associated with the progressive loss of CD4+ T cells through their destruction or decreased production. A central, yet unresolved issue of HIV disease is the mechanism for this loss, and in particular whether HIV-specific CD4+ T cells are preferentially affected. Here we show that HIV-specific memory CD4+ T cells in infected individuals contain more HIV viral DNA than other memory CD4+ T cells, at all stages of HIV disease. Additionally, following viral rebound during interruption of antiretroviral therapy, the frequency of HIV viral DNA in the HIV-specific pool of memory CD4+ T cells increases to a greater extent than in memory CD4+ T cells of other specificities. These findings show that HIV-specific CD4+ T cells are preferentially infected by HIV in vivo. This provides a potential mechanism to explain the loss of HIV-specific CD4+ T-cell responses, and consequently the loss of immunological control of HIV replication. Furthermore, the phenomenon of HIV specifically infecting the very cells that respond to it adds a cautionary note to the practice of structured therapy interruption.

Effect of interleukin-2 on the pool of latently infected, resting CD4+ T cells in HIV-1-infected patients receiving highly active anti-retroviral therapy

The size of the pool of resting CD4+ T cells containing replication-competent HIV in the blood of patients receiving intermittent interleukin (IL)-2 plus highly active anti-retroviral therapy (HAART) was significantly lower than that of patients receiving HAART alone. Virus could not be isolated from the peripheral blood CD4+ T cells in three patients receiving IL-2 plus HAART, despite the fact that large numbers of resting CD4+ T cells were cultured. Lymph node biopsies were done in two of these three patients and virus could not be isolated. These results indicate that the intermittent administration of IL-2 with continuous HAART may lead to a substantial reduction in the pool of resting CD4+ T cells that contain replication-competent HIV.

Macrophage-tropic HIV and SIV envelope proteins induce a signal through the CCR5 chemokine receptor.

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) enter target cells by forming a complex between the viral envelope protein and two cell-surface membrane receptors: CD4 and a 7-span transmembrane chemokine receptor (reviewed in refs 1,2,3). Isolates of HIV that differ in cellular tropism use different subsets of chemokine receptors as entry cofactors: macrophage-tropic HIVs primarily use CCR5, whereas T-cell-tropic and dual-tropic isolates use CXCR4 (refs 1,2,3) receptors. HIV-mediated signal transduction through CCR5 is not required for efficient fusion and entry of HIV in vitro. Here we show that recombinant envelope proteins from macrophage-tropic HIV and SIV induce a signal through CCR5 on CD4+ T cells and that envelope-mediated signal transduction through CCR5 induces chemotaxis of T cells. This chemotactic response may contribute to the pathogenesis of HIV in vivo by chemo-attracting activated CD4+ cells to sites of viral replication. HIV-mediated signalling through CCR5 may also enhance viral replication invivo by increasing the activation state of target cells. Alternatively, envelope-mediated CCR5 signal transduction may influence viral-associated cytopathicity or apoptosis.

Diminished Proliferation of Human Immunodeficiency Virus-Specific CD4+ T Cells Is Associated with Diminished Interleukin-2 (IL-2) Production and Is Recovered by Exogenous IL-2

ABSTRACT Virus-specific CD4+ T-cell function is thought to play a central role in induction and maintenance of effective CD8+ T-cell responses in experimental animals or humans. However, the reasons that diminished proliferation of human immunodeficiency virus (HIV)-specific CD4+ T cells is observed in the majority of infected patients and the role of these diminished responses in the loss of control of replication during the chronic phase of HIV infection remain incompletely understood. In a cohort of 15 patients that were selected for particularly strong HIV-specific CD4+ T-cell responses, the effects of viremia on these responses were explored. Restriction of HIV replication was not observed during one to eight interruptions of antiretroviral therapy in the majority of patients (12 of 15). In each case, proliferative responses to HIV antigens were rapidly inhibited during viremia. The frequencies of cells that produce IFN-γ in response to Gag, Pol, and Nef peptide pools were maintained during an interruption of therapy. In a subset of patients with elevated frequencies of interleukin-2 (IL-2)-producing cells, IL-2 production in response to HIV antigens was diminished during viremia. Addition of exogenous IL-2 was sufficient to rescue in vitro proliferation of DR0101 class II Gag or Pol tetramer+ or total-Gag-specific CD4+ T cells. These observations suggest that, during viremia, diminished in vitro proliferation of HIV-specific CD4+ T cells is likely related to diminished IL-2 production. These results also suggest that relatively high frequencies of HIV-specific CD4+ T cells persist in the peripheral blood during viremia, are not replicatively senescent, and proliferate when IL-2 is provided exogenously.

Pilot Study of the Effects of Intermittent Interleukin-2 on Human Immunodeficiency Virus (HIV)–Specific Immune Responses in Patients Treated during Recently Acquired HIV Infection

Highly active antiretroviral therapy (HAART) initiated during acute human immunodeficiency virus (HIV) infection may preserve HIV-specific CD4+ T cell responses that are thought to enhance HIV-specific CD8+ T cell function. The present pilot study was designed to determine whether preserved HIV-specific immune responses are augmented by the administration of the immunomodulatory agent interleukin (IL)-2. Nine persons recently (<6 months) infected with HIV were randomized to receive HAART alone or HAART plus 3 cycles of intermittent IL-2 during a 12-month period. Although HAART plus IL-2 significantly increased counts of total and naive CD4+ T cells, compared with HAART alone, there was no increase in CD4+ or CD8+ HIV-specific immune responses. In addition, adjuvant IL-2 therapy did not reduce the pool of HIV-infected resting CD4+ T cells. Thus, although intermittent IL-2 plus HAART quantitatively increased CD4+ T cells, this increase was not selective for HIV-specific CD4+ or CD8+ T cell responses in recently infected persons.

Genetic Characterization of Rebounding Human Immunodeficiency Virus Type 1 in Plasma during Multiple Interruptions of Highly Active Antiretroviral Therapy

ABSTRACT Various strategies of interrupting highly active antiretroviral therapy (HAART) are being investigated for the treatment of human immunodeficiency virus (HIV) infection. Interruptions of greater than 2 weeks frequently result in rebound of plasma HIV RNA. In order to discern changes in the viral population that might occur during cycles of treatment interruption, we evaluated the homology of HIV-1 envelope gene sequences over time in 12 patients who received four to seven cycles of 4 weeks off HAART followed by 8 weeks on HAART by using the heteroduplex tracking assay and novel statistical tools. HIV populations in 9 of 12 patients diverged from those found in the first cycle in at least one subsequent cycle. The substantial genetic changes noted in HIV env did not correlate with increased or decreased log changes in levels of plasma HIV RNA (P > 0.5). Thus, genetic changes in HIV env itself did not contribute in a systematic way to changes in levels of plasma viremia from cycle to cycle of treatment interruption. In addition, the data suggest that there may be multiple compartments contributing to the rebound of plasma viremia and to viral diversity from cycle to cycle of intermittent therapy.

Human Immunodeficiency Virus Type 1 Bound to B Cells: Relationship to Virus Replicating in CD4+ T Cells and Circulating in Plasma

ABSTRACT Human immunodeficiency virus type 1 (HIV-1) virions bind to B cells in the peripheral blood and lymph nodes through interactions between CD21 on B cells and complement-complexed virions. B-cell-bound virions have been shown to be highly infectious, suggesting a unique mode of HIV-1 dissemination by B cells circulating between peripheral blood and lymphoid tissues. In order to investigate the relationship between B-cell-bound HIV-1 and viruses found in CD4+ T cells and in plasma, we examined the genetic relationships of HIV-1 found in the blood and lymph nodes of chronically infected patients with heteroduplex mobility and tracking assays and DNA sequence analysis. In samples from 13 of 15 patients examined, HIV-1 variants in peripheral blood-derived B cells were closely related to virus in CD4+ T cells and more divergent from virus in plasma. In samples from five chronically viremic patients for whom analyses were extended to include lymph node-derived HIV-1 isolates, B-cell-associated HIV-1 and CD4+-T-cell-associated HIV-1 in the lymph nodes were equivalent in their divergence from virus in peripheral blood-derived B cells and generally more distantly related to virus in peripheral blood-derived CD4+ T cells. These results indicates virologic cross talk between B cells and CD4+ T cells within the microenvironment of lymphoid tissues and, to a lesser extent, between cells in lymph nodes and the peripheral blood. These findings also indicate that most of the virus in plasma originates from cells other than CD4+ T cells in the peripheral blood and lymph nodes.