ApoA-I mimetics favorably impact cyclooxygenase 2 and bioactive lipids that may contribute to cardiometabolic syndrome in chronic treated HIV.

OBJECTIVE: We investigated whether apolipoprotein A-I (apoA-I) mimetic peptides 4F and 6F can be a novel therapeutic strategy to reduce blood and gut bioactive lipids, proinflammatory effects of endotoxin (LPS) and aberrant activation of cyclooxygenase 2 (COX-2) as instigators of increased risk for cardiometabolic disease in chronic treated HIV. METHODS: We used two humanized murine models of chronic treated HIV infection (n = 109 mice) and gut explants from HIV infected (n = 10) persons to determine whether Tg6F and 4F attenuate in vivo and ex vivo increased blood and gut bioactive lipids (measured by mass spectrometry) and intestinal protein levels of COX-2 (measured by immunoassays) in chronic treated HIV. RESULTS: In these models of HIV, when compared to HIV-1 infected mice on antiretroviral therapy (ART) alone, oral Tg6F in combination with ART attenuated increases in plasma and gut bioactive lipids (and particularly COX lipids) and intestinal COX-2. 4F and Tg6F also reduced ex vivo production of COX-2 protein and associated secretion of bioactive lipids in gut explants from HIV-1 infected persons treated with LPS. CONCLUSION: ApoA-I mimetics favorably impact the proinflammatory effects of LPS, COX-2 and production of bioactive lipids that collectively drive gut and systemic inflammation in chronic treated HIV. Given prior experimental evidence that the proinflammatory effects of LPS, COX-2 and gut dysfunction contribute to cardiometabolic syndrome in chronic HIV, apoA-I mimetic peptides may be a novel therapy to treat cardiometabolic syndrome in chronic HIV.

Initial virological and immunologic response to highly active antiretroviral therapy predicts long-term clinical outcome.

Little is known about the long-term clinical outcomes for human immunodeficiency virus (HIV)-infected patients who have received highly active antiretroviral therapy (HAART). Determining factors associated with long-term clinical outcomes early in the course of treatment may allow modifications to be made for patients who are at a greater risk of treatment failure. To evaluate these factors, we studied 213 HIV-infected patients who had received HAART for at least 115 weeks. In the univariate analysis, virological response, which was measured as the change in virus load from baseline at month 3 of treatment, was the single best predictor of clinical outcome (relative hazard, 0.722; P=.001), independent of virological suppression. In the multivariate analysis, virological response and immunologic response, which was measured as an increase in CD4 cell count of >200 cells/mm(3), resulted in better prediction of clinical outcomes than did use of either variable alone (P=.02). Our results indicate that changes in virus load and immunologic response together are good predictors of clinical outcome and can be assessed after the initiation of HAART, which would allow clinicians to identify patients early in the course of therapy who are at greater risk of negative outcome.

Upregulation of CD4 on CD8+ T cells: CD4dimCD8bright T cells constitute an activated phenotype of CD8+ T cells.

Aside from an intermediate stage in thymic T-cell development, the expression of CD4 and CD8 is generally thought to be mutually exclusive, associated with helper or cytotoxic T-cell functions, respectively. Stimulation of CD8+ T cells, however, induces the de novo expression of CD4. We demonstrate that while superantigen (staphylococcal enterotoxin B, SEB) and anti-CD3/CD28 costimulation of purified CD8+ T cells induced the expression of CD4 on CD8+ T cells by 30 and 17%, respectively, phytohaemagglutinin (PHA) stimulation did not induce CD4 expression on purified CD8+ T cells but significantly induced the expression of both CD4 on CD8 (CD4dimCD8bright) and CD8 on CD4 (CD4brightCD8dim) T cells in unfractionated peripheral blood mononuclear cells (PBMC). The level of the PHA-mediated induction of CD4dimCD8bright and CD4brightCD8dim was at 27 and 17%, respectively. Depletion of CD4+ T cells from PBMC abrogated this PHA-mediated effect. Autologous CD4+ and CD8+ T-cell co-cultures in the presence of PHA induced this CD4dimCD8bright T-cell expression by 33%, demonstrating a role for CD4 cells in the PHA-mediated induction of the double positive cells. The induction of CD4dimCD8bright was independent of a soluble factor(s). Phenotypic analysis of CD4dimCD8bright T cells indicated significantly higher levels of CD95, CD25, CD38, CD69, CD28, and CD45RO expression than their CD8+CD4- counterparts. CD4dimCD8bright T cells were also negative for CD1a expression and were predominantly T-cell receptor (TCR) alphabeta cells. Our data demonstrate that CD4dimCD8bright T cells are an activated phenotype of CD8+ T cells and suggest that CD4 upregulation on CD8+ T cells may function as an additional marker to identify activated CD8+ T cells.

Generation of HIV latency during thymopoiesis.

The use of combination antiretroviral therapy results in a substantial reduction in viremia, a rebound of CD4+ T cells and increased survival for HIV-infected individuals. However, this treatment does not result in the total eradication of HIV. Rather, the virus is thought to remain latent in a subset of cells, where it avoids elimination by the immune system. In this state the virus is capable of reactivation of productive infection following cessation of therapy. These latently infected cells are very few in number and it has thus been difficult to determine their origin and to study the molecular nature of the latent viral genome. HIV replication is linked to cellular gene transcription and requires target cell activation. Therefore, should an activated, infected cell become transcriptionally inactive prior to cytopathic effects, the viral genome might be maintained in a latent state. We used the SCID-hu (Thy/Liv) mouse model to establish that activation-inducible HIV can be generated at high frequency during thymopoiesis, a process where previously activated cells mature towards quiescence. Moreover, we showed that these cells can be exported into the periphery where the virus remains latent until T-cell receptor stimulation, indicating that the thymus might be a source of latent HIV in humans.

Functional reconstitution of thymopoiesis after human immunodeficiency virus infection.

We have utilized combination antiretroviral therapy following human immunodeficiency virus type 1-induced human CD4(+) thymocyte depletion in the SCID-hu mouse to examine the immune competence of reconstituting thymocytes which appear following administration of combination therapy. These cells express a normal distribution of T-cell receptor variable gene families and are responsive to costimulatory signals. These results suggest that normal thymic function may be restored following antiretroviral treatment.

Distribution of the human immunodeficiency virus coreceptors CXCR4 and CCR5 in fetal lymphoid organs: implications for pathogenesis in utero.

HIV entry into a cell requires the coordinate cell surface expression of CD4 and one of several chemokine coreceptors. Here we have examined the expression of the two most widely utilized HIV coreceptors, CXCR4 and CCR5, on various lymphoid tissues derived from the fetus. CXCR4 and CCR5 are differentially expressed on lymphocytes in different lymphoid organs, which may reflect the maturational and functional status of cells within the organ. The different levels of coreceptor expression on CD4+ cells in the various organs may directly affect the targeting of CXCR4- and CCR5-tropic strains of HIV toward different fetal lymphoid tissues during in utero infection.

HIV type 1 infection in lymphoid tissue: natural history and model systems.

The pathogenesis of human immunodeficiency virus (HIV) in the lymphoid compartment has a dramatic effect on disease progression and important implications for therapeutic and vaccine strategies. Here we discuss current understanding of the pathogenesis of HIV in the lymphoid tissue. Various model systems that allow examination of the effect of retroviral infection in primary lymphoid organs are discussed, as well as current progress made with the use of these systems, with particular emphasis on the SCID-hu mouse.

Costimulation of naive CD8(+) lymphocytes induces CD4 expression and allows human immunodeficiency virus type 1 infection.

Human immunodeficiency virus type 1 (HIV-1) infection requires cell surface expression of CD4. Costimulation of CD8(+)/CD4(-) T lymphocytes by anti-CD3 and anti-CD28 antibodies or by allogeneic dendritic cells induced expression of CD4 and rendered these CD8 cells susceptible to HIV-1 infection. Naive CD45RA+ cells responded with greater expression of CD4 than did CD45RO+ cells. CD8(+) lymphocytes derived from fetal or newborn sources exhibited a greater tendency to express CD4, consistent with their naive states. This mechanism of infection suggests HIV-induced perturbation of the CD8 arm of the immune response and could explain the generally rapid disease progression seen in HIV-infected children.

CXCR4 expression during lymphopoiesis: implications for human immunodeficiency virus type 1 infection of the thymus.

Human immunodeficiency virus type 1 (HIV-1) infection of the human thymus results in depletion of CD4-bearing thymocytes. This depletion is initially manifested in the immature CD4+/CD8+ thymocyte subset. To determine cellular factors involved in HIV infection in the thymus, we examined the expression of the recently identified viral coreceptor, CXCR4, on fresh human thymocytes and on human cells from SCID-hu (Thy/Liv) mice. CXCR4 is a member of the chemokine receptor family which is required along with CD4 for entry into the cell of syncytium-inducing (SI) HIV-1 strains. Our analyses show that CXCR4 expression is modulated during T-lymphoid differentiation such that immature thymocytes display an increased frequency and higher surface density of the coreceptor than do more mature cells. In addition, using an SI strain of HIV-1 which directs expression of a reporter protein on the surface of infected cells, we have found that the immature CD4+/CD8+ thymocytes that express the highest levels of both CD4 and CXCR4 are the cells that are preferentially infected and depleted by the virus in vitro. Thus, high levels of both primary receptor and coreceptor may allow efficient infection of the thymus by certain HIV-1 strains. This in part may explain the rapid disease progression seen in some HIV-infected children, where the thymus is actively involved in the production of new T lymphocytes.

Mechanism of human immunodeficiency virus type 1 localization in CD4-negative thymocytes: differentiation from a CD4-positive precursor allows productive infection.

Human immunodeficiency virus (HIV) infection of the thymus could have profound effects on development of the immune response, particularly in children. We and others have established that in addition to infecting and depleting CD4-bearing thymocytes, functional HIV proviruses are found in thymocytes lacking surface CD4 expression. Using in vitro thymocyte cultures, we show that neither HIV-mediated down regulation of CD4 nor CD4-independent infection contributes to the localization of HIV in cells lacking the primary virus receptor. Rather, infection of a CD4-positive precursor cell (CD4 positive/CD8 positive) with subsequent differentiation into a mature CD4-negative phenotype results in productively infected CD4-negative cells. This novel mechanism may contribute to pathogenesis by distributing viral sequences into functional subsets of T cells typically refractory to HIV infection and could account for the presence of viral DNA in CD8-positive lymphocytes recently observed in patients.