Phenotypic variability of lymphocyte populations in peripheral blood and lymph nodes from HIV-infected individuals and the impact of antiretroviral therapy. DATRI 003 Study Group. Division of AIDS Treatment Research Initiative

Regulation of the tonsil cytokine milieu favors HIV susceptibility

Mucosal associated lymphoid tissues are major targets of HIV during early infection and disease progression but can also provide a viral safe haven during highly active antiretroviral therapy. Among these tissues, the tonsils remain enigmatic regarding their status as primary and/or secondary sites of retroviral infection. To dissect the mechanisms underlying susceptibility to HIV in this compartment, isolated tonsil cells were studied for phenotypic and functional characteristics, which may account for their permissiveness to infection. For this, tonsil cells and PBMC were infected in parallel with HIV, and viral replication was monitored by p24 ELISA. Our results demonstrate that unstimulated tonsil cells were more readily infected than PBMC with HIV. Phenotypic characterization of the tonsil cells revealed heterogeneous lymphoid populations but with increased expression of early activation markers and the viral co-receptor CXCR4, relative to PBMC, all of which may contribute to viral susceptibility. Furthermore, the cytokine microenvironment appeared to be key in facilitating HIV infection and tonsil-secreted products enhanced HIV infection in PBMC. Of the cytokines detected in the tonsil supernatants, TH2 cytokines, particularly IL-4, promoted HIV infection and replication. Interestingly, this TH2 profile appeared to dominate, even in the presence of the TH1 cytokine IFNgamma and the anti-viral factor IFNalpha, likely due to the enhanced expression of suppressor of cytokine signaling (SOCS) proteins, which may disengage IFN signaling. These and other local environmental factors may render tonsil cells increasingly susceptible to HIV infection.

Influence of mitochondrial control of apoptosis on the pathogenesis, complications and treatment of HIV infection

HIV infection is inexorably linked with disordered regulation of apoptosis, and consequent alterations in mitochondrial homeostasis, resulting in CD4 T cell death and enhanced susceptibility to opportunistic infections and malignancies. Effective treatment of HIV reverses the changes in mitochondrial homeostasis and apoptosis, and enhances immunocompetence. This review will summarize current knowledge of: i) the associations of apoptosis with HIV disease progression; ii) mechanisms of enhanced apoptosis in HIV infection; iii) putative role of apoptosis in HIV complications; iv) direct effects of HIV therapies on mitochondria and apoptosis; and finally v) treatment strategies for HIV based upon modifying the apoptotic response.

Dressed to kill? A review of why antiviral CD8 T lymphocytes fail to prevent progressive immunodeficiency in HIV-1 infection

CD8 T cells play an important role in protection and control of HIV-1 by direct cytolysis of infected cells and by suppression of viral replication by secreted factors. However, although HIV-1-infected individuals have a high frequency of HIV-1-specific CD8 T cells, viral reservoirs persist and progressive immunodeficiency generally ensues in the absence of continuous potent antiviral drugs. Freshly isolated HIV-specific CD8 T cells are often unable to lyse HIV-1-infected cells. Maturation into competent cytotoxic T lymphocytes may be blocked during the initial encounter with antigen because of defects in antigen presentation by interdigitating dendritic cells or HIV-infected macrophages. The molecular basis for impaired function is multifactorial, due to incomplete T-cell signaling and activation (in part related to CD3zeta and CD28 down-modulation), reduced perforin expression, and inefficient trafficking of HIV-specific CD8 T cells to lymphoid sites of infection. CD8 T-cell dysfunction can partially be corrected in vitro with short-term exposure to interleukin 2, suggesting that impaired HIV-specific CD4 T helper function may play a significant causal or exacerbating role. Functional defects are qualitatively different and more severe with advanced disease, when interferon gamma production also becomes compromised.

Highly active antiretroviral therapy results in HIV type 1 suppression in lymph nodes, increased pools of naive T cells, decreased pools of activated T cells, and diminished frequencies of peripheral activated HIV type 1-specific CD8+ T cells

This study examines sequential lymph nodes from 13 drug-naive patients before and after 24 weeks of highly active antiretroviral therapy (HAART). A multipronged approach was used to study changes in HIV-1 RNA in each paired lymph node in relation to tissue architecture and frequency of naive T cells. After 24 weeks, all patients showed significant suppression of plasma viral load and 12 of 13 showed concordant viral suppression in the lymph node (p = 0.001). Using in situ hybridization and quantitative image analysis, we showed that HIV-1 RNA was reduced to below detectable levels (two copies per cell) in follicular dendritic cell (FDC) and mononuclear cell pools. Independent immunohistochemical analysis of lymph node sections revealed that 5 of 13 patients displayed increased FDC networks and 6 of 13 showed no change and all patients showed increases in tissue-resident CD4+ cells. All lymph node biopsies at 24 weeks showed increased proportions of CD4+ and CD8+ cells coexpressing the naive markers CD45RA and CD62L when compared with baseline values. Significant correlations existed between viral load suppression and loss of activated CD8+ T cells after 24 weeks in both lymph node and blood, which was mirrored by significantly lowered frequencies of activated peripheral Gag peptide/MHC tetramer+ CD8+ cells. Overall, these data show that a potent and successful treatment strategy that significantly suppresses and removes FDC-resident HIV-1 results in improvements in lymphoid architecture and by so doing provides the structures available for increased numbers of naive cells to interact with cognate antigen. In addition, our article shows that suppression of HIV-1 replication results in diminished frequencies of peripherally activated antigen-specific CD8+ cells.

Inverse correlation of telomerase activity/proliferation of CD4+ T lymphocytes and disease progression in simian immunodeficiency virus-infected nonhuman primates

Both increased lymphocyte renewal with subsequent exhaustion of the immune system and impaired T-cell renewal have been put forth to account for CD4+ T-cell depletion and development of AIDS in HIV-1-infected humans and SIV-infected nonhuman primates. In the present study, telomeric terminal restriction fragment length and telomerase activity were used as measures of proliferative activity of T lymphocytes from three nonhuman primate species before and after being infected with SIV. In peripheral blood T cells, our data show both species and T-cell-subset-specific differences in proliferative activity accompanied by different patterns of disease progression. A significant postinfection increase in telomerase/proliferative activity in CD4+ T cells from seropositive sooty mangabeys and from normal progressor rhesus macaques was associated with asymptomatic infection or delayed disease progression, respectively, whereas a decrease in telomerase/proliferative activity detected in CD4+ T cells postinfection from SIVsmmPBj14-infected pigtailed macaques was associated with rapid CD4+ T-cell depletion and disease progression. The levels of telomerase activity observed in CD4+ T cells from peripheral blood closely parallelled those seen in CD4+ T cells in lymph node samples from selected animals. Our data suggest that an increase in proliferative activity of T lymphocytes in vivo may be associated with a favorable course of SIV infection in nonhuman primates.

Activation of CD8 T cells normalizes and correlates with the level of infectious provirus in tonsils during highly active antiretroviral therapy in early HIV-1 infection

OBJECTIVES

To study the effects of antiretroviral therapy on T cell activation in blood and tonsils from HIV-1 infected individuals in relation to CD4 cell count, plasma viremia, and infectious HIV-1 provirus.

DESIGN

A 48-week study of viral load and T cell subsets in blood and tonsils from 12 HIV-1-positive individuals with a mean CD4 cell number of 400 x 10(6) cells/l treated with a combination of zidovudine, lamivudine, and indinavir.

METHODS

Tonsil biopsies and blood samples were collected at regular intervals. Lymphocytes were phenotyped and quantified by three-color flow cytometry; infectious provirus was quantified by a limiting dilution assay. HIV-1-negative individuals were included as controls.

RESULTS

The fraction of tonsillar CD8 T cells expressing CD69, CD38, or HLA-DR in the patients with suppressed virus replication declined to levels comparable with that in controls by 48 weeks and showed a strong positive correlation with tonsillar infectious provirus and plasma viremia. The level of CD4 T cell activation was within normal range in tonsils throughout the study. The fraction of HLA-DR+ cells within CD4 and CD8 T cells in blood declined rapidly in parallel with plasma viremia but remained slightly higher compared with that in uninfected individuals.

CONCLUSION

Antiretroviral therapy normalizes tonsillar CD8 T cell activation in HIV-1-positive individuals in parallel with suppression of viral replication, indicating reduced CD8 cell turnover. Normal tonsillar CD4 T cell activation suggests limited CD4 cell turnover in early HIV infection. Activated CD8 T cells in lymphoid tissue is superior to that in blood as an immunological marker for the virological response to antiretroviral therapy.

Activated memory CD4(+) T helper cells repopulate the intestine early following antiretroviral therapy of simian immunodeficiency virus-infected rhesus macaques but exhibit a decreased potential to produce interleukin-2

Using the simian immunodeficiency virus (SIV)-infected rhesus macaque model, we performed a longitudinal study to determine the effect of antiretroviral therapy on the phenotype and functional potential of CD4(+) T cells repopulating intestinal mucosa in human immunodeficiency virus infection. Severe depletion of CD4(+) and CD4(+) CD8(+) T cells occurred in the intestinal mucosa during primary SIV infection. The majority of these cells were of activated memory phenotype. Phosphonate 9-[2-(phosphomethoxypropyl]adenine (PMPA) treatment led to a moderate suppression of intestinal viral loads and repopulation of intestinal mucosa by predominantly activated memory CD4(+) T-helper cells. This repopulation was independent of the level of viral suppression. Compared to preinfection values, the frequency of naive CD4(+) T cells increased following PMPA therapy, suggesting that new CD4(+) T cells were repopulating the intestinal mucosa. Repopulation by CD4(+) CD8(+) T cells was not observed in either jejunum or colon lamina propria. The majority of CD4(+) T cells repopulating the intestinal mucosa following PMPA therapy were CD29(hi) and CD11ahi. A subset of repopulating intestinal CD4(+) T cells expressed Ki-67 antigen, indicating that local proliferation may play a role in the repopulation process. Although the majority of repopulating CD4(+) T cells in the intestinal mucosa were functionally capable of providing B- and T-cell help, as evidenced by their expression of CD28, these CD4(+) T cells were found to have a reduced capacity to produce interleukin-2 (IL-2) compared to the potential of CD4(+) T cells prior to SIV infection. Persistent viral infection may play a role in suppressing the potential of repopulating CD4(+) T cells to produce IL-2. Hence, successful antiretroviral therapy should aim at complete suppression of viral loads in mucosal lymphoid tissues, such as intestinal mucosa.

Immunological changes in peripheral blood and in lymphoid tissue after treatment of HIV-infected subjects with highly active anti-retroviral therapy (HAART) or HAART + IL-2

This study presents the immunophenotypic and functional analysis of lymphocyte subsets obtained from peripheral blood and lymphoid tissue from HIV+ individuals treated with highly active anti-retroviral therapy (HAART) alone or in combination with 6 million units international (MUI) s.c. IL-2. Before treatment, the HIV+ patients had reduced CD4 and increased CD8 values in the peripheral blood and lymphoid tissue and impaired cytokine production by peripheral blood mononuclear cells (PBMC). After 24 weeks of treatment, all the HIV+ patients demonstrated increased CD4 values in peripheral blood and lymphoid tissue. The use of IL-2 did not promote an additional CD4 expansion compared with HAART alone; increased 'naive' and CD26+ CD4 cells and reduced CD8 cells were found in the peripheral blood and lymphoid tissue of the IL-2-treated, but not of the HAART-treated patients. Both types of treatment induced a significant reduction of the CD8/CD38+ cells. While HAART alone had negligible effects on cytokine production by PBMC, the combined use of HAART + IL-2 was unable to increase the endogenous production of IL-2, but caused an increase of IL-4, IL-13 and interferon-gamma (IFN-gamma) and a reduction of monocyte chemoattractant protein-1 (MCP-1) production. These data suggest that, although in this schedule IL-2 has minimal efficacy on CD4 recovery when compared with HAART alone, it produces an increase of 'naive' and CD26+ CD4 cells and a partial restoration of cytokine production. These data may be used to better define clinical trials aiming to improve the IL-2-dependent immunological reconstitution of HIV-infected subjects.

Altered expression of CD4, CD54, CD62L, and CCR5 in primary lymphocytes productively infected with the human immunodeficiency virus

Infection of T cells with HIV-1 induces loss of CD4 and HLA class I from the cell surface. In the present article we have investigated whether changes in expression of other cell surface molecules could be related to HIV infection. To detect HIV-infected cells at the single-cell level, peripheral blood lymphocytes were infected in vitro with HIV-HSA, a reporter virus encoding the murine heat-stable antigen. Expression of HSA on activated primary lymphocytes was an efficient indicator of productive infection. Expression of the majority of the cell surface proteins studied was unaffected by HIV infection (HLA class I, II, CD11a, CD18, CD25, CD27, CD28, CD29, CD30, CD31, CD38, CD44, CD45R0, CD49d, CD57, CD94, CD95, and CXCR4). However, phenotypic changes specific to the productively infected cells were detected. Expression of the CD4 molecule was progressively lost and this was closely associated with loss of CD62L expression, a molecule involved in T cell homing into the lymph nodes. By contrast, T cells productively infected with this T-tropic reporter virus were enriched for CD54, and for CCR5, the main coreceptor for M-tropic viruses. Given the roles of CD62L, CD54, and CCR5 in lymphocyte trafficking, these results suggest that cells productively infected with HIV might have altered homing patterns in vivo.