Positive regulation of CXCR4 expression and signaling by interleukin-7 in CD4+ mature thymocytes correlates with their capacity to favor human immunodeficiency X4 virus replication

Mesenchymal Stromal Cells: a Possible Reservoir for HIV-1?

The introduction of antiretroviral therapy (ART) and highly active antiretroviral therapy (HAART) has transformed human immunodeficiency virus (HIV)-1 into a chronic, well-managed disease. However, these therapies do not eliminate all infected cells from the body despite suppressing viral load. Viral rebound is largely due to the presence of cellular reservoirs which support long-term persistence of HIV-1. A thorough understanding of the HIV-1 reservoir will facilitate the development of new strategies leading to its detection, reduction, and elimination, ultimately leading to curative therapies for HIV-1. Although immune cells derived from lymphoid and myeloid progenitors have been thoroughly studied as HIV-1 reservoirs, few studies have examined whether mesenchymal stromal/stem cells (MSCs) can assume this function. In this review, we evaluate published studies which have assessed whether MSCs contribute to the HIV-1 reservoir. MSCs have been found to express the receptors and co-receptors required for HIV-1 entry, albeit at levels of expression and receptor localisation that vary considerably between studies. Exposure to HIV-1 and HIV-1 proteins alters MSC properties in vitro, including their proliferation capacity and differentiation potential. However, in vitro and in vivo experiments investigating whether MSCs can become infected with and harbour latent integrated proviral DNA are lacking. In conclusion, MSCs appear to have the potential to contribute to the HIV-1 reservoir. However, further studies are needed using techniques such as those used to prove that cluster of differentiation (CD)4⁺ T cells constitute an HIV-1 reservoir before a reservoir function can definitively be ascribed to MSCs.

Resistance to human immunodeficiency virus infection: a rare but neglected state

The natural history of human immunodeficiency virus (HIV) infection is well understood. In most individuals sexually exposed to HIV, the risk of becoming infected depends on the viral load and on sexual practices and gender. However, a low percentage of individuals who practice frequent unprotected sexual intercourse with HIV-infected partners remain uninfected. Although the systematic study of these individuals has made it possible to identify HIV resistance factors including protective genetic patterns, such epidemiological situations remain paradoxical and not fully understood. In vitro experiments have demonstrated that peripheral blood mononuclear cells (PBMCs) from HIV-free, unexposed blood donors are not equally susceptible to HIV infection; in addition, PBMCs from highly exposed seronegative individuals are generally resistant to infection by primary HIV clinical isolates. We review the literature on permissiveness of PBMCs from healthy blood donors and uninfected hyperexposed individuals to sustained infection and replication of HIV-1 in vitro. In addition, we focus on recent evidence indicating that the gut microbiota may either contribute to natural resistance to or delay replication of HIV infected individuals.

Human Parvovirus B19 (B19V) Up-regulates CXCR4 Surface Expression of Circulating Angiogenic Cells: Implications for Cardiac Ischemia in B19V Cardiomyopathy

Background

Human parvovirus B19 (B19V) infection and damage of circulating angiogenic cells (CAC) results in dysfunctional endogenous vascular repair (DEVR) with secondary end-organ damage. Trafficking of CAC is regulated by SDF-1α and the respective receptor CXCR4. We thus tested the hypothesis of a deregulated CXCR4/SDF-1α axis in symptomatic B19V-cardiomyopathy.

Methods

CAC were infected in vitro with B19V and transfected with B19V-components. Read-out were: CXCR4-expression and migratory capacity at increasing doses of SDF-1α. In 31 patients with chronic B19V-cardiomyopathy compared to 20 controls read-outs were from blood: migratory capacity, CXCR4 expression on CAC, serum SDF-1α; from cardiac biopsies: SDF-1α mRNA, HIF-1α mRNA, microvascular density, resident cardiac stem cells (CSC), transcardiac gradients of CAC.

Results

In vitro B19V-infected CAC showed up-regulation of surface CXCR4 with increased migratory capacity further enhanced by elevated SDF-1α concentrations. Overexpression of the B19V capsid protein VP2 was associated with this effect. Chronic B19V-cardiomyopathy patients showed increased numbers of ischaemia mobilised CAC but DEVR as well as diminished numbers of CAC after transcardiac passage. Cardiac microvascular density and CSC were significantly reduced in B19V-cardiomyopathy.

Conclusions

We thus conclude that B19V infection has a direct VP2-mediated negative impact on trafficking of CAC in the presence of impaired cardiac regeneration.

HIV Impacts CD34+ Progenitors Involved in T-Cell Differentiation During Coculture With Mouse Stromal OP9-DL1 Cells

HIV-1 causes the loss of CD4⁺ T cells via depletion or impairment of their production. The latter involves infection of thymocytes, but the involvement of hematopoietic CD34⁺ cells remains unclear even though HIV-positive patients frequently manifest myelosuppression. In order to have a closer look at the impact of HIV-1 on T-lineage differentiation, this study utilized the OP9-DL1 coculture system, which supports in vitro T-lineage differentiation of human hematopoietic stem/progenitor cells. In the newly developed in vitro OP9-DL1/HIV-1 model, cord-derived CD34⁺ cells were infected with CXCR4-tropic HIV-1_NL4−3 and cocultured. The HIV-infected cocultures exhibited reduced CD4⁺ T-cell growth at weeks 3–5 post infection compared to autologous uninfected cocultures. Further assays and analyses revealed that CD34⁺CD7⁺CXCR4⁺ cells can be quickly depleted as early as 1 week after infection of the subset, and this was accompanied by the emergence of rare CD34⁺CD7⁺CD4⁺ cells. A subsequent theoretical model analysis suggested potential influence of HIV-1 on the differentiation rate or death rate of lymphoid progenitor cells. These results indicate that CXCR4-tropic HIV-1 strains may impact the dynamics of CD34⁺CD7⁺ lymphoid progenitor cell pools, presumably leading to impaired T-cell production potential.

Adaptive Immunodeficiency in WHIM Syndrome

Cysteine-X-cysteine chemokine receptor 4 (CXCR4) is a broadly expressed and multifunctional G protein-coupled chemokine receptor critical for organogenesis, hematopoiesis, and antimicrobial host defense. In the hematopoietic system, the binding of CXCR4 to its cognate chemokine ligand, CXCL12, mediates leukocyte trafficking, distribution, survival, activation, and proliferation. Warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome is a rare, autosomal dominant, combined immunodeficiency disorder caused by mutations in the C-terminus of CXCR4 that prevent receptor downregulation and therefore result in pathologically increased signaling. The "M" in the acronym WHIM refers to myelokathexis, the retention of neutrophils in the bone marrow resulting in neutropenia, which explains in part the increased susceptibility to bacterial infection. However, WHIM patients also present with B and T lymphopenia, which may explain the susceptibility to human papillomavirus (HPV), the cause of warts. The impact of WHIM mutations on lymphocytes and adaptive immunity has received less attention than myelokathexis and is the focus of this review.

Enhancing the Potency and Specificity of Engineered T Cells for Cancer Treatment

The adoptive transfer of chimeric antigen receptor (CAR)-modified T cells has produced tumor responses even in patients with refractory diseases. However, the paucity of antigens that are tumor selective has resulted, on occasion, in "on-target, off-tumor" toxicities. To address this issue, we developed an approach to render T cells responsive to an expression pattern present exclusively at the tumor by using a trio of novel chimeric receptors. Using pancreatic cancer as a model, we demonstrate how T cells engineered with receptors that recognize prostate stem cell antigen, TGFβ, and IL4, and whose endodomains recapitulate physiologic T-cell signaling by providing signals for activation, costimulation, and cytokine support, produce potent antitumor effects selectively at the tumor site. In addition, this strategy has the benefit of rendering our cells resistant to otherwise immunosuppressive cytokines (TGFβ and IL4) and can be readily extended to other inhibitory molecules present at the tumor site (e.g., PD-L1, IL10, and IL13).Significance: This proof-of-concept study demonstrates how sophisticated engineering approaches can be utilized to both enhance the antitumor efficacy and increase the safety profile of transgenic T cells by incorporating a combination of receptors that ensure that cells are active exclusively at the tumor site. Cancer Discov; 8(8); 972-87. ©2018 AACR.See related commentary by Achkova and Pule, p. 918This article is highlighted in the In This Issue feature, p. 899.

Homing receptor expression is deviated on CD56+ blood lymphocytes during pregnancy in Type 1 diabetic women

Type 1 Diabetes Mellitus (T1DM) is characterized by an augmented pro-inflammatory immune state. This contributes to the increased risk for gestational complications observed in T1DM mothers. In normal pregnancies, critical immunological changes occur, including the massive recruitment of lymphocytes, particularly CD56^bright NK cells, into early decidua basalis and a 2^nd trimester shift towards Type 2 immunity. Decidual CD56^bright NK cells arise at least partly from circulating progenitors expressing adhesion molecules SELL and ITGA4 and the chemokine receptors CXCR3 and CXCR4. In vitro studies show that T1DM reduces interactions between blood CD56⁺ NK cells and decidual endothelial cells by reducing SELL and ITGA4-based interactions. To address the mechanisms by which specific lymphocyte subsets may be recruited from the circulation during pregnancy and whether these mechanisms are altered in T1DM, flow cytometry was used to examine eight peripheral blood lymphocyte subsets (Type 1 (IL18R1⁺) and Type 2 (IL1RL1⁺) CD56^bright NK, CD56^dim NK, NKT and T cells) from control and T1DM women. Blood was collected serially over pregnancy and postpartum, and lymphocytes were compared for expression of homing receptors SELL, ITGA4, CXCR3, and CXCR4. The decline of Type 1/Type 2 immune cells in normal pregnancy was driven by an increase in Type 2 cells that did not occur in T1DM. CD56^bright NK cells from control women had the highest expression of all four receptors with greatest expression in 2^nd trimester. At this time, these receptors were expressed at very low levels by CD56^bright NK cells from TIDM patients. Type 1/Type 2 NKT cell ratios were not influenced by either pregnancy or TIDM. Our results suggest that T1DM alters immunological balances during pregnancy with its greatest impact on CD56^bright NK cells. This implicates CD56^bright NK cells in diabetic pregnancy complications.

Chemokine receptor CXCR4: role in gastrointestinal cancer

Chemokines (CK)s, small proinflammatory chemoattractant cytokines that bind to specific G-protein coupled seven-span transmembrane receptors, are major regulators of cell trafficking and adhesion. The CXCL12 [stromal cell-derived factor-1 (SDF-1)] binds primarily to CXC receptor 4 (CXCR4; CD184). The binding of CXCL12 to CXCR4 induces intracellular signaling through several divergent pathways initiating signals related to chemotaxis, cell survival and/or proliferation, increase in intracellular calcium, and gene transcription. CXCR4 is expressed on multiple cell types including lymphocytes, hematopoietic stem cells, endothelial and epithelial cells, and cancer cells. One of the most intriguing and perhaps important roles that CKs and the CK receptors have is in regulating metastasis. Here, CK receptors may potentially facilitate tumor dissemination at each of the key steps of metastasis, including adherence of tumor cells to endothelium, extravasation from blood vessels, metastatic colonization, angiogenesis, proliferation, and protection from the host response via activation of key survival pathways such as ERK/MAPK, PI-3K/Akt/mTOR, or Jak/STAT, etc. In addition, it is increasingly recognized that CKs play an important role in facilitating communication between cancer cells and non-neoplatic cells in the tumor microenvironment (TME), including endothelial cells and fibroblasts, promoting the infiltration, activation of neutrophils, and tumor-associated macrophages within the TME. In this review, we mainly focus on the roles of chemokines CXCL12 and its cognate receptors CXCR4 as they pertain to cancer progression. In particular, we summarizes our current understanding regarding the contribution of CXCR4 and SDF-1 to gastrointestinal tumor behavior and its role in local progression, dissemination, and immune evasion of tumor cells. Also, describes recent therapeutic approaches that target these receptors or their ligands.

Excessive conversion and impaired thymic output contribute to disturbed regulatory T-cell homeostasis in AIDS patients with low CD4 cell counts

OBJECTIVE

T regulatory (Treg) cells are a heterogeneous population that consists of CD4(+)CD25(low)CD45RA(+) [naive Treg (nTreg) cells] and CD4(+)CD25(high)CD45RA(-) [activated Treg (aTreg) cells] subsets. We investigated the effects of HIV infection and HAART on distinct Treg subsets.

METHODS

HIV-infected adult patients naive to HAART (n=57), patients with acute HIV infection (n=13), and healthy controls (n=92) were recruited for a cross-sectional study. Patients receiving HAART were followed up in a longitudinal study.

RESULTS

Compared with healthy controls, we observed a reduced proportion of nTreg cells and an elevated frequency of aTreg cells in peripheral blood from HAART-naïve patients. Moreover, nTreg cells showed a decreased CD31(+) frequency, whereas aTreg cells showed an increased CD31(+) frequency, indicating impaired thymic output and excessive conversion from nTreg to aTreg cells. nTreg and aTreg cells both displayed higher levels of Ki67(+), reflecting hyperproliferation. The longitudinal study showed that HAART successfully recovered nTreg but not aTreg cell frequency. Higher baseline naïve CD4 T-cell percentages were associated with faster reconstitution of nTreg cell frequency as well as CD4(+) T-cell count.

CONCLUSION

Our data suggest that the disturbed homeostasis of Treg cells in HIV-infected patients is probably caused by excessive conversion from nTreg to aTreg cells, and impaired thymic output of nTreg cells. nTreg cells can be recovered by HAART, which was associated with baseline naive CD4(+) T-cell percentages, indicating that reconstitution of nTreg cells may benefit from earlier antiretroviral treatment.

Interleukin-7 facilitates HIV-1 transmission to cervico-vaginal tissue ex vivo

The majority of HIV-1 infections in women occur through vaginal intercourse, in which virus-containing semen is deposited on the cervico-vaginal mucosa. Semen is more than a mere carrier of HIV-1, since it contains many biological factors, in particular cytokines, that may affect HIV-1 transmission. The concentration of interleukin (IL)-7, one of the most prominent cytokines in semen of healthy individuals, is further increased in semen of HIV-1-infected men. Here, we investigated the potential role of IL-7 in HIV-1 vaginal transmission in an ex vivo system of human cervico-vaginal tissue. We simulated an in vivo situation by depositing HIV-1 on cervico-vaginal tissue in combination with IL-7 at concentrations comparable with those measured in semen of HIV-1-infected individuals. We found that IL-7 significantly enhanced virus replication in ex vivo infected cervico-vaginal tissue. Similarly, we observed an enhancement of HIV-1 replication in lymphoid tissue explants. Analysis of T cells isolated from infected tissues showed that IL-7 reduced CD4⁺ T cell depletion preventing apoptosis, as shown by the decrease in the number of cells expressing the apoptotic marker APO2.7 and the increase in the expression of the anti-apoptotic protein B-cell lymphoma (Bcl)-2. Also, IL-7 increased the fraction of cycling CD4⁺ T cells, as evidenced by staining for the nuclear factor Ki-67. High levels of seminal IL-7 in vivo may be relevant to the survival of the founder pool of HIV-1-infected cells in the cervico-vaginal mucosa at the initial stage of infection, promoting local expansion and dissemination of HIV infection.

Male-to-female HIV-1 transmission occurs predominantly through vaginal intercourse when the virus is transmitted with seminal fluid. The identification of the determinants of HIV-1 transmission to the female lower genital tract is of pivotal importance for understanding the basic mechanisms of HIV-1 infection. This understanding is necessary for the development of new strategies to prevent or contain this infection. Semen of HIV-1-infected individuals is highly enriched with IL-7, a crucial cytokine for the life cycle of CD4⁺ T cells, the primary target of HIV-1. Here, we utilized a system of human cervico-vaginal and lymphoid tissues ex vivo to study the effect of IL-7 on HIV-1 transmission and dissemination. Our results show that IL-7 at concentrations comparable to those found in semen of HIV-1-infected individuals enhanced HIV-1 replication by preventing the death and by stimulating the proliferation of CD4⁺ T cells. This allows sustained viral production by infected cells and provides new cellular targets for propagation of infection. The concentration of IL-7 in semen of HIV-1-infected men may be a key determinant of the efficiency of HIV-1 transmission to an uninfected female partner through vaginal intercourse.

Altered responses to homeostatic cytokines in patients with idiopathic CD4 lymphocytopenia

Idiopathic CD4 lymphocytopenia (ICL) is a rare immune deficiency characterized by a protracted CD4(+) T cell loss of unknown etiology and by the occurrence of opportunistic infections similar to those seen in AIDS. We investigated whether a defect in responses to cytokines that control CD4(+) T cell homeostasis could play a role in ICL. Immunophenotype and signaling responses to interleukin-7 (IL-7), IL-2, and thymic stromal lymphopoietin (TSLP) were analyzed by flow cytometry in CD4(+) T cells from 15 ICL patients and 15 healthy blood donors. The induction of phospho-STAT5 after IL-7 stimulation was decreased in memory CD4(+) T cells of some ICL patients, which correlated with a decreased expression of the IL-7Rα receptor chain (R = 0.74, p<0.005) and with lower CD4(+) T cell counts (R = 0.69, p<0.005). IL-2 responses were also impaired, both in the Treg and conventional memory subsets. Decreased IL-2 responses correlated with decreased IL-7 responses (R = 0.75, p<0.005), pointing to combined defects that may significantly perturb CD4(+) T cell homeostasis in a subset of ICL patients. Unexpectedly, responses to the IL-7-related cytokine TSLP were increased in ICL patients, while they remained barely detectable in healthy controls. TSLP responses correlated inversely with IL-7 responses (R = -0.41; p<0.05), suggesting a cross-regulation between the two cytokine systems. In conclusion, IL-7 and IL-2 signaling are impaired in ICL, which may account for the loss of CD4(+) T cell homeostasis. Increased TSLP responses point to a compensatory homeostatic mechanism that may mitigate defects in γc cytokine responses.

Regulated expression of CXCR4 constitutive active mutants revealed the up-modulated chemotaxis and up-regulation of genes crucial for CXCR4 mediated homing and engraftment of hematopoietic stem/progenitor cells

SDF-1/CXCR4 axis plays a principle role in the homing and engraftment of hematopoietic stem/progenitor cells (HSPCs), a process that defines cells ability to reach and seed recipient bone marrow niche following their intravenous infusion. However, the proper functioning of CXCR4 downstream signaling depends upon consistent optimal expression of both SDF-1 ligand and its receptor CXCR4, which in turn is variable and regulated by several factors. The constitutive active mutants of CXCR4 (N119A and N119S) being able to induce autonomous downstream signaling, overcome the limitation of ligand-receptor interaction for induction of CXCR4 signaling. Therefore, we intended to explore their potential in Chemotaxis; a key cellular process which crucially regulates cells homing to bone marrow. In present study, Tet-on inducible gene expression vector system was used for doxycycline inducible regulated transgene expression of CXCR4 active mutants in hematopoietic stem progenitor cell line K-562. Both of these mutants revealed significantly enhanced Chemotaxis to SDF-1 gradient as compared to wild type. Furthermore, gene expression profiling of these genetically engineered cells as assessed by microarray analysis revealed the up-regulation of group of genes that are known to play a crucial role in CXCR4 mediated cells homing and engraftment. Hence, this study suggest the potential prospects of CXCR4 active mutants in research and development aimed to improve the efficiency of cells in the mechanism of homing and engraftment process.

Perspectives on interleukin-7 therapy in HIV infection

PURPOSE OF REVIEW

HIV infection is characterized by depletion of CD4 T cells and altered immune function, leading to severe immune deficiency. Mechanisms leading to this T-cell depletion are not completely understood. Potent antiretroviral therapy restores T-cell counts and improves prognosis. Apart from antiviral therapy for the infection, immunotherapies such as interleukin-7 that influence T-cell homeostatic mechanisms are undergoing clinical evaluation. Because of its pleiotropic effects on developing and mature T cells, interleukin-7 may help to restore immune function during HIV infection.

RECENT FINDINGS

Recent studies explored the therapeutic use of interleukin-7 in simian immunodeficiency virus models and in HIV-infected patients. Interleukin-7 can help to restore CD4 T-cell number and function.

SUMMARY

Numerous recent findings highlight the importance of interleukin-7 pathway impairment in the pathogenesis of HIV infection. Notably, interleukin-7 levels increased with advancing CD4 T-cell lymphopenia, whereas interleukin-7 receptor expression is downregulated mainly on CD8 T cells. Therapeutic trials conducted in monkeys and in humans (phase I) have provided evidence on the role of interleukin-7 in thymopoiesis and in restoration of T-cell functions. Interleukin-7 appeared to be well tolerated and to have no deleterious effects on viral load. These results should be confirmed in larger phase I/II studies.

Recombinant IL-7/HGFβ efficiently induces transplantable murine hematopoietic stem cells

Difficulty obtaining sufficient hematopoietic stem cells (HSCs) directly from the donor has limited the clinical use of HSC transplantation. Numerous attempts to stimulate the ex vivo growth of purified HSCs with cytokines and growth factors generally have induced only modest increases in HSC numbers while decreasing their in vivo reconstituting ability. We previously developed a recombinant single-chain form of a naturally occurring murine hybrid cytokine of IL-7 and the β chain of hepatocyte growth factor (rIL-7/HGFβ) that stimulates the in vitro proliferation and/or differentiation of common lymphoid progenitors, pre-pro-B cells, and hematopoietic progenitor cells (day 12 spleen colony-forming units) in cultures of mouse BM. Here we used the rIL-7/HGFβ in culture to induce large numbers of HSCs from multiple cell sources, including unseparated BM cells, purified HSCs, CD45- BM cells, and embryonic stem cells. In each instance, most of the HSCs were in the G0 phase of the cell cycle and exhibited reduced oxidative stress, decreased apoptosis, and increased CXCR4 expression. Furthermore, when injected i.v., these HSCs migrated to BM, self-replicated, provided radioprotection, and established long-term hematopoietic reconstitution. These properties were amplified by injection of rIL-7/HGFβ directly into the BM cavity but not by treatment with rIL-7, rHGF, and/or rHGFβ.

The role of naïve T-cells in HIV-1 pathogenesis: an emerging key player

Functional naïve T-cells are critical for an effective immune response to multiple pathogens. HIV leads to a significant reduction in CD4+ naïve T-cell number and impaired function and there is incomplete recovery following combination antiretroviral therapy (cART). Here we review the basic homeostatic mechanisms that maintain naïve CD4+ T-cells and discuss recent developments in understanding the impact of HIV infection on naïve CD4+ T-cells. Finally we review therapeutic interventions in HIV-infected individuals aimed at specifically enhancing recovery of naïve CD4+ T-cells.

Transforming growth factor-beta1 upregulates the expression of CXC chemokine receptor 4 (CXCR4) in human breast cancer MCF-7 cells

AIM

To investigate whether rhTGF-beta1 or a recombinant vector encoding a fusion protein comprising an extracellular domain of TGF-beta receptor II and an IgG Fc fragment) affects the regulation of CXC chemokine receptor 4 (CXCR4) expression in MCF-7 human breast cancer cells.

METHODS

MCF-7 breast cancer cells were treated with rhTGF-beta1 or transfected with a recombinant vector, pIRES2-EGFP-TbetaRII-Fc. Expression of CXCR4 in these cells was then analyzed at the mRNA and protein levels by quantitative RT-PCR and flow cytometry assay, respectively. A transwell assay was used to measure the chemotactic response of these cells to SDF-1alpha.

RESULTS

CXCR4 mRNA and protein expression were upregulated in TGF-beta1-treated MCF-7 cells. These cells also demonstrated an enhanced chemotactic response to SDF-1alpha. In MCF-7 cells transiently transfected with pIRES2-EGFP-TbetaRII-Fc, a fusion protein named TbetaRII-Fc (approximately 41 kDa) was produced and secreted. In these transfected cells, there was a reduction in CXCR4 expression and in the SDF-1alpha-mediated chemotactic response.

CONCLUSION

TGF-beta1 upregulated CXCR4 expression in MCF-7 cells, which subsequently enhanced the SDF-1alpha-induced chemotactic response. The results suggest a link between TGF-beta1 and CXCR4 expression in MCF-7 human breast cancer cells, which may be one of the mechanisms of TGF-beta1-mediated enhancement of metastatic potential in breast cancer cells.

Idiopathic CD4+ T-cell lymphocytopenia is associated with impaired membrane expression of the chemokine receptor CXCR4

Idiopathic CD4(+) T-cell lymphocytopenia (ICL) is a rare acquired T-cell immunodeficiency of unknown pathogenic basis. Six adults with ICL who developed opportunistic infections were investigated using extensive immunophenotyping analysis and functional evaluation of the chemokine receptor CXCR4. For all 6 patients studied, a profound defect in CXCR4 expression was detected at the surface of CD4(+) T lymphocytes, in association with an abnormal intracellular accumulation of CXCR4 and of its natural ligand, the chemokine CXCL12. For all patients studied, CD4(+) T-cell chemotactic response toward CXCL12 was decreased, whereas sensitivity to CXCL8 was preserved. CXCR4 recovery after ligand-induced endocytosis was impaired in ICL CD4(+) T cells. Upon in vitro addition of interleukin-2 (IL-2), membrane expression of CXCR4 returned to normal levels in 5 of 6 patients, whereas intracellular accumulation of CXCR4 and CXCL12 disappeared. Upon therapeutic administration of IL-2, CD4(+) T-cell count and membrane CXCR4 expression and function improved over time in 3 of 4 patients treated. Therefore, our data indicate that ICL is associated with defective surface expression of CXCR4, which may be reversed by IL-2.

HIV-1 residual viremia correlates with persistent T-cell activation in poor immunological responders to combination antiretroviral therapy

BACKGROUND

The clinical significance and cellular sources of residual human immunodeficiency virus type 1 (HIV-1) production despite suppressive combination antiretroviral therapy (cART) remain unclear and the effect of low-level viremia on T-cell homeostasis is still debated.

METHODOLOGY/PRINCIPAL FINDINGS

We characterized the recently produced residual viruses in the plasma and short-lived blood monocytes of 23 patients with various immunological responses to sustained suppressive cART. We quantified the residual HIV-1 in the plasma below 50 copies/ml, and in the CD14(high) CD16(-) and CD16+ monocyte subsets sorted by flow cytometry, and predicted coreceptor usage by genotyping V3 env sequences. We detected residual viremia in the plasma of 8 of 10 patients with poor CD4+ T-cell reconstitution in response to cART and in only 5 of 13 patients with good CD4+ T-cell reconstitution. CXCR4-using viruses were frequent among the recently produced viruses in the plasma and in the main CD14(high) CD16(-) monocyte subset. Finally, the residual viremia was correlated with persistent CD4+ and CD8+ T-cell activation in patients with poor immune reconstitution.

CONCLUSIONS

Low-level viremia could result from the release of archived viruses from cellular reservoirs and/or from ongoing virus replication in some patients. The compartmentalization of the viruses between the plasma and the blood monocytes suggests at least two origins of residual virus production during effective cART. CXCR4-using viruses might be produced preferentially in patients on cART. Our results also suggest that low-level HIV-1 production in some patients may contribute to persistent immune dysfunction despite cART.

HIV infection impairs CCR7-dependent T-cell chemotaxis independent of CCR7 expression

OBJECTIVES

CCR7, a chemokine receptor expressed at high levels on naive and central memory T cells, is essential for T-cell recirculation into secondary lymphoid organs. We investigated CCR7 expression and chemotactic function in patient T cells, to gain further insights into mechanisms of T-cell dysfunction in HIV infection.

DESIGN AND METHODS

CCR7 expression and function were measured in T-cell subsets of viremic patients (n = 15), efficiently treated patients (n = 12), and healthy blood donors (n = 14). A whole blood assay was developed to measure chemotaxis in unperturbed T cells with physiological chemokine receptor expression levels.

RESULTS

The proportion of CCR7hi T-cell subsets (naive and central memory) was decreased in HIV-infected patients, but the expression of CCR7 within T-cell subsets did not differ from that in healthy controls. In spite of preserved CCR7 expression, CCR7-dependent chemotactic responses were significantly decreased within most T-cell subsets from viremic patients, including naive, central memory, and effector memory CD4 T cells and naive, central memory, and effector CD8 T cells. The chemotaxis defect was only partially corrected in efficiently treated patients. Importantly, chemotaxis to CXCR4, another chemokine receptor involved in T-cell recirculation, was preserved or even increased in T-cell subsets of HIV-infected patients.

CONCLUSION

These findings provide evidence for an impairment of CCR7 function in patient T cells, which may have major consequences on T-cell recirculation. The fact that CXCR4 function was preserved points to a CCR7-specific functional defect rather than a general block in chemotaxis.

Relationship between HIV coreceptor tropism and disease progression in persons with untreated chronic HIV infection

OBJECTIVE

To assess the effect of HIV coreceptor tropism (CRT) on the relative risk of progression to a composite outcome of CD4 count < or =350 cells per microliter, treatment initiation, or death.

METHODS

CRT assays were performed after study closure in baseline samples obtained from enrollees in a prospectively monitored cohort of treatment-naive adults with > or =450 CD4 cells per microliter and > or =1000 HIV-1 RNA copies per milliliter.

RESULTS

Dual/mixed (D/M) and R5 CRT were detected in 32 and 282 patients, respectively. The baseline CD4 count (617 versus 694 cells/microL; P = 0.05) differed in patients with D/M versus R5 CRT. Otherwise, baseline laboratory characteristics were similar.The relative risk of progression to the composite end point was 2.15 (P = 0.002) for D/M versus R5 CRT, 2.07 per 1.0 log10 higher viral load (P < 0.001) and 0.87 per 50 cells per microliter higher CD4 cell count (P < 0.001). The effect of D/M CRT was also significant in separate analyses of time to initiation of antiretroviral therapy or CD4 cell count < or =350 cells per microliter.

CONCLUSIONS

Untreated patients with D/M rather than R5 CRT had a faster rate of disease progression, whether assessed by a composite outcome of time to CD4 count < or =350 cells per microliter, treatment initiation, or death or by separate analyses of time to CD4 count < or =350 cells per microliter or treatment initiation.

Enhanced T cell recovery in HIV-1-infected adults through IL-7 treatment

HIV infection results in CD4+ T cell deficiency, but efficient combination antiretroviral therapy (c-ART) restores T cells and decreases morbidity and mortality. However, immune restoration by c-ART remains variable, and prolonged T cell deficiency remains in a substantial proportion of patients. In a prospective open-label phase I/IIa trial, we evaluated the safety and efficacy of administration of the T cell regulator IL-7. The trial included 13 c-ART-treated HIV-infected patients whose CD4+ cell counts were between 100 and 400 cells/microl and plasma HIV RNA levels were less than 50 copies/ml. Patients received a total of 8 subcutaneous injections of 2 different doses of recombinant human IL-7 (rhIL-7; 3 or 10 microg/kg) 3 times per week over a 16-day period. rhIL-7 was well tolerated and induced a sustained increase of naive and central memory CD4+ and CD8+ T cells. In the highest dose group, 4 patients experienced transient increases in viral replication. However, functional assays showed that the expanded T cells responded to HIV antigen by producing IFN-gamma and/or IL-2. In conclusion, in lymphopenic HIV-infected patients, rhIL-7 therapy induced substantial functional and quantitative changes in T cells for 48 weeks. Therefore, patients may benefit from intermittent therapy with IL-7 in combination with c-ART.

Chemokine receptor CXCR4-prognostic factor for gastrointestinal tumors

To review the implication of CXCR4 for gastrointestinal cancer, a “Pubmed” analysis was performed in order to evaluate the relevance of CXCR4 and its ligands for gastrointestinal cancers. Search terms applied were “cancer, malignoma, esophageal, gastric, colon, colorectal, hepatic, pancreatic, CXCR4, SDF-1α, and SDF-1β”. CXCR4 expression correlated with dissemination of diverse gastrointestinal malignomas. The CXCR4 ligand SDF-1α might act as “chemorepellent” while SDF-1β might act as "chemorepellent" for CTLs, inducing tumor rejection. The paracrine expression of SDF-1α was furthermore closely associated with neoangiogenesis. CXCR4 and its ligands influence the dissemination, immune rejection, and neoangiogenesis of human gastrointestinal cancers. Inhibition of CXCR4 might be an interesting therapeutic option.

Immunopathogenesis of feline immunodeficiency virus infection in the fetal and neonatal cat

The global incidence of pediatric HIV infection is estimated at 2.3 million children, most acquiring the infection from their mothers in utero, peripartum, or postpartum. Pediatric HIV infection typically causes a rapidly progressive disease when compared with adult infection, due in part to the profound susceptibility of the neonatal thymus to productive infection or degenerative changes. Failed production of naive T-lymphocytes further limits the success of antiviral therapy to restore immunologic function. In this review, we explore the use of feline immunodeficiency virus (FIV) infection of domestic cats as an animal model for pediatric HIV infection. Cats infected with FIV represent the smallest host of a naturally occurring lentivirus, and the immunodeficiency syndrome elicited by FIV infection is similar to that of HIV-AIDS. The feline-FIV model uniquely reproduces several key aspects of immunosuppressive lentivirus infection of the thymus, allowing investigators to define viral determinants of pathogenicity, influence of host age on disease outcome, and therapeutic strategies to restore thymus function.

Naive T-cell depletion related to infection by X4 human immunodeficiency virus type 1 in poor immunological responders to highly active antiretroviral therapy

The reasons for poor CD4+ T-cell recovery in some human immunodeficiency virus (HIV)-infected subjects despite effective highly active antiretroviral therapy (HAART) remain unclear. We recently reported that CXCR4-using (X4) HIV-1 could be gradually selected in cellular reservoirs during sustained HAART. Because of the differential expression of HIV-1 coreceptors CCR5 and CXCR4 on distinct T-cell subsets, the residual replication of R5 and X4 viruses could have different impacts on T-cell homeostasis during immune reconstitution on HAART. We examined this hypothesis and the mechanisms of CD4+ T-cell restoration by comparing the virological and immunological features of 15 poor and 15 good immunological responders to HAART. We found a high frequency of X4 viruses in the poor immunological responders. But the levels of intrathymic proliferation of the two groups were similar regardless of whether they were infected by R5 or X4 virus. The frequency of recent thymic emigrants in the poor immunological responders was also similar to that found in the good immunological responders, despite their reduced numbers of naïve CD4+ T cells. Our data, rather, suggest that the naïve T-cell compartment is drained by a high rate of mature naïve cell loss in the periphery due to bystander apoptosis or activation-induced differentiation. X4 viruses could play a role in the depletion of naïve T cells in poor immunological responders to HAART by triggering persistent T-cell activation and bystander apoptosis via gp120-CXCR4 interactions.

Infection of CD127+ (interleukin-7 receptor+) CD4+ cells and overexpression of CTLA-4 are linked to loss of antigen-specific CD4 T cells during primary human immunodeficiency virus type 1 infection

We recently found that human immunodeficiency virus (HIV)-specific CD4+ T cells express coreceptor CCR5 and activation antigen CD38 during early primary HIV-1 infection (PHI) but then rapidly disappear from the circulation. This cell loss may be due to susceptibility to infection with HIV-1 but could also be due to inappropriate apoptosis, an expansion of T regulatory cells, trafficking out of the circulation, or dysfunction. We purified CD38+++CD4+ T cells from peripheral blood mononuclear cells, measured their level of HIV-1 DNA by PCR, and found that about 10% of this population was infected. However, a small subset of HIV-specific CD4+) T cells also expressed CD127, a marker of long-term memory cells. Purified CD127+CD4+ lymphocytes contained fivefold more copies of HIV-1 DNA per cell than did CD127-negative CD4+ cells, suggesting preferential infection of long-term memory cells. We observed no apoptosis of antigen-specific CD4+ T cells in vitro and only a small increase in CD45RO+CD25+CD127dimCD4+ T regulatory cells during PHI. However, 40% of CCR5+CD38+++ CD4+ T cells expressed gut-homing integrins, suggesting trafficking through gut-associated lymphoid tissue (GALT). Furthermore, 80% of HIV-specific CD4+ T cells expressed high levels of the negative regulator CTLA-4 in response to antigen stimulation in vitro, which was probably contributing to their inability to produce interleukin-2 and proliferate. Taken together, the loss of HIV-specific CD4+ T cells is associated with a combination of an infection of CCR5+ CD127+ memory CD4+ T cells, possibly in GALT, and a high expression of the inhibitory receptor CTLA-4.

HIV interactions with dendritic cells: has our focus been too narrow?

Although few in number, dendritic cells (DCs) are heterogeneous, ubiquitous, and are crucial for protection against pathogens. In this review, the different DC subpopulations have been described and aspects of DC biology are discussed. DCs are important, not only in the pathogenesis of HIV, but also in the generation of anti-HIV immune responses. This review describes the roles that DC are thought to play in HIV pathogenesis, including uptake and transport of virus. We have also discussed the effects that the virus exerts on DCs such as infection and dysfunction. Then we proceed to focus on DC subsets in different organs and show how widespread the effects of HIV are on DC populations. It is clear that the small number of studies on tissue-derived DCs limits current research into the pathogenesis of HIV.

The thymus is a common target organ in infectious diseases

Infectious disease immunology has largely focused on the effector immune response, changes in the blood and peripheral lymphoid organs of infected individuals, and vaccine development. Studies of the thymus in infected individuals have been neglected, although this is progressively changing. The thymus is a primary lymphoid organ, able to generate mature T cells that eventually colonize secondary lymphoid organs, and is therefore essential for peripheral T cell renewal. Recent data show that normal thymocyte development and export can be altered as a result of an infectious disease. One common feature is the severe atrophy of the infected organ, mainly due to the apoptosis-related depletion of immature CD4⁺CD8⁺ thymocytes. Additionally, thymocyte proliferation is frequently diminished. The microenvironmental compartment of the thymus is also affected, particularly in acute infectious diseases, with a densification of the epithelial network and an increase in the deposition of extracellular matrix. In the murine model of Chagas disease, intrathymic chemokine production is also enhanced, and thymocytes from Trypanosoma cruzi-infected mice exhibit greater numbers of cell migration-related receptors for chemokines and extracellular matrix, as well as increased migratory responses to the corresponding ligands. This profile is correlated with the appearance of potentially autoreactive thymus-derived immature CD4⁺CD8⁺ T cells in peripheral organs of infected animals. A variety of infectious agents—including viruses, protozoa, and fungi—invade the thymus, raising the hypothesis of the generation of central immunological tolerance for at least some of the infectious agent-derived antigens. It seems clear that the thymus is targeted in a variety of infections, and that such targeting may have consequences on the behavior of peripheral T lymphocytes. In this context, thymus-centered immunotherapeutic approaches potentially represent a new tool for the treatment of severe infectious diseases.

Effects of human interleukin 7 on HIV-1 replication in monocyte-derived human macrophages

Interleukin 7 (IL-7) contributes to development and proliferation of T cells. We investigated the effect of IL-7 on HIV-1 infected monocyte-derived human macrophages. IL-7 treatment of macrophages at a concentration of 10 ng/ml reduced replication of the R5 HIV-1 strain by approximately 50%. Meanwhile, HIV-1-infected macrophages themselves could excrete approximately 20% more IL-7 than uninfected macrophages. These results suggest that IL-7 could be used as a therapeutic modality to recover CD4 T cells.

The HIV-1 clade C promoter is particularly well adapted to replication in the gut in primary infection

OBJECTIVE

Coinfection of rhesus macaques with human/simian immunodeficiency virus chimeras harbouring the minimal core-promoter/enhancer elements from HIV-1 clade B, C and E viral prototypes (STR-B, STR-C and STR-E) revealed a remarkable dichotomy in terms of spatio-temporal viral replication. The clade C chimera (STR-C) predominated in primary infection. The present study was aimed at identifying the origin of STR-C plasma viraemia at this infection phase.

DESIGN

By competing isogenic viruses differing only in their promoters, it was possible to identify subtle phenotypical differences in viral replication kinetics and compartmentalization in vivo.

METHODS

Two rhesus macaques were coinfected by the three STR chimeras and the relative colonization of different compartments, particularly blood and stool, was determined for each chimera. Moreover, growth competition experiments in thymic histocultures enriched in interleukin (IL)-7 were performed and relative percentages of chimeras were estimated in supernatants and thymocytes lysates at different time points.

RESULTS

It is demonstrated here that at the peak of primary infection, preferential replication of STR-C was supported by the gut-associated lymphoid tissue (GALT), an IL-7 rich microenvironment. This was shown by the correlation of the RNA viral genotype in blood and stools, compartments directly draining virions from the GALT. Thymic histocultures confirmed that replication of STR-C is particularly susceptible to this cytokine, compared to its STR-B and STR-E counterparts.

CONCLUSIONS

These data show that the GALT cytokine network may well favour HIV-1 clade C replication during primary infection. This could result in enhanced transmission.

IL-7 induces immunological improvement in SIV-infected rhesus macaques under antiviral therapy

Despite efficient antiretroviral therapy (ART), CD4+ T cell counts often remain low in HIV-1-infected patients. This has led to IL-7, a crucial cytokine involved in both thymopoiesis and peripheral T cell homeostasis, being suggested as an additional therapeutic strategy. We investigated whether recombinant simian IL-7-treatment enhanced the T cell renewal initiated by ART in rhesus macaques chronically infected with SIVmac251. Six macaques in the early chronic phase of SIV infection received antiretroviral treatment. Four macaques also received a 3-wk course of IL-7 injections. Viral load was unaffected by IL-7 treatment. IL-7 treatment increased the number of circulating CD4+ and CD8+ memory T cells expressing activation (HLA-DR+, CD25+) and proliferation (Ki-67+) markers. It also increased naive (CD45RAbrightCD62L+) T cell counts by peripheral proliferation and enhanced de novo thymic production. The studied parameters returned to pretreatment values by day 29 after the initiation of treatment, concomitantly to the appearance of anti-IL-7 neutralizing Abs, supporting the need for a nonimmunogenic molecule for human treatment. Thus, IL-7, which increases T cell memory and de novo renewal of naive T cells may have additional benefits in HIV-infected patients receiving ART.

Differential susceptibility of human thymic dendritic cell subsets to X4 and R5 HIV-1 infection

OBJECTIVES

Human thymus can be infected by HIV-1 with potential consequences on immune regeneration and homeostasis. We previously showed that CD4 thymocytes preferentially replicate CXCR4 tropic (X4) HIV-1 dependently on interleukin (IL)-7. Here we addressed the susceptibility of thymic dendritic cells (DC) to HIV-1 infection.

METHODS

We investigated the replication ability of CXCR4 or CCR5 (R5) tropic HIV-1 in thymic micro-explants as well as in isolated thymic CD11clowCD14- DC, CD11chighCD14+ DC and plasmacytoid DC subsets.

RESULTS

Thymic tissue was productively infected by both X4 and R5 viruses. However, X4 but not R5 HIV-1 replication was enhanced by IL-7 in thymic micro-explants, suggesting that R5 virus replication occurred in cells other than thymocytes. Indeed, we found that R5 HIV-1 replicated efficiently in DC isolated from thymic tissue. The replicative capacity of X4 and R5 viruses differed according to the different DC subsets. R5 but not X4 HIV-1 efficiently replicated in CD11chighCD14+ DC. In contrast, no HIV-1 replication was detected in CD11clowCD14- DC. Both X4 and R5 viruses efficiently replicated in plasmacytoid DC, which secreted interferon-alpha upon HIV-1 exposure. Productive HIV-1 infection also caused DC loss, consistent with different permissivity of each DC subset.

CONCLUSIONS

Thymic DC sustain high levels of HIV-1 replication. DC might thus be the first target for R5 HIV-1 infection of thymus, acting as a Trojan horse for HIV-1 spread to thymocytes. Furthermore, DC death induced by HIV-1 infection may affect thymopoiesis.

Uncoupled anti-HIV and immune-enhancing effects when combining IFN-alpha and IL-7

Cytokine-based therapies have been examined for purging viral reservoirs and immunomodulation in HIV infection. However, single cytokines did not result in either HIV eradication or an efficient HIV-specific immune response. We hypothesize that cytokines with distinct biologic effects need to be combined for immunotherapy of HIV infection. In this study, we investigated the anti-HIV activity and immune-enhancing effects of the combination of IFN-alpha and IL-7. In human lymphocyte aggregate cultures infected ex vivo with the X4 HIV strain NL4-3, IFN-alpha/IL-7 potently inhibited HIV replication and preserved CD4(+) T cells, probably by up-regulating Bcl-2. IFN-alpha/IL-7 also strongly inhibited R5 HIV replication. Furthermore, in allogeneic MLRs, IFN-alpha/IL-7 increased T cell proliferation and IFN-gamma production. IFN-alpha alone also had strong anti-HIV activity, but neither preserved CD4(+) T cells nor increased T cell responses in MLRs. IL-7 alone maintained T cells and enhanced T cell activation in MLRs, but only moderately inhibited or increased HIV replication. Thus, coadministration of IFN-alpha/IL-7 combines the potent anti-HIV activity of IFN-alpha with the beneficial effects of IL-7 on T cell survival and function. We speculate that IFN-alpha will block viral replication, activate APCs, and up-regulate MHC molecules, thus allowing IL-7 to display its effects for generating an efficient immune response. In this scenario, the known reactivation of latent HIV by IL-7 may be advantageous.

Thymic function in HIV infection

Current models hold that CD4+ depletion occurs as a result of direct and indirect effects of HIV, which both kill peripheral CD4+ cells and prevent adequate regeneration. Although age-associated involution diminishes thymic reserve and HIV is clearly thymotoxic, clinical trials have nonetheless shown that large proportions of patients who sustain adequate control of viral replication with highly active antiretroviral therapy (HAART) will demonstrate some evidence for thymic-dependent immune reconstitution, which is associated with improved immune competence. Furthermore, patients with insufficient or absent immune reconstitution following HAART generally lack evidence for thymopoiesis. Current studies are focused on improving our understanding of the causes for thymic failure in HIV infection. Recent work has demonstrated that some HIV strains, especially those that are CXCR4 trophic, are more thymotoxic and may contribute to irreversible thymic damage in this population.

Role of antiretroviral therapies in mucocutaneous manifestations in HIV-infected children over a period of two decades

BACKGROUND

Human immunodeficiency virus (HIV) infection causes a severe cellular immunodeficiency, which results in a greater susceptibility to infectious, inflammatory and malignant conditions. Among these, pathologies of the skin seem to be those most frequently observed in HIV+ patients. However, there are few reports on how antiretroviral therapy affects skin disorders in HIV-infected children.

OBJECTIVE

To study the incidence and prevalence of skin disorders in a cohort of HIV-infected children, in relation to the antiviral therapy [nontreated, monotherapy, combined therapy and highly active antiretroviral therapy (HAART)] received, and their impact on immunological and virological markers. The treatments were those available in different calendar periods in the history of antiviral treatment.

MATERIALS AND METHODS

A retrospective, observational study in a cohort of 210 HIV-infected children was carried out. These children were followed up every 3 months throughout 22 years. The viral load (HIV RNA copies mL(-1)) was quantified using reverse transcriptase-polymerase chain reaction and the viral phenotype of HIV-1 isolates was determined by in vitro culture. T-lymphocyte subsets in peripheral blood were quantified by flow cytometry.

RESULTS

Mucocutaneous manifestations were diagnosed in 17% of the untreated infected children. Of the treated children in different treatment periods, 22% in the monotherapy period, 25% in the combined therapy period but only 10% on HAART had some type of mucocutaneous manifestation, concordant with a higher number of CD4+ T cells, a lower viral load and less cytopathic virus in the last group. Mucocutaneous manifestations of infectious aetiology were most frequently observed; they were detected in 13% of the children during the first calendar period (untreated children), 16% during the second and third periods (monotherapy and combined therapy) and only 5% in the last period (HAART). Interestingly, syncytium-inducing virus was present in 69% of all children with mucocutaneous manifestations of infectious aetiology.

CONCLUSION

Only in the last calendar period (HAART) was a significant decrease observed in the prevalence of mucocutaneous manifestations with HIV infection associated with an increase in CD4+ T cells. In addition, we found a strong association between children who had mucocutaneous manifestations with an infectious aetiology and a more cytopathic (X4/SI) viral phenotype.

Immunological changes after highly active antiretroviral therapy with lopinavir-ritonavir in heavily pretreated HIV-infected children

We evaluated the effect of salvage antiretroviral therapy with lopinavir/ritonavir (LPV/r) on the immune system of heavily antiretroviral pretreated HIV-infected children. We carried out a longitudinal study in 20 antiretroviral experienced HIV-infected children to determine the changes in several immunological parameters (T cell subsets, thymic function) every 3 months during 18 months of follow-up on salvage therapy with LPV/r. Statistical analyses were performed with the Wilcoxon test, taking as a reference the basal value at the entry in the study. HIV-infected children showed an increase of CD4+ T cells, a decrease in CD8+ T cells, and an increase in T cell rearrangement excision circle (TRECs) levels. The percentage of HIV children with undetectable viral load (VL < or = 400 copies/ml) increased significantly (p = 0.007) and the percentage with SI viral phenotype decreased significantly (p = 0.002) at the end of the study. Thus, the viral phenotype changed to NSI/R5 after salvage therapy with LPV/r. Interestingly, we observed a significant decrease of memory (CD4+ CD45RO+) and a moderate decrease of activated (CD4+ HLA-DR+, CD4+ HLA-DR+CD38, CD4+, CD45RO+HLA-DR+) CD4+ T cells during the follow-up. On the other hand, memory (CD8+ CD45RO+ and CD8+ CD45RO+CD38+), activated (CD8+ HLA-DR+CD38+, CD8+ HLA-DR+, CD8+ CD38+), and effector (CD8+ CD57+, CD8+ CD28(-)CD57+) CD8+ T cells had a very significant decrease during follow-up. Our data indicate an immune system reconstitution in heavily pretreated HIV-infected children in response to salvage therapy with LPV/r as a consequence of a decrease in immune system activation and an increase in thymic function.

Analysis of Chemokine and Cytokine Expression in Patients with HIV and GB Virus Type C Coinfection

BACKGROUND

Plasma levels of several chemokines and cytokines were evaluated in a cohort of 161 human immunodeficiency virus (HIV)positive patients to shed light on a clinically relevant mechanism that would explain the putative beneficial effect of GB virus type C (GBV-C) coinfection.

METHODS

Markers for GBV-C infection were assessed in plasma samples. The syncitium-inducing (SI) capacity of isolated virus from each patient was determined in MT-2 cells. Plasma cytokine and chemokine levels were quantified with use of a commercial enzyme-linked immunosorbent assay.

RESULTS

GBV-C viremia was found in 44 (27%) of 161 patients, and anti-E2 antibodies were found in 18 (21%) of 87. In contrast to the findings of ex vivo analysis, no statistically significant differences were observed in levels of CCL5, stromal cell-derived factor 1, interleukin-7, and tumor necrosis factor-alpha in plasma of patients with or without GBV-C viremia. Seventy-two (45%) and 89 (55%) of our patients harbored SI and non-SI (NSI) strains, respectively. GBV-C viremia was less prevalent among patients with SI strains (13 [18%] of 72) than among patients with NSI strains (30 [34%] of 89; P = .6). Of interest, coinfected patients with SI strains had significantly higher CD4+ T cell values than did patients who were not coinfected.

CONCLUSIONS

Our results suggest that GBV-C infection does not appear to influence the expression of the cytokines and chemokines analyzed herein in a clinically relevant context. Alternative explanations for the elevated levels of HIV-inhibitory chemokines are needed to explain the putative beneficial effect of GBV-C.

Transforming growth factor-beta1 increases CXCR4 expression, stromal-derived factor-1alpha-stimulated signalling and human immunodeficiency virus-1 entry in human monocyte-derived macrophages

Stromal-derived factor-1 (SDF-1/CXCL12) and its receptor CXCR4 play crucial roles in leukocyte migration and activation, as well as embryogenesis, angiogenesis, cancer and viral pathogenesis. CXCR4 is one of the major human immunodeficiency virus-1 (HIV-1) coreceptors on macrophages. In many tissues macrophages are one of the predominant cell types infected by HIV-1 and act as a reservoir for persistent infection and viral dissemination. In patients infected by HIV-1, blood and tissue levels of transforming growth factor-beta1 (TGF-beta1) are increased. The purpose of this study was to evaluate the effects of TGF-beta1 on CXCR4 expression and function in primary human monocyte-derived macrophages (MDMs) and rat microglia. TGF-beta1 up-regulated CXCR4 and enhanced SDF-1alpha-stimulated ERK1,2 phosphorylation in these cells. The increased CXCR4 expression in human MDMs resulted in increased susceptibility of the cells to entry by dual-tropic CXCR4-using HIV-1 (D-X4). In contrast, TGF-beta1 failed to increase CCR5 expression or infection by a CCR5-using virus in MDMs. Our data demonstrate that TGF-beta1 enhances macrophage responsiveness to SDF-1alpha stimulation and susceptibility to HIV-1 by selectively increasing expression of CXCR4. The results suggest that increased expression of CXCR4 on macrophages may contribute to the emergence of dual-tropic X4 viral variants at later stages of HIV-1 infection.

R5 to X4 Switch of the Predominant HIV-1 Population in Cellular Reservoirs During Effective Highly Active Antiretroviral Therapy

HIV-1 coreceptor usage plays a critical role for virus tropism and pathogenesis. A switch from CCR5 to CXCR4-using viruses can occur in the natural course of infection and correlates with subsequent disease progression. To investigate whether HIV-1 genetic evolution might lead to changes in virus coreceptor usage during highly active antiretroviral therapy (HAART), a longitudinal genotypic analysis of the virus found in cellular reservoirs was conducted in 32 patients with undetectable viral loads on HAART for 5 years. The genotype of the 3rd variable region of the env gene predicting coreceptor usage was retrospectively determined in the plasma or in peripheral blood mononuclear cells (PBMC) at baseline and then in PBMCs at months 30 and 60 of HAART. There was a switch from R5 to X4 variants in 11 of the 23 patients who harbored a majority virus population of R5 variants at baseline. X4 variants remained predominant in the 9 patients who harbored mainly X4 variants at baseline. The patients harboring predominantly X4 variants during HAART, either from baseline or after an R5 to X4 switch, tended to have lower CD4+ T-cell counts on HAART than did patients harboring continuously a majority population of R5 variants. These results suggest that potent antiretroviral therapy produces the conditions necessary for the gradual emergence of X4 variants in cellular reservoirs.

Interleukin 7 increases human immunodeficiency virus type 1 LAI-mediated Fas-induced T-cell death

Fas-mediated T-cell death is known to occur during human immunodeficiency virus (HIV) infection. In this study, we found that HIV type 1 LAI (HIV-1(LAI)) primes CD8(+) T cells from healthy donors for apoptosis, which occurs after Fas ligation. This effect is counteracted by a broad caspase inhibitor (zVAD-fmk). Fas-mediated cell death does not depend on CD8(+) T-cell infection, because it occurred in the presence of reverse transcriptase inhibitors. However, purified CD8(+) T cells are sensitive to Fas only in the presence of soluble CD4. Finally, we found that interleukin 7 (IL-7) increases Fas-mediated CD4(+) and CD8(+) T-cell death induced by HIV-1(LAI). Since high levels of IL-7 are a marker of poor prognosis during HIV infection, our data suggest that enhancement of Fas-mediated T-cell death by HIV-1(LAI) and IL-7 is one of the mechanisms involved in progression to AIDS.

Homeostatic role of IL-7 in HIV-1 infected children on HAART: association with immunological and virological parameters

AIM

To investigate the role of IL-7 in HIV-infected children on highly active antiretroviral therapy (HAART) and its association with laboratory parameters related to disease progression.

PATIENTS AND METHODS

A cross-sectional study in 31 vertically HIV-infected children (median age 8.4 y) treated with HAART, and a longitudinal study in four of those same children was carried out. In both studies, viral load, CD4+ T-cell counts, thymic production of T cells by TCR rearrangement excision circles (TRECs), IL-7 plasma levels and viral phenotype were determined.

RESULTS

IL-7 levels were higher in HIV-infected children than in age-matched, uninfected controls. In addition, HIV children with CD4+ T cells between 200 and 500 T cells/mm3 had higher IL-7 levels and lower TREC values than HIV-infected children with CD4+ T cells >500 T cells/mm3. IL-7 levels were higher in children with syncytium-inducing (SI) phenotype than in those with non-syncytium-inducing (NSI) variants. During the follow-up of four HIV children, the decrease in viral load after HAART was always associated with a recovery of CD4+ T cells and TRECs, which was followed by a decrease in IL-7 returning to the levels present prior to the drop in CD4+ T cells. The four HIV-infected children had SI/X4 isolates in PBMC before HAART, and the viral phenotype switched to NSI/R5 after HAART.

CONCLUSION

Our data suggest that IL-7 plays a key role in the maintenance of T-cell homeostasis in HIV-infected children on HAART, both through peripheral expansion and through a thymus-dependent mechanism.

Role of cytokines and chemokines in the regulation of innate immunity and HIV infection

The earliest defense against microbial infection is represented by the responses of the innate (or natural) immune system, that also profoundly regulates the adaptive (or acquired) T- and B-cell immune responses. Activation of the innate immune system is primed by microbial invasion in response to conserved structures present in large groups of microorganisms (LPS, peptidoglycan, double-stranded RNA), and is finely tuned by different cell types (including dendritic cells, macrophages, natural killer cells, natural killer T cells, and gammadelta T cells). In addition, several soluble factors (complement components, defensins, mannose-binding lectins, interferons, cytokines and chemokines) can play a major role in the regulation of both the innate and adaptive immunity. In this review, we will briefly overview the regulation of some cellular subsets of the innate immune system particularly involved in human immunodeficiency virus (HIV) infection and then focus our attention on those cytokines and chemokines whose levels of expression are more profoundly affected by HIV infection and that, conversely, can modulate virus infection and replication.

CXCR4 mutations in WHIM syndrome: a misguided immune system?

Chemokines and their receptors are key molecules in the development and function of immune cell populations and the organization of lymphoid organs. Despite their central role in immunologic function, genetic studies exploring the intersection of chemokines or their receptors and human health have revealed few associations of unambiguous significance. The best-characterized examples have revealed striking selective advantage conferred by loss of receptors used as portals of entry by pathogens. Recently, mutations in the CXCR4 chemokine receptor gene were identified in a dominantly inherited immunodeficiency disease, WHIM syndrome. Genetic and biochemical evidences suggest that the loss of the receptor cytoplasmic tail domain results in aberrant signaling. Analyses of mutant cell responses to the receptor ligand CXCL12 have revealed enhanced chemotaxis, confirming the gain-of-function effect of the truncation mutations. The clinical features and potential mechanism of immunodeficiency in WHIM syndrome patients are discussed in this review.

R5 human immunodeficiency virus type 1 infection of fetal thymic organ culture induces cytokine and CCR5 expression

Late-stage CCR5 tropic human immunodeficiency virus type 1 (HIV-1) isolates (R5 HIV-1) can deplete nearly all CD4+ thymocytes from human thymus/liver grafts, despite the fact that fewer than 5% of these cells express CCR5. To resolve this paradox, we studied the replication and cytopathic effects (CPE) of late-stage R5 HIV-1 biological clones from two progressors and two long-term nonprogressors (LTNP) in fetal thymic organ culture (FTOC) with and without added cytokines. We found that R5 HIV-1 clones from progressors but not LTNP were cytopathic in untreated FTOC. Moreover, R5 HIV-1 clones from progressors replicated to higher levels than LTNP-derived R5 HIV-1 clones in this system. In contrast, when FTOC was maintained in the presence of interleukin 2 (IL-2), IL-4, and IL-7, both progressor and LTNP clones exhibited similar replication and CPE, which were equal to or greater than the levels achieved by progressor-derived R5 HIV-1 clones in untreated FTOC. This finding was likely due to IL-2-induced CCR5 expression on CD4+ thymocytes in FTOC. R5 HIV-1 clones showed greater pathogenesis for CCR5+ cells but also showed evidence of CPE on CCR5- cells. Furthermore, infection of FTOC by R5 HIV-1 induced IL-10 and transforming growth factor beta (TGF-beta) expression. Both IL-10 and TGF-beta in turn induced CCR5 expression in FTOC. Induction of CCR5 expression via cytokine induction by R5 HIV-1 infection of CCR5+ thymocytes likely permitted further viral replication in newly CCR5+ thymocytes. CCR5 expression, therefore, is a key determinant of pathogenesis of R5 HIV-1 in FTOC.

Thymic volume is associated independently with the magnitude of short- and long-term repopulation of CD4+ T cells in HIV-infected adults after highly active antiretroviral therapy (HAART)

Age is one of the main factors involved in the rapidity and the magnitude of CD4(+) T cell repopulation in human immunodeficiency virus (HIV)-infected patients on highly active antiretroviral treatment (HAART). Improved thymic function has been suggested as the main factor associated with CD4(+) T cell restoration after HAART. This work was undertaken to determine, among host factors, the predictor variable at baseline involved in the magnitude of short- and long-term recovery of CD4(+) T cells after HAART. HIV-RNA levels and CD4(+) T cell numbers were determined in 54 HIV-infected adults at baseline and at weeks 4, 12, 48 and 96 after HAART. T cell subpopulations were determined by flow cytometry, thymic volume by computed tomography, T cell receptor excision circle (TREC)-bearing cells by quantitative polymerase chian reaction (PCR) and interleukin (IL)-7 levels by enzyme linked immunosorbent assay at baseline. The phenotype of patients' isolates was determined by infecting GHOST cells expressing CCR5 and CXCR4. The possible interference of phenotype with thymic function was also analysed. Baseline thymic volume was associated independently with the magnitude of short- and long-term recovery of CD4(+) T cells after HAART, despite the patients' viral phenotype. The measurement of thymic volume before therapy may predict the magnitude of T cell increase. This result could have important clinical implications not only in HIV-infected patients, but also in other scenarios of T cell depletion such as bone marrow transplantation and chemotherapy.