Human immunodeficiency virus inhibits multilineage hematopoiesis in vivo

Contrasting mechanistic susceptibilities of hematopoietic and endothelial stem-progenitor cells in respective pathogeneses of HIV-1 and SARS-CoV-2 infections

The multitude of cellular types can be expected to behave differently when receiving invading pathogens such as mammalian viruses. The nature-dictated causes for such intrinsic cellular diversity become the criteria for the emergence of specific virus-receptor interactions on that particular host cellular surface, in order to accommodate contact with various other living entities whether desirable to the host or not. At present, we are presented with an example of two contrasting behaviours wherein the well-known HIV-1 and the more recently emergent SARS-CoV-2 cause adverse consequences to the differentiation and functions of progenitor stem cells. These include the two different downstream multipotent CD34+ hematopoietic (HSPC) and CD133+ endothelial (ESPC) stem-progenitor cells of their common pluripotent hemangioblast precursors. The two viruses target the respective endothelial and hematopoietic stem-progenitor cells to thrive upon the relevant host cellular surrounded stromal microenvironments by adopting reciprocally-driven mechanistic routes, which incidentally cause pathogenesis either directly of ESPC (SARS-CoV-2), or indirectly of HSPC (HIV-1). HIV-1 utilizes the CD4+ T-lymphocyte receptor thereby advancing pathogenesis indirectly to the CD34+ HSPC. SARS-CoV-2 directly targets the CD133+ ESPC via ACE2 receptor causing cytokine storms of the CD4+ T-lymphocytes. In this manner, these two viruses cause and extend their damage to the other cellular sub/types coexisting in the host cellular microenvironments. The infected individuals require clinical interventions that are efficacious to prevent cellular dysfunction and ultimate cell depletion or death. We infer from these viruses mediated pathogeneses mechanisms a potential common origin of microRNA molecular therapies to address cellular dysfunctions and prevent cell loss.

HIV-1 Infection of Long-Lived Hematopoietic Precursors In Vitro and In Vivo

Latent reservoirs in human-immunodeficiency-virus-1 (HIV-1)-infected individuals represent a major obstacle in finding a cure for HIV-1. Hematopoietic stem and progenitor cells (HSPCs) have been described as potential HIV-1 targets, but their roles as HIV-1 reservoirs remain controversial. Here we provide additional evidence for the susceptibility of several distinct HSPC subpopulations to HIV-1 infection in vitro and in vivo. In vitro infection experiments of HSPCs were performed with different HIV-1 Env-pseudotyped lentiviral particles and with replication-competent HIV-1. Low-level infection/transduction of HSPCs, including hematopoietic stem cells (HSCs) and multipotent progenitors (MPP), was observed, preferentially via CXCR4, but also via CCR5-mediated entry. Multi-lineage colony formation in methylcellulose assays and repetitive replating of transduced cells provided functional proof of susceptibility of primitive HSPCs to HIV-1 infection. Further, the access to bone marrow samples from HIV-positive individuals facilitated the detection of HIV-1 gag cDNA copies in CD34+ cells from eight (out of eleven) individuals, with at least six of them infected with CCR5-tropic HIV-1 strains. In summary, our data confirm that primitive HSPC subpopulations are susceptible to CXCR4- and CCR5-mediated HIV-1 infection in vitro and in vivo, which qualifies these cells to contribute to the HIV-1 reservoir in patients.

HIV-1LAI Nef blocks the development of hematopoietic stem/progenitor cells into myeloid-erythroid lineage cells

Background

A variety of hematopoietic abnormalities are commonly seen in human immunodeficiency virus-1 (HIV-1) infected individuals despite antiviral therapy, but the underlying mechanism remains elusive. Nef plays an important role in HIV-1 induced T cell loss and disease progression, but it is not known whether Nef participates in other hematopoietic abnormalities associated with infection.

Results

In the current study we investigated the influence of HIV-1_LAI Nef (LAI Nef) on the development of hematopoietic stem/progenitor cells (HSPCs) into myeloid-erythroid lineage cells, and found that nef expression in HSPCs blocked their differentiation both in vitro and in humanized mice reconstituted with nef-expressing HSPCs.

Conclusions

Our novel findings demonstrate LAI Nef compromised the development of myeloid-erythroid lineage cells, and therapeutics targeting Nef would be promising in correcting HIV-1 associated hematopoietic abnormalities.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13062-021-00317-3.

HIV-1LAI Nef blocks the development of hematopoietic stem/progenitor cells into T lymphoid cells

OBJECTIVE

Despite successful antiviral therapy, the recovery of CD4+ T cells may not be complete in certain HIV-1-infected individuals. In our previous work with humanized mice infected with CXCR4-tropic HIV-1LAI (LAI), viral protein Nef was found the major factor determining rapid loss of both CD4+ T cells and CD4+CD8+ thymocytes but its effect on early T-cell development is unknown. The objective of this study is to investigate the influence of LAI Nef on the development of hematopoietic stem/progenitor cells (HSPCs) into T lymphoid cells.

DESIGN

HSPC-OP9-DL1 cell co-culture and humanized mouse model was used to investigate the objective of our study in vitro and in vivo. RNA-seq was exploited to study the change of gene expression signature after nef expression in HSPCs.

RESULTS

Nef expression in HSPCs was found to block their development into T lymphoid cells both in vitro and in the mice reconstituted with nef-expressing HSPCs derived from human cord blood. More surprisingly, in humanized mice nef expression preferentially suppressed the production of CD4+ T cells. This developmental defect was not the result of CD34+ cell loss. RNA-seq analysis revealed that Nef affected the expression of 176 genes in HSPCs, including those involved in tumor necrosis factor, Toll-like receptor, and nucleotide-binding oligomerization domain-like receptor signaling pathways that are important for hematopoietic cell development.

CONCLUSION

Our results demonstrate that Nef compromises the development of HSPCs into T lymphoid cells, especially CD4+ T cells. This observation suggests that therapeutics targeting Nef may correct HIV-1-associated hematopoietic abnormalities, especially defects in T-cell development.

Hematopoietic Stem/Progenitor Cells and the Pathogenesis of HIV/AIDS

The interaction between human immunodeficiency virus (HIV) and hematopoietic stem/progenitor cells (HSPCs) has been of great interest. However, it remains unclear whether HSPCs can act as viral reservoirs. Many studies have reported the presence of latently infected HSPCs in the bone marrow of HIV-infected patients, whereas many other investigators have reported negative results. Hence, further evidence is required to elucidate this controversy. The other arm of HSPC investigations of HIV infection involves dynamics analysis in the early and late stages of infection to understand the impact on the pathogenesis of acquired immunodeficiency syndrome. Several recent studies have suggested reduced amounts and/or functional impairment of multipotent, myeloid, and lymphoid progenitors in HIV infection that may contribute to hematological manifestations, including anemia, pancytopenia, and T-cell depletion. In addition, ongoing and future studies on the senescence of HSPCs are expected to further the understanding of HIV pathogenesis. This mini review summarizes reports describing the basic aspects of hematopoiesis in response to HIV infection and offers insights into the association of HIV infection/exposure of the host HSPCs and hematopoietic potential.

HIV-1 inhibits haematopoiesis via microRNA secreted by virus-infected CD4+ T cells

INTRODUCTION

HIV-1-infected patients develop haematological disorders such as cytopenias. One possible explanation is the inhibition of haematopoiesis at the level of differentiation of CD34+ haematopoietic progenitor stem cells. Based on our previous studies, we hypothesised that there may be viral encoded, or host cellular factors which participate in the process of inhibition of haematopoiesis.

MATERIALS AND METHODS

Virus-depleted media from infected CD4+ T cells was prepared by filtration and added to CD34+ cell differentiation semisolid medium. We have also used the virus-depleted media to isolate host/viral factors including miRNA. Isolated miRNAs were screened for their haematopoietic inhibitory function using the miRNA mining approach.

RESULTS

Addition of virus-depleted media caused a 40% inhibition of differentiation of CD34+ cells into myeloid and erythroid colony formation. Real-time RT-PCR showed miR-15a and miR-24 from both pIndie-C1 and pNL4.3 HIV-1-infected cells showed a significant differential expression when compared to control media.

CONCLUSION

In this study, we have identified two miRNAs, miR-15a and miR-24 secreted from purified HIV-1-infected CD4+ T cells that inhibited CD34+ haematopoietic progenitor stem cell differentiation into myeloid and erythroid colonies in vitro.

Gene Therapy Approaches to Functional Cure and Protection of Hematopoietic Potential in HIV Infection

Although current antiretroviral drug therapy can suppress the replication of human immunodeficiency virus (HIV), a lifelong prescription is necessary to avoid viral rebound. The problem of persistent and ineradicable viral reservoirs in HIV-infected people continues to be a global threat. In addition, some HIV-infected patients do not experience sufficient T-cell immune restoration despite being aviremic during treatment. This is likely due to altered hematopoietic potential. To achieve the global eradication of HIV disease, a cure is needed. To this end, tremendous efforts have been made in the field of anti-HIV gene therapy. This review will discuss the concepts of HIV cure and relative viral attenuation and provide an overview of various gene therapy approaches aimed at a complete or functional HIV cure and protection of hematopoietic functions.

The Role of HIV-1 in Affecting the Proliferation Ability of HPCs Derived From BM

HIV-1 causes chronic infection characterized by the depletion of CD4+ T lymphocytes and the development of AIDS. Current antiretroviral drugs inhibit viral spread, but they do not lead to a full immune recovery. Hematopoietic stem cells (HSCs) and multipotent hematopoietic progenitor cells (HPCs) give rise to all blood and immune cells, and in HIV infection, hematological abnormalities frequently occur in patients. Here, we used bone marrow samples from HIV-1-infected people to study the relationship between the proliferation ability of HSCs/HPCs and peripheral CD4+ T lymphocytes. Three indexes were used to reflect the proliferation ability of HSCs and HPCs: (1) colony-forming units of bone marrow mononuclear cells (BMMCs), (2) amplification of CD34+ cells purified from bone marrow mononuclear cells, (3) expression of HOXB4 and HOXA9 in CD34+ cells. We observed a direct correlation between peripheral number of CD4+ T lymphocytes and the HSCs/HPCs proliferation ability in our study. We also compared HIV-infected patients with or without antiretroviral therapy (ART). Our results demonstrated that after antiretroviral therapy, CD4+ T-cell recovery and HPCs proliferation ability are correlated. Our findings have implications in understanding whether bone marrow-derived HPCs can supplement for the loss of CD4+ T lymphocytes during HIV-1 infection.

Studies of retroviral infection in humanized mice

Many important aspects of human retroviral infections cannot be fully evaluated using only in vitro systems or unmodified animal models. An alternative approach involves the use of humanized mice, which consist of immunodeficient mice that have been transplanted with human cells and/or tissues. Certain humanized mouse models can support robust infection with human retroviruses including different strains of human immunodeficiency virus (HIV) and human T cell leukemia virus (HTLV). These models have provided wide-ranging insights into retroviral biology, including detailed information on primary infection, in vivo replication and pathogenesis, latent/persistent reservoir formation, and novel therapeutic interventions. Here we describe the humanized mouse models that are most commonly utilized to study retroviral infections, and outline some of the important discoveries that these models have produced during several decades of intensive research.

Prevalence and correlates of cytopenias in HIV-infected adults initiating highly active antiretroviral therapy in Uganda

Background

Cytopenias are the most common HIV-associated hematological abnormality. Cytopenias have been associated with several factors including sex, race/ethnicity, geographical location and comorbidities such as tuberculosis, hepatitis B infection, fever and oral candidiasis. Cytopenias become more prevalent as HIV progresses and are often fatal. Data from resource-limited settings about the prevalence and correlates of cytopenia are limited. Therefore we conducted this cross-sectional study to assess the prevalence and correlates of cytopenia among adult AIDS patients at initiation of HAART in Uganda.

Methods

400 HIV-infected subjects who were HAART-naïve or on HAART for ≤ 6 months were enrolled into the Multivitamins, HAART and HIV/AIDS Trial. Anemia was defined according to WHO guidelines as any hemoglobin concentration < 12 g/dl for non-pregnant females and < 13 g/dl for males. Leucopenia and thrombocytopenia were defined using study site laboratory reference ranges for lack of generally accepted definitions for these 2 cell lines as leucopenia if white blood cell count < 2.75 × 10⁹ cells/litre and thrombocytopenia if platelets < 125 × 10⁹ cells/litre for females and < 156 × 10⁹ cells/litre for males. Univariate and bivariate analyses were done to describe the patient population and log-binomial regression was used to quantify the correlates of cytopenia.

Results

Sixty five percent of the 400 subjects had at least one form of cytopenia. Anemia occurred in 47.8%, leucopenia in 24.3%, thrombocytopenia in 8.3%, bicytopenia in 21.9% and only 2 had a pancytopenia. Cytopenia was more prevalent in females (prevalence ratio [PR]:1.33, 95% confidence interval [CI]:1.12-1.59); CD4 count category 50 to <200 (PR: 0.75, 95% CI: 0.64 -0.88) and CD4 count category 200 to <350 (PR: 0.74, 95% CI: 0.59 - 0.92) compared to CD4 count category <50; normal BMI (PR: 0.82, 95% CI:0.68-1.00) and overweight BMI (PR: 0.64, 95% CI:0.50- 0.82) compared to underweight BMI and those with a history or presence of oral candidiasis.

Conclusions

Cytopenias are a frequent complication in HIV-infected adults at initiation of HAART in Uganda. The presence of any cytopenia was associated with female sex, decreasing CD4 count and decreasing body mass index. Prospective studies in resource-limited settings on the trend in HIV-related cytopenias are needed.

HIV-1 infection of hematopoietic progenitor cells in vivo in humanized mice

HIV infection has been associated with defective hematopoiesis since the earliest days of the HIV/AIDS epidemic. Generation of all hematopoietic lineages suffers in the face of infection. The mechanisms by which HIV impairs normal blood cell development remain unclear, and direct infection of intermediate hematopoietic progenitors has not been established as a source of HIV-associated hematopoietic pathology. Here, we demonstrate infection of multiple subsets of highly purified intermediate hematopoietic progenitors by wild-type HIV both in vitro and in vivo. Although direct infection is clearly cytotoxic, we find that some infected progenitors can survive and harbor proviral DNA. We report intermediate hematopoietic progenitors to be a novel target of infection and their permissivity to infection increases with development. Further, the nonobese diabetic severe combined immunodeficiency common γ chain knockout-bone marrow-liver-thymus humanized mouse provides a unique model for studying the impact of HIV infection on bone marrow-based human hematopoiesis.

A synthetic double-stranded RNA, poly I:C, induces a rapid apoptosis of human CD34(+) cells

Toll-like receptor 3 (TLR3), retinoic acid-inducible gene I, and melanoma differentiation-associated antigen 5 (RIG-I/MDA-5) helicases are known to sense double-stranded RNA (dsRNA) virus and initiate antiviral responses, such as production of type-I interferons (IFNs). Recognition of dsRNA by TLR3 or RIG-I/MDA-5 is cell-type-dependent and recent studies have shown a direct link between TLRs and hematopoiesis. We hypothesized that viral dsRNA recognized by either TLR3 or RIG-I/MDA-5, affects the growth of human hematopoietic stem/progenitor cells. Here we show that polyinosinic polycytidylic acid (poly I:C)-mediated very rapid apoptosis occurs within 1 hour in CD34(+) cells in a dose-dependent manner. Polyadenylic-polyuridylic acid, another synthetic dsRNA that signals only through TLR3, had no effect. Poly I:C-LMW/LyoVec, a complex between low molecular-weight poly I:C and the transfection reagent LyoVec, which signals only through RIG-I/MDA-5, induces apoptosis of CD34(+) cells. A strong and sustained upregulation of messenger RNA and protein levels of Noxa, a proapoptotic BH3-only protein that can be induced by RIG-I/MDA-5 pathway, is found in CD34(+) cells treated by poly I:C. Although poly I:C upregulates type-I IFNs in CD34(+) cells, neither exogenous IFN-α nor IFN-β induces rapid apoptosis in CD34(+) cells and neutralization or blocking of type-I IFN receptor does not rescue CD34(+) cells, whereas Z-VAD, a pan-caspase inhibitor, rescues the cells from apoptosis. These results suggest that RIG-I/MDA-5, but not TLR3, signaling triggers poly I:C-induced rapid apoptosis of human CD34(+) cells, which will provide an insight into the mechanisms of dsRNA virus-mediated hematopoietic disorders.

HIV-1 determinants of thrombocytopenia at the stage of CD34+ progenitor cell differentiation in vivo lie in the viral envelope gp120 V3 loop region

HIV-1 V3 loop clones of virus isolates derived from patients suffering from thrombocytopenia were used for infection of the human thymus/liver conjoint hematopoietic organ that developed in the severe combined immunodeficient mouse (SCID-hu Thy/Liv). The V3 loop clones showed a significantly greater degree of inhibition of megakaryopoiesis than myelopoiesis and erythropoiesis of the human CD34+ progenitor cells, in vivo. Inhibition of megakaryopoiesis occurs through reduction in c-Mpl expression and consequent decrease in STAT5 activation. Therefore HIV-1 V3 loop sequences of thrombocytopenic patients exhibit preferential inhibition of megakaryocyte lineage-specific differentiation of CD34+ progenitor cells, thus reflecting the patients' clinical condition.

The utilization of humanized mouse models for the study of human retroviral infections

The development of novel techniques and systems to study human infectious diseases in both an in vitro and in vivo settings is always in high demand. Ideally, small animal models are the most efficient method of studying human afflictions. This is especially evident in the study of the human retroviruses, HIV-1 and HTLV-1, in that current simian animal models, though robust, are often expensive and difficult to maintain. Over the past two decades, the construction of humanized animal models through the transplantation and engraftment of human tissues or progenitor cells into immunocompromised mouse strains has allowed for the development of a reconstituted human tissue scaffold in a small animal system. The utilization of small animal models for retroviral studies required expansion of the early CB-17 scid/scid mouse resulting in animals demonstrating improved engraftment efficiency and infectivity. The implantation of uneducated human immune cells and associated tissue provided the basis for the SCID-hu Thy/Liv and hu-PBL-SCID models. Engraftment efficiency of these tissues was further improved through the integration of the non-obese diabetic (NOD) mutation leading to the creation of NODSCID, NOD/Shi-scid IL2rγ^-/-, and NOD/SCID β2-microglobulin^null animals. Further efforts at minimizing the response of the innate murine immune system produced the Rag2^-/-γ_c^-/- model which marked an important advancement in the use of human CD34+ hematopoietic stem cells. Together, these animal models have revolutionized the investigation of retroviral infections in vivo.

Infection of hematopoietic progenitor cells by HIV-1 subtype C, and its association with anemia in southern Africa

Reports from southern Africa, an area in which human immunodeficiency virus type 1 (HIV-1) infection is caused almost exclusively by subtype C (HIV-1C), have shown increased rates of anemia in HIV-infected populations compared with similar acquired immunodeficiency syndrome (AIDS) patients in the United States, an area predominantly infected with subtype B (HIV-1B). Recent findings by our group demonstrated a direct association between HIV-1 infection and hematopoietic progenitor cell health in Botswana. Therefore, using a single-colony infection assay and quantitative proviral analysis, we examined whether HIV-1C could infect hematopoietic progenitor cells (HPCs) and whether this phenotype was associated with the higher rates of anemia found in southern Africa. The results show that a significant number of HIV-1C, but not HIV-1B, isolates can infect HPCs in vitro (P < .05). In addition, a portion of HIV-1C-positive Africans had infected progenitor cell populations in vivo, which was associated with higher rates of anemia in these patients (P < .05). This represents a difference in cell tropism between 2 geographically separate and distinct HIV-1 subtypes. The association of this hematotropic phenotype with higher rates of anemia should be considered when examining anti-HIV drug treatment regimens in HIV-1C-predominant areas, such as southern Africa.

Effects of HIV type 1 infection on hematopoiesis in Botswana

Clinical observations suggest that HIV-1 infection causes higher anemia rates in patients in southern Africa than in those in the United States. To explore this difference we performed a cross-sectional exploratory study on the effect of HIV-1 infection on hematopoiesis in Botswana by examining hematological presentation, HIV disease state, hematopoietic progenitor cell number, and circulating viral levels in HIV-infected patients and HIV-uninfected controls. We found significant associations between CD34(+) and CD4(+) cell counts in HIV-positive patients. Significant relationships were also seen between the CD34(+) CD4(+) cell population and hemoglobin levels, as well as colony-forming ability. These associations, however, were not seen in uninfected controls. Circulating viral p24 levels were found to correlate significantly with CD34(+) cell count, CD34(+) CD4(+) cell count, and colony-forming ability. These results demonstrate a direct association between HIV-1 infection in southern Africa and hematopoietic progenitor cell health.

Validation of the SCID-hu Thy/Liv mouse model with four classes of licensed antiretrovirals

Background

The SCID-hu Thy/Liv mouse model of HIV-1 infection is a useful platform for the preclinical evaluation of antiviral efficacy in vivo. We performed this study to validate the model with representatives of all four classes of licensed antiretrovirals.

Methodology/Principal Findings

Endpoint analyses for quantification of Thy/Liv implant viral load included ELISA for cell-associated p24, branched DNA assay for HIV-1 RNA, and detection of infected thymocytes by intracellular staining for Gag-p24. Antiviral protection from HIV-1-mediated thymocyte depletion was assessed by multicolor flow cytometric analysis of thymocyte subpopulations based on surface expression of CD3, CD4, and CD8. These mice can be productively infected with molecular clones of HIV-1 (e.g., the X4 clone NL4-3) as well as with primary R5 and R5X4 isolates. To determine whether results in this model are concordant with those found in humans, we performed direct comparisons of two drugs in the same class, each of which has known potency and dosing levels in humans. Here we show that second-generation antiretrovirals were, as expected, more potent than their first-generation predecessors: emtricitabine was more potent than lamivudine, efavirenz was more potent than nevirapine, and atazanavir was more potent than indinavir. After interspecies pharmacodynamic scaling, the dose ranges found to inhibit viral replication in the SCID-hu Thy/Liv mouse were similar to those used in humans. Moreover, HIV-1 replication in these mice was genetically stable; treatment of the mice with lamivudine did not result in the M184V substitution in reverse transcriptase, and the multidrug-resistant NY index case HIV-1 retained its drug-resistance substitutions.

Conclusion

Given the fidelity of such comparisons, we conclude that this highly reproducible mouse model is likely to predict clinical antiviral efficacy in humans.

Natural Killer Cell Receptor NKG2A/HLA-E Interaction Dependent Differential Thymopoiesis of Hematopoietic Progenitor Cells Influences the Outcome of HIV Infection

HIV infection and its outcome is complex because there is great heterogeneity not only in clinical presentation, incomplete clinical information of markers of immunodeficiency and in measurements of viral loads. Also, there many gene variants that control not only viral replication but immune responses to the virus; it has been difficult to study the role of the many AIDS restricting genes (ARGs) because their influence vary depending on the ethnicity of the populations studies and because the cost to follow infected individuals for many years. Nevertheless, at least genes of the major histocompatibility locus (MHC) such as HLA alleles have been informative to classify infected individuals following HIV infection; progression to AIDS and long-term-non-progressors (LTNP). For example, progressors could be defined as up to 5 years, up to 11 years or as we describe in this report up to 15 years from infection, and LTNP could be individuals with normal CD4+ T cell counts for more than 15 years with or without high viral loads. In this review, we emphasized that in the studies of ARGs the HLA alleles are important in LTNP; HLA-B alleles influencing the advantage to pathogens to produce immune defense mediated by CD8+ T cells (cognate immunuity). Our main point we make in this report is that contrary to recent reports claiming that this dominant effect was unlikely due to differences in NK activation through ligands such as HLA-Bw4 motif, we believe that cognate immunity as well as innate immunity conferred by NK cells are involved. The main problem is that HLA-Bw4 alleles can be classified according the aminoacid in position 80. Isoleucine determines LTNP, which is a ligand for 3DS1. Such alleles did not include HLA-B*44. B*13 and B*27 which have threonine at that position. The authors have not considered the fact that in addition to the NK immunoglobulin receptors, NK receptors can be of the lectin like such as NKG2A/HLA-E to influence the HIV infection outcome. HLA-Bw4 as well as HLA-Bw6 alleles can be classified into those with threonine or methionine in the second position of their leader peptides. These leader peptides are ligands for NKG2A in which methionine influences the inhibitory role of NKG2A for killing infected targets. Functional studies have not been done as well as studies of these receptors in infected individuals. However, analyses of the leader peptides of HLA-B alleles in published reports, suggested that threonine in the second position can explain the importance of HLA-B*57, B*13, B*44 as well as certain Bw6 alleles in LNTP. In addition, we analyzed the San Francisco database that was reported and found that the association of HLA-B alleles with LNTP or with progressors can be due to the presence of threonine or methionine in their second position. Therefore, studies of outcome of HIV infection should include not only mechanisms of cognate immunity mediated by peptides and CD8+ T cells but also, NK receptors of two types, NKG2A as well as 3DSI. We propose that the SCID mouse should be used to understand mechanisms mediated by many of the ARGs especially the importance of thymus derived cells as well as NK receptor interactions with their ligands in this experimental animal transplanted with human stem cells, thymus or NK cells obtained from individuals of known HLA genotypes.

Lower hemoglobin levels in human immunodeficiency virus-infected patients with a positive direct antiglobulin test (DAT): relationship with DAT strength and clinical stages

BACKGROUND

There are conflicting opinions regarding the effect of positive direct antiglobulin test (DAT) on hemoglobin (Hb) levels in human immunodeficiency virus-infected (HIV+) patients.

STUDY DESIGN AND METHODS

A total of 166 samples from HIV+ outpatients were studied. The DAT was performed with the tube test and column agglutination technology (CAT).

RESULTS

The DAT was positive in 18.67 percent with the tube method and 33.73 percent with the CAT. Patients with DAT-positive results showed lower Hb levels than DAT-negative patients, 12.3 g per dL versus 14.3 g per dL (p = 0.0002). The univariate logistic regression enabled us to study the phenomenon better and fit the probability of having a DAT-positive result on the basis of the Hb levels. The relationship between the CAT and the tube test when washing the red blood cells (RBC) at 4 degrees C was stronger than when washing these at room temperature (phi = 0.8156; p = 0.000). The Hb levels were significantly lower in the positive DATs of Stage C (acquired immune deficiency syndrome [AIDS]) and Stage B (symptomatic non-AIDS patients), which showed decreasing Hb values for increasing agglutination strengths (p = 0.000). Anemia was related with the DAT results (odds ratio [OR], 8.005; p = 0.000) but not to the AIDS condition (OR, 1.741; p = 0.221).

DISCUSSION

Our study indicates that the DAT-positive results may be specifically related to lower Hb levels in HIV+ patients. The immunologic RBC clearance could be part of the anemic multifactorial condition in HIV+ patients.

Hematopoietic stem cell–engrafted NOD/SCID/IL2Rγnull mice develop human lymphoid systems and induce long-lasting HIV-1 infection with specific humoral immune responses

Critical to the development of an effective HIV/AIDS model is the production of an animal model that reproduces long-lasting active replication of HIV-1 followed by elicitation of virus-specific immune responses. In this study, we constructed humanized nonobese diabetic/severe combined immunodeficiency (NOD/SCID)/interleukin-2 receptor γ-chain knockout (IL2Rγnull) (hNOG) mice by transplanting human cord blood–derived hematopoietic stem cells that eventually developed into human B cells, T cells, and other monocytes/macrophages and 4 dendritic cells associated with the generation of lymphoid follicle–like structures in lymphoid tissues. Expressions of CXCR4 and CCR5 antigens were recognized on CD4+ cells in peripheral blood, the spleen, and bone marrow, while CCR5 was not detected on thymic CD4+ T cells. The hNOG mice showed marked, long-lasting viremia after infection with both CCR5- and CXCR4-tropic HIV-1 isolates for more than the 40 days examined, with R5 virus–infected animals showing high levels of HIV-DNA copies in the spleen and bone marrow, and X4 virus–infected animals showing high levels of HIV-DNA copies in the thymus and spleen. Furthermore, we detected both anti–HIV-1 Env gp120– and Gag p24–specific antibodies in animals showing a high rate of viral infection. Thus, the hNOG mice mirror human systemic HIV infection by developing specific antibodies, suggesting that they may have potential as an HIV/AIDS animal model for the study of HIV pathogenesis and immune responses.

CXCR4 tropic human immunodeficiency virus type 1 induces an apoptotic cascade in immature infected thymocytes that resembles thymocyte negative selection

HIV-1 often replicates in the thymus of infected individuals, causing thymocyte depletion and thymic dysfunction. Nevertheless, the mechanisms by which thymocyte depletion occurs are not clear. Here we report that HIV-1 infection induced apoptosis primarily in productively infected thymocytes; aldrithiol-2 or Efavirenz treatment largely abrogated HIV-1-induced apoptosis. Moreover, X4-HIV-1 induced apoptosis primarily in immature CD4+ CD8+ (DP) thymocytes whereas most mature CD4 or CD8 single-positive (SP) thymocytes were resistant to X4 HIV-1-induced apoptosis despite infection. Consistent with this, we observed significant induction of several genes involved in negative selection of DP thymocytes. Furthermore, treatment of thymocytes with cycloheximide abrogated HIV-1-induced apoptosis, implying a requirement for de novo protein synthesis. Our results suggest that HIV-1-induced apoptosis of thymocytes requires the activation of caspases and the participation of mitochondrial apoptosis effectors, which serve to amplify the apoptotic signal, a process similar to that elaborated during thymocyte negative selection.

Aetiological factors related to a positive direct antiglobulin test result in human immunodeficiency virus-infected patients

BACKGROUND AND OBJECTIVES

The aim of this study was to examine the clinical importance and causes of a positive result in the direct antiglobulin test (DAT) in human immunodeficiency virus-infected (HIV(+)) patients. We therefore studied haematological parameters in outpatient samples, and also analysed the impact of highly active anti-retroviral therapy (HAART) on the DAT results.

STUDY DESIGN AND METHODS

Haematological parameters, clinical stages, chemo-antibiotic treatments and HAART treatment were studied to determine any relationships with DAT results in 115 consecutive HIV(+) patients.

RESULTS

Significantly lower haemoglobin (Hb) levels were detected in patients with HIV who had a positive DAT result. Hepatitis C virus (HCV) co-infection (odds ratio 2.529) and trimethoprim-suphamethoxazfole (TMP-SMX) prophylaxis (odds ratio 3.751) had a significant association with DAT positivity. Patients receiving HAART were less likely to have a positive DAT [odds ratio (OR) 0.383; P = 0.035]. Among the patients treated with TMP-SMX, those with a positive DAT had lower Hb levels (11.9 g/dl) than those with a negative DAT (14.2 g/dl; P = 0.04). HCV antibody positivity and TMP-SMX prophylaxis showed a cumulative effect on positive DATs (OR 4.533). The surface exploratory analysis indicated the distribution of the positive DATs in relationship with the CD4(+) count and Hb levels.

CONCLUSIONS

Significantly lower Hb levels were detected in DAT-positive HIV(+) patients. HCV co-infection and TMP-SMX prophylaxis appear to confer an increased risk of DAT positivity. The presence of red blood cell autoantibodies may be associated with anaemia in HIV disease in the absence of overt haemolysis.

KSHV/HHV-8 infection of human hematopoietic progenitor (CD34+) cells: persistence of infection during hematopoiesis in vitro and in vivo

The cellular reservoir for Kaposi sarcoma-associated herpesvirus (KSHV) infection in the hematopoietic compartment and mechanisms governing latent infection and reactivation remain undefined. To determine susceptibility of human CD34+ hematopoietic progenitor cells (HPCs) to infection with KSHV, purified HPCs were exposed to KSHV, and cells were differentiated in vitro and in vivo. Clonogenic colony-forming activity was significantly suppressed in KSHV-infected CD34+ cells, and viral DNA was predominantly localized to granulocyte-macrophage colonies differentiated in vitro. rKSHV.219 is a recombinant KSHV construct that expresses green fluorescent protein from a cellular promoter active during latency and red fluorescent protein from a viral lytic promoter. Infection of CD34+ HPCs with rKSHV.219 showed similar patterns of infection, persistence, and hematopoietic suppression in vitro in comparison with KSHV. rKSHV.219 infection was detected in human CD14+ and CD19+ cells recovered from NOD/SCID mouse bone marrow and spleen following reconstitution with rKSHV.219-infected CD34+ HPCs. These results suggest that rKSHV.219 establishes persistent infection in NOD/SCID mice and that virus may be disseminated following differentiation of infected HPCs into the B-cell and monocyte lineages. CD34+ HPCs may be a reservoir for KSHV infection and may provide a continuous source of virally infected cells in vivo.

The HIV-1 Tat protein enhances megakaryocytic commitment of K562 cells by facilitating CREB transcription factor coactivation by CBP

The human immunodeficiency virus type 1 (HIV-1) Tat protein regulates transcription factor functions and alters cellular gene expression. Because hematopoietic progenitor cell (HPC) differentiation requires activation of lineage-specific transcription factors, Tat may affect hematopoiesis in HIV-1-infected micro-environments. We have monitored the molecular effects of Tat on megakaryocytic differentiation in the HPC line, K562. Flow cytometry analysis of CD61 indicated that phorbol myristate acetate (PMA) (16 nM) stimulated megakaryocytic commitment of K562 cells was increased (3- to 4-fold) following exposure to Tat (1-100 ng/ml). Activation of the megakaryocytic transcription factor cAMP regulatory element binding protein (CREB) and its coactivation by the CREB binding protein (CBP) was subsequently monitored. CREB phosphorylation and DNA binding were measured by Western immunodetection and electrophoretic mobility shift assays (EMSA), respectively. Within 2 hrs after stimulation, Tat increased both CREB phosphorylation and DNA binding by 7- to 10-fold. Transient cotransfection with CREB reporter and CBP expression plasmids demonstrated that Tat treatment increases (3- to 4-fold) both PMA-stimulated and CBP-mediated transcription via the cAMP regulatory element. Histone acetyl transferase (HAT) activity was increased (8- to 10-fold) in Tat-stimulated cells, which suggested increased chromosomal accessibility of transcription factors. Two-hybrid cotransfection assays using reporter plasmid containing the GAL4 DNA-binding domain and expression plasmid coding for the GAL4-CBP fusion protein, showed that Tat increases (2-fold) CBP-mediated coactivation of CREB. Both reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis showed that Tat treatment increases CBP gene expression (7- to 9-fold) and protein levels (5- to 7-fold) within 6-12 hrs after stimulation. Our findings indicated that Tat treatment increases both CREB function and CREB coactivation by CBP, which may facilitate megakaryocytic commitment of K562 cells. Induction of this molecular signaling by HIV-1 Tat protein may have relevance in understanding the HIV-induced hematologic manifestations and possibly in regulation of viral infectivity parameters in progenitor cell reservoirs.

Chimeric SCID-hu Model as a Human Hematopoietic Stem Cell Host That Recapitulates the Effects of HIV-1 on Bone Marrow Progenitors in Infected Patients

The chimeric small animal model system wherein the severe combined immunodeficient mouse is transplanted with human fetal thymus and liver tissues (SCID-hu Thy/Liv) has been used in different areas of experimental research [1]. A living model system offers the advantage that studies of longer duration than in vitro can be performed. Here we discuss the importance of experimental in vivo studies and how well the data generated using this model system correlates with epidemiological studies from HIV-positive humans. Patients with HIV-1 infection often suffer from cytopenias, with thrombocytopenia typically having an earlier onset than anemia and neutropenia. The cytopenias in patients may be caused by virus effects at the stem cell level, or the mature blood cell level, or by other factors like medications used to treat the infection. Several studies preformed in SCID-hu animals show that the function of human hematopoietic progenitor stem cells are indirectly affected by HIV-1 infection. Colony forming activity (CFA) assays on hematopoietic progenitor cells derived from SCID-hu animals and human bone marrow have been performed as a measure of progenitor cellular function, and HIV-1 infection decreased CFA in multiple lineages that include megakaryoid, erythroid and myeloid types. Highly active antiretroviral therapy (HAART) partially and transiently reduces the inhibition of multilineage CFA and data suggest that HIV-1 indirectly affects stem cell differentiation into multiple lineages. The cojoint human hematopoietic organ of this small animal model system recapitulates the inhibitory effects of HIV-1 infection on the function of progenitor cells of the human bone marrow. Thus the SCID-hu (Thy/Liv) model is a useful in vivo system for preclinical translational research towards development of stem cell therapies in HIV infection.

Stem Cells in Aging: Influence of Ontogenic, Genetic and Environmental Factors

Aging is a genetically programmed decline in the functional effectiveness of the organism. It is manifested by a collective group of changes in cells or organs that occur over the course of a lifespan, limiting the duration of life. Longevity usually refers to long-lived members of a population within species. Organs develop and can involute according to specific timetables. Such timetables correlate with a preordained proliferative capacity of cells mediated by cell and organ clocks. In this review, we discuss different aspects related to genetic and environmental factors that are involved in determining life span. We discuss the influence of ontogenic, genetic and environmental factors in aging. The genetic factors can be studied in embryonic stem cells (ESC) and in niches (microenvironments) of stem cells (SC) using cellular or experimental animal models. We discuss molecular mechanisms involving genes and proteins associated with death pathways, niches, or hubs, on longevity. Moreover, we also discuss genes and proteins, associated with death pathways, on longevity. Unraveling these mechanisms may further our understanding of human aging leading to development of therapeutic interventions with the potential of prolonging life.

Targeting c-Mpl for revival of human immunodeficiency virus type 1-induced hematopoietic inhibition when CD34+ progenitor cells are re-engrafted into a fresh stromal microenvironment in vivo

The inhibition of multilineage hematopoiesis which occurs in the severe combined immunodeficiency mouse with transplanted human fetal thymus and liver tissues (SCID-hu Thy/Liv) due to human immunodeficiency virus type 1 (HIV-1) infection is also accompanied by a severe loss of c-Mpl expression on these progenitor cells. Inhibition of colony-forming activity (CFA) of the CD34(+) progenitor cells is partially revived to about 40% of mock-infected Thy/Liv implants, following reconstitution of the CD34(+) cells that were exposed to HIV-1 infection, in a new Thy/Liv stromal microenvironment of irradiated secondary SCID-hu recipients at 3 weeks post-re-engraftment. In addition, in these reconstituted animals, the proportion of c-Mpl(+) CD34(+) cells relative to c-Mpl(-) CD34(+) cells increased by about 25%, to 35% of mock-infected implants, suggesting a reacquirement of c-Mpl phenotype by the c-Mpl(-) CD34(+) cells. These results suggest a correlation between c-Mpl expression and multilineage CFA of the human CD34(+) progenitor cells that have experienced the effects of HIV-1 infection. Treatment of the secondary-recipient animals with the c-Mpl ligand, thrombopoietin (Tpo), further increased c-Mpl expression and CFA of re-engrafted CD34(+) cells previously exposed to virus in the primary implants to about 50 to 70% over that of those re-engrafted CD34(+) cells derived from implants of untreated animals. Blocking of c-Mpl with anti-c-Mpl monoclonal antibody in vivo by injecting the SCID-hu animals resulted in the reduction or loss of CFA. Thus, inhibition, absence, or loss of c-Mpl expression as in the c-Mpl(-) CD34(+) subset of cells is the likely cause of CFA inhibition. Further, CFA of the CD34(+) cells segregates with their c-Mpl expression. Therefore, c-Mpl may play a role in hematopoietic inhibition during HIV-1 infection, and control of its expression levels may aid in hematopoietic recovery and thereby reduce the incidence of cytopenias occurring in infected individuals.

Simian Immunodeficiency Virus Infection of Hematopoietic Stem Cells and Bone Marrow Stromal Cells

Using a well-characterized fetal rhesus monkey model, simian immunodeficiency virus (SIV) infection of hematopoietic stem cells (HSCs) and stromal cells was investigated to characterize bone marrow abnormalities in SIV-infected animals in vivo. Fetuses (n = 4) were inoculated in utero with pathogenic SIVmac251 using established techniques at 65 days; gestation (early second trimester), then harvested for tissues 65 days after inoculation (late third trimester), and compared with findings from controls of a comparable age (n = 11). Sorted bone marrow CD34CD38, CD34CD38, and marrow stromal cells were analyzed for the SIV genome. Results indicate that CD34CD38 HSCs were not infected, whereas the SIV genome was detected in the CD34CD38 hematopoietic cell population by PCR analysis. The SIV proviral sequence was not detected in stromal cells from SIV-infected fetuses, although SIVmac251 was found to readily infect these cells when assessed in vitro. Flow cytometric analysis revealed that stromal cells express low levels (1 in 600 total cells) of CD4 and CCR5 viral receptors, whereas CXCR4 expression was not observed. These data suggest the following: (1) SIV infection of HSCs requires some degree of differentiation for viral entry similar to findings for humans infected with HIV type 1, and (2) SIV can infect bone marrow stromal cells that express CD4 and CCR5 in vitro, but infected stromal cells are not readily found in vivo.

Human T-cell leukemia virus type 1 tax oncoprotein suppression of multilineage hematopoiesis of CD34+ cells in vitro

Human T-cell leukemia virus type 1 (HTLV-1) and HTLV-2 are highly related viruses that differ in disease manifestation. HTLV-1 is the etiologic agent of adult T-cell leukemia and lymphoma, an aggressive clonal malignancy of human CD4-bearing T lymphocytes. Infection with HTLV-2 has not been conclusively linked to lymphoproliferative disorders. We previously showed that human hematopoietic progenitor (CD34(+)) cells can be infected by HTLV-1 and that proviral sequences were maintained after differentiation of infected CD34(+) cells in vitro and in vivo. To investigate the role of the Tax oncoprotein of HTLV on hematopoiesis, bicistronic lentiviral vectors were constructed encoding the HTLV-1 or HTLV-2 tax genes (Tax1 and Tax2, respectively) and the green fluorescent protein marker gene. Human hematopoietic progenitor (CD34(+)) cells were infected with lentivirus vectors, and transduced cells were cultured in a semisolid medium permissive for the development of erythroid, myeloid, and primitive progenitor colonies. Tax1-transduced CD34(+) cells displayed a two- to fivefold reduction in the total number of hematopoietic clonogenic colonies that arose in vitro, in contrast to Tax2-transduced cells, which showed no perturbation of hematopoiesis. The ratio of colony types that developed from Tax1-transduced CD34(+) cells remained unaffected, suggesting that Tax1 inhibited the maturation of relatively early, uncommitted hematopoietic stem cells. Since previous reports have linked Tax1 expression with initiation of apoptosis, lentiviral vector-mediated transduction of Tax1 or Tax2 was investigated in CEM and Jurkat T-cell lines. Ectopic expression of either Tax1 or Tax2 failed to induce apoptosis in T-cell lines. These data demonstrate that Tax1 expression perturbs development and maturation of pluripotent hematopoietic progenitor cells, an activity that is not displayed by Tax2, and that the suppression of hematopoiesis is not attributable to induction of apoptosis. Since hematopoietic progenitor cells may serve as a latently infected reservoir for HTLV infection in vivo, the different abilities of HTLV-1 and -2 Tax to suppress hematopoiesis may play a role in the respective clinical outcomes after infection with HTLV-1 or -2.

Hematopoietic stem cells in HIV disease

The hematopoietic stem cell has long been hypothesized to be a target of human immunodeficiency virus type-1 (HIV) infection that limits the potential for compensatory immune cell production. Data have recently emerged documenting stem cell dysfunction in HIV disease and indicating that immune recovery from potent antiretroviral therapy is partly driven by new T-cell generation. Effects of HIV on stem cell physiology, however, appear to be indirect, as stem cells are highly resistant to HIV infection. Despite the presence of surface receptors for HIV, the hematopoietic stem cell is not infectible with HIV. However, stem transduction can be achieved with HIV constructs in which the envelope glycoproteins have been replaced by vesicular stomatitis virus G protein. Therefore, hematopoietic stem cells are likely participants in HIV-related cytopenias, but they are spared direct infection and can serve as a resource for cellular therapies for AIDS.

HIV-1 replication and pathogenesis in the human thymus

How HIV replicates and causes destruction of the thymus, and how to restore thymic function, are among the most important questions of HIV-1 pathogenesis and therapy in adult as well as pediatric patients. The thymus appears to function, albeit at reduced levels, throughout the life of adults, to respond to T cell depletion induced by HIV and to be suppressed by HIV. In this review, we summarize recent findings concerning HIV replication and pathogenesis in the human thymus, focusing on mechanistic insights gleaned from studies in the SCID-hu Thy/Liv mouse and human fetal-thymus organ culture (HF-TOC) models. First, we discuss HIV viral determinants and host factors involved in the replication of HIV in the thymus. Second, we consider evidence that both viral factors and host factors contribute to HIV-induced thymocyte depletion. We thus propose that multiple mechanisms, including depletion and suppression of progenitor cells, paracrine and direct lytic depletion of thymocytes, and altered thymocyte selection are involved in HIV-induced pathology in the thymus. With the SCID-hu Thy/Liv mouse and HF-TOC models, it will be important in the coming years to further clarify the virological, cell biological, and immunological mechanisms of HIV replication and pathogenesis in human thymus, and to correlate their significance in HIV disease progression.

Activation of the signal transducer and activator of transcription 1 signaling pathway in thymocytes from HIV-1-infected human thymus

OBJECTIVE

To identify HIV-induced host factors in the severe combined immunodeficient (SCID)-hu Thy/Liv mouse that may contribute to HIV pathogenesis in the thymus.

DESIGN

To identify genes specifically altered by HIV-1 infection using the cDNA microarray assay, SCID-hu Thy/Liv organs derived from the same donors were used. Therefore, no genetic variations existed between HIV and mock-infected samples. In addition, the 12-14 day post-infection timepoint was chosen because no significant thymocyte depletion was detected in HIV-infected Thy/Liv organs, so mRNA from the same cell types could be compared.

METHODS

Using SCID-hu Thy/Liv mice constructed from the same donor tissues, we analysed the expression of 9183 host genes in response to HIV infection with cDNA microarrays. Expression of selected genes with more than threefold induction was confirmed by measuring RNA (reverse transcriptase-polymerase chain reaction; RT-PCR) and proteins.

RESULTS

HIV-1 (JD or NL4-3) infection of the SCID-hu Thy/Liv mouse led to more than threefold induction of 19 genes, 12 of which were IFN-inducible and six were unknown EST clones. We confirmed induction by RT-PCR and protein blots. Both signal transducer and activator of transcription (STAT)1 and STAT2 proteins were induced, and STAT1 was also activated by phosphorylation at the Tyr701 and Ser727 sites in human thymus infected with HIV-JD or NL4-3. Treatment of human fetal thymus organ culture or human thymocytes with recombinant HIV-1 gp120 proteins also led to induction or activation of STAT1.

CONCLUSION

HIV-1 infection of the thymus led to activation of the STAT1 signaling pathway in thymocytes, which may contribute to HIV-1 pathogenesis in the thymus.

HIV type 1 infection alters cytokine mRNA expression in thymus

We and others have previously shown that HIV infection of human thymus/liver implants in severe combined immunodeficient (SCID-hu Thy/Liv) mice results in a loss of CD4(+) thymocytes and a decreased recovery of human myeloid and erythroid colony-forming activity. Furthermore, our previous studies have shown that this decrease in colony-forming potential is due to indirect effects, rather than to massive loss of CD34(+) hematopoietic progenitor cells, suggesting that HIV infection might alter expression of hematopoietic cytokines. Herein we have investigated potential HIV-1-induced perturbations of hematolymphoid microenvironments by determining the effect of HIV-1 infection on levels of cytokine mRNAs in human stroma and thymocytes, using the reverse transcription-polymerase chain reaction (RT-PCR). The levels of interleukin 6 (IL-6), interferon gamma (IFN-gamma), and IL-2 RNAs increased and macrophage inflammatory protein 1beta (MIP-1beta) RNA decreased significantly in infected thymocytes. IL-6 RNA levels in stroma also increased somewhat with infection; however, expression of stromal cell-derived factor 1 (SDF-1) by stromal elements was not affected. IL-4 RNA levels were unaffected by infection in both stroma and thymocytes. Antiretroviral drug treatment of the infected animals, which results in restoration of colony-forming potential, tends to restore the cytokine mRNA levels in HIV-1-infected implants to those of mock-infected implants. These results indicate that HIV-1 infection can greatly distort the cytokine profiles in Thy/Liv implants, and suggest that cytokine perturbation could be involved in virus-induced inhibition of hematopoiesis.

Sustained impairment of IFN-gamma secretion in suppressed HIV-infected patients despite mature NK cell recovery: evidence for a defective reconstitution of innate immunity

The impairment of NK cell functions in the course of HIV infection contributes to a decreased resistance against HIV and other pathogens. We analyzed the proportion of mature and immature NK cell subsets, and measured subsets of IFN-gamma and TNF-alpha-producing NK and T cells in viremic or therapy-suppressed HIV-infected subjects, and noninfected control donors. Viremic HIV(+) individuals had significantly lower proportions of mature CD3(-)/CD161(+)/CD56(+) NK cells and of IFN-gamma-producing NK cells compared with noninfected donors, independent of CD4(+) T cell counts. HIV-infected subjects with undetectable viral load recovered mature CD3(-)/CD161(+)/CD56(+) NK cells and cytotoxicity against tumor (K562) and HSV-infected target cells to percentages comparable with those of uninfected individuals, but their NK cells remained impaired in their ability to produce IFN-gamma. In parallel to these ex vivo findings, in vitro NK cell differentiation of CD34-positive cord blood precursors in the presence of R5 or X4 HIV-1 resulted in the production of NK cells with a normal mature phenotype, but lacking the ability to produce IFN-gamma, whereas coculture of uninfected PBMC with HIV failed to affect mature NK cell properties or IFN-gamma secretion. Altogether, our findings support the hypothesis that mature NK cell phenotype may be uncoupled from some mature functions following highly active antiretroviral therapy-mediated suppression of HIV-1, and indicate that relevant innate immune functions of NK cell subsets may remain altered despite effective viral suppression following antiretroviral treatment.

Myelodysplastic features in patients with long-term HIV infection and haemophilia

HIV-related bone marrow changes are consistent with myelodysplastic features (MDF). Their pathogenesis may differ from primary myelodysplastic syndromes (MDS) and is associated with various factors including the virus itself or the antiretroviral therapy. In order to evaluate the differences between HIV-related MDF and MDS, the morphological changes in peripheral blood and bone marrow, cytogenetic analysis and the response to anaemia treatment were studied in 158 HIV+ patients with haemophilia and the results were compared with those of 61 patients with primary MDS (31 with RA, 10 with RARS, 11 with RAEB, three with RAEB-t and six with CMML). The eligibility criteria for patients with MDS were primary MDS, Hb levels < 10 g dL(-1), and no significant organ disease. The peripheral blood and bone marrow examination revealed MDF in 44 HIV-infected haemophilic patients (27.8%). The median time from seroconversion was 12.5 years and the mean time under AZT therapy was 44.1 months. Nineteen of these patients (43.1%) had Hb levels < 10 g dL(-1), while neutropenia and thrombocytopenia were observed in 29.5% and 25%, respectively. Every patient of this study with Hb < 10 g dL(-1) received erythropoietin (Epo). There were statistically significant morphological alterations between HIV-related MDF and MDS: hypocellularity, plasmatocytosis and eosinophilia were more pronounced in HIV haemophiliacs with MDF, while dysplasia of erythroblasts, megakaryocytes and granulocytes was more frequent in MDS patients. No HIV haemophilic patient with MDF had more than 5% blasts in the bone marrow nor did any develop RAEB or acute leukaemia during the period of this study. The cytogenetic analysis was normal in HIV-infected patients with haemophilia whereas 42.6% of patients with MDS had an abnormal karyotype. Complete erythroid response was achieved with Epo administration in 84.2% of HIV+ haemophilic patients with anaemia compared to 19.7% of patients with MDS. These data suggest that bone marrow changes in long-term HIV patients have different characteristics from primary MDS and constitute the entity for which the name HIV-myelopathy has been proposed in the literature.

T-cell progenitor function during progressive human immunodeficiency virus-1 infection and after antiretroviral therapy

Impairment of T-cell renewal has been proposed as contributing to CD4+ T-cell depletion in persons infected with human immunodeficiency virus-1. We analyzed the T-cell development capacity of progenitors using fetal thymus organ culture. Those who progressed to AIDS had a dramatic loss in T-cell development capacity shortly after seroconversion. In contrast, long-term nonprogressors retained progenitor capacity 8 years after seroconversion. Approximately 70% of patients experienced an improvement in T-cell development capacity after receiving 6 months of potent antiretroviral therapy. Improvement in T-cell development in fetal thymus organ culture correlated with an increase in the number of naive CD4+ T cells in peripheral blood. Numbers of progenitors in blood and bone marrow after seroconversion or during therapy did not correlate with the change observed in T-cell development capacity. These data provide evidence that HIV-1 infection can interfere with T-cell renewal at the level of the progenitor cell. Interference with T-cell renewal may contribute to CD4+ T-cell depletion.

T-cell progenitor function during progressive human immunodeficiency virus-1 infection and after antiretroviral therapy

Impairment of T-cell renewal has been proposed as contributing to CD4+ T-cell depletion in persons infected with human immunodeficiency virus-1. We analyzed the T-cell development capacity of progenitors using fetal thymus organ culture. Those who progressed to AIDS had a dramatic loss in T-cell development capacity shortly after seroconversion. In contrast, long-term nonprogressors retained progenitor capacity 8 years after seroconversion. Approximately 70% of patients experienced an improvement in T-cell development capacity after receiving 6 months of potent antiretroviral therapy. Improvement in T-cell development in fetal thymus organ culture correlated with an increase in the number of naive CD4+ T cells in peripheral blood. Numbers of progenitors in blood and bone marrow after seroconversion or during therapy did not correlate with the change observed in T-cell development capacity. These data provide evidence that HIV-1 infection can interfere with T-cell renewal at the level of the progenitor cell. Interference with T-cell renewal may contribute to CD4+ T-cell depletion.

In vitro and in vivo responses to interleukin 12 are maintained until the late SIV infection stage but lost during AIDS

The in vitro proliferative responses of macaque peripheral blood mononuclear cells (PBMCs) to IL-12 appeared similar before and early after SIV infection, whereas macaque PBMCs sampled during symptomatic stages of SIV infection showed markedly decreased responses. IL-12 was administered to SIVmac239-infected rhesus macaques either during the asymptomatic or the AIDS stage of infection in efforts to evaluate the effect of this cytokine on immune responses, viral loads, and hematopoietic functions in vivo. IFN-gamma secretion levels induced during the asymptomatic or early symptomatic phase were similar to preinfection induced levels, whereas in later AIDS stages this response was lost. The constitutive levels of other measured cytokines were not affected by IL-12 administration in vivo. The frequency and activity of circulating NK cells were markedly enhanced at early stages but not at symptomatic stages of SIV infection. pCTL frequencies were enhanced at early symptomatic stages but not at late AIDS stages. Despite its immunomodulatory effect, IL-12 did not seem to exacerbate or inhibit the replication of SIV in vivo, or the frequency of circulating infected lymphocytes. IL-12 administration was associated with a significant yet subclinical and transient decrease in hematocrit and hemoglobin levels without evidence of hemolysis, hemodilution, or reduction in the frequency of colony-forming unit potential of bone marrow CD34+ cells. This phenomenon may be explained by a functional inhibition of differentiation rather than an altered generation of bone marrow precursors. Thus, these results suggest that IL-12 may benefit HIV-1-infected patients only as long as their immune system retains its capability to respond to cytokine stimulation.

Pathogenesis of HIV-1 infection within bone marrow cells

Mononuclear phagocytic cells and CD4+ T lymphocytes represent the major targets for infection by HIV-1 in vivo. The most severe pathogenic features associated with HIV-1 infection can be attributed to malfunction or premature death of these cells that are of hematopoietic origin. Patients with acquired immunodeficiency syndrome (AIDS), suffer from many hematologic disorders, particularly those persons with long-term infection of HIV-1. These disorders include anemia, lymphocytopenia, thrombocytopenia and neutropenia. The mechanisms that lead to the induction of these disorders are multi-factorial. However, sufficient evidence has accumulated which suggests that HIV-1 infection of cells within the microenvironment of the bone marrow can lead to the induction of hematopoietic deficits. Most studies indicate that marrow-derived hematopoietic stem cells cannot be infected by HIV-1 until they undergo modest differentiation in order to express the appropriate receptors to enable virus entry and subsequent replication. Some cells within the mixed environment of the marrow stroma appear to support HIV-1 replication however. These cells include marrow microvascular endothelial cells, sometimes referred to as blanket cells, stromal fibroblasts, as well as mononuclear phagocytes. Our recent experiments suggest that the HIV-1 accessory protein, Vpr, plays some role in the activation of marrow-derived mononuclear phagocytes which appears to result in premature phagocytosis of non-adherent marrow cells present in the in vitro cultures. This phenomenon could account, in part, for the induction of cytopenias that are typical of individuals infected by HIV-1.

Productive infection of CD34+-cell-derived megakaryocytes by X4 and R5 HIV-1 isolates

The human immunodeficiency virus (HIV-1) causes various hematopoietic abnormalities, with thrombocytopenia (TP) occurring in 30% of infected individuals. In the present study, we aimed to determine whether HIV-1 in the bone marrow of TP patients can infect primary megakaryocytes in vitro, which may contribute to the development of thrombocytopenia. We amplified the V3 loop of HIV-1 envelope from the bone marrow of TP and non-TP patients and constructed recombinant viruses. We demonstrate that the bone marrow of TP and non-TP patients contained R5 strains, whereas X4 strains were present only in the bone marrow of TP patients. Furthermore, HIV-1 from the bone marrow of TP and non-TP patients infected megakaryocytes to similar levels, suggesting that the V3 loop of HIV-1 may not contain the viral determinants of HIV-associated TP. Chemokine receptor analysis determined that CD34+-cell-derived megakaryocytes express CD4, CXCR4, and CCR5 and are productively infected by both X4 and R5 HIV-1 isolates. Finally, we showed that CD34+-cell-derived megakaryocytes express the chemokine receptor CCR3.

Immune reconstitution in AIDS: oncologic implications and hematologic approaches

Combination anti-retroviral therapy for HIV disease has profoundly altered the nature of the AIDS epidemic. Mitigating the impact of an uncontrollable decline in immune function is no longer the focal point for AIDS therapy, but has evolved to an emphasis on maximizing the potential for immune regeneration. Improved control of HIV replication has diminished, albeit unevenly, the frequency of AIDS-related malignancies and has altered the focus of hematologic and oncologic interventions in HIV disease. Now, with adoptive cellular therapies and the genetic engineering of cells in the clinical arena, the potential for cellular therapeutics in enhancing immune restoration is being tested. These approaches are based on better understanding of the immunobiology of HIV and its impact on hematopoietic tissues.

Human immunodeficiency virus type 1-induced hematopoietic inhibition is independent of productive infection of progenitor cells in vivo

Human immunodeficiency virus (HIV)-infected individuals exhibit a variety of hematopoietic dysfunctions. The SCID-hu mouse (severe combined immunodeficient mouse transplanted with human fetal thymus and liver tissues) can be used to model the loss of human hematopoietic precursor cell function following HIV infection and has a distinct advantage in that data can be obtained in the absence of confounding factors often seen in infected humans. In this study, we establish that HIV type 1 (HIV-1) bearing a reporter gene inserted into the viral vpr gene is highly aggressive in depleting human myeloid and erythroid colony-forming precursor activity in vivo. Human CD34(+) progenitor cells can be efficiently recovered from infected implants yet do not express the viral reporter gene, despite severe functional defects. Our results indicate that HIV-1 infection alone leads to hematopoietic inhibition in vivo; however, this effect is due to indirect mechanisms rather than to direct infection of CD34(+) cells in vivo.

Reconstitution of human thymic implants is limited by human immunodeficiency virus breakthrough during antiretroviral therapy

Human immunodeficiency virus type 1 (HIV-1)-infected SCID-hu thymic implants depleted of CD4(+) cells can support renewed thymopoiesis derived from both endogenous and exogenous T-cell progenitors after combination antiretroviral therapy. However, successful production of new thymocytes occurs transiently. Possible explanations for the temporary nature of this thymic reconstitution include cessation of the thymic stromal support function, exhaustion of T-cell progenitors, and viral resurgence. Distinguishing between these processes is important for the development of therapeutic strategies aimed at reconstituting the CD4(+) T-cell compartment in HIV-1 infection. Using an HIV-1 strain engineered to express the murine HSA heat-stable antigen surface marker, we explored the relationship between HIV-1 expression and CD4(+) cell resurgence kinetics in HIV-1-depleted SCID-hu implants following drug therapy. Antiviral therapy significantly suppressed HIV-1 expression in double-positive (DP) CD4/CD8 thymocytes, and the eventual secondary decline of DP thymocytes following therapy was associated with renewed viral expression in this cell subset. Thymocytes derived from exogenous T-cell progenitors induced to differentiate in HIV-1-depleted, drug-treated thymic implants also became infected. These results indicate that in this model, suppression of viral replication occurs transiently and that, in spite of drug therapy, virus resurgence contributes to the transient nature of the renewed thymic function.

Induction of MHC Class I Expression on Immature Thymocytes in HIV-1-Infected SCID-hu Thy/Liv Mice: Evidence of Indirect Mechanisms

The SCID-hu Thy/Liv mouse and human fetal thymic organ culture (HF-TOC) models have been used to explore the pathophysiologic mechanisms of HIV-1 infection in the thymus. We report here that HIV-1 infection of the SCID-hu Thy/Liv mouse leads to the induction of MHC class I (MHCI) expression on CD4+CD8+ (DP) thymocytes, which normally express low levels of MHCI. Induction of MHCI on DP thymocytes in HIV-1-infected Thy/Liv organs precedes their depletion and correlates with the pathogenic activity of the HIV-1 isolates. Both MHCI protein and mRNA are induced in thymocytes from HIV-1-infected Thy/Liv organs, indicating induction of MHCI gene expression. Indirect mechanisms are involved, because only a fraction (&lt;10%) of the DP thymocytes were directly infected by HIV-1, although the majority of DP thymocytes are induced to express high levels of MHCI. We further demonstrate that IL-10 is induced in HIV-1-infected thymus organs. Similar HIV-1-mediated induction of MHCI expression was observed in HF-TOC assays. Exogenous IL-10 in HF-TOC induces MHCI expression on DP thymocytes. Therefore, HIV-1 infection of the thymus organ leads to induction of MHCI expression on immature thymocytes via indirect mechanisms involving IL-10. Overexpression of MHCI on DP thymocytes can interfere with thymocyte maturation and may contribute to HIV-1-induced thymocyte depletion.

Induction of MHC class I expression on immature thymocytes in HIV-1-infected SCID-hu Thy/Liv mice: evidence of indirect mechanisms

The SCID-hu Thy/Liv mouse and human fetal thymic organ culture (HF-TOC) models have been used to explore the pathophysiologic mechanisms of HIV-1 infection in the thymus. We report here that HIV-1 infection of the SCID-hu Thy/Liv mouse leads to the induction of MHC class I (MHCI) expression on CD4+CD8+ (DP) thymocytes, which normally express low levels of MHCI. Induction of MHCI on DP thymocytes in HIV-1-infected Thy/Liv organs precedes their depletion and correlates with the pathogenic activity of the HIV-1 isolates. Both MHCI protein and mRNA are induced in thymocytes from HIV-1-infected Thy/Liv organs, indicating induction of MHCI gene expression. Indirect mechanisms are involved, because only a fraction (<10%) of the DP thymocytes were directly infected by HIV-1, although the majority of DP thymocytes are induced to express high levels of MHCI. We further demonstrate that IL-10 is induced in HIV-1-infected thymus organs. Similar HIV-1-mediated induction of MHCI expression was observed in HF-TOC assays. Exogenous IL-10 in HF-TOC induces MHCI expression on DP thymocytes. Therefore, HIV-1 infection of the thymus organ leads to induction of MHCI expression on immature thymocytes via indirect mechanisms involving IL-10. Overexpression of MHCI on DP thymocytes can interfere with thymocyte maturation and may contribute to HIV-1-induced thymocyte depletion.

Population biology of HIV-1 infection: viral and CD4+ T cell demographics and dynamics in lymphatic tissues

Human immunodeficiency virus-1 (HIV-1) is usually transmitted through sexual contact and in the very early stages of infection establishes a persistent infection in lymphatic tissues (LT). Virus is produced and stored at this site in a dynamic process that slowly depletes the immune system of CD4+ T cells, setting the stage for AIDS. In this review, I describe the changes in viral and CD4+ T cell populations in LT over the course of infection and after treatment. I present recent evidence that productively infected CD4+ T cells play an important role in establishing persistent infection from the onset, and that the LT are the major reservoir where virus is produced and stored on follicular dendritic cells (FDCs). I discuss the methods used to define the size of viral and CD4+ T cell populations in LT and the nature of virus-host cell interactions in vivo. These experimental approaches have identified populations of latently and chronically infected cells in which virus can elude host defenses, perpetuate infection, and escape eradication by highly active antiretroviral treatment (HAART). I discuss the dramatic impact of HAART on suppressing virus production, reducing the pool of stored virus, and restoring CD4+ T cell populations. I discuss the contributions of thymopoiesis and other renewal mechanisms, lymphatic homeostasis and trafficking to these changes in CD4+ T cell populations in LT, and conclude with a model of immune depletion and repopulation based on the limited regenerative capacity of the adult and the uncompensated losses of productively infected cells that treatment stems. The prediction of this model is that immune regeneration will be slow, variable, and partial. It is nonetheless encouraging to know that even in late stages of infection, control of active replication of HIV-1 provides an opportunity for the immune system to recover from the injuries inflicted by infection.

Gastrointestinal epithelium is an early extrathymic site for increased prevalence of CD34(+) progenitor cells in contrast to the thymus during primary simian immunodeficiency virus infection

The objective of this study was to determine the effects of primary simian immunodeficiency virus (SIV) infection on the prevalence and phenotype of progenitor cells present in the gastrointestinal epithelia of SIV-infected rhesus macaques, a primate model for human immunodeficiency virus pathogenesis. The gastrointestinal epithelium was residence to progenitor cells expressing CD34 antigen, a subset of which also coexpressed Thy-1 and c-kit receptors, suggesting that the CD34(+) population in the intestine comprised a subpopulation of primitive precursors. Following experimental SIVmac251 infection, an early increase in the proportions of CD34(+) Thy-1(+) and CD34(+) c-kit+ progenitor cells was observed in the gastrointestinal epithelium. In contrast, the proportion of CD34(+) cells in the thymus declined during primary SIV infection, which was characterized by a decrease in the frequency of CD34(+) Thy-1(+) progenitor cells. A severe depletion in the frequency of CD4-committed CD34(+) progenitors was observed in the gastrointestinal epithelium 2 weeks after SIV infection which persisted even 4 weeks after infection. A coincident increase in the frequency of CD8- committed CD34(+) progenitor cells was observed during primary SIV infection. These results indicate that in contrast to the primary lymphoid organs such as the thymus, the gastrointestinal epithelium may be an early extrathymic site for the increased prevalence of both primitive and committed CD34(+) progenitor cells. The gastrointestinal epithelium may potentially play an important role in maintaining T-cell homeostasis in the intestinal mucosa during primary SIV infection.

Growth hormone in immune reconstitution

Immune cell death or dysfunction is induced by HIV infection and results in an immunocompromised state. Newer treatments are able to control viral replication to prevent massive cytoreduction. Attention must now focus on therapies that will rapidly reconstitute the immune system to provide defense against future HIV attacks as well as opportunistic infections. In addition to increasing the rate of differentiation of myeloid and lymphoid precursors from marrow stem cells, ideal therapies should improve thymic function as well. Growth hormone (GH), a member of the hematopoietic cytokine superfamily and its receptors, is expressed in multiple sites within the immune system. GH has been shown to have a stimulatory effect on the function of thymic cells, as well as other immune cell types. In this paper, we consider the use of GH to reconstitute the immune system following cytoreduction due to HIV infection.