Decreased haematopoietic colony growth in long-term bone marrow cultures of HIV-positive patients

Early bone marrow hematopoietic defect in simian/human immunodeficiency virus C2/1-infected macaques and relevance to advance of disease

To clarify hematological abnormalities following infection with human immunodeficiency virus (HIV), we examined the hematopoietic capability of bone marrow by using cynomolgus monkeys infected with pathogenic simian/human immunodeficiency virus (SHIV) strain C2/1, an animal model of HIV infection. The relationship between the progress of the infection and the CD4/CD8 ratio of T lymphocytes or the amount of SHIV C2/1 viral load in the peripheral blood was also investigated. A colony assay was performed to assess the hematopoietic capability of bone marrow stem cells during the early and advanced phases of the infection. Colonies of granulocytes-macrophages (GM) were examined by PCR for the presence of the SIVmac239 gag region to reveal direct viral infection. There was a remarkable decrease in the CFU-GM growth on days 1 and 3 postinoculation, followed by recovery on day 56. During the more advanced stage, the CFU-GM growth decreased again. There was minimal evidence of direct viral infection of pooled cultured CFU-GM despite the continuously low CD4/CD8 ratios. These results indicate that the decrease in colony formation by bone marrow stem cells is reversible and fluctuates with the advance of the disease. This decrease was not due to direct viral infection of CFU-GM. Our data may support the concept that, in the early phase, production of inhibitory factors or deficiency of a stimulatory cytokine is responsible for some of the bone marrow defects described in the SHIV C2/1 model.

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.

Basic fibroblast growth factor (bFGF) and its receptor expression (bek and flg) In bone marrow stroma of murine AIDS

Murine acquired immunodeficiency disease (MAIDS) induced by LPBM5 MuLV is characterized by a late-stage lymphoma and hematopoietic cytopenias similar to those observed in human AIDS. The pathogenesis of MAIDS-related lymphoma/cytopenia is unknown but it has been postulated to involve a defective marrow microenvironment or stroma. The basic Fibroblast Growth Factor (bFGF) of stromal origin is an important stimulator for hematopoietic progenitors of several lineages. Long-term bone marrow cultures (LTBMCs) were established and pure stromal cell cultures were used for in vitro infection hematopoietic reconstitution studies. Reverse transcription-polymerase chain reaction (RT-PCR) was used to analyze bFGF gene expression in stromal cells derived from either viral-infected marrow or uninfected marrow. RT-PCR analysis showed a 40% reduction in the expression of bFGF transcript expression from viral-infected stromal cells, however, the levels of bek and flg bFGF receptors remained unchanged indicating virus-infection only inhibited bFGF gene expression in stromal cells. Viral infection was associated with a progressive decrease in bFGF transcript expression 35% of control at day 7, 50% of control at day 14 and 60% of control at day 21 compared to the mock-infected cultures. In addition, for bek and flg the transcript expression in, in vitro-infected primary cultures were comparable to the mock-infected cultures and remained essentially unchanged throughout culture period. Western blot analysis revealed viral-infected stromal cells produced a 45% decrease in bFGF protein production. Reduction of bFGF protein was confirmed by indirect immunofluorescent staining. We report MuLV infection reduces bFGF transcript expression but not its surface-receptors (bek and flg) in infected stromal cells. Impaired hematopoiesis consistently exhibited from MuLV-infected stromal cultures was restored by exogenous bFGF; therefore, bFGF was responsible in restoration of normal marrow stromal support function. These results suggest a role for bFGF deficiency in the pathogenesis of MAIDS-related marrow failure.

Increase in plasmacytoid and myeloid dendritic cells by progenipoietin-1, a chimeric Flt-3 and G-CSF receptor agonist, in SIV-Infected rhesus macaques

As in HIV-1 infection in humans, SIVsm infection of rhesus macaques causes a slow progressive loss of CD4 T-cells followed by the onset of AIDS. In addition, there is a loss of dendritic cells (DC) in peripheral blood, peripheral lymphoid tissues, and the skin. Increasing the number of CD4 T cells and DC may be an important step in restoring immune competence and thus delay disease progression. Recently, progenipoietins (ProGP), a new family of chimeric Flt3 and G-CSF receptor agonists, were demonstrated to possess the capacity to mobilize hematopoietic progenitor cells in normal rhesus monkeys. In addition, these molecules induced increased numbers of myeloid cells, including dendritic cells, in the blood. Here we demonstrate that SIVsm-infected macaques, treated with ProGP-1, developed increased numbers of both plasmacytoid (CD123+, CD11c-) and myeloid (both CD11b+, CD11c+, and CD123-, CD11c+ subsets) DC and CD4 and CD8 T cells in peripheral blood. Importantly, during treatment, no changes in plasma virus load were observed. After 14 to 20 days of treatment, antibodies were formed against ProGP in all animals. As a consequence, white blood cell levels returned to baseline in several animals. In other animals values only returned to baseline after termination of ProGP treatment. In conclusion, ProGP-1 may be used to generate a transient increase in DC as well as CD4 T-cell numbers, thereby creating a window of opportunity for immunotherapeutic intervention.

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.

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.

Hematologic and virologic effects of lineage-specific and non-lineage-specific recombinant human and rhesus cytokines in a cohort of SIVmac239-infected macaques

The hematologic abnormalities of SIV and HIV are well described, although the mechanisms that lead to hematopoietic dysfunction are yet to be fully defined. A number of growth factors and cytokines have been used to induce the differentiation, maturation, and proliferation of appropriate lineages, with the aim that such therapy will lead to functional hematopoietic reconstitution. Within this context, some cytokines have been shown to influence HIV and SIV replication in vitro and, in selected cases, in vivo. However, few studies detail the effects of hematopoietic cytokines such as IL-3, Flt-3 ligand, G-CSF, Tpo, and Epo or correlate the effects on virus replication. In an effort to address this issue, we infected 12 rhesus macaques with 500 TCID50 of SIVmac239 and intensively evaluated hematologic, virologic, and immunologic parameters during administration of cytokines. When all animals had lymphadenopathy, hepatosplenomegaly, and CD4+ cell counts > or =1000/microl, subgroups of three rhesus macaques were administered either rhFlt-3; rrIL-3a; combination of rhG-CSF, rhTpo, and rhEpo (rhGET); or rrIL-12. Fourteen days of rhFlt-3 administration induced expansion of the bone marrow CD34+ cells and granulocyte-macrophage colony-forming units (GM-CFUs) and increased absolute peripheral blood CD34+ cells and total CFUs. Following rrIL-3 and rhGET administration absolute peripheral blood CD34+ cells and total CFUs increased. rhGET also increased granulocyte, platelet, and reticulocyte counts by day 14 of administration. Branched DNA and coculture assays did not demonstrate any significant change in viral load with any of the cytokines administered. These data suggest that SIV-infected rhesus macaques have the hematopoietic capability to expand and mobilize CD34+ and GM-CFU progenitors and formed elements at 6-8 months postinfection in response to various cytokines, without increasing viral load.

Neither Human Immunodeficiency Virus-1 (HIV-1) nor HIV-2 Infects Most-Primitive Human Hematopoietic Stem Cells as Assessed in Long-Term Bone Marrow Cultures

Attempts to clarify the pathophysiology of human immunodeficiency virus (HIV)-mediated bone marrow (BM) dysfunction have yielded inconsistent results regarding the susceptibility of BM progenitors to the viral infection. To specifically address this question, we exposed highly purified subpopulations of human BM progenitor cells to various HIV-1 and HIV-2 strains and assessed (pro)viral gene presence and expression in more-committed (CD34+CD38+) as well as most-primitive (CD34+CD38−) cells in long-term BM cultures. Quantitative analysis of long-term culture-initiating cells (LTCIC) failed to demonstrate adverse effects of exposing hematopoietic stem cells to HIV. Our results show that HIV-2, similar to HIV-1, does not infect hematopoietic stem cells in vitro with any significant frequency and infected cells are not present within LTCICs. Cytofluorometric analysis of CD34+ cells for surface molecules that facilitate HIV entry was consistent with the functional assay in that expression of virus receptors was predominantly on the more-committed subsets of BM progenitors. The failure to detect productive or latent HIV in the most-primitive human BM progenitor and stem cells has important implications for future therapeutic strategies, including those dealing with transduction of these cells with protective genes as a treatment modality for AIDS.

Neither Human Immunodeficiency Virus-1 (HIV-1) nor HIV-2 Infects Most-Primitive Human Hematopoietic Stem Cells as Assessed in Long-Term Bone Marrow Cultures

Attempts to clarify the pathophysiology of human immunodeficiency virus (HIV)-mediated bone marrow (BM) dysfunction have yielded inconsistent results regarding the susceptibility of BM progenitors to the viral infection. To specifically address this question, we exposed highly purified subpopulations of human BM progenitor cells to various HIV-1 and HIV-2 strains and assessed (pro)viral gene presence and expression in more-committed (CD34+CD38+) as well as most-primitive (CD34+CD38−) cells in long-term BM cultures. Quantitative analysis of long-term culture-initiating cells (LTCIC) failed to demonstrate adverse effects of exposing hematopoietic stem cells to HIV. Our results show that HIV-2, similar to HIV-1, does not infect hematopoietic stem cells in vitro with any significant frequency and infected cells are not present within LTCICs. Cytofluorometric analysis of CD34+ cells for surface molecules that facilitate HIV entry was consistent with the functional assay in that expression of virus receptors was predominantly on the more-committed subsets of BM progenitors. The failure to detect productive or latent HIV in the most-primitive human BM progenitor and stem cells has important implications for future therapeutic strategies, including those dealing with transduction of these cells with protective genes as a treatment modality for AIDS.

Secondary colony formation after long-term bone marrow culture using peripheral blood and bone marrow of HIV-infected patients

OBJECTIVE

To determine if defective bone marrow function in HIV infection is associated with decreased numbers of progenitor cells or defective stromal cell function.

DESIGN

Defective bone marrow function may in part be responsible for the cytopenias so frequently seen in patients with AIDS. Although a number of investigators have reported impaired growth of committed hematopoietic progenitor cells in HIV-1-infected patients, few studies have examined the most primitive hematopoietic stem cells. Our study was designed to determine the function and quality of the most immature hematopoietic progenitor and stem cells in the peripheral blood and bone marrow of HIV-1-infected patients and to assess stromal cell function.

METHODS

For quantification of these cells we used a modified long-term culture-initiating cell (LTCIC) assay in which the number of secondary colony-forming cells after 5 weeks of stromal culture served as a measure of LTCIC. Stromal cells from normal controls and HIV-1-infected patients were used for cross-matching experiments. Normal CD34+ cells or those derived from HIV-infected patients were plated and colony growth assessed.

RESULTS

We found that HIV-1-infected patients had a mean of 0.8 secondary colony-forming cells/10(5) peripheral blood mononuclear cells (PBMC), whereas normal controls showed 1.2 secondary colony-forming cells/10(5) PBMC (P = not significant) after long-term culture. Asymptomatic patients showed well preserved numbers of secondary colony-forming cells after long-term culture of PBMC, but a significant reduction was seen in patients with a history of opportunistic infections (P < 0.01), low CD4+ cell count (< 200 x 10(6)/l; P < 0.05), or leukopenia (P < 0.05). Decreased numbers of secondary colony-forming cells have also been found in bone marrow of HIV-1-infected patients with advanced disease. When normal CD34+ cells were cultured on stromal layers from bone marrow of HIV-1-infected patients or normal controls, no differences in the numbers of surviving progenitor cells were found.

CONCLUSIONS

Our data indicate that the hematopoietic defect in HIV-1 infection involves the most immature hematopoietic cells and becomes evident in advanced disease. Stromal function of HIV-infected patients appears normal.

Infection of Human Marrow Stroma by Human Immunodeficiency Virus-1 (HIV-1) Is Both Required and Sufficient for HIV-1–Induced Hematopoietic Suppression In Vitro: Demonstration by Gene Modification of Primary Human Stroma

Patients with human immunodeficiency virus-1 (HIV-1) infection often present with bone marrow (BM) failure that may affect all hematopoietic lineages. It is presently unclear whether this failure reflects a direct viral impairment of the CD34+ hematopoietic progenitor cells or whether the virus affects the BM microenvironment. To study the effects of HIV-1 on the BM microenvironment, we examined the stromal cell monolayers in long-term BM culture (LTBMC), which are the in vitro equivalent of the hematopoietic microenvironment. We assessed the hematopoietic support function (HSF ) of human stromal layers by determining the cellular proliferation and colony-forming ability of hematopoietic progenitors from BM cells grown on the stromal layers. We show that the HSF is reduced by in vitro infection of the human stromal cell layer by a monocytotropic isolate of HIV-1 (JR-FL). There is no loss of HSF when the stromal cell layer is resistant to HIV-1 replication, either using murine stromal cell layers that are innately resistant to HIV-1 infection or using human stromal cells genetically modified to express a gene that inhibits HIV-1 replication (an RRE decoy). Decreased HSF was seen using either human or murine hematopoietic cells, if the stromal cells were human cells that were susceptible to HIV-1 infection. These in vitro studies implicate HIV-1 replication in the stroma as the essential component causing decreased hematopoietic cell production in HIV-1 infection.

Hematopoietic Potential and Retroviral Transduction of CD34+Thy-1+ Peripheral Blood Stem Cells From Asymptomatic Human Immunodeficiency Virus Type-1–Infected Individuals Mobilized With Granulocyte Colony-Stimulating Factor

The potential of hematopoietic stem cells (HSCs) from human immunodeficiency virus type-1 (HIV-1)–infected individuals, eg, self-renewal and multilineage differentiative capacity, might be perturbed due to the underlying disease. In this study, we assessed the HSC activity in the CD34+Thy-1+ cell population of peripheral blood stem cells (PBSCs) of three asymptomatic HIV-1–infected individuals after granulocyte colony-stimulating factor (G-CSF; 10 μg/kg/d) mobilization. On day 4 of G-CSF treatment, 0.8% to 1% of the total blood mononuclear cells were CD34+. Leukapheresis followed by a two-step cell isolation process yielded a CD34+Thy-1+ cell population of high purity (76% to 92% CD34+Thy-1+ cells). This cell population showed no evidence of HIV-1–containing cells based on a semiquantitative HIV-1 DNA polymerase chain reaction. Furthermore, the purified cells showed normal hematopoietic potential in in vitro clonogenic assays. Successful gene transfer into committed progenitor cells (colony-forming units-cells) and more primitive stem/progenitor cells (long-term culture colony-forming cells) could be shown after amphotropic retroviral transduction. These data provide evidence that the CD34+Thy-1+ stem cell compartment can be mobilized and enriched in early stage HIV-1–infected patients. Furthermore, successful transduction of this cell population as a prerequisite for stem cell-based clinical gene therapy protocols was demonstrated.

Hematopoietic Stem Cell–Based Gene Therapy for Acquired Immunodeficiency Syndrome: Efficient Transduction and Expression of RevM10 in Myeloid Cells In Vivo and In Vitro

Gene delivery via the hematopoietic stem cell (HSC) offers an attractive means to introduce antiviral genes into both T cells and macrophages for acquired immunodeficiency syndrome (AIDS) gene therapy. An amphotropic retroviral vector encoding a bicistronic gene coexpressing RevM10 and the murine CD8α′ chain (lyt2) was developed to transduce HSC/progenitor cells. After transduction of CD34+ cells isolated from human umbilical cord blood, the lyt2 molecule detected by flow cytometry was used to monitor the level of gene transduction and expression and to enrich RevM10-expressing cells by cell sorting without drug selection. Using this quantitative method, high levels of gene transduction and expression (around 20%) were achieved by high-speed centrifugation of CD34+ cells with the retroviral supernatant (spinoculation). After reconstitution of human bone marrow implanted in SCID mice (SCID-hu bone) with the transduced HSC/progenitor cells, a significant number of donor-derived CD14+ bone marrow cells were found to express the RevM10/lyt2 gene. Finally, replication of a macrophage-tropic human immunodeficiency virus–type 1 (HIV-1) isolate was greatly inhibited in the lyt2+/CD14+ cells differentiated from transduced CD34+ cells after the enrichment of lyt2+ population. Thus, the RevM10 gene did not appear to inhibit the differentiation of HSC/progneitor cells into monocytes/macrophages. The level of retrovirus-mediated RevM10 expression in monocytes/macrophages derived from transduced HSCs is sufficient to suppress HIV-1 replication.

Modified antisense oligodeoxynucleotides against the splice acceptor site of tat do not inhibit in vitro hematopoietic colony growth in HIV-positive patients

The hematopoietic failure in the majority of patients with progressive HIV infection is further aggravated by virustatic agents like azidothymidine. As an alternative therapeutic attempt, three derivatives of an antisense oligodeoxynucleotide (ODN) against the splice acceptor site of the tat gene have been shown to inhibit HIV replication in vitro. This study was aimed at examining whether these agents are toxic to the hematopoietic progenitor cells. To this end, bone marrow cells from HIV-positive and healthy persons were depleted from adherent cells to eliminate fibroblasts. In further experiments, the cells were additionally enriched for CD34-positive hematopoietic progenitor cells or were depleted from delta TCS-1-positive T lymphocytes. At concentrations of 1.25-10 microM, the three antisense ODN did not inhibit any erythrocyte or granulocyte-monocyte colony growth from CD34-positive cells, either from the HIV-positive or from the HIV-negative cohort. In contrast to azidothymidine, which served as inhibitory control, a significant increase of colony growth was seen after depletion of fibroblasts, of delta TCS-1-positive cells, or without cell separation. In conclusion, the three oligodeoxynucleotides do not exert any hematotoxic effect but do increase colony formation from low-density bone marrow cells in vitro and could therefore be useful in future clinical studies.

Impaired cytokine production by bone marrow stromal cells of immunodeficient mice

The aetiology of the bone marrow suppression in HIV-infected patients is unknown. We have demonstrated previously that the ability of bone marrow cells, derived from mice made immunodeficient by infection with the retrovirus LP-BM5, to establish long-term stromal cultures is impaired. In this study we determined the ability of bone marrow stromal cells from these immunodeficient mice to produce cytokines important in haemopoiesis. Neither SCF, IL-3, GM-CSF nor TNF alpha were found in conditioned media of long-term bone marrow cultures (LTBMC) of normal or MAIDS mice. We failed to detect mRNA for TNF or IL-1 alpha, by reverse transcription polymerase chain reaction (RT-PCR), in cultures derived from either normal or immunodeficient mice. Steady-state levels of transcripts for IL-6 were equal in cells from normal and MAIDS mice. Steady-state levels of mRNA for TGF beta 1, a known inhibitor of haemopoiesis, were decreased in cultures derived from MAIDS mice at late stages of infection. The mRNA level of the multipotent haemopoietic regulator stem cell factor was also decreased in MAIDS cultures as compared with normals. Transcripts encoding the transmembrane form of the growth factor were almost absent. Addition of soluble GM-CSF and SCF only transiently increased the production of CFUs (BFUE and CFU-G/M) in MAIDS LTBMC. These findings suggest that derangements in cytokine production in stromal cells of immunodeficient mice may contribute to the suppression of haemopoiesis observed in this disease. One mechanism of HIV-induced depression of haemopoiesis may be via alterations of the haemopoietic microenvironment.

Human immunodeficiency virus type 1 (HIV-1) and human hematopoietic progenitor cells

Besides a progressive depletion of CD4+ T-lymphocytes, other peripheral blood cytopenias, (granulocytopenia, anemia and thrombocytopenia) are frequently observed in HIV-1 seropositive individuals, especially in patients with overt AIDS. Various experimental evidences suggest that HIV-1 could play a direct role in the pathogenesis of HIV-1 related peripheral blood cytopenias, affecting the survival/proliferation capacity of hematopoietic progenitors. CD34+ human hematopoietic progenitors, however, are substantially not susceptible to HIV-1 infection either in vitro and in vivo and their defects seem rather related to an alteration of bone marrow and peripheral blood microenvironments due to the presence of soluble HIV-1 specific products.