Stem cell repopulation efficiency but not pool size is governed by p27(kip1).

Sustained blood cell production requires preservation of a quiescent, multipotential stem cell pool that intermittently gives rise to progenitors with robust proliferative potential. The ability of cells to shift from a highly constrained to a vigorously active proliferative state is critical for maintaining stem cells while providing the responsiveness necessary for host defense. The cyclin-dependent kinase inhibitor (CDKI), p21(cip1/waf1) (p21) dominates stem cell kinetics. Here we report that another CDKI, p27(kip1) (p27), does not affect stem cell number, cell cycling, or self-renewal, but markedly alters progenitor proliferation and pool size. Therefore, distinct CDKIs govern the highly divergent stem and progenitor cell populations. When competitively transplanted, p27-deficient stem cells generate progenitors that eventually dominate blood cell production. Modulating p27 expression in a small number of stem cells may translate into effects on the majority of mature cells, thereby providing a strategy for potentiating the impact of transduced cells in stem cell gene therapy.

Generation of human T lymphocytes from bone marrow CD34+ cells in vitro.

Analysis of the events that regulate development of red blood cells or granulocytes has led to therapies altering clinical conditions associated with anemia or neutropenia. The development of therapeutic approaches to target conditions associated with lymphopenia, such as AIDS, has been thwarted by limited techniques for studying T-lymphocyte development. We describe an in vitro system in which human bone marrow CD34+ cells proliferate, acquire the expression of the lymphoid-specific RAG-2 gene and a broad repertoire of rearranged T-cell receptor genes, develop the ability to produce T cell-specific interleukin-2 and achieve a range of T-cell immunophenotypes. The cells also become susceptible to infection with the T-lymphotropic strain of human immunodeficiency virus-1, HIV-1IIIB. This culture system induces human T lymphopoiesis and may permit further analysis of the events regulating human T-lineage differentiation. It provides a preclinical model for screening stem cell gene therapies directed toward AIDS.

Epstein-Barr virus-driven gene therapy for EBV-related lymphomas.

Genetic alterations in malignant tissues are potential targets for gene-based cancer therapies. Alternatively, aberrant expression of certain specific genes associated with malignant transformation may be envisioned to enhance the expression of chemosensitizing drugs. Epstein-Barr virus (EBV)-related B-cell lymphomas are fatal complications of immunosuppression due to AIDS, organ transplantation or congenital immune abnormalities. The malignant cells latently infected with EBV typically express the transcription factor EBNA2 as one of nine latent viral genes. We tested whether an EBNA2-responsive EBV promoter may selectively target EBV-related lymphoma cells by virus-regulated expression of a suicide gene. Using the BamC promoter driving a hygromycin-thymidine kinase fusion gene or controls, we demonstrated that sensitivity to ganciclovir was selectively enhanced in cells expressing EBNA2. Further, there was complete macroscopic regression of established B-cell lymphomas in mice with severe combined immunodeficiency disease (SCID mice) treated with a single course of ganciclovir. These data provide in vitro and in vivo support for a model of exploiting the molecular basis of tumor development to enhance the specificity of gene therapy.

Active movement of T cells away from a chemokine.

Movement towards or away from a given stimulus guides the directional migration of prokaryotes, simple eukaryotes and neurons. As bi-directional cues may influence entry and exit of immune effector cells from tissue sites, we evaluated the migratory responses of T-cell subsets to varying concentrations of the chemokine stromal cell derived factor-1 (SDF-1). There was selective repulsion of subpopulations of T cells at high concentrations of recombinant SDF-1 or naturally occurring bone marrow-derived SDF-1, which could be inhibited by pertussis toxin and antibody against the chemokine receptor CXCR4. Distinct sensitivity profiles to genistein, herbimycin and 8-Br-cAMP biochemically distinguished movement of cells towards or away from an SDF-1 gradient. In vivo, antigen-induced T-cell recruitment into the peritoneal cavity was reversed by high but not low concentrations of SDF-1. The phenomenon of movement away from a chemokine represents a previously unknown mechanism regulating the localization of mature T cells. It adds to the functional repertoire of chemokines that may participate in immune physiology and may be applied therapeutically to alter the immune response.

Osteoblastic cells regulate the haematopoietic stem cell niche.

Stem cell fate is influenced by specialized microenvironments that remain poorly defined in mammals. To explore the possibility that haematopoietic stem cells derive regulatory information from bone, accounting for the localization of haematopoiesis in bone marrow, we assessed mice that were genetically altered to produce osteoblast-specific, activated PTH/PTHrP receptors (PPRs). Here we show that PPR-stimulated osteoblastic cells that are increased in number produce high levels of the Notch ligand jagged 1 and support an increase in the number of haematopoietic stem cells with evidence of Notch1 activation in vivo. Furthermore, ligand-dependent activation of PPR with parathyroid hormone (PTH) increased the number of osteoblasts in stromal cultures, and augmented ex vivo primitive haematopoietic cell growth that was abrogated by gamma-secretase inhibition of Notch activation. An increase in the number of stem cells was observed in wild-type animals after PTH injection, and survival after bone marrow transplantation was markedly improved. Therefore, osteoblastic cells are a regulatory component of the haematopoietic stem cell niche in vivo that influences stem cell function through Notch activation. Niche constituent cells or signalling pathways provide pharmacological targets with therapeutic potential for stem-cell-based therapies.

Functional isolation and characterization of human hematopoietic stem cells.

Hematopoietic cells differentiate in steps marked by the acquisition or loss of specific phenotypic characteristics. Human bone marrow cells that were responsive to the early-acting cytokines Kit ligand and interleukin-3 were forced to a metabolic death. The subfraction remaining represented 1 in 10(5) bone marrow mononuclear cells, were determined to be quiescent by cell cycle analysis, and had a stem cell immunophenotype. The cells were highly enriched for long-term culture-initiating cells, were capable of secondary colony formation, and produced both myeloid and lymphoid progeny. Thus, this technically simple strategy led to the efficient purification of cells with characteristics of hematopoietic stem cells.

Hematopoietic stem cell quiescence maintained by p21cip1/waf1.

Relative quiescence is a defining characteristic of hematopoietic stem cells, while their progeny have dramatic proliferative ability and inexorably move toward terminal differentiation. The quiescence of stem cells has been conjectured to be of critical biologic importance in protecting the stem cell compartment, which we directly assessed using mice engineered to be deficient in the G1 checkpoint regulator, cyclin-dependent kinase inhibitor, p21cip1/waf1 (p21). In the absence of p21, hematopoietic stem cell proliferation and absolute number were increased under normal homeostatic conditions. Exposing the animals to cell cycle-specific myelotoxic injury resulted in premature death due to hematopoietic cell depletion. Further, self-renewal of primitive cells was impaired in serially transplanted bone marrow from p21-/- mice, leading to hematopoietic failure. Therefore, p21 is the molecular switch governing the entry of stem cells into the cell cycle, and in its absence, increased cell cycling leads to stem cell exhaustion. Under conditions of stress, restricted cell cycling is crucial to prevent premature stem cell depletion and hematopoietic death.

A niche opportunity for stem cell therapeutics.

The success of hematopoietic stem cell (HSC)-based therapies relies on the ability of the stem cells to both engraft and self-renew sufficiently in the bone marrow microenvironment. Previous studies identified that a number of components of bone contribute to the regulation of HSCs indicating that they participate in a stem cell 'niche'. This niche is a dynamic microenvironment that changes during development and with varying physiologic states. Components of it, such as the osteoblast, can be modulated through pharmacological treatment. Reasoning that the stem cell niche may be manipulated to augment the effectiveness of stem cell therapies, we demonstrated that daily treatment with parathyroid hormone (a clinically approved method for increasing osteoblast function) resulted in therapeutic benefit in three clinically relevant models of stem cell therapy. These results suggest that the niche may be a pharmacological target for altering stem cell function in settings of regenerative medicine.

Production of tumor necrosis factor alpha and interleukin 1 beta by monocytic cells infected with human immunodeficiency virus.

The production of tumor necrosis factor alpha (TNF alpha) and IL-1 beta by the monocytic cell line THP-1, productively infected with HIV-1, was investigated using specific RIA and Northern blot analysis. HIV-infected cells, like uninfected cells, did not constitutively produce any detectable amounts of protein or mRNA for TNF alpha or IL-1 beta. After stimulation with LPS or a combination of LPS plus IFN-gamma, TNF alpha and IL-1 beta were detected in tissue culture supernatants and cell lysates and transcripts for both cytokines were seen on Northern blots. No significant difference in production of these two cytokines was observed between uninfected and chronically infected cells. Acutely HIV-infected cells, however, showed phenotypic changes compatible with maturation and an increase in TNF alpha and IL-1 beta mRNA production, and released significantly higher levels of TNF alpha and IL-1 beta compared with chronically infected or uninfected cells. Furthermore, LPS stimulation of HIV-infected cells increased virus production. These results suggest that HIV-infected monocytic cells may produce increased amounts of TNF alpha and IL-1 beta in response to stimuli that could be present in vivo.

Extracellular calcium elicits a chemokinetic response from monocytes in vitro and in vivo.

Recruitment of macrophages to sites of cell death is critical for induction of an immunologic response. Calcium concentrations in extracellular fluids vary markedly, and are particularly high at sites of injury or infection. We hypothesized that extracellular calcium participates in modulating the immune response, perhaps acting via the seven-transmembrane calcium-sensing receptor (CaR) on mature monocytes/macrophages. We observed a dose-dependent increase in monocyte chemotaxis in response to extracellular calcium or the selective allosteric CaR activator NPS R-467. In contrast, monocytes derived from mice deficient in CaR lacked the normal chemotactic response to a calcium gradient. Notably, CaR activation of monocytes bearing the receptor synergistically augmented the transmigration response of monocytes to the chemokine MCP-1 in association with increased cell-surface expression of its cognate receptor, CCR2. Conversely, stimulation of monocytes with MCP-1 or SDF-1alpha reciprocally increased CaR expression, suggesting a dual-enhancing interaction of Ca(2+) with chemokines in recruiting inflammatory cells. Subcutaneous administration in mice of Ca(2+), MCP-1, or (more potently) the combination of Ca(2+) and MCP-1, elicited an inflammatory infiltrate consisting of monocytes/macrophages. Thus extracellular calcium functions as an ionic chemokinetic agent capable of modulating the innate immune response in vivo and in vitro by direct and indirect actions on monocytic cells. Calcium deposition may be both consequence and cause of chronic inflammatory changes at sites of injury, infection, and atherosclerosis.

CCAAT/enhancer binding protein alpha is a regulatory switch sufficient for induction of granulocytic development from bipotential myeloid progenitors.

The transcription factor CCAAT/enhancer binding protein alpha (C/EBPalpha) regulates a number of myeloid cell-specific genes. To delineate the role of C/EBPalpha in human granulopoiesis, we studied its expression and function in human primary cells and bipotential (granulocytic/monocytic) myeloid cell lines. We show that the expression of C/EBPalpha initiates with the commitment of multipotential precursors to the myeloid lineage, is specifically upregulated during granulocytic differentiation, and is rapidly downregulated during the alternative monocytic pathway. Conditional expression of C/EBPalpha alone in stably transfected bipotential cells triggers neutrophilic differentiation, concomitant with upregulation of the granulocyte-specific granulocyte colony-stimulating factor receptor and secondary granule protein genes. Moreover, induced expression of C/EBPalpha in bipotential precursors blocks their monocytic differentiation program. These results indicate that C/EBPalpha serves as a myeloid differentiation switch acting on bipotential precursors and directing them to mature to granulocytes.

Tat peptide-derivatized magnetic nanoparticles allow in vivo tracking and recovery of progenitor cells.

The ability to track the distribution and differentiation of progenitor and stem cells by high-resolution in vivo imaging techniques would have significant clinical and research implications. We have developed a cell labeling approach using short HIV-Tat peptides to derivatize superparamagnetic nanoparticles. The particles are efficiently internalized into hematopoietic and neural progenitor cells in quantities up to 10-30 pg of superparamagnetic iron per cell. Iron incorporation did not affect cell viability, differentiation, or proliferation of CD34+ cells. Following intravenous injection into immunodeficient mice, 4% of magnetically CD34+ cells homed to bone marrow per gram of tissue, and single cells could be detected by magnetic resonance (MR) imaging in tissue samples. In addition, magnetically labeled cells that had homed to bone marrow could be recovered by magnetic separation columns. Localization and retrieval of cell populations in vivo enable detailed analysis of specific stem cell and organ interactions critical for advancing the therapeutic use of stem cells.

Pulsed electric fields for selection of hematopoietic cells and depletion of tumor cell contaminants.

Purging of tumor cells and selection of stem cells are key technologies for enabling stem cell transplantation and stem cell gene therapy. Here we report a strategy for cell selection based on physical properties of the cells. Exposing cells to an external pulsed electric field (PEF) increases the natural potential difference across the cell membrane until a critical threshold is reached and pore formation occurs, resulting in fatal perturbation of cell physiology. Attaining this threshold is a function of the applied field intensity and cell size, with larger cells porated at lower field intensities than smaller cells. Since hematopoietic stem cells are smaller than other hematopoietic cells and tumor cells, we found that exposure of peripheral blood mononuclear cells (PBMCs) to PEFs caused stepwise elimination of monocytes without affecting the function of smaller lymphocyte populations. Mobilized peripheral blood exposed to PEFs was enriched for CD34+/CD38- cells and stem cell function was preserved. Furthermore, PEF treatment was able to selectively purge blood preparations of tumor cells and eradicate transplantable tumor.

Efficient generation of human T cells from a tissue-engineered thymic organoid.

Biocompatible inorganic matrices have been used to enhance bone repair by integrating with endogenous bone architecture. Hypothesizing that a three-dimensional framework might support reconstruction of other tissues as well, we assessed the capacity of a tantalum-coated carbon matrix to support reconstitution of functioning thymic tissue. We engineered a thymic organoid by seeding matrices with murine thymic stroma. Co-culture of human bone marrow-derived hematopoietic progenitor cells within this xenogeneic environment generated mature functional T cells within 14 days. The proportionate T-cell yield from this system was highly reproducible, generating over 70% CD3+ T cells from either AC133+ or CD34+ progenitor cells. Cultured T cells expressed a high level of T-cell receptor excision circles (TREC), demonstrating de novo T lymphopoiesis, and function of fully mature T cells. This system not only facilitates analysis of the T-lymphopoietic potential of progenitor cell populations; it also permits ex vivo genesis of T cells for possible applications in treatment of immunodeficiency.

Thrombopoietin receptor expression in human cancer cell lines and primary tissues.

c-mpl is the receptor for the recently identified megakaryocyte growth and differentiation factor thrombopoietin. Thrombopoietin has been shown to be capable of raising platelet counts in animals and is about to enter clinical trials in humans. In anticipation of its likely use in the care of patients receiving cancer chemotherapy, we evaluated the expression of human c-mpl by reverse transcription PCR on 39 human cell lines and 20 primary human tissue samples derived from both normal and malignant sources. c-mpl transcripts were found in all megakaryocytic cell lines tested (CMK, CMK-2B, CMK-2D, SO, and DAMI), the CD34+ leukemia cell line KMT-2, and a hepatocellular carcinoma cell line (Hep3B). Among primary tissues, fetal liver cells and brain had detectable levels of c-mpl message, and among primary tumors, none were found to express c-mpl. These data support the conclusion that c-mpl has restricted expression that is primarily, but not exclusively, related to megakaryocytopoiesis. These observations suggest that thrombopoietin is unlikely to have direct effects on other malignant or normal tissue should it have a clinical role in the treatment of chemotherapy-induced thrombocytopenia.

Hematopoietic Stem Cell and Its Bone Marrow Niche.

Stem cells do not thrive without their niche. The bone marrow microenvironment is where hematopoietic stem cells maintain their cell state while receiving physiological input to modify their activity in response to changing physiological demands. The complexity of the bone marrow microenvironment is being unraveled and indicates that multiple different cell types contribute to the regulation of stem and progenitor cells. Further, it is becoming evident that the bone marrow represents a composite of niches with different components and different functional roles in hematopoiesis. It is now evident that alterations in specific stromal cells that comprise the bone marrow microenvironment can contribute to hematologic pathology. In this chapter, we will review the history of the niche concept, evolving information about its components and how niche dysfunction may contribute to disease.

Results of a randomized study of IM862 nasal solution in the treatment of AIDS-related Kaposi's sarcoma.

PURPOSE: Although advances have been made in the treatment of AIDS-related Kaposi's sarcoma (AIDS-KS) with systemic chemotherapy, less toxic therapies are needed. IM862 is a naturally occurring peptide with antiangiogenic properties and was thus studied in patients with AIDS-KS. PATIENTS AND METHODS: IM862 was given as intranasal drops at a dose of 5 mg. Patients were randomized to two dosing schedules given in repeated cycles until disease progression or unacceptable toxicity: 5 days of therapy followed by 5 days off (n = 18) and every other day dosing (n = 26). RESULTS: Forty-two male patients and two female patients with a median age of 38 years (range, 22 to 53 years) were accrued. Twenty-one patients (47%) had more than 50 mucocutaneous lesions, 14 (32%) had lymphedema, and none had visceral involvement. Thirty-three patients (75%) had received prior systemic chemotherapy. Twenty-four patients (55%) had CD4(+) lymphocyte count

Granulocyte-macrophage colony-stimulating factor mitigates the neutropenia of combined interferon alfa and zidovudine treatment of acquired immune deficiency syndrome-associated Kaposi's sarcoma.

The combined use of zidovudine (ZDV) and interferon (IFN) alfa-2a has been shown to have antiretroviral and antitumor potential benefit in the treatment of acquired immune deficiency syndrome (AIDS)-associated Kaposi's sarcoma (KS). However, the clinical use of this combination is frequently complicated by the overlapping myelotoxicity of these agents. We report here the results of a phase I/II study in which granulocyte-macrophage colony-stimulating factor (GM-CSF) was used for those KS patients who became neutropenic while receiving ZDV (1,200 mg/d) and IFN (9 x 10(6) U/d). Nineteen of 29 patients (66%) developed an absolute neutrophil count (ANC) of less than 1,000 cells per cubic millimeter and were begun on GM-CSF. All experienced a prompt increase in the ANC. Those patients receiving GM-CSF/ZDV/IFN alfa-2a had an improved end of study ANC when compared with the ZDV/IFN alfa-2a group, but did not have an increased rate of tumor response, end of study CD4 cell count, or improvement in any other hematologic variable. The use of GM-CSF was not associated with increased toxicity and, in particular, was not associated with a change in serum human immunodeficiency virus (HIV) p24 antigen. Tumor response was noted in 50% of the assessable patients (33% overall) despite "high-risk" characteristics in 80%. Of the responding patients, seven were on GM-CSF and might have otherwise required an alteration in ZDV/IFN alfa-2a dose level. Further study of GM-CSF as an alternate to dose modification of this (ZDV/IFN alfa-2a) and other combination therapies for AIDS patients is warranted.

Phase II trial of liposomal daunorubicin in the treatment of AIDS-related pulmonary Kaposi's sarcoma.

PURPOSE: Kaposi's sarcoma (KS) is the most common tumor in patients with AIDS and can be fatal in patients with lung involvement. Systemic chemotherapy is the most effective treatment for pulmonary KS. We thus conducted this study to determine the efficacy of liposomal daunorubicin in the treatment of patients with pulmonary KS. METHODS: Patients with biopsy-proven, symptomatic pulmonary KS were accrued. Liposomal daunorubicin was given at a dose of 60 mg/m2 intravenously every 2 weeks. Response was monitored by chest radiographs, pulmonary function tests, arterial blood gases, and grading of pulmonary symptoms. RESULTS: Fifty-three male patients were accrued. The median CD4+ lymphocyte count was 13/microL (range, 0 to 200); 70% reported a prior AIDS-defining opportunistic infection. All patients were symptomatic, with cough reported in all patients, shortness of breath in 94%, and hemoptysis in 55%. The mean study entry diffusing capacity of carbon monoxide (DLCO) was 58.5% (percent of predicted). The median dose of liposomal daunorubicin delivered was 360 mg/m2 (range, 60 to 1,380). More than 75% of patients had complete or partial resolution of baseline pulmonary symptoms. Complete or partial improvement in DLCO was observed in 22%; complete or partial resolution of radiographic abnormalities was reported in 32%. The most common treatment-related toxicity was neutropenia, which occurred in 85%. There were no instances of cardiac toxicity observed, even at high cumulative doses. CONCLUSION: Liposomal daunorubicin at 60 mg/m2 is safe and active in patients with pulmonary KS. Trials combining liposomal daunorubicin with other active agents in KS should be considered.