Angptl4 maintains in vivo repopulation capacity of CD34+ human cord blood cells.

Objectives: Methods to expand hematopoietic stem cells (HSCs) ex vivo encompass an attractive approach that would substantially broaden the clinical applicability of HSCs derived from cord blood (CB). Recently, members of the angiopoietin-like (Angptl) family of growth factors were shown to expand both murine and human HSCs. Specifically, Angptl5 has been implicated in the expansion of human NOD/SCID-repopulating cells (SRCs) ex vivo.

Hoxa9/hoxb3/hoxb4 compound null mice display severe hematopoietic defects.

Objective: Members of the hox family of homeodomain-containing transcription factors, including hoxa9, hoxb3, and hoxb4 play an important role in the regulation of differentiation, proliferation and self-renewal of hematopoietic stem and progenitor cells. Lack-of-function studies using hoxa9, hoxb4, or hoxb3/hoxb4 null mice demonstrate that all these mutations compromise the repopulating ability of hematopoietic stem cells (HSC), implying similar functions of each of these genes in hematopoiesis. Because cross regulation and cooperativity are known features of hox proteins, we investigated mice with a compound deficiency in hoxa9, hoxb3 and hoxb4 (hoxa9/b3/b4) for evidence of synergy between these genes in hematopoiesis.

Hematopoietic stem cell-targeted neonatal gene therapy reverses lethally progressive osteopetrosis in oc/oc mice.

Infantile malignant osteopetrosis (IMO) is a fatal disease caused by lack of functional osteoclasts, and the only available treatment is hematopoietic stem cell (HSC) transplantation. In the majority of patients, the TCIRG1 gene, coding for a subunit of a proton pump essential for bone resorption, is mutated. Oc/oc mice have a deletion in the homologue gene (tcirg1) and die at 3 to 4 weeks, but can be rescued by neonatal transplantation of HSCs.

Adenoviral vectors for transient gene expression in human primitive hematopoietic cells: applications and prospects.

The proliferation and differentiation of primitive hematopoietic cells is tightly controlled by a number of signaling pathways. Transient blockage or enhancement of these signaling pathways may provide a new approach to manipulate the proliferation and differentiation of primitive hematopoietic cells. Adenoviral vectors have in recent years emerged as powerful tools for transient gene expression in human primitive hematopoietic cells.

HOXA10 is a critical regulator for hematopoietic stem cells and erythroid/megakaryocyte development.

The Homeobox (Hox) transcription factors are important regulators of normal and malignant hematopoiesis because they control proliferation, differentiation, and self-renewal of hematopoietic cells at different levels of the hematopoietic hierarchy. In transgenic mice we show that the expression of HOXA10 is tightly regulated by doxycycline. Intermediate concentrations of HOXA10 induced a 15-fold increase in the repopulating capacity of hematopoietic stem cells (HSCs) after 13 days of in vitro culture.

HOXB4-induced self-renewal of hematopoietic stem cells is significantly enhanced by p21 deficiency.

Enforced expression of the HOXB4 transcription factor and downregulation of p21(Cip1/Waf) (p21) can each independently increase proliferation of murine hematopoietic stem cells (HSCs). We asked whether the increase in HSC self-renewal generated by overexpression of HOXB4 is enhanced in p21-deficient HSCs. HOXB4 was overexpressed in hematopoietic cells from wild-type (wt) and p21-/- mice.

Hoxb4-deficient mice undergo normal hematopoietic development but exhibit a mild proliferation defect in hematopoietic stem cells.

Enforced expression of Hoxb4 dramatically increases the regeneration of murine hematopoietic stem cells (HSCs) after transplantation and enhances the repopulation ability of human severe combined immunodeficiency (SCID) repopulating cells. Therefore, we asked what physiologic role Hoxb4 has in hematopoiesis. A novel mouse model lacking the entire Hoxb4 gene exhibits significantly reduced cellularity in spleen and bone marrow (BM) and a subtle reduction in red blood cell counts and hemoglobin values.

Enforced adenoviral vector-mediated expression of HOXB4 in human umbilical cord blood CD34+ cells promotes myeloid differentiation but not proliferation.

Retroviral overexpression of the transcription factor HOXB4 results in a rapid increase in proliferation of murine hematopoietic stem cells both in vivo and in vitro. Therefore, we asked whether transient overexpression of HOXB4 would increase proliferation of human primitive hematopoietic progenitors. Transient overexpression of HOXB4 was generated in umbilical cord blood (CB) CD34(+) cells by a recombinant adenovirus (AdHOXB4) expressing HOXB4 together with the enhanced green fluorescent protein (GFP).

Reduced proliferative capacity of hematopoietic stem cells deficient in Hoxb3 and Hoxb4.

Several homeobox transcription factors, such as HOXB3 and HOXB4, have been implicated in regulation of hematopoiesis. In support of this, studies show that overexpression of HOXB4 strongly enhances hematopoietic stem cell regeneration. Here we find that mice deficient in both Hoxb3 and Hoxb4 have defects in endogenous hematopoiesis with reduced cellularity in hematopoietic organs and diminished number of hematopoietic progenitors without perturbing lineage commitment.

Proliferation deficiency of multipotent hematopoietic progenitors in ribosomal protein S19 (RPS19)-deficient diamond-Blackfan anemia improves following RPS19 gene transfer.

Diamond-Blackfan anemia (DBA) is a congenital bone marrow failure syndrome characterized by a specific deficiency in erythroid progenitors. Since some patients with DBA develop a reduction in thrombocytes and granulocytes with age, we asked whether multipotent hematopoietic progenitors from DBA patients had normal proliferative capacity in liquid expansion cultures. CD34(+) cells derived from DBA patients showed deficient proliferation in liquid culture containing IL-3, IL-6, and SCF.

Gene transfer improves erythroid development in ribosomal protein S19-deficient Diamond-Blackfan anemia.

Diamond-Blackfan anemia (DBA) is a congenital bone marrow failure syndrome characterized by a specific deficiency in erythroid progenitors. Forty percent of the patients are blood transfusion-dependent. Recent reports show that the ribosomal protein S19 (RPS19) gene is mutated in 25% of all patients with DBA.

Overexpression of gibbon ape leukemia virus (GALV) receptor (GLVR1) on human CD34(+) cells increases gene transfer mediated by GALV pseudotyped vectors.

Retroviral transduction of CD34(+) cells on Retronectin using gibbon ape leukemia virus (GALV) pseudotyped vectors is inhibited by high concentrations of vector containing medium (VCM). Furthermore, this inhibitory activity is stable for at least 48 hours at 37 degrees C and partially blocks a second hit with a GALV pseudotyped vector. We hypothesized that this inhibition was due to interference at the receptor level between infectious and noninfectious vector particles and that it might be possible to overcome it by increasing receptor expression on target cells.

Transient disruption of autocrine TGF-beta signaling leads to enhanced survival and proliferation potential in single primitive human hemopoietic progenitor cells.

Hemopoietic stem cells (HSCs) are maintained at relative quiescence by the balance between the positive and negative regulatory factors that stimulate or inhibit their proliferation. Blocking the action of negative regulatory factors may provide a new approach for inducing HSCs into proliferation. A variety of studies have suggested that TGF-beta negatively regulates cell cycle progression of HSCs.