Preincubation with endothelial cell monolayers increases gene transfer efficiency into human bone marrow CD34(+)CD38(-) progenitor cells

Epidermal growth factor regulates hematopoietic regeneration after radiation injury

The mechanisms which regulate HSC regeneration following myelosuppressive injury are not well understood. We identified epidermal growth factor (EGF) to be highly enriched in the bone marrow (BM) serum of mice bearing deletion of Bak and Bax in Tie2⁺ cells (Tie2Cre;Bak1^−/−;Bax^fl/− mice), which displayed radioprotection of the HSC pool and 100% survival following lethal dose total body irradiation (TBI). BM HSCs from wild type mice expressed functional EGFR and systemic administration of EGF promoted the recovery of the HSC pool in vivo and the improved survival of mice following TBI. Conversely, administration of erlotinib, an EGFR antagonist, significantly decreased both HSC regeneration and mice survival following TBI. VavCre;EGFR^fl/+ mice also demonstrated delayed recovery of BM stem/progenitor cells following TBI compared to VavCre;EGFR^+/+ mice. Mechanistically, EGF reduced radiation-induced apoptosis of HSCs and mediated this effect via repression of the proapoptotic protein, PUMA. EGFR signaling regulates HSC regeneration following myelosuppressive injury.

Separate mechanisms cause anemia in ischemic vs. nonischemic murine heart failure

In ischemic congestive heart failure (CHF), anemia is associated with poor prognosis. Whether anemia develops in nonischemic CHF is uncertain. The hematopoietic inhibitors TNF-α and nitric oxide (NO) are activated in ischemic CHF. We examined whether mice with ischemic or nonischemic CHF develop anemia and whether TNF-α and NO are involved. We studied mice ( n = 7–9 per group) with CHF either due to myocardial infarction (MI) or to overexpression of the Ca2+-binding protein calsequestrin (CSQ) or to induced cardiac disruption of the sarcoplasmic reticulum Ca2+-ATPase 2 gene (SERCA2 KO). Hematopoiesis was analyzed by colony formation of CD34+bone marrow cells. Hemoglobin concentration was 14.0 ± 0.4 g/dl (mean ± SD) in controls, while it was decreased to 10.1 ± 0.4, 9.7 ± 0.4, and 9.6 ± 0.3 g/dl in MI, CSQ, and SERCA2 KO, respectively ( P < 0.05). Colony numbers per 100,000 CD34+cells in the three CHF groups were reduced to 33 ± 3 (MI), 34 ± 3 (CSQ), and 39 ± 3 (SERCA2 KO) compared with 68 ± 4 in controls ( P < 0.05). Plasma TNF-α nearly doubled in MI, and addition of anti-TNF-α antibody normalized colony formation. Inhibition of colony formation was completely abolished with blockade of endothelial NO synthase in CSQ and SERCA2 KO, but not in MI. In conclusion, the mechanism of anemia in CHF depends on the etiology of cardiac disease; whereas TNF-α impairs hematopoiesis in CHF following MI, NO inhibits blood cell formation in nonischemic murine CHF.

Molecular Profile and Partial Functional Analysis of Novel Endothelial Cell-Derived Growth Factors that Regulate Hematopoiesis

Recent progress has been made in the identification of the osteoblastic cellular niche for hematopoietic stem cells (HSCs) within the bone marrow (BM). Attempts to identify the soluble factors that regulate HSC self-renewal have been less successful. We have demonstrated that primary human brain endothelial cells (HUBECs) support the ex vivo amplification of primitive human BM and cord blood cells capable of repopulating non-obese diabetic/severe combined immunodeficient repopulating (SCID) mice (SCID repopulating cells [SRCs]). In this study, we sought to characterize the soluble hematopoietic activity produced by HUBECs and to identify the growth factors secreted by HUBECs that contribute to this HSC-supportive effect. Extended noncontact HUBEC cultures supported an eight-fold increase in SRCs when combined with thrombopoietin, stem cell factor, and Flt-3 ligand compared with input CD34(+) cells or cytokines alone. Gene expression analysis of HUBEC biological replicates identified 65 differentially expressed, nonredundant transcripts without annotated hematopoietic activity. Gene ontology studies of the HUBEC transcriptome revealed a high concentration of genes encoding extracellular proteins with cell-cell signaling function. Functional analyses demonstrated that adrenomedullin, a vasodilatory hormone, synergized with stem cell factor and Flt-3 ligand to induce the proliferation of primitive human CD34(+)CD38(-)lin(-) cells and promoted the expansion of CD34(+) progenitors in culture. These data demonstrate the potential of primary HUBECs as a reservoir for the discovery of novel secreted proteins that regulate human hematopoiesis.

Quantitative analysis demonstrates expansion of SCID-repopulating cells and increased engraftment capacity in human cord blood following ex vivo culture with human brain endothelial cells

Initial clinical trials examining the transplantation of ex vivo expanded cord blood (CB) cells have failed to demonstrate an impact on hematopoietic recovery compared with historical unmanipulated CB controls. In this study, we tested whether coculture with primary human brain endothelial cells (HUBECs) could increase the engraftment capacity and repopulating cell frequency within CB CD34+ cells. Quantitative analysis demonstrated that HUBEC coculture for 7 days supported a 19-fold greater number of CD34+ cells and 3.4-fold and 2.6-fold greater severe combined immunodeficient (SCID)-repopulating cell (SRC) frequencies than fresh CB CD34+ cells and liquid suspension-cultured cells. Mice transplanted with day-14 HUBEC-cultured cells showed 4.2-fold higher levels of human engraftment than mice transplanted with day-7 HUBEC-cultured cells, indicating that SRC enrichment continued to occur through day 14. Noncontact HUBEC cultures also maintained SRCs at levels comparable with contact HUBEC cultures, demonstrating that HUBEC-secreted soluble factors critically supported SRC self-renewal. Seeding efficiency studies demonstrated that HUBEC-cultured CB CD34+ cells engrafted nonobese diabetic/SCID marrow at significantly higher levels than either fresh CB CD34+ cells or liquid suspension-cultured CD34+ cells. These studies indicate that the application of HUBEC coculture or HUBEC-conditioned media can potentially improve upon current strategies for the clinical expansion of CB stem cells.

Ex vivo culture with human brain endothelial cells increases the SCID-repopulating capacity of adult human bone marrow

Adult human bone marrow (ABM) is an important source of hematopoietic stem cells for transplantation in the treatment of malignant and nonmalignant diseases. However, in contrast to the recent progress that has been achieved with umbilical cord blood, methods to expand ABM stem cells for therapeutic applications have been disappointing. In this study, we describe a novel culture method that uses human brain endothelial cells (HUBECs) and that supports the quantitative expansion of the most primitive measurable cell within the adult bone marrow compartment, the nonobese diabetic/severe combined immunodeficient (NOD/SCID) repopulating cell (SRC). Coculture of human ABM CD34(+) cells with brain endothelial cells for 7 days supported a 5.4-fold increase in CD34(+) cells, induced more than 95% of the CD34(+)CD38(-) subset to enter cell division, and produced progeny that engrafted NOD/SCID mice at significantly higher rates than fresh ABM CD34(+) cells. Using a limiting dilution analysis, we found the frequency of SRCs within fresh ABM CD34(+) cells to be 1 in 9.9 x 10(5) cells. Following HUBEC culture, the estimated frequency of SRCs increased to 1 in 2.4 x 10(5) cells. All mice that received transplants of HUBEC-cultured cells showed B-lymphoid and myeloid differentiation, indicating that a primitive hematopoietic cell was preserved during culture. Noncontact HUBEC cultures also maintained SRCs at a level comparable to contact HUBEC cultures, suggesting that cell-to-cell contact was not required. These data demonstrate that human brain endothelial cells possess a unique hematopoietic activity that increases the repopulating capacity of adult human bone marrow.

Serum Flt3 ligand variation as a predictive indicator of hematopoietic stem cell mobilization

Flt3 ligand (FL) is a good indicator of bone marrow (BM) cellularity, having a reciprocal relationship with white blood cell (WBC) count in aplastic anemia and chemotherapy-induced neutropenia. In this report, serum FL level was measured by enzyme-linked immunosorbent assay (ELISA), in 16 consecutive patients undergoing autologous peripheral stem cell transplantation, with an average of 12 selected levels for each patient based on major changes of WBC counts at different procedure stations. We found a significant increase of serum FL level at the WBC nadir after mobilization chemotherapy and a more dramatic increase at the WBC nadir post transplantation, consistent with a more profound BM aplasia after myeloablative chemotherapy as compared to high-dose cyclophosphamide used for mobilization. Hence, we reproduced the reciprocal relationship between serum FL and BM cellularity. A direct correlation between the increase of FL level after mobilization chemotherapy and the length of mobilization was also established, which may help physicians, at the individual patient level, to predict the time of stem cell collection. Finally, we showed a direct correlation between the peripheral CD34+ count at the time of stem cell collection and the peak FL level after transplantation, which can reflect BM stromal cell function. Our results suggest that variation of serum FL level may be used as predictive indicator of hematopoietic stem cell (HSC) mobilization.

C-terminal cyclization of an SDF-1 small peptide analogue dramatically increases receptor affinity and activation of the CXCR4 receptor

In an effort to improve the activities and bioavailabilities of stromal cell-derived factor-1 (SDF-1, CXCL12) sdf-(1-67)-OH (1), we have prepared a linear peptide analogue [sdf-(1-31)-NH(2) (2)] and two lactam analogues [cyclo(Lys(20)-Glu(24))-sdf-(1-31)-NH(2) (3) and cyclo(Glu(24)-Lys(28))-sdf-(1-31)-NH(2) (4)], consisting of the N-terminal region (amino acids 1-14) joined by a four-glycine linker to the C-terminal region (amino acids 56-67) of 1. Analogues 2 and 4 had eight residues of alpha-helix, as estimated from its circular dichroism (CD) spectra, in contrast to 10 residues in analogue 3. Cyclization of analogue 2 at residues 20 and 24 to give analogue 3 resulted in only a slight change to the theta;(222)/theta;(209) ratio (0.81 to 0.86, where 1.09 is considered a perfect alpha-helix), although an increase in the alpha-helix length of analogue 3 was observed. In contrast, cyclization between residues 24 and 28 by lactamization to give analogue 4 only slightly affected the helical content but clearly resulted in a more classical alpha-helical structure (theta;(222)/theta;(209) = 0.98). Cyclization of the linear analogue 2 enhanced the SDF-1 receptor CXCR4 binding approximately 114-fold, where the IC(50) values derived from (125)I-SDF-1 competitive binding assays with CEM cells were found to be 39.5 +/- 5.9 nM, 28.9 +/- 6.3 microM, 225.8 +/- 11.8 nM, and 254.1 +/- 5.4 nM for analogues 1-4, respectively. Intracellular calcium mobilization ([Ca(2+)](i)) induced after interaction with CXCR4, as measured by EC(50), was significantly reduced in analogue 4 compared to 3, and approached the EC(50) of native SDF-1, indicating a correlation between the degree of alpha-helix and biological activity. Therefore, the biological activity of small peptide SDF-1 analogues is highly dependent on the conformation of its C-terminal region.