Scientific Resources

There is potential interest for combining allogeneic hematopoietic cell transplantation (HCT),and particularly allogeneic HCT with a nonmyeloablative regimen,to the tyrosine kinase inhibitor imatinib (Glivec; Novartis,Basel,Switzerland,http://www.novartis.com) in order to maximize anti-leukemic activity against Philadelphia chromosome-positive leukemias. However,because imatinib inhibits c-kit,the stem cell factor receptor,it could interfere with bone marrow engraftment. In this study,we examined the impact of imatinib on normal progenitor cell function. Imatinib decreased the colony-forming capacity of mobilized peripheral blood human CD133(+) cells but not that of long-term culture-initiating cells. Imatinib also decreased the proliferation of cytokine-stimulated CD133(+) cells but did not induce apoptosis of these cells. Expression of very late antigen (VLA)-4,VLA-5,and CXCR4 of CD133(+) cells was not modified by imatinib,but imatinib decreased the ability of CD133(+) cells to migrate. Finally,imatinib did not decrease engraftment of CD133(+) cells into irradiated nonobese diabetic/severe combined immunodeficient/beta2m(null) mice conditioned with 3 or 1 Gy total body irradiation. In summary,our results suggest that,despite inhibition of hematopoietic progenitor cell growth in vitro,imatinib does not interfere with hematopoietic stem cell engraftment. View Publication

Hematopoiesis is maintained by specific interactions between both hematopoietic and nonhematopoietic cells. Whereas hematopoietic stem cells (HSCs) have been extensively studied both in vitro and in vivo,little is known about the in vivo characteristics of stem cells of the nonhematopoietic component,known as mesenchymal stem cells (MSCs). Here we have visualized and characterized human MSCs in vivo following intramedullary transplantation of enhanced green fluorescent protein-marked human MSCs (eGFP-MSCs) into the bone marrow (BM) of nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice. Between 4 to 10 weeks after transplantation,eGFP-MSCs that engrafted in murine BM integrated into the hematopoietic microenvironment (HME) of the host mouse. They differentiated into pericytes,myofibroblasts,BM stromal cells,osteocytes in bone,bone-lining osteoblasts,and endothelial cells,which constituted the functional components of the BM HME. The presence of human MSCs in murine BM resulted in an increase in functionally and phenotypically primitive human hematopoietic cells. Human MSC-derived cells that reconstituted the HME appeared to contribute to the maintenance of human hematopoiesis by actively interacting with primitive human hematopoietic cells. View Publication

Human cord blood (CB)-derived CD133+ cells carry characteristics of primitive hematopoietic cells and proffer an alternative for CD34+ cells in hematopoietic stem cell (HSC) transplantation. To characterize the CD133+ cell population on a genetic level,a global expression analysis of CD133+ cells was performed using oligonucleotide microarrays. CD133+ cells were purified from four fresh CB units by immunomagnetic selection. All four CD133+ samples showed significant similarity in their gene expression pattern,whereas they differed clearly from the CD133- control samples. In all,690 transcripts were differentially expressed between CD133+ and CD133- cells. Of these,393 were increased and 297 were decreased in CD133+ cells. The highest overexpression was noted in genes associated with metabolism,cellular physiological processes,cell communication,and development. A set of 257 transcripts expressed solely in the CD133+ cell population was identified. Colony-forming unit (CFU) assay was used to detect the clonal progeny of precursors present in the studied cell populations. The results demonstrate that CD133+ cells express primitive markers and possess clonogenic progenitor capacity. This study provides a gene expression profile for human CD133+ cells. It presents a set of genes that may be used to unravel the properties of the CD133+ cell population,assumed to be highly enriched in HSCs. View Publication

Hematopoietic stem cells (HSCs) can be isolated from murine bone marrow by their ability to efflux the Hoechst 33342 dye. This method defines an extremely small and hematopoietically potent subset of cells known as the side population (SP). Recent studies suggest that transplanted single SP cells are capable of lymphohematopoietic repopulation at near absolute efficiencies. Here,we carefully reevaluate the hematopoietic potential of individual SP cells and find substantially lower rates of reconstitution. Our strategy involved the cotransplantation of single SP cells along with different populations of competitor cells that varied in their self-renewal capacity. Even with minimized HSC competition,SP cells were only able to reconstitute up to 35% of recipient mice. Furthermore,through immunophenotyping and clonal in vitro assays we find that SP cells are virtually homogeneous. Isolation of HSCs on the basis of Hoechst exclusion and a single cell-surface marker allows enrichment levels similar to that obtained with complex multicolor strategies. Altogether,our results indicate that even an extremely homogeneous HSC population,based on phenotype and dye efflux,cannot reconstitute mice at absolute efficiencies. View Publication

Reduced-intensity conditioning regimens for transplant recipients have heightened awareness of immunologic resistance to allogeneic bone marrow transplants (BMT). Although T cell-mediated cytotoxicity has been assumed to play a role in the resistance against donor allogeneic hematopoietic stem and progenitor cell grafts,several studies have reported relatively unimpaired resistance by recipients who lack perforin,Fas ligand (FasL),and other cytotoxic mediators. This study compared the early kinetics of T cell-mediated resistance in B6 (H2b) cytotoxically normal versus deficient recipients after transplantation with major histocompatibility complex-matched,minor histocompatibility antigen (MiHA)-mismatched allogeneic marrow grafts. Wild-type B6 or cytotoxic double-deficient perforin-/-/ gld+/+ (B6-cdd) mice were sensitized against major histocompatibility complex-matched BALB.B or C3H.SW (H2b) MiHA and transplanted with a high dose (1 ?? 107) of T cell-depleted bone marrow. CD8 T memory cells were shown to be present in recipients before BMT,and anti-CD8 monoclonal antibody infusion abolished resistance,thus demonstrating that CD8 T cells are the host effector population. Donor-committed and high proliferative potential progenitor numbers were markedly diminished by 48 hours after transplantation in both wild-type B6 and B6-cdd anti-donor MiHA-sensitized recipients. These observations indicate that the resistance pathway used in the cytotoxic deficient mice was both potent and rapidly induced - consistent with a CD8 memory T-cell response. To examine the role of Tumor necrosis factor-like weak inducer of apoptosis (TWEAK)- and TL1A-mediated cytotoxicity in this strong resistance,newly generated monoclonal antibodies specific for these ligands were administered to B6-cdd recipients sensitized to donor antigens. Recipients of syngeneic B6-gfp bone marrow exhibited significant donor colony-forming unit numbers after BMT. In contrast,low or absent colony-forming unit levels were detected in allogeneic recipients,including those that lacked perforin and FasL and that received anti-TWEAK,anti-tumor necrosis factor-related apoptosis-inducing ligand,and anti-TL1A monoclonal antibodies. These findings extend previous observations by demonstrating the existence of a rapidly effected resistance pathway mediated by memory CD8 effector T cells independent of the 2 major pathways of cytotoxicity. Together with previous findings,these results support the notion that effector cells derived from memory CD8 T-cell populations can mediate strong resistance against donor allogeneic MiHA-disparate hematopoietic engraftment by using a mechanism that is independent of the contribution of perforin,FasL,and the known death ligand receptor pathways. ?? 2005 American Society for Blood and Marrow Transplantation. View Publication

To test the hypothesis that aging has negative effects on stem-cell homing and engraftment,young or old C57BL/6 bone marrow (BM) cells were injected,using a limiting-dilution,competitive transplantation method,into old or young Ly5 congenic mice. Numbers of hematopoietic stem cells (HSCs) and progenitor cells (HPCs) recovered from BM or spleen were measured and compared with the numbers initially transplanted. Although the frequency of marrow competitive repopulation units (CRUs) increased approximately 2-fold from 2 months to 2 years of age,the BM homing efficiency of old CRUs was approximately 3-fold lower than that of young CRUs. Surprisingly,the overall size of individual stem-cell clones generated in recipients receiving a single CRU was not affected by donor age. However,the increased ages of HSC donors and HSC transplant recipients caused marked skewing of the pattern of engraftment toward the myeloid lineage,indicating that HSC-intrinsic and HSC-extrinsic (microenvironmental) age-related changes favor myelopoiesis. This correlated with changes after transplantation in the rate of recovery of circulating leukocytes,erythrocytes,and platelets. Recovery of the latter was especially blunted in aged recipients. Collectively,these findings may have implications for clinical HSC transplantation in which older persons increasingly serve as donors for elderly patients. View Publication

Taking advantage of fluorescent substrates for their metabolic marker aldehyde dehydrogenase (ALDH),hematopoietic stem cells (HSC) were defined as SSC(lo)ALDH(br) - reflecting their low orthogonal light scattering and bright fluorescence intensity in flow cytometry. Based thereon,we investigated the usefulness of ALDH activity for characterizing HSC graft quality,particularly under stress conditions. We first compared the expression of ALDH vs CD34 in bone marrow and peripheral blood stem cell (PBSC) samples over 7 days. We noted that (i) only ALDH activity but not CD34 expression strongly reflected colony-forming ability over time,and that (ii) PBSC grafts stored at room temperature lost most of their progenitor cells within just 48 h. We then retrospectively related ALDH and CD34 expression as well as granulocyte-macrophage colony-forming units (CFU-GM) potential for 19 cryopreserved allogeneic PBSC grafts to engraftment data. Strikingly,in all six patients who received markedly decreased numbers of SSC(lo)ALDH(br) cells,this was associated not only with almost complete loss of CFU-GM potential but also with delayed establishment/permanent absence of full hematopoietic donor cell chimerism,whereas all other patients showed early complete donor chimerism. In conclusion,we suggest to measure ALDH activity as a surrogate marker for HSC activity,and to transport and store PBSC under controlled cooling conditions. View Publication

Internal tandem duplications (ITDs) of the FMS-like tyrosine kinase 3 (FLT3) receptor tyrosine kinase are found in approximately 30% of patients with acute myelogenous leukemia (AML) and are associated with a poor prognosis. FLT3 ITD mutations result in constitutive kinase activation and are thought to be pathogenetically relevant,implicating FLT3 as a plausible therapeutic target. MLN518 (formerly CT53518) is a small molecule inhibitor of the FLT3,KIT,and platelet-derived growth-factor receptor (PDGFR) tyrosine kinases with significant activity in murine models of FLT3 ITD-positive leukemia. Given the importance of FLT3 and KIT for normal hematopoietic progenitor cells,we analyzed the effect of MLN518 on murine hematopoiesis under steady-state conditions,after chemotherapy-induced myelosuppression,and during bone marrow transplantation. In these assays,we show that MLN518 has mild toxicity toward normal hematopoiesis at concentrations that are effective in treating FLT3 ITD-positive leukemia in mice. We also demonstrate that MLN518 preferentially inhibits the growth of blast colonies from FLT3 ITD-positive compared with ITD-negative patients with AML,at concentrations that do not significantly affect colony formation by normal human progenitor cells. In analogy to imatinib mesylate in BCR-ABL-positive acute leukemia,MLN518-induced remissions may not be durable. Our studies provide the basis for integrating this compound into chemotherapy and transplantation protocols. View Publication

Hematopoietic stem cells (HSCs) are a subset of bone marrow cells that are capable of self-renewal and of giving rise to all types of blood cells. However,the mechanisms involved in controlling the number and abilities of HSCs remain largely unknown. The Indian hedgehog (Ihh) signal has an essential role in inducing hematopoietic tissue during embryogenesis. We investigated the roles of the Ihh in coculture with CD34+ cells and human stromal cells. Ihh mRNA was expressed in primary and telomerized human (hTERT) stromal cells,and its receptor molecules were detected in CD34+ cells. Ihh gene transfer into hTERT stromal cells enhanced their hematopoietic supporting potential,which was elevated compared with control stromal cells,as indicated by the colony-forming units in culture (CFU-Cs) (26-fold +/- 2-fold versus 59-fold +/- 3-fold of the initial cell number; mixed colony-forming units [CFU-Mix's],63-fold +/- 37-fold versus 349-fold +/- 116-fold). Engraftments of nonobese diabetic/severe combined immunodeficiency-beta2m-/- (NOD/SCID-beta2-/-) repopulating cells (RCs) expanded on Ihh stromal cells were significantly higher compared with control coculture results,and engraftment was neutralized by addition of an antihedgehog antibody. Limiting dilution analysis indicated that NOD/SCID-beta2m-/- RCs proliferated efficiently on Ihh stromal cells,compared with control stromal cells. These results indicate that Ihh gene transfer could enhance the primitive hematopoietic support ability of human stromal cells. View Publication

The development of immunodeficient mouse xenograft models has greatly facilitated the investigation of some human hematopoietic malignancies,but application of this approach to the myelodysplastic syndromes (MDSs) has proven difficult. We now show that cells from most MDS patients (including all subtypes) repopulate nonobese diabetic-severe combined immunodeficient (scid)/scid-beta2 microglobulin null (NOD/SCID-beta2m(-/-)) mice at least transiently and produce abnormal differentiation patterns in this model. Normal marrow transplants initially produce predominantly erythroid cells and later predominantly B-lymphoid cells in these mice,whereas most MDS samples produced predominantly granulopoietic cells. In 4 of 4 MDS cases,the regenerated cells showed the same clonal markers (trisomy 8,n = 3; and 5q-,n = 1) as the original sample and,in one instance,regenerated trisomy 8(+) B-lymphoid as well as myeloid cells were identified. Interestingly,the enhanced growth of normal marrow obtained in NOD/SCID-beta2m(-/-) mice engineered to produce human interleukin-3,granulocyte-macrophage colony-stimulating factor,and Steel factor was seen only with 1 of 7 MDS samples. These findings support the concept that human MDS originates in a transplantable multilineage hematopoietic stem cell whose genetic alteration may affect patterns of differentiation and responsiveness to hematopoietic growth factors. They also demonstrate the potential of this new murine xenotransplant model for future investigations of MDS. View Publication

Successful blood and marrow transplant (BMT),both autologous and allogeneic,requires the infusion of a sufficient number of hematopoietic progenitor/stem cells (HPCs) capable of homing to the marrow cavity and regenerating a full array of hematopoietic cell lineages in a timely fashion. At present,the most commonly used surrogate marker for HPCs is the cell surface marker CD34,identified in the clinical laboratory by flow cytometry. Clinical studies have shown that infusion of at least 2 x 10(6) CD34(+) cells/kg recipient body weight results in reliable engraftment as measured by recovery of adequate neutrophil and platelet counts approximately 14 days after transplant. Recruitment of HPCs from the marrow into the blood is termed mobilization,or,more commonly,stem cell mobilization. In Section I,Dr. Tsvee Lapidot and colleagues review the wide range of factors influencing stem cell mobilization. Our current understanding focuses on chemokines,proteolytic enzymes,adhesion molecules,cytokines and stromal cell-stem cell interactions. On the basis of this understanding,new approaches to mobilization have been designed and are now starting to undergo clinical testing. In Section II,Dr. Michele Cottler-Fox describes factors predicting the ability to mobilize the older patient with myeloma. In addition,clinical approaches to improving collection by individualizing the timing of apheresis and adjusting the volume of blood processed to achieve a desired product are discussed. Key to this process is the daily enumeration of blood CD34(+) cells. Newer methods of enumerating and mobilizing autologous blood HPCs are discussed. In Section III,Dr. John DiPersio and colleagues provide data on clinical results of mobilizing allogeneic donors with G-CSF,GM-CSF and the combination of both as relates to the number and type of cells collected by apheresis. Newer methods of stem cell mobilization as well as the relationship of graft composition on immune reconstitution and GVHD are discussed. View Publication

Infusion of transduced hematopoietic stem cells into nonmyeloablated hosts results in ineffective in vivo levels of transduced cells. To increase the proportion of transduced cells in vivo,selection based on P140K O6-methylguanine-DNA-methyltransferase (MGMT[P140K]) gene transduction and O6-benzylguanine/1,3-bis(2-chloroethyl)-1-nitrosourea (BG/BCNU) treatment has been devised. In this study,we transduced human NOD/SCID repopulating cells (SRCs) with MGMT(P140K) using a lentiviral vector and infused them into BG/BCNU-conditioned NOD/SCID mice before rounds of BG/BCNU treatment as a model for in vivo selection. Engraftment was not observed until the second round of BG/BCNU treatment,at which time human cells emerged to compose up to 20% of the bone marrow. Furthermore,99% of human CFCs derived from NOD/SCID mice were positive for provirus as measured by PCR,compared with 35% before transplant and 11% in untreated irradiation-preconditioned mice,demonstrating selection. Bone marrow showed BG-resistant O6-alkylguanine-DNA-alkyltransferase (AGT) activity,and CFUs were stained intensely for AGT protein,indicating high transgene expression. Real-time PCR estimates of the number of proviral insertions in individual CFUs ranged from 3 to 22. Selection resulted in expansion of one or more SRC clones containing similar numbers of proviral copies per mouse. To our knowledge,these results provide the first evidence of potent in vivo selection of MGMT(P140K) lentivirus-transduced human SRCs following BG/BCNU treatment. View Publication