Planned Granulocyte Colony-Stimulating Factor Adversely Impacts Survival after Allogeneic Hematopoietic Cell Transplantation Performed with Thymoglobulin for Myeloid Malignancy

The in vivo depletion of recipient and donor T lymphocytes using antithymocyte globulin (ATG; Thymoglobulin) is widely adopted in allogeneic hematopoietic stem cell transplantation (HCT) to reduce the incidence of both graft failure and graft-versus-host disease (GVHD). However, excess toxicity to donor lymphocytes may hamper immune reconstitution, compromising antitumor effects and increasing infection. Granulocyte-colony stimulating factor (G-CSF) administered early after HCT may increase ATG-mediated lymphotoxicity. This study aimed to investigate the effect of an interaction between ATG and post-transplantation granulocyte colony-stimulating factor (G-CSF) on allogeneic HCT outcomes, using the Center for International Blood and Marrow Transplant Research (CIBMTR) registry. We studied patients age ≥18 years with acute myelogenous leukemia (AML) and myelodysplastic syndrome (MDS) who received Thymoglobulin-containing preparative regimens for HLA-matched sibling/unrelated or mismatched unrelated donor HCT between 2010 and 2018. The effect of planned G-CSF that was started between pretransplantation day 3 and post-transplantation day 12 was studied in comparison with transplantations that did not include G-CSF. Cox regression models were built to identify risk factors associated with outcomes at 1 year after transplantation. A total of 874 patients met the study eligibility criteria, of whom 459 (53%) received planned G-CSF. HCT with planned G-CSF was associated with a significantly increased risk for nonrelapse mortality (NRM) (hazard ratio [HR] 2.03; P <.0001; 21% versus 12%) compared to HCT without G-CSF. The 6-month incidence of viral infection was higher with G-CSF (56% versus 47%; P = .007), with a particular increase in Epstein-Barr virus infections (19% versus 11%; P = .002). The observed higher NRM with planned G-CSF led to lower overall survival (HR, 1.52; P = .0005; 61% versus 72%). There was no difference in GVHD risk between the treatment groups. We performed 2 subgroup analyses showing that our findings held true in patients age ≥50 years and in centers where G-CSF was used in some, but not all, patients. In allogeneic peripheral blood HCT performed with Thymoglobulin for AML and MDS, G-CSF administered early post-transplantation resulted in a 2-fold increase in NRM and a 10% absolute decrement in survival. The use of planned G-CSF in the early post-transplantation period should be carefully considered on an individual patient basis, weighing any perceived benefits against these risks.

HLA-haploidentical vs matched unrelated donor transplants with posttransplant cyclophosphamide-based prophylaxis

Posttransplant cyclophosphamide (PTCy) graft-versus-host disease (GVHD) prophylaxis has enabled haploidentical (Haplo) transplantation to be performed with results similar to those after matched unrelated donor (MUD) transplantation with traditional prophylaxis. The relative value of transplantation with MUD vs Haplo donors when both groups receive PTCy/calcineurin inhibitor/mycophenolate GVHD prophylaxis is not known. We compared outcomes after 2036 Haplo and 284 MUD transplantations with PTCy GVHD prophylaxis for acute leukemia or myelodysplastic syndrome in adults from 2011 through 2018. Cox regression models were built to compare outcomes between donor types. Recipients of myeloablative and reduced-intensity regimens were analyzed separately. Among recipients of reduced-intensity regimens, 2-year graft failure (3% vs 11%), acute grades 2 to 4 GVHD (hazards ratio [HR], 0.70; P = .022), acute grades 3 and 4 GVHD (HR, 0.41; P = .016), and nonrelapse mortality (HR, 0.43; P = .0008) were lower after MUD than with Haplo donor transplantation. Consequently, disease-free (HR, 0.74; P = .008; 55% vs 41%) and overall (HR, 0.65; P = .001; 67% vs 54%) survival were higher with MUD than with Haplo transplants. Among recipients of myeloablative regimens, day-100 platelet recovery (95% vs 88%) was higher and grades 3 and 4 acute (HR, 0.39; P = .07) and chronic GVHD (HR, 0.66; P = .05) were lower after MUD than with Haplo donor transplantation. There were no differences in graft failure, relapse, nonrelapse mortality, and disease-free and overall survival between donor types with myeloablative conditioning regimens. These data extend and confirm the importance of donor-recipient HLA matching for allogeneic transplantation. A MUD is the preferred donor, especially for transplantations with reduced-intensity conditioning regimens.

Standardization, workforce development and advocacy in cell and gene therapies: a summary of the 2020 Regenerative Medicine InterCHANGE

Cell and gene therapy is a promising and disruptive new field of medicine for diseases lacking effective treatments. Collaboration among stakeholders has become critically important as investigators, health care providers, manufacturers, couriers, data registries, regulators and payers all become more invested in the success of this field. Many organizations have collaborated with each other to increase clarity, advocate for improvements and share lessons learned. These efforts appear to be making an impact, although the potential for duplicative efforts could slow progress. The second Regenerative Medicine InterCHANGE, hosted by the Foundation for the Accreditation of Cellular Therapy, took place at the Phacilitate Leaders World/World Stem Cell Summit conference in Miami, Florida, on January 24, 2020. Participants from several organizations outlined needs to advance cell and gene therapies. Efforts to address these include standardization, workforce development and advocacy. This article summarizes the major challenges and opportunities discussed during the InterCHANGE.

Umbilical cord blood graft engineering: challenges and opportunities

We are entering a very exciting era in umbilical cord blood transplantation (UCBT), where many of the associated formidable challenges may become treatable by ex vivo graft manipulation and/or adoptive immunotherapy utilizing specific cellular products. We envisage the use of double UCBT rather than single UCBT for most patients; this allows for greater ability to treat larger patients as well as to manipulate the graft. Ex vivo expansion and/or fucosylation of one cord will achieve more rapid engraftment, minimize the period of neutropenia and also give certainty that the other cord will provide long-term engraftment/immune reconstitution. The non-expanded (and future dominant) cord could be chosen for characteristics such as better HLA matching to minimize GvHD, or larger cell counts to enable part of the unit to be utilized for the development of specific cellular therapies such as the production of virus-specific T-cells or chimeric-antigen receptor T-cells which are reviewed in this study.

International Society for Cellular Therapy perspective on immune functional assays for mesenchymal stromal cells as potency release criterion for advanced phase clinical trials

Mesenchymal stromal cells (MSCs) as a pharmaceutical for ailments characterized by pathogenic autoimmune, alloimmune and inflammatory processes now cover the spectrum of early- to late-phase clinical trials in both industry and academic sponsored studies. There is a broad consensus that despite different tissue sourcing and varied culture expansion protocols, human MSC-like cell products likely share fundamental mechanisms of action mediating their anti-inflammatory and tissue repair functionalities. Identification of functional markers of potency and reduction to practice of standardized, easily deployable methods of measurements of such would benefit the field. This would satisfy both mechanistic research as well as development of release potency assays to meet Regulatory Authority requirements for conduct of advanced clinical studies and their eventual registration. In response to this unmet need, the International Society for Cellular Therapy (ISCT) addressed the issue at an international workshop in May 2015 as part of the 21st ISCT annual meeting in Las Vegas. The scope of the workshop was focused on discussing potency assays germane to immunomodulation by MSC-like products in clinical indications targeting immune disorders. We here provide consensus perspective arising from this forum. We propose that focused analysis of selected MSC markers robustly deployed by in vitro licensing and metricized with a matrix of assays should be responsive to requirements from Regulatory Authorities. Workshop participants identified three preferred analytic methods that could inform a matrix assay approach: quantitative RNA analysis of selected gene products; flow cytometry analysis of functionally relevant surface markers and protein-based assay of secretome. We also advocate that potency assays acceptable to the Regulatory Authorities be rendered publicly accessible in an "open-access" manner, such as through publication or database collection.

Novel clinical uses for cord blood derived mesenchymal stromal cells

Regenerative medicine offers new hope for many debilitating diseases that result in damage to tissues and organs. The concept is straightforward with replacement of damaged cells with new functional cells. However, most tissues and organs are complex structures involving multiple cell types, supportive structures, a microenvironment producing cytokines and growth factors and a vascular system to supply oxygen and other nutrients. Therefore repair, particularly in the setting of ischemic damage, may require delivery of multiple cell types providing new vessel formation, a new microenvironment and functional cells. The field of stem cell biology has identified a number of stem cell sources including embryonic stem cells and adult stem cells that offer the potential to replace virtually all functional cells of the body. The focus of this article is a discussion of the potential of mesenchymal stromal cells (MSCs) from cord blood (CB) for regenerative medicine approaches.

Concise review: umbilical cord blood transplantation: past, present, and future

Allogeneic hematopoietic stem cell transplantation is an important treatment option for fit patients with poor-risk hematological malignancies; nevertheless, the lack of available fully matched donors limits the extent of its use. Umbilical cord blood has emerged as an effective alternate source of hematopoietic stem cell support. Transplantation with cord blood allows for faster availability of frozen sample and avoids invasive procedures for donors. In addition, this procedure has demonstrated reduced relapse rates and similar overall survival when compared with unrelated allogeneic hematopoietic stem cell transplantation. The limited dose of CD34-positive stem cells available with single-unit cord transplantation has been addressed by the development of double-unit cord transplantation. In combination with improved conditioning regimens, double-unit cord transplantation has allowed for the treatment of larger children, as well as adult patients with hematological malignancies. Current excitement in the field revolves around the development of safer techniques to improve homing, engraftment, and immune reconstitution after cord blood transplantation. Here the authors review the past, present, and future of cord transplantation.

Does transendocardial injection of mesenchymal stem cells improve myocardial function locally or globally?: An analysis from the Percutaneous Stem Cell Injection Delivery Effects on Neomyogenesis (POSEIDON) randomized trial

RATIONALE

Transendocardial stem cell injection (TESI) with mesenchymal stem cells improves remodeling in chronic ischemic cardiomyopathy, but the effect of the injection site remains unknown.

OBJECTIVE

To address whether TESI exerts its effects at the site of injection only or also in remote areas, we hypothesized that segmental myocardial scar and segmental ejection fraction improve to a greater extent in injected than in noninjected segments.

METHODS AND RESULTS

Biplane ventriculographic and endocardial tracings were recorded. TESI was guided to 10 sites in infarct-border zones. Sites were mapped according to the 17-myocardial segment model. As a result, 510 segments were analyzed in 30 patients before and 13 months after TESI. Segmental early enhancement defect (a measure of scar size) was reduced by TESI in both injected (-43.7 ± 4.4%; n=95; P<0.01) and noninjected segments (-25.1 ± 7.8%; n=148; P<0.001; between-group comparison P<0.05). Conversely, segmental ejection fraction (a measure of contractile performance) improved in injected scar segments (19.9 ± 3.3-26.3 ± 3.5%; P=0.003) but not in noninjected scar segments (21.3 ± 2.6-23.5 ± 3.2%; P=0.20; between-group comparison P<0.05). Furthermore, segmental ejection fraction in injected scar segments improved to a greater degree in patients with baseline segmental ejection fraction <20% (12.1 ± 1.2-19.9 ± 2.7%; n=18; P=0.003), versus <20% (31.7 ± 3.4-35.5 ± 3.3%; n=12; P=0.33, between-group comparison P<0.0001).

CONCLUSIONS

These findings illustrate a dichotomy in regional responses to TESI. Although scar size reduction was evident in all scar segments, scar size reduction and ventricular functional responses preferentially occurred at the sites of TESI versus non-TESI sites. Furthermore, improvement was greatest when segmental left ventricular dysfunction was severe.

Transendocardial mesenchymal stem cells and mononuclear bone marrow cells for ischemic cardiomyopathy: the TAC-HFT randomized trial

IMPORTANCE

Whether culture-expanded mesenchymal stem cells or whole bone marrow mononuclear cells are safe and effective in chronic ischemic cardiomyopathy is controversial.

OBJECTIVE

To demonstrate the safety of transendocardial stem cell injection with autologous mesenchymal stem cells (MSCs) and bone marrow mononuclear cells (BMCs) in patients with ischemic cardiomyopathy.

DESIGN, SETTING, AND PATIENTS

A phase 1 and 2 randomized, blinded, placebo-controlled study involving 65 patients with ischemic cardiomyopathy and left ventricular (LV) ejection fraction less than 50% (September 1, 2009-July 12, 2013). The study compared injection of MSCs (n=19) with placebo (n = 11) and BMCs (n = 19) with placebo (n = 10), with 1 year of follow-up.

INTERVENTIONS

Injections in 10 LV sites with an infusion catheter.

MAIN OUTCOMES AND MEASURES

Treatment-emergent 30-day serious adverse event rate defined as a composite of death, myocardial infarction, stroke, hospitalization for worsening heart failure, perforation, tamponade, or sustained ventricular arrhythmias.

RESULTS

No patient had a treatment-emergent serious adverse events at day 30. The 1-year incidence of serious adverse events was 31.6% (95% CI, 12.6% to 56.6%) for MSCs, 31.6% (95% CI, 12.6%-56.6%) for BMCs, and 38.1% (95% CI, 18.1%-61.6%) for placebo. Over 1 year, the Minnesota Living With Heart Failure score improved with MSCs (-6.3; 95% CI, -15.0 to 2.4; repeated measures of variance, P=.02) and with BMCs (-8.2; 95% CI, -17.4 to 0.97; P=.005) but not with placebo (0.4; 95% CI, -9.45 to 10.25; P=.38). The 6-minute walk distance increased with MSCs only (repeated measures model, P = .03). Infarct size as a percentage of LV mass was reduced by MSCs (-18.9%; 95% CI, -30.4 to -7.4; within-group, P = .004) but not by BMCs (-7.0%; 95% CI, -15.7% to 1.7%; within-group, P = .11) or placebo (-5.2%; 95% CI, -16.8% to 6.5%; within-group, P = .36). Regional myocardial function as peak Eulerian circumferential strain at the site of injection improved with MSCs (-4.9; 95% CI, -13.3 to 3.5; within-group repeated measures, P = .03) but not BMCs (-2.1; 95% CI, -5.5 to 1.3; P = .21) or placebo (-0.03; 95% CI, -1.9 to 1.9; P = .14). Left ventricular chamber volume and ejection fraction did not change.

CONCLUSIONS AND RELEVANCE

Transendocardial stem cell injection with MSCs or BMCs appeared to be safe for patients with chronic ischemic cardiomyopathy and LV dysfunction. Although the sample size and multiple comparisons preclude a definitive statement about safety and clinical effect, these results provide the basis for larger studies to provide definitive evidence about safety and to assess efficacy of this new therapeutic approach.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00768066.

Bone marrow-derived c-kit+ cells attenuate neonatal hyperoxia-induced lung injury

Recent studies suggest that bone marrow (BM)-derived stem cells have therapeutic efficacy in neonatal hyperoxia-induced lung injury (HILI). c-kit, a tyrosine kinase receptor that regulates angiogenesis, is expressed on several populations of BM-derived cells. Preterm infants exposed to hyperoxia have decreased lung angiogenesis. Here we tested the hypothesis that administration of BM-derived c-kit(+) cells would improve angiogenesis in neonatal rats with HILI. To determine whether intratracheal (IT) administration of BM-derived c-kit(+) cells attenuates neonatal HILI, rat pups exposed to either normobaric normoxia (21% O2) or hyperoxia (90% O2) from postnatal day (P) 2 to P15 were randomly assigned to receive either IT BM-derived green fluorescent protein (GFP)(+) c-kit(-) cells (PL) or BM-derived GFP(+) c-kit(+) cells on P8. The effect of cell therapy on lung angiogenesis, alveolarization, pulmonary hypertension, vascular remodeling, cell proliferation, and apoptosis was determined at P15. Cell engraftment was determined by GFP immunostaining. Compared to PL, the IT administration of BM-derived c-kit(+) cells to neonatal rodents with HILI improved alveolarization as evidenced by increased lung septation and decreased mean linear intercept. This was accompanied by an increase in lung vascular density, a decrease in lung apoptosis, and an increase in the secretion of proangiogenic factors. There was no difference in pulmonary vascular remodeling or the degree of pulmonary hypertension. Confocal microscopy demonstrated that 1% of total lung cells were GFP(+) cells. IT administration of BM-derived c-kit(+) cells improves lung alveolarization and angiogenesis in neonatal HILI, and this may be secondary to an improvement in the lung angiogenic milieu.

Comparison of allogeneic vs autologous bone marrow–derived mesenchymal stem cells delivered by transendocardial injection in patients with ischemic cardiomyopathy: the POSEIDON randomized trial

CONTEXT

Mesenchymal stem cells (MSCs) are under evaluation as a therapy for ischemic cardiomyopathy (ICM). Both autologous and allogeneic MSC therapies are possible; however, their safety and efficacy have not been compared.

OBJECTIVE

To test whether allogeneic MSCs are as safe and effective as autologous MSCs in patients with left ventricular (LV) dysfunction due to ICM.

DESIGN, SETTING, AND PATIENTS

A phase 1/2 randomized comparison (POSEIDON study) in a US tertiary-care referral hospital of allogeneic and autologous MSCs in 30 patients with LV dysfunction due to ICM between April 2, 2010, and September 14, 2011, with 13-month follow-up.

INTERVENTION

Twenty million, 100 million, or 200 million cells (5 patients in each cell type per dose level) were delivered by transendocardial stem cell injection into 10 LV sites.

MAIN OUTCOME MEASURES

Thirty-day postcatheterization incidence of predefined treatment-emergent serious adverse events (SAEs). Efficacy assessments included 6-minute walk test, exercise peak VO2, Minnesota Living with Heart Failure Questionnaire (MLHFQ), New York Heart Association class, LV volumes, ejection fraction (EF), early enhancement defect (EED; infarct size), and sphericity index.

RESULTS

Within 30 days, 1 patient in each group (treatment-emergent SAE rate, 6.7%) was hospitalized for heart failure, less than the prespecified stopping event rate of 25%. The 1-year incidence of SAEs was 33.3% (n = 5) in the allogeneic group and 53.3% (n = 8) in the autologous group (P = .46). At 1 year, there were no ventricular arrhythmia SAEs observed among allogeneic recipients compared with 4 patients (26.7%) in the autologous group (P = .10). Relative to baseline, autologous but not allogeneic MSC therapy was associated with an improvement in the 6-minute walk test and the MLHFQ score, but neither improved exercise VO2 max. Allogeneic and autologous MSCs reduced mean EED by −33.21% (95% CI, −43.61% to −22.81%; P < .001) and sphericity index but did not increase EF. Allogeneic MSCs reduced LV end-diastolic volumes. Low-dose concentration MSCs (20 million cells) produced greatest reductions in LV volumes and increased EF. Allogeneic MSCs did not stimulate significant donor-specific alloimmune reactions.

CONCLUSIONS

In this early-stage study of patients with ICM, transendocardial injection of allogeneic and autologous MSCs without a placebo control were both associated with low rates of treatment-emergent SAEs, including immunologic reactions. In aggregate, MSC injection favorably affected patient functional capacity, quality of life, and ventricular remodeling.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01087996.

Differential Hematopoietic Supportive Potential and Gene Expression of Stroma Cell Lines from Midgestation Mouse Placenta and Adult Bone Marrow

During mouse embryogenesis, hematopoietic development takes place in several distinct anatomic locations. The microenvironment of different hematopoietic organs plays an important role in the proliferation and maturation of the hematopoietic cells. We hypothesized that fetal stromal cells would be distinct to adult bone marrow (BM)-derived stromal cells because the BM contributes mainly to the homeostasis of hematopoietic stem cells (HSCs), while extensive expansion of HSCs occurs during fetal development. Here we report the establishment of stromal cell lines from fetal hematopoietic organs, namely aorta-gonad-mesonephros (AGM), midgestation placenta (PL), and fetal liver (FL) together with adult bone marrow (BM). The growth patterns and hematopoietic supportive potential were studied. Their phenotypic and molecular gene expression profiles were also determined. Stromal cell lines from each tissue were able to support cobblestone area formation of BM c-Kit+Sca-1+ hematopoietic cells: 22 (22/47) from AGM, three (3/4) from PL, three (3/4) from FL, and three (3/3) from BM. There were similar levels of expansion of total mononuclear cells (TMNs) when HSCs were cocultured with fetal stroma and adult BM stroma. However, PL-derived stromal cells supported higher levels of generation of colony-forming progenitor cell (CFU-C), indicated by more colonies and colonies with significantly larger size. Flow cytometric analysis of the PL1 cells demonstrated a phenotype of CD45-, CD105+, Sca-1+, CD34+, and CD49d+, compared to adult BM1 cells, which were CD45-, CD105+, Sca-1+, CD34-, and CD49d-. Using Affymetrix microarray analysis, we identified that genes specifically express in endothelial cells, such as Tie1, Tek, Kdr, Flt4, Emcn, Pecam1, Icam2, Cdh5, Esam1, Prom1, Cd34, and Sele were highly expressed in stroma PL1, consistent with an endothelial phenotype, while BM1 expressed a mesenchymal stromal phenotype. In summary, these data demonstrate distinct characteristics of stromal cells that provide insights into the microenvironmental control of HSCs.

Mesenchymal stem cell therapy for cardiac repair

Stem cell therapy for repair of damaged cardiac tissue is an attractive option to improve the health of the growing number of heart failure patients. Mesenchymal stem cells (MSCs) possess unique properties that may make them a better option for cardiac repair than other cell types. Unlike other adult stem cells, they appear to escape allorecognition by the immune system and they have immune-modulating properties, thus making it possible to consider them for use as an allogeneic cell therapy product. There is a large and growing body of preclinical and early clinical experience with MSC therapy that shows great promise in realizing the potential of stem cell therapy to effect repair of damaged cardiac tissue. This review discusses the mechanism of action of MSC therapy and summarizes the current literature in the field.

Ex vivo expansion and transplantation of hematopoietic stem/progenitor cells supported by mesenchymal stem cells from human umbilical cord blood

Human mesenchymal stem cells (MSCs) are multipotential and are detected in bone marrow (BM), adipose tissue, placenta, and umbilical cord blood (UCB). In this study, we examined the ability of UCB-derived MSCs (UCB-MSCs) to support ex vivo expansion of hematopoietic stem/progenitor cells (HSPCs) from UCB and the engraftment of expanded HSPCs in NOD/SCID mice. The result showed that UCB-MSCs supported the proliferation and differentiation of CD34+ cells in vitro. The number of expanded total nucleated cells (TNCs) in MSC-based culture was twofold higher than cultures without MSC (control cultures). UCB-MSCs increased the expansion capabilities of CD34+ cells, long-term culture-initiating cells (LTC-ICs), granulocyte-macrophage colony-forming cells (GM-CFCs), and high proliferative potential colony-forming cells (HPP-CFCs) compared to control cultures. The expanded HSPCs were transplanted into lethally irradiated NOD/SCID mice to assess the effects of expanded cells on hematopoietic recovery. The number of white blood cells (WBCs) in the peripheral blood of mice transplanted with expanded cells from both the MSC-based and control cultures returned to pretreatment levels at day 25 posttransplant and then decreased. The WBC levels returned to pretreatment levels again at days 45-55 posttransplant. The level of human CD45+ cell engraftment in primary recipients transplanted with expanded cells from the MSC-based cultures was significantly higher than recipients transplanted with cells from the control cultures. Serial transplantation demonstrated that the expanded cells could establish long-term engraftment of hematopoietic cells. UCB-MSCs similar to those derived from adult bone marrow may provide novel targets for cellular and gene therapy.

Large-scale expansion and transplantation of CD34(+) hematopoietic cells: in vitro and in vivo confirmation of neutropenia abrogation related to the expansion process without impairment of the long-term engraftment capacity

BACKGROUND

Herein are reported the results obtained in all multiple myeloma patients transplanted with peripheral blood hematopoietic progenitor cells submitted to ex vivo expansion.

STUDY DESIGN AND METHODS

Patients had blood progenitor cell mobilization with cyclophosphamide and filgrastim. CD34+ cells were expanded for 10 days in a medium containing granulocyte-colony-stimulating factor (G-CSF), stem cell factor, and megakaryocyte growth and development factor (MGDF). Twenty-seven patients underwent transplantation with expanded and nonexpanded cells and 7 patients underwent transplantation with expanded cells only.

RESULTS

The median fold cell expansion was 29.1. The number of colony-forming unit-granulocyte-macrophage (CFU-GM) and CD34+ cells, and the long-term culture-initiating cell (LTC-IC) activity increased with median fold values of 14.7, 2.75, and 2.25, respectively. Postmyeloablative neutropenia was abrogated in 24 of 27 patients transplanted with expanded cells plus nonexpanded cells. The median duration of severe neutropenia was 0 days and correlated with the number of cells and CFU-GM infused. Survival was similar to that of a historical control group. Our LTC-IC and NOD-SCID mice studies showed that the expanded cells are able of sustaining long-term hematopoiesis. Seven other patients received transplantation with expanded cells alone. Absolute neutropenia was abrogated in 6 patients. The median duration of neutropenia was 0 days. Two patients who received the lower number of total cells or CFU-GM had brief secondary neutropenia, which resolved after G-CSF injections.

CONCLUSION

CD34+ cells expanded ex vivo can abrogate absolute and severe neutropenia after high-dose therapy. The results of the amplification process are strongly related to the delay of hematopoietic recovery.

Outgrowth of a transformed cell population derived from normal human BM mesenchymal stem cell culture

BACKGROUND

Human mesenchymal stem cells (hMSC) have been isolated and characterized extensively for a variety of clinical applications. Yet it is unclear how the phenomenon of hMSC plasticity can be safely and reasonably exploited for therapeutic use.

METHODS

We have generated mesenchymal stem cells (MSC) from normal human BM and identified a novel cell population with a transformed phenotype. This cell population was characterized by morphologic, immunophenotypic, cytogenetic analyzes and telomerase expression. Its tumorigenicity in NOD/SCID mice was also studied.

RESULTS

A subpopulation of cells in hMSC culture was noted to appear morphologically distinct from typical MSC. The cells were spherical, cuboidal to short spindle in shape, adherent and exhibited contact independent growth. Phenotypically the cells were CD133(+), CD34(-), CD45(-), CD90(low), CD105(-), VEGFR2(+). Cytogenetic analysis showed chromosome aneuploidy and translocations. These cells also showed a high level of telemerase activity compared with typical MSC. Upon transplantation into NOD/SCID mice, multiple macroscopic solid tumors formed in multiple organs or tissues. Histologically, these tumors were very poorly differentiated and showed aggressive growth with large areas of necrosis.

DISCUSSION

The possible explanations for the origin of this cell population are: (1) the cells represent a transformed population of MSC that developed in culture; (2) abnormal cells existed in the donor BM at rare frequency and subsequently expanded in culture. In either case, the MSC culture may provide a suitable environment for transformed cells to expand or propagate in vitro. In summary, our data demonstrate the potential of transformed cells in hMSC culture and highlight the need for karyotyping as a release criteria for clinical use of MSC.

Support of hMSCs transduced with TPO/FL genes to expansion of umbilical cord CD34+ cells in indirect co-culture

A novel indirect co-culture system was established to support ex vivo expansion of hematopoietic progenitors in umbilical cord blood (UCB) by using thrombopoietin (TPO)/Flt-3 ligand (FL)-transduced human-marrow-derived mesenchymal stem cells (tfhMSCs) as a feeder. UCB CD34+ cells were isolated and cultured by using five culture systems in serum-containing or serum-free medium. Suitable aliquots of cultured cells were taken to monitor cell production, clonogenic activity, and long-term culture-initiating culture (LTC-IC) output. Finally, the severe-combined immunodeficient mouse (SCID) repopulating cell (SRC) assay was performed to confirm the ability of the indirect co-cultured cells from the tfhMSCs system to reconstitute long-term hematopoiesis. Results showed significant differences in the number of total nucleated cells (TNCs) among the culture systems with respect to serum-containing medium or serum-free medium during 14-day culture. In addition, on day 14, the outputs of CD34+ cells, the colony-forming units (CFUs) in culture, and the CFUs in mixed colonies containing erythroid and myeloid cells and megakaryocytes in the tfhMSC indirect co-culture system were significantly enhanced. The LTC-IC assay demonstrated that the tfhMSCs indirect co-culture system had the strongest activity. The SCID-SRC assay confirmed the extensive ability of the expanded cells from the tfhMSCs indirect co-culture systems to reconstitute long-term hematopoiesis. Furthermore, polymerase chain reaction analysis demonstrated the presence of human hematopoietic cells in the bone marrow and peripheral blood cells of non-obese diabetic/SCID mice. Thus, hMSCs transduced with TPO/FL, in combination with additive cytokines, can effectively expand hematopoietic progenitors from UCB in vitro. The tfhMSC indirect co-culture system may therefore be a suitable system for ex vivo manipulation of primitive progenitor cells under non-contact culture conditions.

Prognostic analysis of pre-transplant peripheral T-cell levels in patients receiving an autologous hematopoietic progenitor-cell transplant

The purpose of this study was to evaluate pre-transplant T-cell status in autologous hematopoietic progenitor-cell transplantation (HPCT) recipients. Between 1999 and 2002 we prospectively enrolled 85 autologous HPCT recipients with solid tumors (N = 50) or hematological malignancies (n = 35). Patient diagnoses included breast cancer (N = 49), non-Hodgkin's lymphoma (N = 20), myeloma (N = 11), Hodgkin's disease (N = 3), germ-cell tumor (N = 1) and amyloidosis (N = 1). Levels of CD3, CD4, CD8, memory and naïve CD4, and CD8 T-cell subsets were analyzed before autologous HPCT. Autologous HPCT recipients presented with lower pre-transplant counts of CD3, CD4, but not CD8 T cells, as compared to healthy controls. Pre-transplant CD4 T-cell levels correlated with progression-free survival (PFS) (P = 0.002) and overall survival (OS) (P = 0.05), in patients with hematologic malignancies (P = 0.02) and breast cancer (P = 0.04). Specifically, pre-transplant memory CD4 + CD45RA - CD62L - T-cell levels correlated with PFS (P = 0.01). The prognostic effects of pre-transplant CD4 and CD4 + CD45RA - CD62L - T cells were independent of tumor diagnosis, tumor stage, tumor sensitivity, and, for breast cancer patients, Her2 / neu status. Our results suggest that pre-transplant CD4 T-cell status, specifically CD4 + CD45RA - CD62L - memory T cells, correlates with the outcome of autologous HPCT recipients. These observations suggest the feasibility of prospective identification of those patients at higher risk of relapse, based on their immune status.

[Biological characteristics of mesenchymal stem cells in human umbilical cord blood and their supporting capacities in ex vivo expansion of CD34+ hematopoietic stem cells]

OBJECTIVE

To explore the biological characteristics of mesenchymal stem cells (MSC) derived from umbilical cord blood (UCB) and their supporting capacities in ex vivo expansion of hematopoietic stem/progenitor cells (HSPCs).

METHODS

Low-density mononuclear cells (MNCs) from UCB were cultured in IMDM containing 20% FBS to form confluent adherent cells through 15 passages. Some cytokines in the conditioned medium were determined with ELISA. UCB-derived adherent cells were displayed with antibodies and analyzed with flow cytometry. The supporting capacity of UCB-derived adherent cells for ex vivo expansion of CD34(+) cells was assayed by co-culture in a two step culture. UCB-derived adherent cells were induced for chondrogenic differentiation with chondrogenic medium, and the induced cells were analyzed for the type II pro-collagen gene expression with RT-PCR.

RESULTS

The mean number of adherent fibroblast like colonies derived from UCB was (3.5 +/- 0.7)/10(6) MNCs. UCB-derived MSCs could survive for at least 15 passages of expansion. In their undifferentiated status, UCB-derived MSCs were CD13(+), CD29(+), CD90(+), CD105(+), CD166(+), SH2(+), SH3(+), SH4(+), CD45(-), CD34(-), and CD14(-). Stem cell factor (SCF), interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-alpha) could be detected in the supernatant of the cultures. The MSCs cultured in chondrogenic media could differentiate into chondrogenic cells and express type II pro-collagen mRNA. UCB-derived MSCs could support the proliferation and differentiation of UCB CD34(+) cells in vitro.

CONCLUSION

UCB-derived MSCs are similar to those derived from adult bone marrow and can support the proliferation of hematopoietic stem/progenitor cells.

Prognostic analysis of early lymphocyte recovery in patients with advanced breast cancer receiving high-dose chemotherapy with an autologous hematopoietic progenitor cell transplant

PURPOSE

The purpose of this study was to evaluate the prognostic effect of early posttransplant lymphocyte recovery in patients with advanced breast cancer receiving high-dose chemotherapy with autologous hematopoietic progenitor cell transplantation.

EXPERIMENTAL DESIGN

We analyzed the effect of the absolute lymphocyte count on day +15 posttransplant on freedom from relapse and overall survival in patients with high-risk primary breast cancer or metastatic breast cancer, enrolled between 1990 and 2001 in prospective high-dose chemotherapy trials, using a uniform regimen of cyclophosphamide, cisplatin, and 1,3-bis(2-chloroethyl)-1-nitrosourea.

RESULTS

Four hundred and seventy-six patients (264 high-risk primary breast cancer and 212 metastatic breast cancer patients) were evaluated at median follow-up of 8 years (range, 1.5-11 years). The disease-free survival and overall survival rates in the high-risk primary breast cancer group were 67% and 70%, respectively. Patients with metastatic breast cancer patients had 21.8% disease-free survival and 31.5% overall survival rates. Day +15 absolute lymphocyte count correlated with freedom from relapse (P = 0.007) and overall survival (P = 0.04) in the metastatic breast cancer group, but not in the high-risk primary breast cancer group (P = 0.5 and 0.8, respectively). The prognostic effect of absolute lymphocyte count in metastatic breast cancer was restricted to those patients receiving unmanipulated peripheral blood progenitor cells (P = 0.04). In contrast, absolute lymphocyte count had no significant effect in those metastatic breast cancer patients receiving bone marrow or a CD34-selected product. In multivariate analyses, the prognostic effect of day +15 absolute lymphocyte count in metastatic breast cancer was independent of other predictors, such as disease status, pre-high-dose chemotherapy treatment, number of tumor sites, or HER2.

CONCLUSIONS

Early lymphocyte recovery is an independent outcome predictor in metastatic breast cancer patients receiving high-dose chemotherapy and an autologous peripheral blood progenitor cell transplant. These observations suggest that immune strategies targeting minimal posttransplant residual disease may prove worthwhile.

Mesenchymal stem/progenitor cells in human umbilical cord blood as support for ex vivo expansion of CD34(+) hematopoietic stem cells and for chondrogenic differentiation

BACKGROUND AND OBJECTIVES

Human mesenchymal stem/progenitor cells (MSPC) ar pluripotent, being the precursors for marrow stroma, bone, cartilage, muscle and connective tissues. Although the presence of hematopoietic stem/progenitor cells (HSPC) in umbilical cord blood (UCB) is well known, that of MSPC has been not fully evaluated.

DESIGN AND METHODS

In this study, we examined the immunophenotype, the supporting function in relation to ex vivo expansion of hematopoietic stem progenitor cells and the chondrogenic differentiation of cultured cells with characteristics of MSPC from UCB. When UCB nucleated cells were isolated and 107 cells cultured in IMDM with 20% fetal bovine serum, the mean number of adherent fibroblastlike colonies was 3.5+/-0.7/10(6) monuclear cells.

RESULTS

UCB-derived MSPC could be expanded for at least 15 passages. In their undifferentiated state, UCB-derived MSPC were CD13(+), CD29(+), CD90(+), CD105(+), CD166(+), SH2(+), SH3(+), SH4(+), CD45(-), CD34(-), and CD14(-); they produced stem cell factor, interleukin 6 and tumor necrosis factor alpha. UCB-derived MSPC cultured in chondrogenic media differentiated into chondrogenic cells. UCB-derived MSPC supported the proliferation and differentiation of CD34(+) cells from UCB in vitro.

INTERPRETATION AND CONCLUSIONS

UCB-derived MSPC have the potential to support ex vivo expansion of HSPC and chondrogenic differentiation. UCB should not be regarded as medical waste. It can serve as an alternative source of mesenchymal stem cells and may provide a unique source of fetal cells for cellular and gene therapy.

Hypoxia-induced pulmonary artery adventitial remodeling and neovascularization: contribution of progenitor cells

Information is rapidly emerging regarding the important role of the arterial vasa vasorum in a variety of systemic vascular diseases. In addition, increasing evidence suggests that progenitor cells of bone marrow (BM) origin may contribute to postnatal neovascularization and/or vascular wall thickening that is characteristic in some forms of systemic vascular disease. Little is known regarding postnatal vasa formation and the role of BM-derived progenitor cells in the setting of pulmonary hypertension (PH). We sought to determine the effects of chronic hypoxia on the density of vasa vasorum in the pulmonary artery and to evaluate if BM-derived progenitor cells contribute to the increased vessel wall mass in a bovine model of hypoxia-induced PH. Quantitative morphometric analyses of lung tissue from normoxic and hypoxic calves revealed that hypoxia results in a dramatic expansion of the pulmonary artery adventitial vasa vasorum. Flow cytometric analysis demonstrated that cells expressing the transmembrane tyrosine kinase receptor for stem cell factor, c-kit, are mobilized from the BM in the circulation in response to hypoxia. Immunohistochemistry revealed an increase in the expression of c-kit+ cells together with vascular endothelial growth factor, fibronectin, and thrombin in the hypoxia-induced remodeled pulmonary artery vessel wall. Circulating mononuclear cells isolated from neonatal calves exposed to hypoxia were found to differentiate into endothelial and smooth muscle cell phenotypes depending on culture conditions. From these observations, we suggest that the vasa vasorum and circulating progenitor cells could be involved in vessel wall thickening in the setting of hypoxia-induced PH.

Ex vivo expansions and transplantations of mouse bone marrow-derived hematopoietic stem/progenitor cells

To examine the effects of co-culture with bone marrow mesenchymal stem cells on expansion of hematopoietic stem/progenitor cells and the capacities of rapid neutrophil engraftment and hematopoietic reconstitution of the expanded cells, we expanded mononuclear cells (MNCs) and CD34+/c-kit+ cells from mouse bone marrow and transplanted the expanded cells into the irradiated mice. MNCs were isolated from mouse bone marrow and CD34+/c-kit+ cells were selected from MNCs by using MoFlo Cell Sorter. MNCs and CD34+/c-kit+ cells were co-cultured with mouse bone marrow-derived mesenchymal stem cells (MSCs) under a two-step expansion. The expanded cells were then transplanted into sublethally irradiated BDF1 mice. Results showed that the co-culture with MSCs resulted in expansions of median total nucleated cells, CD34+ cells, GM-CFC and HPP-CFC respectively by 10.8-, 4.8-, 65.9- and 38.8-fold for the mononuclear cell culture, and respectively by 76.1-, 2.9-, 71.7- and 51.8-fold for the CD34+/c-kit+ cell culture. The expanded cells could rapidly engraft in the sublethally irradiated mice and reconstitute their hematopoiesis. Co-cultures with MSCs in conjunction with two-step expansion increased expansions of total nucleated cells, GM-CFC and HPP-CFC, which led us to conclude MSCs may create favorable environment for expansions of hematopoietic stem/progenitor cells. The availability of increased numbers of expanded cells by the co-culture with MSCs may result in more rapid engraftment of neutrophils following infusion to transplant recipients.

[Study of ex vivo expansion of mouse hematopoietic stem/progenitor cells and the use of them for hematopoiesis reconstitution]

OBJECTIVE

To explore the rapid neutrophil engraftment and long-term hematopoietic reconstitution.

METHODS

Mononuclear cells (MNCs) were isolated from 5-Fu treated male BDF1 mouse bone marrow and CD(34)(+)/c-kit(+) cells were selected from the MNCs by using MoFlo Cell Sorter. MNCs and CD(34)(+)/c-kit(+) cells were co-cultured with mouse bone marrow-derived mesenchymal stem cells (MSCs) in a two-step expansion. The expanded cells were then transplanted into sublethally irradiated female BDF1 mice.

RESULTS

Co-culture with MSCs resulted in 10.8-, 4.8-, 65.9- and 38.8-fold increases yields of median total nucleated cells, CD(34)(+) cells, GM-CFC and HPP-CFC, respectively, as for the MNCs culture, and 76.1-, 2.9-, 71.7- and 51.8-fold increase respectively for the CD(34)(+)/c-kit(+) cell culture. The expanded cells could rapidly engraft in the sublethally, irradiated mice, reconstitute their hematopoiesis, and be detected in the recipients bone marrow 2 months after transplantation.

CONCLUSIONS

Hematopoietic stem/progenitor cells co-cultures with MSCs in two-step expansion could increase expansion yields of total nucleated cells, GM-CFC and HPP-CFC. The availability of increased numbers of expanded cells may result in more rapid engraftment of neutrophils following infusion to transplant recipients.

Transplantation of ex vivo expanded cord blood

Umbilical cord blood (CB) from unrelated donors is increasingly used to restore hematopoiesis after myeloablative therapy. CB transplants are associated with higher rates of delayed and failed engraftment than are bone marrow transplants, particularly for adult patients. We studied the ex vivo expansion of CB in an attempt to improve time to engraftment and reduce the graft failure rate in the recipients. In this feasibility study, 37 patients (25 adults, 12 children) with hematologic malignancies (n = 34) or breast cancer (n = 3) received high-dose therapy followed by unrelated allogeneic CB transplantation. A fraction of each patient's CB allograft was CD34-selected and cultured ex vivo for 10 days prior to transplantation in defined media with stem cell factor, granulocyte colony-stimulating factor, and megakaryocyte growth and differentiation factor. The remainder of the CB graft was infused without further manipulation. Two sequential cohorts of patients were accrued to the study. The first cohort had 40% and the second cohort had 60% of their CB graft expanded. Patients received a median of 0.99 x 10(7) total nucleated cells (expanded plus unexpanded) per kilogram. The median time to engraftment of neutrophils was 28 days (range, 15-49 days) and of platelets was 106 days (range, 38-345 days). All evaluable patients who were followed for 28 days or longer achieved engraftment of neutrophils. Grade III/IV acute GVHD was documented in 40% and extensive chronic GVHD in 63% of patients. At a median follow-up of 30 months, 13 (35%) of 37 of patients survived. This study demonstrates that the CD34 selection and ex vivo expansion of CB prior to transplantation of CB is feasible. Additional accrual will be required to assess the clinical efficacy of expanded CB progenitors.

Ex vivo expanded cord blood cells provide rapid engraftment in fetal sheep but lack long-term engrafting potential

OBJECTIVE

Cord blood (CB) products are becoming routinely used in unrelated allogeneic transplantation for smaller pediatric patients. Because of the low numbers of cells in CB compared to bone marrow or peripheral blood progenitor cells, their use is more limited in larger adults. Therefore, we developed ex vivo expansion conditions for CB and currently are transplanting ex vivo expanded CB products to patients receiving high-dose chemotherapy. As there is concern that ex vivo expansion may exhaust long-term engrafting cells, the current clinical protocols consist of both an expanded fraction and an unexpanded fraction. To determine the effect of expansion culture on long-term engrafting cells, we evaluated the short- and long-term engrafting potential of ex vivo expanded CB using a fetal sheep xenogeneic transplant model.

MATERIAL AND METHODS

CD 34(+) cells were selected from CB products and cultured in a two-step procedure in the presence of stem cell factor, megakaryocyte growth and differentiation factor, and granulocyte colony-stimulating factor for 14 days. Starting cells (CD34(+) cells), and cultured cells (day 7 and day 14 cells) were transplanted in 60-day-old fetal sheep and evaluated at various time points post transplant for the presence of human cells. Long-term engrafting cells were assessed by serial passage into secondary and tertiary recipients.

RESULTS

Day 14 expanded CB cells provided more rapid engraftment than either the day 7 expanded cells or the day 0 cells; however, this engraftment was transient, and no human cells were detectable at 16 months post transplant in the animals that received the day 14 expanded cells. Day 0 cells had engrafted animals at 2 months post transplant and both the day 0 and day 7 cells persisted to 16 months or longer. In the secondary animals, the day 0 and day 7 cells engrafted equivalently at 3 months post transplant; however, no secondary engraftment resulted from the day 14 cells. The levels of engraftment in secondary animals receiving day 7 cells decreased with time to barely detectable levels at 12 months post transplant.

CONCLUSIONS

Ex vivo expansion of CB CD34(+) cells under the conditions described results in the generation of increased mature cells and progenitors that are capable of more rapid engraftment in fetal sheep compared to unexpanded CB CD34(+) cells. The expanded cells engrafted primary sheep but lacked secondary and tertiary engrafting potential. These studies demonstrate that although ex vivo expanded cells may be able to provide rapid short-term engraftment, the long-term potential of expanded grafts may be compromised. Therefore, clinical protocols may require transplantation of two fractions of cells, an expanded CB graft to provide rapid short-term engraftment and an unmanipulated fraction of CB graft to provide stem cells for long-term engraftment.

Deletion of the Src homology 3 domain and C-terminal proline-rich sequences in Bcr-Abl prevents Abl interactor 2 degradation and spontaneous cell migration and impairs leukemogenesis

The hematopoietic cells from patients with Bcr-Abl-positive chronic myelogenous leukemia exhibit multiple abnormalities of cytoskeletal function. The molecular events leading to these abnormalities are not fully understood. Previously we showed that Bcr-Abl elicits ubiquitin-dependent degradation of Abl interactor proteins. Because recent studies have suggested a role of Abl interactor proteins in the pathway that regulates cytoskeletal function, we investigated whether mutations in Bcr-Abl that interfere with the signaling to Abl interactor proteins affect its leukemogenic activity. We report here that the Src homology 3 domain and C-terminal proline-rich sequences of Bcr-Abl are required for its binding to Abl interactor 2 as well as for the induction of Abl interactor 2 degradation. Although the deletion of these regions did not affect the ability of the mutant Bcr-Abl to transform hematopoietic cells to growth factor independence, it abrogated its ability to stimulate spontaneous cell migration on fibronectin-coated surfaces. Furthermore, the mutant Bcr-Abl, defective in binding to Abl interactor 2 and inducing its degradation, failed to induce chronic myelogenous leukemia-like disease in mouse. These results are consistent with a role of Abl interactor proteins in the regulation of cytoskeletal function as well as in the pathogenesis of Bcr-Abl-induced leukemogenesis.

Engraftment of primates with G-CSF mobilized peripheral blood CD34+ progenitor cells expanded in G-CSF, SCF and MGDF decreases the duration and severity of neutropenia

We used a primate model of autologous peripheral blood progenitor cell (PBPC) transplantation to study the effect of in vitro expansion on committed progenitor cell engraftment and marrow recovery after transplantation. Four groups of baboons were transplanted with enriched autologous CD34+ PBPC collected by apheresis after five days of G-CSF administration (100 microg/kg/day). Groups I and III were transplanted with cryopreserved CD34+ PBPC and Groups II and IV were transplanted with CD34+ PBPC that had been cultured for 10 days in Amgen-defined (serum free) medium and stimulated with G-CSF, megakaryocyte growth and development factor (MGDF), and stem cell factor each at 100 etag/ml. Group III and IV animals were administered G-CSF (100 microg/kg/day) and MGDF (25 microg/kg/day) after transplant, while animals in Groups I and II were not. For the cultured CD34+ PBPC from groups II and IV, the total cell numbers expanded 14.4 +/- 8.3 and 4.0 +/- 0.7-fold, respectively, and CFU-GM expanded 7.2 +/- 0.3 and 8.0 +/- 0.4-fold, respectively. All animals engrafted. If no growth factor support was given after transplant (Groups II and I), the recovery of WBC and platelet production after transplant was prolonged if cells had been cultured prior to transplant (Group II). Administration of post-transplant G-CSF and MGDF shortened the period of neutropenia (ANC < 500/microL) from 13 +/- 4 (Group I) to 10 +/- 4 (Group III) days for animals transplanted with non-expanded CD34+ PBPC. For animals transplanted with ex vivo-expanded CD34+ PBPC, post-transplant administration of G-CSF and MGDF shortened the duration of neutropenia from 14 +/- 2 (Group II) to 3 +/- 4 (Group IV) days. Recovery of platelet production was slower in all animals transplanted with expanded CD34+ PBPC regardless of post-transplant growth factor administration. Progenitor cells generated in vitro can contribute to early engraftment and mitigate neutropenia when growth factor support is administered post-transplant. Thrombocytopenia was not decreased despite evidence of expansion of megakaryocytes in cultured CD34+ populations.

Peripheral blood stem cell transplantation in breast cancer

Over the past decade, peripheral blood progenitor cells (PBPCs) have replaced bone marrow as the major source of haematopoietic support. This transition from marrow to PBPCs is due to the fact that, for many clinical studies, a significantly faster rate of engraftment, particularly for platelets, has been demonstrated for patients who receive PBPC support when compared to similarly treated patients who are transplanted with bone marrow. The leukapheresis procedure itself, quality of PBPC graft, methods of PBPC mobilization, purging, and ex vivo expansion will be discussed in detail.

CD34+ cell selection from frozen cord blood products using the Isolex 300i and CliniMACS CD34 selection devices

Ex vivo expansion of cord blood (CB) cells requires CD34+ cell selection before expansion to obtain optimal numbers of progenitor cells. As a preliminary step to preclinical development of CB expansion, we have evaluated two clinical scale selection devices, the Isolex 300i (Baxter Healthcare, Immunotherapy Division) and the CliniMACS (Miltenyi Biotech Inc.), for CD34+ cell selection from frozen CB products. As expansion of CB results in differentiation of cells, there may be a depletion of stem cells. Therefore, only a fraction of the CB should be expanded while a portion of the CB is maintained unmanipulated for infusion. After thawing of 40% fractions of each CB product, we observed >95% viable cells, with a median total WBC count of 1.8 x 10(8) cells. Use of the Isolex 300i resulted in a median purity of 51% CD34+ cells (n=8) and a median recovery of 34% CD34+ cells. Use of the CliniMACS resulted in a median purity of 54% CD34+ cells (n=10) and a median recovery of 80% CD34+ cells. The absolute number of CD34+ cells recovered after selection varied with samples from 6.7 x 10(4) to 3.2 x 10(6) CD34+ cells. Expansion of CD34+ cells from both systems resulted in >20-fold expansion of CFU-GM, with a median of 44-fold expansion. These data demonstrate the feasibility of selecting small fractions of frozen CB products using clinical scale CD34+ cell selection devices.

Marrow repopulating cells in mobilized PBPC can be serially transplanted for up to five generations or be remobilized in PBPC reconstituted mice

We have evaluated the durability of engraftment and the potential of remobilization in mice reconstituted with mobilized peripheral blood progenitor cells (PBPC). Female mice which had been reconstituted with cytokine-mobilized PBPC from male donors were serially transplanted into second, third, fourth and fifth lethally irradiated female recipients at intervals of 6-10 months. Male-derived hematopoiesis was determined in recipient mice at each serial transplantation. Male-positive CFCs were detected after 5 passages for 45 months, but declined from >95% at passage 1 to 74% at passage 2, 33% at passage 4, and 28% at passage 5. Long-term survival also declined from 97% at passage 2 to 53% at passage 4, and 27% at passage 5. The results demonstrated that mobilized PBPC were able to provide engraftment for more than 45 months, but the engraftment provided by mobilized PBPC decreased at each serial passage. In addition, mice reconstituted with mobilized PBPC (at 1 year post transplantation) were treated with the same cytokines as in the primary mobilization (remobilization). The remobilized PBPC were harvested and transplanted into lethally irradiated secondary recipients. Male-derived CFCs were evaluated at 20 months post transplantation. Mice transplanted with PBPC remobilized with rhG-CSF or rhG-CSF plus rrSCF-PEG showed 70% and 89% male-positive CFCs respectively, demonstrating that mice reconstituted with mobilized PBPC could be remobilized and that the remobilized PBPC were also capable of providing long-term hematopoietic reconstitution. Our studies demonstrated that mobilized PBPC have extensive proliferative or self-renewal capacity to provide durable engraftment and that marrow repopulating cells in PBPC reconstituted mice can be remobilized, suggesting that patients who relapse after PBPC transplantation may be remobilized for a second transplantation to support additional chemotherapy.

Peripheral blood progenitor cell mobilization using stem cell factor in combination with filgrastim in breast cancer patients

The safety and optimal dose and schedule of stem cell factor (SCF) administered in combination with filgrastim for the mobilization of peripheral blood progenitor cells (PBPCs) was determined in 215 patients with high-risk breast cancer. Patients received either filgrastim alone (10 microg/kg/d for 7 days) or the combination of 10 microg/kg/d filgrastim and 5 to 30 microg/kg/d SCF for either 7, 10, or 13 days. SCF patients were premedicated with antiallergy prophylaxis. Leukapheresis was performed on the final 3 days of cytokine therapy and, after high-dose chemotherapy and infusion of PBPCs, patients received 10 microg/kg/d filgrastim until absolute neutrophil count recovery. The median number of CD34+ cells collected was greater for patients receiving the combination of filgrastim and SCF, at doses greater than 10 microg/kg/d, than for those receiving filgrastim alone (7.7 v 3.2 x 10(6)/kg, P < .05). There were significantly (P < .05) more CD34+ cells harvested for the 20 microg/kg/d SCF (median, 7.9 x 10(6)/kg) and 25 microg/kg/d SCF (median, 13.6 x 10(6)/kg) 7-day combination groups than for the filgrastim alone patients (median, 3.2 x 10(6)/kg). The duration of administration of SCF and filgrastim (7, 10, or 13 days) did not significantly affect CD34+ cell yield. Treatment groups mobilized with filgrastim alone or with the cytokine combination had similar hematopoietic engraftment and overall survival after PBPC infusion. In conclusion, the results of this study indicate that SCF therapy enhances CD34+ cell yield and is associated with manageable levels of toxicity when combined with filgrastim for PBPC mobilization. The combination of 20 microg/kg/d SCF and 10 microg/kg/d filgrastim with daily apheresis beginning on day 5 was selected as the optimal dose and schedule for the mobilization of PBPCs.

Effects of prior therapy on the in vitro proliferative potential of stem cell factor plus filgrastim-mobilized CD34-positive progenitor cells

The quantity of hematopoietic progenitors in an apheresis collection is defined by the number of CD34(+) cells or granulocyte macrophage colony-forming units present. These parameters are believed to give roughly equivalent information on graft quality. We here report that the in vitro proliferative potential of r-metHuSCF (stem cell factor) plus filgrastim (granulocyte colony-stimulating factor; r-metHuG-CSF) mobilized peripheral blood (PB) CD34(+) cells obtained from previously heavily treated non-Hodgkin's lymphoma patients inversely correlates with extent of prior therapy. CD34(+) cells were enriched using the CellPro Ceprate system and placed in liquid culture for 4 weeks in the presence of either r-metHuSCF, IL-3, IL-6, filgrastim (S36G), or S36G plus erythropoietin (S36GE) with a weekly exchange of media and cytokines with reestablishment of culture at the starting cell concentration (Delta assay) and enumeration of progenitors. Starting with 4 x 10(4) CD34(+) cells from apheresis samples from patients who had received <10 cycles of prior chemotherapy, progenitors were detectable in culture at 4 weeks 81% of the time as compared to 14% with CD34(+) cells from patients who had received >10 cycles and 5% for >10 cycles plus radiotherapy. The total number of progenitors generated over the duration of culture (area under the curve) was calculated using the trapezoidal rule as a novel measure of the proliferative potential of the enriched PB CD34(+) cell population. The median area under the curve of CD34(+) cells from patients receiving <10 cycles of prior chemotherapy was 7.4 and 5.7 (x10(5)) using S36G or S36GE, respectively, 1.8 and 1.9 if the patients received >10 cycles of prior chemotherapy, and 1.4 and 1.2 if the patients received >10 cycles of prior chemotherapy plus radiotherapy (P < 0.001). These data show that prior therapy impacts on the quality of PB CD34(+) cells as measured by their ability to generate committed progenitors over a number of weeks in liquid culture.

Chronic expression of murine flt3 ligand in mice results in increased circulating white blood cell levels and abnormal cellular infiltrates associated with splenic fibrosis

The effect of chronic expression of flt3 ligand (FL) on in vivo hematopoiesis was studied. Retroviral vector-mediated gene transfer was used in a mouse model of bone marrow transplantation to enforce expression of mouse FL cDNA in hematopoietic tissues. As early as 2 weeks posttransplantation, peripheral blood white blood cell counts in FL-overexpressing recipients were significantly elevated compared with controls. With the exception of eosinophils, all nucleated cell lineages studied were similarly affected in these animals. Experimental animals also exhibited severe anemia and progressive loss of marrow-derived erythropoiesis. All of the FL-overexpressing animals, but none of the controls, died between 10 and 13 weeks posttransplantation. Upon histological examination, severe splenomegaly was noted, with progressive fibrosis and infiltration by abnormal lymphoreticular cells. Abnormal cell infiltration also occurred in other organ systems, including bone marrow and liver. In situ immunocytochemistry on liver sections showed that the cellular infiltrate was CD3+/NLDC145+/CD11c+, but B220- and F4/80-, suggestive of a mixed infiltrate of dendritic cells and activated T lymphocytes. Infiltration of splenic blood vessel perivascular spaces resulted in vascular compression and eventual occlusion, leading to splenic necrosis consistent with infarction. These results show that FL can affect both myeloid and lymphoid cell lineages in vivo and further demonstrate the potential toxicity of in vivo treatment with FL.

Purification of CD34+ cells is essential for optimal ex vivo expansion of umbilical cord blood cells

Allogeneic umbilical cord blood (UCB) cells have recently been used for transplantation following high-dose chemotherapy. However, the numbers of total cells, including progenitor cells, harvested are low compared with bone marrow or peripheral blood progenitor cell harvests. Therefore, we evaluated the potential of UCB cells for their ability to expand granulocyte-macrophage colony-forming cells (GM-CFC) and burst-forming unit-erythroid (BFU-E) cells over 10 days. We used an ammonium chloride lysing buffer to eliminate the majority of contaminating red blood cells. An average recovery of 61% of the starting number of white blood cells was obtained, while retaining 100% of the CD34+ cells. Ex vivo expansion cultures were established in Teflon cell culture bags (American Fluoroseal Corp, Columbia, MD) in 25 ml defined medium (Amgen Inc, Thousand Oaks, CA) containing 100 ng/ml each of stem cell factor (SCF), granulocyte colony-stimulating factor (G-CSF), and megakaryocyte growth and development factor. Either unselected UCB cells or CD34+ UCB cells, selected with Magnetic Activation Cell Sorting technology (Miltenyi Biotech GmbH, Bergisch Gladbach, Germany), were incubated for 10 days at 37 degrees C without refeeding. Unselected UCB cells seeded at 1 X 10(6)/ml produced an average expansion of 1.4-fold in total cells, 0.8-fold in GM-CFC, and 0.3-fold in BFU-E cells. By contrast, CD34+ selected UCB cells seeded at 1.0 X 10(4)/ml produced an average expansion of 113-fold in total cells, 72.6-fold in GM-CFC, and 49-fold in BFU-E cells. These data demonstrate that CD34+ cell selection is necessary for optimal expansion of both GM-CFC and BFU-E cells. The cell numbers thus obtained postexpansion may be sufficient for transplantation in adults.

Identification and mapping of Casp7, a cysteine protease resembling CPP32 beta, interleukin-1 beta converting enzyme, and CED-3

Cloning of interleukin-1 beta converting enzyme (ICE) and Caenorhabditis elegans death protein CED-3 revealed the structural and functional homology between these two proteases. It also suggested the involvement of ICE-like cysteine proteases in apoptosis. Several CED-3- and ICE-like cysteine proteases have been described, including Nedd2/Ich-1, CPP32 beta, Tx, ICErel3, and Mch2. We have previously described a mouse ortholog of cysteine protease CPP32 beta that shares strong homology with ICE and CED-3. Here, we describe the cloning of mouse and human Casp7, another member of this family of cysteine proteases. Mouse Casp7 encodes a putative 340-amino-acid polypeptide that contains all the known conserved residues required for protease function, including the QACRG sequence, aspartic acid residues for internal cleavage sites, and the residues required for substrate binding. Three RNA variants of human Casp7 were also cloned. Amino acid sequence analysis indicated that Casp7 shared high homology with CPP32 beta/Casp3 and Mch2/Casp6. Northern blot analysis demonstrated that a 2.6-kb Casp7 mRNA was expressed in various tissues except brain. Mouse interspecific backcross mapping allowed localization of Casp7 to the distal region of mouse chromosome 19, linked to Mxi1, Adra2a, and Aop1.

Recombinant human ligand for MPL, megakaryocyte growth and development factor (MGDF), stimulates thrombopoiesis in vivo in normal and myelosuppressed baboons

Megakaryocyte growth and development factor (MGDF) is a ligand for c-mpl and a member of the hematopoietic growth factor superfamily. Recombinant murine MGDF specifically stimulates thrombopoiesis in mice. Recombinant human (rHu) MGDF stimulates megakaryocytic differentiation of baboon CD34+ marrow cells in vitro. Therefore, we determined the in vivo biological effects of rHuMGDF administered to normal baboons in the absence and presence of myelosuppression with 5-fluorouracil (5-FU). rHuMGDF was administered to normal baboons as a single s.c. injection at doses of 1, 10, 25 and 50 micrograms/kg/day for 10 days and, as a control, heat-inactivated MGDF was administered at a dose of 10 micrograms/kg/day. Platelet counts were markedly increased in all animals administered native rHuMGDF but not in animals given heat-inactivated rHuMGDF. Platelet counts began to increase between three and six days after starting rHuMGDF administration and the maximum average increases were 1.7-, 3.4-, 5.1- and 4.0-fold above baseline in animals administered 1, 10, 25 and 50 micrograms/kg/day, respectively. Maximum platelet counts were reached between 7 and 10 days after starting rHuMGDF and maintained for four days after the last dose. Thereafter, platelet counts decreased, reaching stable pretreatment values between 11 and 14 days after the last dose of rHuMGDF. No changes in red cell mass, peripheral blood white blood cell counts or differentials were observed during rHuMGDF treatment. For animals administered 10, 25 and 50 micrograms/kg/day of rHuMGDF, megakaryocytes increased more than threefold in marrow, were markedly enlarged, and had increased numbers of lobes. Overall marrow cellularity remained unchanged, as did red cell and white cell morphology. No marrow fibrosis was detected. Progenitor cells were not increased in marrow but did increase modestly in the peripheral blood, associated with increased numbers of CD34+ cells in the circulation. Following a single dose of 5-FU (120 mg/kg) animals were given either saline or pegylated (PEG) rHuMGDF (25 micrograms/kg/day) for 14 days. Platelet counts recovered to baseline by 13.8 +/- 1.8 days for PEG-rHuMGDF-treated baboons compared with 16.8 +/- 0.6 days for saline treated controls. Marrow biopsies revealed more rapid recovery of overall marrow cellularity and megakaryocytes in PEG-rHuMGDF-treated animals compared with controls. Thus, rHuMGDF specifically stimulates thrombopoiesis in normal and myelosuppressed baboons. rHuMGDF may be useful for stimulating thrombopoiesis in humans in clinical settings after myelosuppression.

Molecular characterization of mouse and rat CPP32 beta gene encoding a cysteine protease resembling interleukin-1 beta converting enzyme and CED-3

Interleukin-1 beta converting enzyme (ICE) defines a new class of mammalian cysteine protease that shares strong homology with the Caenorhabditis elegans death gene ced-3. Both ICE and CED-3, when introduced into cultured cells, induce apoptosis, indicating that this type of cysteine protease may play an important role in the process of programmed cell death. Here, we report the cloning of a mouse and rat gene encoding a novel cysteine protease. The putative proteins encoded by these cDNAs contain the conserved sequence (QACRG) necessary for covalent linkage to the substrate as well as the three amino acids responsible for substrate binding and catalysis in ICE. Amino acid sequence analysis indicates that this rodent cysteine protease is the homolog of human CPP32 beta. Mouse CPP32 beta mRNA is highly expressed in spleen, and to a lesser degree in brain, lung, liver, and kidney. The mouse CPP32 beta genomic locus spans a region of approximately 20 kb, including seven exons and six introns. Mouse interspecific backcross mapping allowed localization of CPP32 beta to the central region of mouse chromosome 8, linked to Scvr, Lpl, Jund1 and Mlr.

Megakaryocyte growth and development factor stimulates enhanced platelet recovery in mice after bone marrow transplantation

Megakaryocyte growth and development factor (MGDF) is a recently characterized ligand for the cell surface receptor mpl. We have evaluated the effects of polyethylene glycollated recombinant human MGDF (PEG-rHuMGDF) on recovery of hematopoietic cells in mice following bone marrow transplantation (BMT) to support lethal irradiation. Mice treated with PEG-rHuMGDF (50 micrograms/kg/d) had accelerated recovery of platelet numbers compared with BMT mice treated with carrier or recombinant human granulocyte colony-stimulating factor (rHuG-CSF, 72 or 200 micrograms/kg/d). In contrast, PEG-rHuMGDF had no effect on white blood cell (WBC) or red blood cell (RBC) recovery. As previously reported, animals treated with rHuG-CSF had an enhanced recovery of WBC but not platelet or RBC levels. Interestingly, BMT receipient mice treated with the combination of PEG-rHuMGDF and rHuG-CSF showed simultaneous enhanced recovery of both leukocytes and platelets. PEGylated rHuMGDF was found to be considerably more potent than non-PEGylated rHuMGDF in this setting. PEG-rHuMGDF is an effective growth factor for enhancing platelet recovery in mice following BMT either alone or in combination with rHuG-CSF. It will be of interest to evaluate in a clinical setting the ratios of PEG-rHuMGDF and rHuG-CSF for simultaneous administration of these factors and accelerated recovery of both leukocytes and platelets.

A model of myelofibrosis and osteosclerosis in mice induced by overexpressing thrombopoietin (mpl ligand): reversal of disease by bone marrow transplantation

We have previously shown that mice induced to overexpress thrombopoietin (TPO) by retroviral-mediated gene transfer into bone marrow (BM) cells develop myelofibrosis and osteosclerosis. It was speculated that these effects were secondary to TPO, resulting from high levels of megakaryocytes and platelets. Also, it was proposed that these mice represent a model for myelofibrosis and osteosclerosis. In this report, we show that levels of both transforming growth factor-beta 1 and platelet-derived growth factor are increased twofold to fivefold in the platelet-poor plasma of TPO overexpressing mice compared with control mice. These data suggest that the increased megakaryocytes produce elevated levels of these cytokines that lead to the pathogenesis of disease. Further, we retransplanted TPO overexpressing mice, at 40 to 42 weeks after primary transplantation, with normal BM cells. After the secondary transplantation, megakaryocytes and platelets returned to normal levels and the myelofibrosis and osteosclerosis were completely corrected. These data extend our initial studies of the effects of overexpression of TPO and show the potential use of this model to explore the underlying cause of myelofibrosis and osteosclerosis and potential treatments for these diseases.

Megakaryocyte growth and development factor accelerates platelet recovery in peripheral blood progenitor cell transplant recipients

We have investigated the potential of PEGylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF), a molecule related to thrombopoietin (mpl ligand or TPO) in minimizing the thrombocytopenia associated with hematopoietic ablation and peripheral blood progenitor cell (PBPC) transplant. Irradiated mice that received PBPC mobilized by PEG-rHuMGDF or granulocyte colony-stimulating factor (G-CSF) had a reduced number of thrombocytopenic days with platelets below 100 x 10(6) per mL of blood. Recipients of unmobilized PBPC had a 9 day thrombocytopenic phase which was shortened to 7 days if they were given granulocyte-macrophage colony-stimulating factor (GM-CSF)-mobilized PBPC. This was further reduced to 2 or 3 days of thrombocytopenia in recipients of G-CSF- or PEG-MGDF-mobilized PBPC. Despite our observation that PEG-rHuMGDF is a relatively modest stimulator of the mobilization of myeloid progenitors to the blood, MGDF-mobilized PBPC do effect accelerated recovery of platelets after transplantation. However, the most effective use of PEG-rHuMGDF is when it is given during the recovery phase after PBPC transplantation to hematopoietically ablated mice. Posttransplant treatment with PEG-rHuMGDF reduces thrombocytopenia to a single day or less, in recipients of most types of PBPC. Mice that were treated during the first 2 weeks after PBPC transplant with PEG-rHuMGDF had 1 thrombocytopenic day compared to 9 days in carrier-treated recipients of unmobilized PBPC and 2 to 3 days in carrier-treated recipients of the optimally mobilized PBPC from G-CSF or G-CSF/PEG-rHuMGDF treated donors. In groups where PEG-rHuMGDF was included in the mobilization protocol and used to treat recipients as well thrombocytopenia was effectively eliminated. These data show that PEG-rHuMGDF is a highly effective agent in eliminating the thrombocytopenia associated with PBPC transplantation.

Chronic exposure to retroviral vector encoded MGDF (mpl-ligand) induces lineage-specific growth and differentiation of megakaryocytes in mice

Megakaryocyte growth and development factor (MGDF) has recently been identified as a ligand for the c-mpl receptor. Using retroviral-mediated gene transfer, MGDF has been overexpressed in mice to evaluate the systematic effects due to chronic exposure to this growth factor. MGDF overexpressing mice had more rapid platelet recovery than control mice after transplantation. Following this recovery, the platelet levels continued increasing to fourfold to eightfold above normal baseline levels and remained elevated (five-fold above control mice) in these animals, which are alive and well at more than 4 months posttransplantation. Increased megakaryocyte numbers were detected in a number of organs in these mice including bone marrow, spleen, liver, and lymph nodes. Prolonged overexpression of MGDF led to decreased marrow hematopoiesis, especially erythropoiesis, with a shift to extramedullary hematopoiesis in the spleen and liver. All the MGDF overexpressing mice analyzed to date developed myelofibrosis and osteosclerosis, possibly induced by megakaryocyte and platelet produced cytokines. No significant effect on other hematopoietic lineages was seen in the MGDF overexpressing mice, showing that the stimulatory effect of MGDF in vivo is restricted to the megakaryocyte lineage.

Stem cell factor

Stem cell factor (SCF) is the ligand for the tyrosine kinase receptor c-kit, which is expressed on both primitive and mature hematopoietic progenitor cells. In vitro, SCF synergizes with other growth factors, such as granulocyte colony-stimulating factor (G-CSF), granulocyte macrophage-colony-stimulating factor, and interleukin-3 to stimulate the proliferation and differentiation of cells of the lymphoid, myeloid, erythroid, and megakaryocytic lineages. In vivo, SCF also synergizes with other growth factors and has been shown to enhance the mobilization of peripheral blood progenitor cells in combination with G-CSF. In phase I/II clinical studies administration of the combination of SCF and G-CSF resulted in a two- to threefold increase in cells that express the CD34 antigen compared with G-CSF alone. Other potential clinical uses include ex vivo expansion protocols and in vitro culture for gene therapy.

Rapid engraftment by peripheral blood progenitor cells mobilized by recombinant human stem cell factor and recombinant human granulocyte colony-stimulating factor in nonhuman primates

We have previously shown that administration of low-dose recombinant human stem cell factor (rhSCF) plus recombinant human granulocyte colony-stimulating factor (rhG-CSF) to baboons mobilizes greater numbers of progenitor cells in the blood than does administration of rhG-CSF alone. The purpose of the present study was to determine whether marrow repopulating cells are present in the blood of nonhuman primates administered low-dose rhSCF plus rhG-CSF, and if present, whether these cells engraft lethally irradiated recipients as rapidly as blood cells mobilized by treatment with rhG-CSF alone. One group of baboons was administered low-dose rhSCF (25 micrograms/kg/d) plus rhG-CSF (100 micrograms/kg/d) while a second group received rhG-CSF alone (100 micrograms/kg/d). Each animal underwent a single 2-hour leukapheresis occurring the day when the number of progenitor cells per volume of blood was maximal. For baboons administered low-dose rhSCF plus rhG-CSF, the leukapheresis products contained 1.8-fold more mononuclear cells and 14.0-fold more progenitor cells compared to the leukapheresis products from animals treated with rhG-CSF alone. All animals successfully engrafted after transplantation of cryopreserved autologous blood cells. In animals transplanted with low-dose rhSCF plus rhG-CSF mobilized blood cells, we observed a time to a platelet count of > 20,000 was 8 days +/- 0, to a white blood cell count (WBC) of > 1,000 was 11 +/- 1 days, and to an absolute neutrophil count (ANC) of > 500 was 12 +/- 1 days. These results compared with 42 +/- 12, 16 +/- 1, and 24 +/- 4 days to achieve platelets > 20,000, WBC > 1,000, and ANC > 500, respectively, for baboons transplanted with rhG-CSF mobilized blood cells. Animals transplanted with low-dose rhSCF plus rhG-CSF mobilized blood cells had blood counts equivalent to pretransplant values within 3 weeks after transplant. The results suggest that the combination of low-dose rhSCF plus rhG-CSF mobilizes greater numbers of progenitor cells that can be collected by leukapheresis than does rhG-CSF alone, that blood cells mobilized by low-dose rhSCF plus rhG-CSF contain marrow repopulating cells, and finally that using a single 2-hour leukapheresis to collect cells, the blood cells mobilized by low-dose rhSCF plus rhG-CSF engraft lethally irradiated recipients more rapidly than do blood cells mobilized by rhG-CSF alone.

The role of stem cell factor in mobilization of peripheral blood progenitor cells

Stem cell factor (SCF) is a hematopoietic growth factor which acts on both primitive and mature progenitors cells. In animals, high doses of SCF alone stimulate increases in cells of multiple lineages and mobilize peripheral blood progenitor cells (PBPC). Phase I studies of rhSCF have demonstrated dose related side effects which are consistent with mast cell activation. Based upon in vitro synergy between SCF and G-CSF we have demonstrated the potential of low doses of SCF to synergize with G-CSF to give enhanced mobilization of PBPC. These PBPC have increased potential for both short and long term engraftment in lethally irradiated mice and lead to more rapid recovery of platelets. On going Phase I/II studies with rhSCF plus rhG-CSF for mobilization of PBPC, demonstrated similar increases in PBPC compared to rhG-CSF alone. These data suggest a clinical role of rhSCF in combination with rhG-CSF for optimal mobilization of PBPC.