Clinical applications of CD34(+) peripheral blood progenitor cells (PBPC)

Purging myeloma cell contaminants and simultaneous expansion of peripheral blood-mobilized stem cells

Human hematopoietic stem cells (HSCs) are widely used as a cellular source for hematopoietic stem cell transplantation (HSCT) in the clinical treatment of hematological malignancies. After transplantation therapy, delays in hematopoietic recovery due to insufficient donor-derived HSCs can lead to increased risks of life-threatening infections and bleeding. Our previous studies developed an efficient ex vivo expansion culture medium (3a medium) for umbilical cord blood-derived HSCs (CBSCs), offering a potential solution to this problem. Nevertheless, the broader applicability of our culture method to alternative cell sources and, of greater significance, its efficacy in eliminating potentially disease-associated contaminated tumor cells, especially in autologous transplantation, raise critical clinical questions. In this study, we modified the 3a medium by incorporating UM729 to replace UM171, adding FMS-like tyrosine kinase 3 (Flt3) ligand, and adjusting the concentrations of butyzamide, 740Y-P, polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft copolymer (PCL-PVAc-PEG, Soluplus) to create the modified-3a medium. This sophistication allowed the efficient expansion of not only CBSCs but also peripheral blood-mobilized HSCs (PBSCs). Additionally, we successfully removed contaminated myeloma cells by adding bortezomib and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) at appropriate concentrations, although we maintained HSCs through the addition of lenalidomide. Our research findings present the potential for widespread clinical application of the modified-3a medium and suggest a safe ex vivo culture technique for expanding human HSCs within peripheral blood-derived donor grafts used for autologous HSCT.

Impact of Mantle Cell Lymphoma Contamination of Autologous Stem Cell Grafts on Outcome after High-Dose Chemotherapy

Simple Summary

High-dose chemotherapy followed by autologous hematopoietic stem cell transplantation (Auto-HSCT) is a standard frontline treatment for fit mantle cell lymphoma (MCL) patients. As there is a need for predictive factors to identify patients unlikely to benefit from this therapy, we investigated the prognostic impact of lymphoma cell contamination of autologous stem cell grafts. Analyzing a cohort of 36 MCL patients, we show that lymphoma cell contamination of stem cell grafts is associated with poor outcomes after Auto-HSCT. Its analysis might thus improve risk assessment and enable risk-stratified treatment strategies for MCL patients.

Abstract

Novel predictive factors are needed to identify mantle cell lymphoma (MCL) patients at increased risk for relapse after high-dose chemotherapy and autologous hematopoietic stem cell transplantation (HDCT/Auto-HSCT). Although bone marrow and peripheral blood involvement is commonly observed in MCL and lymphoma cell contamination of autologous stem cell grafts might facilitate relapse after Auto-HSCT, prevalence and prognostic significance of residual MCL cells in autologous grafts are unknown. We therefore performed a multiparameter flow cytometry (MFC)-based measurable residual disease (MRD) assessment in autologous stem cell grafts and analyzed its association with clinical outcome in an unselected retrospective cohort of 36 MCL patients. MRD was detectable in four (11%) autologous grafts, with MRD levels ranging from 0.002% to 0.2%. Positive graft-MRD was associated with a significantly shorter progression-free and overall survival when compared to graft-MRD negative patients (median 9 vs. 56 months and 25 vs. 132 months, respectively) and predicted early relapse after Auto-HSCT (median time to relapse 9 vs. 44 months). As a predictor of outcome after HDCT/Auto-HSCT, MFC-based assessment of graft-MRD might improve risk stratification and support clinical decision making for risk-oriented treatment strategies in MCL.

Human CD34-negative hematopoietic stem cells: The current understanding of their biological nature

Hematopoietic stem cell (HSC) heterogeneity and hierarchy are a current topic of interest, having major implications for clinical HSC transplantation and basic research on human HSCs. It was long believed that the most primitive HSCs in mammals, including mice and humans, were CD34 antigen positive (CD34⁺). However, 2 decades ago, it was reported that murine long-term multilineage reconstituting HSCs were lineage marker negative (Lin^-, i.e., c-kit⁺Sca-1⁺CD34^low/-), known as CD34^low/- KSL cells. In contrast, human CD34^- HSCs, a counterpart of murine CD34^low/- KSL cells, were hard to identify for a long time mainly because of their rarity. We previously identified very primitive human cord blood (CB)-derived CD34^- severe combined immunodeficiency (SCID)-repopulating cells (SRCs) using the intra-bone marrow injection method and proposed the new concept that CD34^- SRCs (HSCs) reside at the apex of the human HSC hierarchy. Through a series of studies, we identified two positive/enrichment markers: CD133 and GPI-80. The combination of these two markers enabled the development of an ultrahigh-resolution purification method for CD34^- as well as CD34⁺ HSCs and the successful purification of both HSCs at the single-cell level. Cell population purity is a crucial prerequisite for reliable biological and molecular analyses. Clonal analyses of highly purified human CD34^- HSCs have revealed their potent megakaryocyte/erythrocyte differentiation potential. Based on these observations, we propose a revised road map for the commitment of human CB-derived CD34^- HSCs. This review updates the current understanding of the stem cell nature of human CB-derived primitive CD34^- as well as CD34⁺ HSCs.

Efficient and nontoxic biomolecule delivery to primary human hematopoietic stem cells using nanostraws

Introduction of exogenous genetic material into primary stem cells is essential for studying biological function and for clinical applications. Traditional delivery methods for nucleic acids, such as electroporation, have advanced the field, but have negative effects on stem cell function and viability. We introduce nanostraw-assisted transfection as an alternative method for RNA delivery to human hematopoietic stem and progenitor cells (HSPCs). Nanostraws are hollow alumina nanotubes that can be used to deliver biomolecules to living cells. We use nanostraws to target human primary HSPCs and show efficient delivery of mRNA, short interfering RNAs (siRNAs), DNA oligonucleotides, and dextrans of sizes ranging from 6 kDa to 2,000 kDa. Nanostraw-treated cells were fully functional and viable, with no impairment in their proliferative or colony-forming capacity, and showed similar long-term engraftment potential in vivo as untreated cells. Additionally, we found that gene expression of the cells was not perturbed by nanostraw treatment, while conventional electroporation changed the expression of more than 2,000 genes. Our results show that nanostraw-mediated transfection is a gentle alternative to established gene delivery methods, and uniquely suited for nonperturbative treatment of sensitive primary stem cells.

Impact of the CD4:CD8 ratio in bone marrow on stem cell mobilization and engraftment in autologous stem cell transplant patients

Bone marrow (BM) damage after previous chemotherapy, such as that involving alkylating agents, and radiation therapy alone cannot explain poor hematopoietic progenitor cell mobilization. We examined the T lymphocytes of BM in 67 autologous peripheral blood stem cell transplant (auto-PBSCT) patients with non-Hodgkin lymphoma (NHL) or multiple myeloma (MM) to establish whether the cellular phenotype predicts mobilization and engraftment between January 2000 and January 2020 at the Japanese Red Cross Society Wakayama Medical Center. The total number of mobilized CD34+ cells was <2 × 10⁶ /kg in 30 patients (group A) and ≥2 × 10⁶ /kg in 37 (group B). The median absolute number of CD3+CD4+ cells was lower in group A than in group B (P = .013), and the median absolute number of CD3+CD8+ cells was higher in group A than in group B (P = .016). A low CD4:CD8 ratio was observed in all patients in group A, whereas all patients in group B showed a normal CD4:CD8 ratio (P < .001). A strong correlation was found between the CD4:CD8 ratio and median total CD34+ cells yield (r = .723, P < .001). The present results showed that a lower CD4:CD8 ratio correlated with later neutrophil and platelet engraftment (r = .662, P = .007 and r = .571, P = .008, respectively). The present results indicate that the CD4:CD8 ratio in BM contributes to the prediction of mobilization and engraftment in auto-PBSCT patients.

CD34 cells in somatic, regenerative and cancer stem cells: Developmental biology, cell therapy, and omics big data perspective

The transmembrane phosphoglycoprotein protein CD34 has conventionally been regarded as a marker for hematopoietic progenitors. Its expression on these cells has been leveraged for cell therapy applications in various hematological disorders. More recently, the expression of CD34 has also been reported on cells of nonhematopoietic origin. The list includes somatic cells such as endothelial cells, fibrocytes and interstitial cells and regenerative stem cells such as corneal keratocytes, muscle satellite cells, and muscle-derived stem cells. Furthermore, its expression on some cancer stem cells (CSCs) has also been reported. Till date, the functional roles of this molecule have been implicated in a multitude of cellular processes including cell adhesion, signal transduction, and maintenance of progenitor phenotype. However, the complete understanding about this molecule including its developmental origins, its embryonic connection, and associated functions is far from complete. Here, we review our present understanding of the structure and putative functions of the CD34 molecule based upon our literature survey. We also probed various biological databases to retrieve data related to the expression and associated molecular functions of CD34. Such information, upon synthesis, is hence likely to provide the suitability of such cells for cell therapy. Moreover, we have also covered the existing cell therapy and speculated cell therapy applications of CD34⁺ cells isolated from various lineages. We have also attempted here to speculate the role(s) of CD34 on CSCs. Finally, we discuss number of large-scale proteomics and transcriptomics studies that have been performed using CD34⁺ cells.

Monopoiesis in humans and mice

Monocytes are a widely conserved cell population in vertebrates with important roles in both inflammation and homeostasis. Under both settings, monocytes continuously arise from hematopoietic progenitors in the bone marrow and, on demand, migrate into tissues through the bloodstream. Monocytes are classified into three subsets-classical, intermediate and non-classical-based on their cell surface expression of CD14 and CD16 in humans and Ly6C, CX3CR1 and CCR2 in mice. In tissues, monocytes differentiate further into monocyte-derived macrophages and dendritic cells to mediate innate and adaptive immune responses and maintain tissue homeostasis. Recently, the progenitors that strictly give rise to monocytes were identified in both humans and mice, thereby revealing the monocyte differentiation pathways.

Prospectively defined murine mesenchymal stem cells inhibit Klebsiella pneumoniae-induced acute lung injury and improve pneumonia survival

Background

Numerous studies have described the immunosuppressive capacity of mesenchymal stem cells (MSC) but these studies use mixtures of heterogeneous progenitor cells for in vitro expansion. Recently, multipotent MSC have been prospectively identified in murine bone marrow (BM) on the basis of PDFGRa⁺ SCA1⁺ CD45⁻ TER119⁻ (PαS) expression but the immunomodulatory capacity of these MSC is unknown.

Methods

We isolated PαS MSC by high-purity FACS sorting of murine BM and after in vitro expansion we analyzed the in vivo immunomodulatory activity during acute pneumonia. PαS MSC (1 × 10⁶) were applied intratracheally 4 h after acute respiratory Klebsiella pneumoniae induced infection.

Results

PαS MSC treatment resulted in significantly reduced alveolitis and protein leakage in comparison to mock-treated controls. PαS MSC-treated mice exhibited significantly reduced alveolar TNF-α and IL-12p70 expression, while IL-10 expression was unaffected. Dissection of respiratory dendritic cell (DC) subsets by multiparameter flow cytometry revealed significantly reduced lung DC infiltration and significantly reduced CD86 costimulatory expression on lung CD103⁺ DC in PαS MSC-treated mice. In the post-acute phase of pneumonia, PαS MSC-treated animals exhibited significantly reduced respiratory IL-17⁺ CD4⁺ T cells and IFN-γ⁺ CD4⁺ T cells. Moreover, PαS MSC treatment significantly improved overall pneumonia survival and did not increase bacterial load.

Conclusion

In this study we demonstrated for the first time the feasibility and in vivo immunomodulatory capacity of prospectively defined MSC in pneumonia.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-015-0288-1) contains supplementary material, which is available to authorized users.

Automated CD34+ cell isolation of peripheral blood stem cell apheresis product

BACKGROUND AIMS

Immunomagnetic enrichment of CD34+ hematopoietic "stem" cells (HSCs) using paramagnetic nanobead coupled CD34 antibody and immunomagnetic extraction with the CliniMACS plus system is the standard approach to generating T-cell-depleted stem cell grafts. Their clinical beneficence in selected indications is established. Even though CD34+ selected grafts are typically given in the context of a severely immunosuppressive conditioning with anti-thymocyte globulin or similar, the degree of T-cell depletion appears to affect clinical outcomes and thus in addition to CD34 cell recovery, the degree of T-cell depletion critically describes process quality. An automatic immunomagnetic cell processing system, CliniMACS Prodigy, including a protocol for fully automatic CD34+ cell selection from apheresis products, was recently developed. We performed a formal process validation to support submission of the protocol for CE release, a prerequisite for clinical use of Prodigy CD34+ products.

METHODS

Granulocyte-colony stimulating factor-mobilized healthy-donor apheresis products were subjected to CD34+ cell selection using Prodigy with clinical reagents and consumables and advanced beta versions of the CD34 selection software. Target and non-target cells were enumerated using sensitive flow cytometry platforms.

RESULTS

Nine successful clinical-scale CD34+ cell selections were performed. Beyond setup, no operator intervention was required. Prodigy recovered 74 ± 13% of target cells with a viability of 99.9 ± 0.05%. Per 5 × 10E6 CD34+ cells, which we consider a per-kilogram dose of HSCs, products contained 17 ± 3 × 10E3 T cells and 78 ± 22 × 10E3 B cells.

CONCLUSIONS

The process for CD34 selection with Prodigy is robust and labor-saving but not time-saving. Compared with clinical CD34+ selected products concurrently generated with the predecessor technology, product properties, importantly including CD34+ cell recovery and T-cell contents, were not significantly different. The automatic system is suitable for routine clinical application.

HLA-haploidentical transplantations for primary immunodeficiencies: a single-center experience

SCID is characterized by profound deficiencies of T and B lymphocytes. HSCT is the only curative treatment for children with SCID. The clinical characteristics and outcome of 30 HLA-haploidentical transplantations in 18 patients (15 SCID, two Omenn syndrome, and one MHC Class II deficiency) are reported here. The age of patients at diagnosis ranged from one and half to nine months (median: four months). The median time was one month between the diagnosis and the time of the initial transplantation. Infused CD34+ stem cell dose was ranged between 7 and 94.2 × 10(6) /kg. Nine of 18 patients were found to be positive for CMV antigenemia at diagnosis; therefore, none of them received a conditioning regimen. The most common complication was graft failure (61%), so repeated transplantations (two to four) were performed in seven patients. The mean time of lymphoid engraftment was 17.5 days (median: 16, range: 11-29 days). Ten of 15 SCID (67%) patients survived with a stable complete donor chimerism. However, all three non-SCID patients died. In conclusion, in the absence of a matched family donor, HLA-haploidentical transplantation from parental donors represents a readily available treatment option especially for patients with SCID, offering a high chance of cure.

Hematopoiesis: a human perspective

Despite its complexity, blood is probably the best understood developmental system, largely due to seminal experimentation in the mouse. Clinically, hematopoietic stem cell (HSC) transplantation represents the most widely deployed regenerative therapy, but human HSCs have only been characterized relatively recently. The discovery that immune-deficient mice could be engrafted with human cells provided a powerful approach for studying HSCs. We highlight 2 decades of studies focusing on isolation and molecular regulation of human HSCs, therapeutic applications, and early lineage commitment steps, and compare mouse and humanized models to identify both conserved and species-specific mechanisms that will aid future preclinical research.

Long-term results after transplantation of CD34+ selected (CellPro) versus unselected peripheral blood progenitor cells (PBPC) from related allogeneic donors

PURPOSE

To determine the long-term outcome of patients after allogeneic transplantation of T-cell depleted versus unmanipulated hematopoietic stem cell grafts with respect to incidence of GvHD and overall survival in 50 consecutive patients.

METHODS

In this prospective phase II study utilizing biological randomization, 50 sibling donors were mobilized with G-CSF. Positive selection of CD34+ cells (Ceprate SC; CellPro, USA) was performed in good mobilizers (n = 25; group A), but not in poor mobilizers (n = 25; group B). Patients had hematological malignancies. Median patient age was 44 years (range, 19-57). Numbers of CD3+ cells were 0.5 ± 0.4 × 10(6)/kg in group A and 216 ± 127 × 10(6)/kg in group B.

RESULTS

Hematological recovery was rapid in both groups. Patients in group A had no grade III-IV acute GvHD, whereas 6 out of 22 evaluable patients in group B had grade III-IV acute GvHD with fatal outcome in four cases (P < 0.01). Similarly, the incidence of chronic GvHD was lower in patients in group A (35 vs. 65%). However, there was a higher relapse rate in group A (11/25) versus group B (4/25, P < 0.05). At a follow-up of 10 years after transplantation, eight (32%) and 10 patients (40%) were relapse-free and alive in groups A and B, respectively.

CONCLUSIONS

Risk factors for survival in a multivariate analysis were remission status prior to transplantation (CR vs. no CR), occurrence of acute and chronic GvHD, and relapse. The use of the CellPro device for CD34 positive selection per se did not have an influence on overall survival.

CD34(+) hematopoietic progenitor cell selection of bone marrow grafts for autologous transplantation in pediatric patients

CD34(+)-selection of hematopoietic grafts for patients undergoing autologous hematopoietic stem cell transplantation (HSCT) is frequently used to obtain a tumor-free graft. The majority of published experience is with peripheral blood stem cell (PBSC) products; only scant information has been published on bone marrow (BM) grafts. We reviewed our experience using CD34(+) selection of BM grafts in children undergoing autologous BM transplantation. After obtaining institutional approval, we performed a retrospective review of the medical records of patients who underwent autologous stem cell collection at St. Jude. From January 1, 1999, to December 31, 2003, 373 patients underwent autologous HSCT; 131 received marrow grafts, 237 received PBSC grafts, and 5 received a combination. Seventeen patients underwent BM harvests for CD34(+) selection of their stem cell grafts. Sixteen patients received 19 CD34 purified grafts processed on the Isolex 300i Magnetic Cell Selection System device. Four patients were not included in the engraftment analysis as 1 did not receive the collected product, 1 received a tandem product, and 2 received products that were composed of 2 or 3 combined purified products. Following selection, marrow grafts contained a median of 1.4 x 10(6) CD34(+) cells/kg (range: 0.09-8.3 x 10(6)/kg) and a median of 0.014 x10(8) total nucleated cell cells/kg (range: 0.001-0.09 x 10(8)/kg). The median CD34% recovery was 30.9% (range: 9.3%-57.1%), with the median CD34 purity being 95.5% (range: 62.2%-98.8%). All patients engrafted. The median time to absolute neutrophil count > or = 500/mm(3) was 19 days (range: 12-35 days), and to platelet recovery was 28 days (range 18-37 days). No patient died from transplant-related complications. Our study demonstrates that CD34(+)-selection of marrow grafts is feasible, and these grafts are able to successfully reconstitute hematopoiesis in patients undergoing autologous BMT.

Ewing Sarcoma tumor cells express CD34: implications for autologous stem cell transplantation

The significance of tumor cell contamination in marrow and peripheral blood stem cell (PBSC) collections of patients with solid tumors remains controversial. Various methods have been developed to purge tumor cells from autologous stem cell products, including CD34+ selection. PBSC harvests from patients with Ewing family of tumors (EFT) were analyzed for contaminating tumor cells prior and after CD34+ selection using reverse transcription-polymerase chain reaction (RT-PCR) and flow cytometry (FC) analyzes. The expression of CD34 was studied by RT-PCR and FC in 14 primary tumors and 13 PBSC harvests, respectively. Tumor cells were identified in the harvests by both methods. In two patients, contaminating tumor cells were evident by RT-PCR only after positive selection. FC analysis confirmed a higher level of tumor cells in the CD34+ fraction. In an attempt to explore this finding, expression of CD34 was detected in 93% of primary tumors and 67% of contaminated harvests. As CD34 is expressed on EFT cells, these cells may be enriched following CD34+ selection of harvests, although the total number of tumor cells is reduced. Other methods of purging, rather than CD34+ selection, should be explored in patients with EFT undergoing autologous stem cell transplantation.

Cell tracking velocimetry as a tool for defining saturation binding of magnetically conjugated antibodies

BACKGROUND

Continuous flow immunomagnetic separation is an attractive alternative to current batch mode immunomagnetic separation methods because it is capable of high sorting speeds at mild cell conditions, and grants the operator better control of separation process. The control of the separation is dependent on knowledge of the amount of magnetic label attached to the cell (magnetic labeling intensity), however. Determination of the magnetic labeling is accomplished by measuring cell magnetophoretic mobility using a newly developed technique of Cell Tracking Velocimetry (CTV).

METHODS

Flow cytometry was used to define the antibody binding characteristics of a fluorescently tagged primary antibody. Subsequently, CTV was used to measure antibody-binding characteristics of a magnetically tagged secondary antibody.

RESULTS

The results of this study show that CTV is capable of providing valuable information concerning the cell labeling by magnetically tagged antibodies. It was demonstrated that the magnetically conjugated antibody binding curve exhibits the same exponential increase to saturation characteristics as that seen with the fluorescently tagged antibody. Further, it was shown that the intensity of the secondary magnetic labeling is directly proportional to the intensity of the primary fluorescent label.

CONCLUSIONS

CTV is an accurate tool for evaluation of magnetically conjugated antibodies. The ability to determine the intensity of magnetic labeling is necessary for the development of continuous flow immunomagnetic separations based on cell magnetophoresis.

Catalytic Activities of G1Cyclin-Dependent Kinases and Phosphorylation of Retinoblastoma Protein in Mobilized Peripheral Blood CD34+Hematopoietic Progenitor Cells

Depending on the source of cells, the cell cycle status of hematopoietic stem and progenitor cells capable of repopulating the marrow of transplant recipients is controversial. In this study, using biochemical methods, the cell cycle status of mobilized CD34+ cells was analyzed. It was demonstrated in CD34+ cell extracts that there was high catalytic activity of G(1) cyclin-dependent kinases 4 and 6 (CDK4 and CDK6) but low activity of CDK2. This was in contrast to the resting reference cells that showed only minimal or no activity of these CDKs. Since at the G0-->G1-->S transition CDK4/6 and CDK2 sequentially phosphorylate the retinoblastoma protein (pRB), its phosphorylation status was analyzed. Previously, we showed that p110RB was unphosphorylated at serine (Ser)-608 in CD34+ cells, consistent with the ability to suppress cell growth. Here, it was established that this form of pRB was phosphorylated at Ser-780, Ser-795, and Ser-807/811 in CD34+ but not in resting reference cells. This result was therefore consistent with the presence of high CDK4/6 activities in CD34+ cells. Conversely, CDK2 activity was low and the pRB residues Ser-612 and threonine (Thr)-821, which are exclusively phosphorylated by CDK2 in conjunction with either cyclin E or A, were unphosphorylated in >90% of CD34+ cells. We therefore show for the first time the exact position of mobilized CD34+ cells within the cell cycle; that is, they do not reside in G0 but in early G1 phase and did not cross the restriction point into late G1 phase.

Autologous haematopoietic-stem-cell transplantation for multiple sclerosis

Intense immunosuppression followed by autologous haematopoietic-stem-cell transplantation (HSCT) is being assessed as a potential treatment for patients with severe multiple sclerosis (MS). The treatment was developed from research that showed autologous HSCT was as effective as allogeneic HSCT in the treatment of experimental autoimmune encephalomyelitis. The treatment is thought to eradicate the defective immune system, and the infused haematopoietic stem cells reconstitute an immune system that is more tolerant to the nervous system. About 250 patients with MS have been treated with autologous HSCT as part of phase I and phase II open trials. Autologous HSCT seems feasible in MS and assessment with clinical and MRI measures suggests it induces a profound and long-lasting suppression of inflammation. The course of MS seems to be stabilised after autologous HSCT, especially in ambulatory patients with evidence of active disease. Autologous HSCT deserves further study in randomised controlled trials.

Myeloma cell contamination of peripheral blood stem-cell grafts can predict the outcome in multiple myeloma patients after high-dose chemotherapy and autologous stem-cell transplantation

PURPOSE

High-dose chemotherapy with hematopoietic stem-cell rescue is increasingly being used in the treatment of multiple myeloma. Bone marrow and also peripheral blood stem-cell (PBSC) grafts contain measurable quantities of plasma cells, the biological significance of which is unknown.

METHODS

Patients with multiple myeloma were mobilized with chemotherapy and filgrastim. The number of CD38++/CD138+ cells/kg in the grafts for autologous transplantation was determined by flow cytometry. Patients were stratified into two groups (threshold 4.5 x 10(5) plasma cells kg(-1)) of reinfused plasma cells in the first autologous graft.

RESULTS

The median statistical progression-free survival was 14 months (4-34 months) in the high-contamination group (>4.5 x 10(5) plasma cells kg(-1)) compared to 26 months (4-43 months) in the low-contamination group (<4.5 x 10(5) plasma cells kg(-1), P =0.0096). Patients with 13q deletion were more frequently found to have a high contamination of the stem-cell graft with malignant plasma cells.

CONCLUSIONS

Patients with graft contamination of more than 4.5 x 10(5) plasma cells kg(-1) had a high risk of early disease progression after high-dose chemotherapy. In vivo tumor cell purging prior to mobilization chemotherapy might be one strategy to improve the time to progression of high-risk patients.

Rituximab consolidation after high-dose chemotherapy and autologous blood stem cell transplantation in follicular and mantle cell lymphoma: a prospective, multicenter phase II study

BACKGROUND

Patients with follicular (FL) or mantle cell lymphoma (MCL) are incurable with conventional therapy. We investigated the safety and efficacy of rituximab consolidation after autologous stem cell transplantation (ASCT) in order to prevent relapse by clearance of minimal residual disease (MRD).

METHODS

Rituximab was given approximately 8 weeks after CD34+ cell enriched ASCT at 375 mg/m2, weekly for 4 weeks. Monitoring of MRD was performed by repetitive PCR analyses.

RESULTS

Thirty-one patients were included; one died early after ASCT before rituximab administration. Thirty patients (20 FL, 10 MCL) were evaluable after rituximab consolidation, and 27 of these were assessable for MRD detection. Rituximab consolidation post-ASCT was safe, the most common toxicity being infection. At a median follow-up of 42 months (range 13-96) after ASCT, 25 patients were censored with an actuarial event-free survival (EFS) of 81% at 4 and 5 years. Four patients (two FL, two MCL) relapsed, and one additional MCL patient died unexpectedly in complete remission. PCR-negativity was observed in 22% of the patients before ASCT, 53% post-ASCT (P=0.0547), 72% after rituximab (P=0.0018) and 100% at 6 months post-transplant (P < 0.001).

CONCLUSIONS

One single course of rituximab consolidation given after ASCT is safe, may help to eliminate MRD and may translate into improved EFS in both FL and MCL patients.

Identification and isolation of hematopoietic stem cells

Hematopoietic stem cells (HSCs) are defined by their ability to repopulate all of the hematopoietic lineages in vivo and sustain the production of these cells for the life span of the individual. In the absence of reliable direct markers for HSCs, their identification and enumeration depends on functional long-term, multilineage, in vivo repopulation assays. The extremely low frequency of HSCs in any tissue and the absence of a specific HSC phenotype have made their purification and characterization a highly challenging goal. HSCs and primitive hematopoietic cells can be distinguished from mature blood cells by their lack of lineage-specific markers and presence of certain other cell-surface antigens, such as CD133 (for human cells) and c-kit and Sca-1 (for murine cells). Functional analyses of purified subpopulations of primitive hematopoietic cells have led to the development of several procedures for isolating cell populations that are highly enriched in cells with in vivo stem cell activity. Simplified methods for obtaining these cells at high yield have been important to the practical exploitation of such advances. This article reviews recent progress in identifying human and mouse HSCs and current techniques for their purification.

Impaired stem cell function of CD34+ cells selected by two different immunomagnetic beads systems

We have been investigating the hematopoietic stem cell (HSC) activity of peripheral blood-derived CD34(+) cells selected by two different laboratory immunomagnetic beads systems (MiniMACS and Isolex 50). In this study, the quality of purified CD34(+) cells was directly compared using clonal cell culture, a cobblestone area-forming cell (CAFC) assay, and an in vivo severe combined immunodeficiency (SCID)-repopulating cell (SRC) assay. It was found that CD34(+) cells selected by these two immunomagnetic methods showed a reduced yield of colony-forming cells and CAFCs compared with cells enriched by the StemSep device (a negative selection method). However, these CD34(+) cells still showed significant SRC activity, including multilineage lymphomyeloid reconstitution. The percentage of human CD45(+) cells in murine bone marrow after transplanting 5 x 10(5) CD34(+) cells selected by the Isolex 50 was significantly lower than after transplanting cells selected by the MiniMACS or the StemSep. Our findings clearly demonstrated that CD34(+) cells selected by the MiniMACS system had superior HSC functions, including SRC activity, compared with cells separated by the Isolex 50 system. More detailed functional analysis of immunomagnetically separated CD34(+) cells may provide useful knowledge for basic research on HSCs as well as for clinical HSC transplantation.

Clinical applications of CD34+ cell-selected peripheral blood stem cells

Peripheral blood stem cells (PBSC) are increasingly used for stem cell transplantation after high dose chemotherapy. CD34+ cell selection has also been done for use in autologous transplantation studies Bone marrow (BM) may contain tumor cells at the time of harvesting, and on re-infusion, these cells could contribute to a subsequent relapse. Similarly, tumor cell contamination of PBSC collections has been found in a number of studies. Therefore, purging contaminating tumor cells may prevent cases of relapse. As most tumor cell types do not express CD34 antigen, one of the most widespread applications of CD34+ cell selection is likely to be in tumor cell purging. Similarly, CD34+ cell selection has aided allogeneic transplantation studies. Acute graft-versus-host disease (aGVHD) is a major cause of morbidity and mortality in cases of allogeneic transplantation. As aGVHD is mediated by donor T cells, removal of T cells from the graft by CD34+ cell selection may ensure prophylaxis against aGVHD. Further, high-dose immunosuppression followed by CD34+ cell-selected stem cell rescue is theoretically reasonable as a therapeutic tool for patients with autoimmune disease resistant to conventional therapy. However, patients given T cell-depleted transplantation have an increased risk of opportunistic infection as well as malignancies related to immunosuppression; therefore, close monitoring is warranted. We describe here clinical applications of CD34+ cell-selected PBSC for a variety of diseases, with special emphasis on the efficacy as well as drawbacks of this novel technique.

SCID-repopulating cell activity of human cord blood-derived CD34- cells assured by intra-bone marrow injection

Precise analysis of human CD34-negative (CD34(-)) hematopoietic stem cells (HSCs) has been hindered by the lack of a simple and reliable assay system of these rare cells. Here, we successfully identify human cord blood-derived CD34(-) severe combined immunodeficiency (SCID)- repopulating cells (SRCs) with extensive lymphoid and myeloid repopulating ability using the intra-bone marrow injection (IBMI) technique. Lineage-negative (Lin(-)) CD34(-) cells did not show SRC activity by conventional tail-vein injection, possibly due to their low levels of homing receptor expression and poor SDF-1/CXCR4- mediated homing abilities, while they clearly showed a high SRC activity by IBMI. They generated CD34(+) progenies not only in the injected left tibia but also in other bones following migration. Moreover, they showed slower differentiating and reconstituting kinetics than CD34(+) cells in vivo. These in vivo-generated CD34(+) cells showed a distinct SRC activity after secondary transplantation, clearly indicating the long-term human cell repopulating capacity of our identified CD34(-) SRCs in nonobese diabetic (NOD)/SCID mice. The unveiling of this novel class of primitive human CD34(-) SRCs by IBMI will provide a new concept of the hierarchy in the human HSC compartment and has important implications for clinical HSC transplantation as well as for basic research of HSC.

Side effects of retroviral gene transfer into hematopoietic stem cells

Recent conceptual and technical improvements have resulted in clinically meaningful levels of gene transfer into repopulating hematopoietic stem cells. At the same time, evidence is accumulating that gene therapy may induce several kinds of unexpected side effects, based on preclinical and clinical data. To assess the therapeutic potential of genetic interventions in hematopoietic cells, it will be important to derive a classification of side effects, to obtain insights into their underlying mechanisms, and to use rigorous statistical approaches in comparing data. We here review side effects related to target cell manipulation; vector production; transgene insertion and expression; selection procedures for transgenic cells; and immune surveillance. We also address some inherent differences between hematopoiesis in the most commonly used animal model, the laboratory mouse, and in humans. It is our intention to emphasize the need for a critical and hypothesis-driven analysis of "transgene toxicology," in order to improve safety, efficiency, and prognosis for the yet small but expanding group of patients that could benefit from gene therapy.

Heterologous cells cooperate to augment stem cell migration, homing, and engraftment

T-lymphocyte depletion of bone marrow grafts compromises engraftment, suggesting a facilitating mechanism provided by the T cells that has been shown to associate with CD8(+) but not CD4(+) T cells. Explanations for this phenomenon have focused on immune targeting of residual host cells or cytokine production. We provide evidence for an alternative mechanism based on cooperative effects on cell motility. We observed that engraftment of CD34(+) cells in a beta(2)-microglobulin-deficient nonobese diabetic/severe combined immunodeficiency (beta(2)m(-/-) NOD/SCID) mouse model paralleled clinical observations in humans, with an enhancing effect noted from the addition of CD8(+) cells but not CD4(+) cells. This correlated with CD8(+) augmentation of CD34(+) cell homing to the bone marrow in vivo and CD8(+) cell-associated increases of CD34(+) cell transmigration through a bone marrow endothelial cell line in vitro. The cooperative interaction was not sensitive to brefeldin A inhibition of protein secretion. However, cytochalasin D-induced inhibition of CD8(+) cytoskeletal rearrangements abrogated CD34(+) transendothelial migration and impaired CD34(+) cell homing in vivo. CD8(+) cells did not migrate in tandem with CD34(+) cells or alter endothelial barrier integrity; rather, they affected phosphotyrosine-mediated signaling in CD34(+) cells in response to the chemokine stromal derived factor-1alpha (SDF-1alpha). These data demonstrate cell-cell cooperativity between different cell types in mediating chemotactic events and provide one potential explanation for the clinically observed effect of CD8(+) cells on bone marrow transplantation. This modification of cell migration by neighboring cells provides broad possibilities for combinatorial effects between cells of different types to influence cell localization.

Second transplantation with CD34+ blood cells from an HLA-mismatched related donor after engraftment failure of transplanted cord blood cells

Unrelated cord blood transplantation (CBT) has been worldwide for bone marrow reconstitution. CBT is associated with a high frequency of engraftment failure and rejection due to a small dose of graft cells. In cases of engraftment failure or rejection following unrelated CBT, retransplantation from the original donors is impossible. We report a successful transplantation with CD34+ blood cells selected from a 2-loci HLA-mismatched mother to a child with acute monocytic leukemia after engraftment failure of the primary CBT. Selected CD34+ blood cell transplantation is a useful approach for retransplantation in the setting of engraftment failure.

Immunomagnetic purging of Ewing's sarcoma from blood and bone marrow: quantitation by real-time polymerase chain reaction

PURPOSE

A propensity for hematogenous spread with resulting contamination of autologous cell products complicates cellular therapies for Ewing's sarcoma. We used a new approach to purge artificially contaminated cellular specimens of Ewing's sarcoma and show the capacity for real-time polymerase chain reaction (PCR) to quantify the contamination level of Ewing's sarcoma in such specimens.

PATIENTS AND METHODS

Binding of monoclonal antibody (MoAb) 8H9 to Ewing's sarcoma cell lines and normal hematopoietic cells was studied using flow cytometry. Using real-time PCR--based amplification of t(11;22), levels of Ewing's contamination of experimental and clinical cellular products were monitored. Purging was accomplished using immunomagnetic-based depletion. Monitoring of the function of residual hematopoietic progenitors and T cells was performed using functional assays.

RESULTS

MoAb 8H9 shows binding to Ewing's sarcoma but spares normal hematopoietic tissues. Nested real-time PCR is capable of detecting contaminating Ewing's sarcoma cells with a sensitivity of one cell in 10(6) normal cells. After 8H9-based purging, a 2- to 3-log reduction in contaminating Ewing's sarcoma was shown by real-time PCR, with purging to PCR negativity at levels of contamination of 1:10(6). Levels of contamination in clinical samples ranged from 1:10(5) to 10(6). Therefore, 8H9-based purging of clinical samples is predicted to reduce tumor cell contamination to a level below the limit of detection of PCR.

CONCLUSION

These results demonstrate a new approach for purging contaminated cellular products of Ewing's sarcoma and demonstrate the capacity of real-time PCR to provide accurate quantitative estimates of circulating tumor burden in this disease.