Clinical scale isolation of highly purified peripheral CD34+progenitors for autologous and allogeneic transplantation in children

Ex vivo and in vivo T-cell depletion in allogeneic transplantation: towards less or non-cytotoxic conditioning regimens

INTRODUCTION

Although tremendous progress has been made since the introduction of allogeneic hematopoietic stem cell transplantation (HSCT) decades ago, there are still many obstacles to overcome. A major obstacle is the presence of T-lymphocytes in the recipient and in the donor. Recipient-derived T-lymphocytes not eliminated by the conditioning regimen are a major barrier and can lead to mixed chimerism or to complete rejection of the graft. Donor-derived T-lymphocytes can induce severe acute and chronic Graft-versus-Host Disease (GvHD).

AREAS COVERED

Currently published strategies for in vivo depletion of recipient-derived T-lymphocytes are discussed including the increase of the intensity of the conditioning regimen, the addition of anti-thymocyte globulin (ATG) or the anti-CD52 monoclonal antibody Campath. For the depletion or tolerization of the donor-derived T-lymphocytes, ex vivo-T-cell depletion methods, such as positive selection of CD34+ stem cells, negative depletion of CD3+ or TcRαβ+ T-lymphocytes or the use of post-transplant cyclophosphamide (PTCy) have been developed.

EXPERT COMMENTARY

All these currently used approaches have their disadvantages and new approaches should be investigated. In this review, we discuss current and propose new possible strategies to overcome the HLA barrier by using more specific T-cell directed therapies and/or by the combinations of current methods.

Label-free separation of neuroblastoma patient-derived xenograft (PDX) cells from hematopoietic progenitor cell products by acoustophoresis

Background

Graft-contaminating tumor cells correlate with inferior outcome in high-risk neuroblastoma patients undergoing hematopoietic stem cell transplantation and can contribute to relapse. Motivated by the potential therapeutic benefit of tumor cell removal as well as the high prognostic and diagnostic value of isolated circulating tumor cells from stem cell grafts, we established a label-free acoustophoresis-based microfluidic technology for neuroblastoma enrichment and removal from peripheral blood progenitor cell (PBPC) products.

Methods

Neuroblastoma patient-derived xenograft (PDX) cells were spiked into PBPC apheresis samples as a clinically relevant model system. Cells were separated by ultrasound in an acoustophoresis microchip and analyzed for recovery, purity and function using flow cytometry, quantitative real-time PCR and cell culture.

Results

PDX cells and PBPCs showed distinct size distributions, which is an important parameter for efficient acoustic separation. Acoustic cell separation did not affect neuroblastoma cell growth. Acoustophoresis allowed to effectively separate PDX cells from spiked PBPC products. When PBPCs were spiked with 10% neuroblastoma cells, recoveries of up to 98% were achieved for PDX cells while more than 90% of CD34⁺ stem and progenitor cells were retained in the graft. At clinically relevant tumor cell contamination rates (0.1 and 0.01% PDX cells in PBPCs), neuroblastoma cells were depleted by more than 2-log as indicated by RT-PCR analysis of PHOX2B, TH and DDC genes, while > 85% of CD34⁺ cells could be retained in the graft.

Conclusion

These results demonstrate the potential use of label-free acoustophoresis for PBPC processing and its potential to develop label-free, non-contact tumor cell enrichment and purging procedures for future clinical use.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02612-2.

Magnetic separation of peripheral nerve-resident cells underscores key molecular features of human Schwann cells and fibroblasts: an immunochemical and transcriptomics approach

Nerve-derived human Schwann cell (SC) cultures are irreplaceable models for basic and translational research but their use can be limited due to the risk of fibroblast overgrowth. Fibroblasts are an ill-defined population consisting of highly proliferative cells that, contrary to human SCs, do not undergo senescence in culture. We initiated this study by performing an exhaustive immunological and functional characterization of adult nerve-derived human SCs and fibroblasts to reveal their properties and optimize a protocol of magnetic-activated cell sorting (MACS) to separate them effectively both as viable and biologically competent cells. We next used immunofluorescence microscopy imaging, flow cytometry analysis and next generation RNA sequencing (RNA-seq) to unambiguously characterize the post-MACS cell products. High resolution transcriptome profiling revealed the identity of key lineage-specific transcripts and the clearly distinct neural crest and mesenchymal origin of human SCs and fibroblasts, respectively. Our analysis underscored a progenitor- or stem cell-like molecular phenotype in SCs and fibroblasts and the heterogeneity of the fibroblast populations. In addition, pathway analysis of RNA-seq data highlighted putative bidirectional networks of fibroblast-to-SC signaling that predict a complementary, yet seemingly independent contribution of SCs and fibroblasts to nerve regeneration. In sum, combining MACS with immunochemical and transcriptomics approaches provides an ideal workflow to exhaustively assess the identity, the stage of differentiation and functional features of highly purified cells from human peripheral nerve tissues.

Effect of alemtuzumab-based T-cell depletion on graft compositional change in vitro and immune reconstitution early after allogeneic stem cell transplantation

BACKGROUND AIMS

To reduce the risk of graft-versus-host disease (GVHD) after allogeneic stem cell transplantation (alloSCT), T-cell depletion (TCD) of grafts can be performed by the addition of alemtuzumab (ALT) "to the bag" (in vitro) before transplantation. In this prospective study, the authors analyzed the effect of in vitro incubation with 20 mg ALT on the composition of grafts prior to graft infusion. Furthermore, the authors assessed whether graft composition at the moment of infusion was predictive for T-cell reconstitution and development of GVHD early after TCD alloSCT.

METHODS

Sixty granulocyte colony-stimulating factor-mobilized stem cell grafts were obtained from ≥9/10 HLA-matched related and unrelated donors. The composition of the grafts was analyzed by flow cytometry before and after in vitro incubation with ALT. T-cell reconstitution and incidence of severe GVHD were monitored until 12 weeks after transplantation.

RESULTS

In vitro incubation of grafts with 20 mg ALT resulted in an initial median depletion efficiency of T-cell receptor (TCR) α/β T cells of 96.7% (range, 63.5-99.8%), followed by subsequent depletion in vivo. Graft volumes and absolute leukocyte counts of grafts before the addition of ALT were not predictive for the efficiency of TCR α/β T-cell depletion. CD4^pos T cells were depleted more efficiently than CD8^pos T cells, and naive and regulatory T cells were depleted more efficiently than memory and effector T cells. This differential depletion of T-cell subsets was in line with their reported differential CD52 expression. In vitro depletion efficiencies and absolute numbers of (naive) TCR α/β T cells in the grafts after ALT incubation were not predictive for T-cell reconstitution or development of GVHD post- alloSCT.

CONCLUSIONS

The addition of ALT to the bag is an easy, fast and generally applicable strategy to prevent GVHD in patients receiving alloSCT after myeloablative or non-myeloablative conditioning because of the efficient differential depletion of donor-derived lymphocytes and T cells.

New graft manipulation strategies improve the outcome of mismatched stem cell transplantation in children with primary immunodeficiencies

BACKGROUND

Mismatched stem cell transplantation is associated with a high risk of graft loss, graft-versus-host disease (GvHD), and transplant-related mortality. Alternative graft manipulation strategies have been used over the last 11 years to reduce these risks.

OBJECTIVE

We investigated the outcome of using different graft manipulation strategies among children with primary immunodeficiencies.

METHODS

Between 2006 and 2017, 147 patients with primary immunodeficiencies received 155 mismatched grafts: 30 T-cell receptor (TCR) αβ/CD19-depleted grafts, 43 cord blood (CB) grafts (72% with no serotherapy), 17 CD34⁺ selection with T-cell add-back grafts, and 65 unmanipulated grafts.

RESULTS

The estimated 8-year survival of the entire cohort was 79%, transplant-related mortality was 21.7%, and the graft failure rate was 6.7%. Posttransplantation viral reactivation, grade II to IV acute graft-versus-host disease (aGvHD), and chronic graft-versus-host disease (cGvHD) complicated 49.6%, 35%, and 15% of transplantations, respectively. Use of TCRαβ/CD19 depletion was associated with a significantly lower incidence of grade II to IV aGvHD (11.5%) and cGvHD (0%), although with a greater incidence of viral reactivation (70%) in comparison with other grafts. T-cell immune reconstitution was robust among CB transplants, although with a high incidence (56.7%) of grade II to IV aGvHD. Stable full donor engraftment was significantly greater at 80% among TCRαβ⁺/CD19⁺-depleted and CB transplants versus 40% to 60% among the other groups.

CONCLUSIONS

Rapidly accessible CB and haploidentical grafts are suitable alternatives for patients with no HLA-matched donor. Cord transplantation without serotherapy and TCRαβ⁺/CD19⁺-depleted grafts produced comparable survival rates of around 80%, although with a high rate of aGvHD with the former and a high risk of viral reactivation with the latter that need to be addressed.

A strategy to ensure safety of stem cell-derived retinal pigment epithelium cells

Cell replacement and regenerative therapy using embryonic stem cell-derived material holds promise for the treatment of several pathologies. However, the safety of this approach is of prime importance given the teratogenic potential of residual stem cells, if present in the differentiated cell product. Using the example of embryonic stem cell-derived retinal pigment epithelium (RPE) for the treatment of age-related macular degeneration, we present a novel strategy for ensuring the absence of stem cells in the RPE population. Based on an unbiased screening approach, we identify and validate the expression of CD59, a cell surface marker expressed on RPE but absent on stem cells. We further demonstrate that flow sorting on the basis of CD59 expression can effectively purify RPE and deplete stem cells, resulting in a population free from stem cell impurity. This purification helps to ensure removal of stem cells and hence increases the safety of cells that may be used for clinical transplantation. This strategy can potentially be applied to other pluripotent stem cell-derived material and help mitigate concerns of using such cells for therapy.

Expression analysis of radiation-responsive genes in human hematopoietic stem/progenitor cells

To clarify the nature of the genes that contribute to the radiosensitivity of human hematopoietic stem/progenitor cells (HSPCs), we analyzed the gene expression profiles detected in HSPCs irradiated with 2 Gy X-rays after culture with or without an optimal combination of hematopoietic cytokines. Highly purified CD34(+) cells from human placental/umbilical cord blood were used as HSPCs. The cells were exposed to 2 Gy X-irradiation and treated in serum-free medium under five different sets of conditions for 6 h. The gene expression levels were analyzed by cDNA microarray, and then the network of responsive genes was investigated. A comprehensive genetic analysis to search for genes associated with cellular radiosensitivity was undertaken, and we found that expression of the genes downstream of MYC oncogene increased after X-irradiation. In fact, the activation of MYC was observed immediately after X-irradiation, and MYC was the only gene still showing activation at 6 h after irradiation. Furthermore, MYC had a significant impact on the biological response, particularly on the tumorigenesis of cells and the cell cycle control. The activated gene regulator function of MYC resulting from irradiation was suppressed by culturing the HSPCs with combinations of cytokines (recombinant human thrombopoietin + interleukin 3 + stem cell factor), which exerted radioprotective effects. MYC was strongly associated with the radiosensitivity of HSPCs, and further study and clarification of the genetic mechanisms that control the cell cycle following X-irradiation are required.

Prospective isolation of human bone marrow stromal cell subsets: A comparative study between Stro-1-, CD146- and CD105-enriched populations

Stro-1 has proved an efficacious marker for enrichment of skeletal stem and progenitor cells although isolated populations remain heterogeneous, exhibiting variable colony-forming efficiency and osteogenic differentiation potential. The emerging findings that skeletal stem cells originate from adventitial reticular cells have brought two further markers to the fore including CD146 and CD105 (both primarily endothelial and perivascular). This study has compared CD146-, CD105- and Stro-1 (individual and in combination)-enriched human bone marrow stromal cell subsets and assessed whether these endothelial/perivascular markers offer further selection over conventional Stro-1. Fluorescent cell sorting quantification showed that CD146 and CD105 both targeted smaller (2.22% ± 0.59% and 6.94% ± 1.34%, respectively) and potentially different human bone marrow stromal cell fractions compared to Stro-1 (16.29% ± 0.78%). CD146+, but not CD105+, cells exhibited similar alkaline phosphatase-positive colony-forming efficiency in vitro and collagen/proteoglycan deposition in vivo to Stro-1+ cells. Molecular analysis of a number of select osteogenic and potential osteo-predictive genes including ALP, CADM1, CLEC3B, DCN, LOXL4, OPN, POSTN and SATB2 showed Stro-1+ and CD146+ populations possessed similar expression profiles. A discrete human bone marrow stromal cell fraction (2.04% ± 0.41%) exhibited positive immuno-labelling for both Stro-1 and CD146. The data presented here show that CD146+ populations are comparable but not superior to Stro-1+ populations. However, this study demonstrates the critical need for new candidate markers with which to isolate homogeneous skeletal stem cell populations or skeletal stem cell populations which exhibit homogeneous in vitro/in vivo characteristics, for implementation within tissue engineering and regenerative medicine strategies.

FAS-based cell depletion facilitates the selective isolation of mouse induced pluripotent stem cells

Cellular reprogramming of somatic cells into induced pluripotent stem cells (iPSC) opens up new avenues for basic research and regenerative medicine. However, the low efficiency of the procedure remains a major limitation. To identify iPSC, many studies to date relied on the activation of pluripotency-associated transcription factors. Such strategies are either retrospective or depend on genetically modified reporter cells. We aimed at identifying naturally occurring surface proteins in a systematic approach, focusing on antibody-targeted markers to enable live-cell identification and selective isolation. We tested 170 antibodies for differential expression between mouse embryonic fibroblasts (MEF) and mouse pluripotent stem cells (PSC). Differentially expressed markers were evaluated for their ability to identify and isolate iPSC in reprogramming cultures. Epithelial cell adhesion molecule (EPCAM) and stage-specific embryonic antigen 1 (SSEA1) were upregulated early during reprogramming and enabled enrichment of OCT4 expressing cells by magnetic cell sorting. Downregulation of somatic marker FAS was equally suitable to enrich OCT4 expressing cells, which has not been described so far. Furthermore, FAS downregulation correlated with viral transgene silencing. Finally, using the marker SSEA-1 we exemplified that magnetic separation enables the establishment of bona fide iPSC and propose strategies to enrich iPSC from a variety of human source tissues.

New approaches to graft engineering for haploidentical bone marrow transplantation

Haploidentical transplantation opens the possibility to offer this treatment to a large number of patients with an otherwise incurable disease, such as some hematologic or oncologic malignancies, inborn or acquired bone marrow failure syndromes, hemoglobinopathies, immunodeficiencies, or other genetic diseases. Initial attempts at haploidentical transplantation using unmanipulated bone marrow were associated with a high transplant-related mortality. However, recent insights into the biology of haploidentical transplantation, the availability of effective in vivo large-scale graft-manipulation technology, and improved supportive care strategies have led to and are still leading to significantly better outcomes compared to previous decades. Methods for the in vitro depletion of T lymphocytes from mobilized peripheral blood stem cells (PBSC) to prevent graft-versus-host disease (GvHD) have facilitated the wider use and acceptance of haploidentical transplantation in children and adult patients. Besides in vitro T-cell depletion techniques, other methods, such as the isolation of alloreactive natural killer (NK) cells, virus-specific T lymphocytes, and other effector or regulatory cells are nowadays available to rapidly rebuild the immune system after haploidentical transplantation for the prevention of severe infections or relapses of the underlying diseases.

Cell separation: Terminology and practical considerations

Cell separation is a powerful tool in biological research. Increasing usage, particularly within the tissue engineering and regenerative medicine communities, means that researchers from a diverse range of backgrounds are utilising cell separation technologies. This review aims to offer potential solutions to cell sorting problems and to clarify common ambiguities in terminology and experimental design. The frequently used cell separation terms of 'purity', 'recovery' and 'viability' are discussed, and attempts are made to reach a consensus view of their sometimes ambiguous meanings. The importance of appropriate experimental design is considered, with aspects such as marker expression, tissue isolation and original cell population analysis discussed. Finally, specific technical issues such as cell clustering, dead cell removal and non-specific antibody binding are considered and potential solutions offered. The solutions offered may provide a starting point to improve the quality of cell separations achieved by both the novice and experienced researcher alike.

Haploidentical allogeneic hematopoietic cell transplantation in adults using CD3/CD19 depletion and reduced intensity conditioning: an update

Haploidentical hematopoietic cell transplantation (HHCT) after high dose conditioning with CD34-selected stem cells has been complicated by high regimen related toxicities, slow engraftment and delayed immune reconstitution leading to increased treatment related mortality (TRM). A new regimen using reduced intensity conditioning (RIC) and graft CD3/CD19 depletion with anti-CD3 and anti-CD19 coated microbeads on a CliniMACS device may allow HHCT with lower toxicity and faster engraftment. CD3/CD19 depleted grafts not only contain CD34+ stem cells but also CD34 negative progenitors, natural killer, graft facilitating and dendritic cells. RIC was performed with fludarabine (150-200 mg/m(2)), thiotepa (10 mg/kg), melphalan (120 mg/m(2)) and OKT-3 (5 mg/day, day -5 to +14) and no posttransplant immunosuppression. Twenty nine patients (median age=42 (range, 21-59) years) have been transplanted with this regimen. Diagnosis were AML (n=16), ALL (n=7), NHL (n=3), MM (n=2) and CML (n=1). Patients were "high risk" with refractory disease or relapse after preceding HCT. The CD3/CD19 depleted haploidentical grafts contained a median of 7.6x10(6) (range, 3.4-17x10(6)) CD34+ cells/kg, 4.4x10(4) (range, 0.006-44x10(4)) CD3+ T cells/kg and 7.2x10(7) (range, 0.02-37.3x10(7)) CD56+ cells/kg. Donor-recipient KIR-ligand-mismatch was found in 19 of 29 patients. The regimen was well tolerated with maximum acute toxicity being grade 2-3 mucositis. Because of severe neurotoxicity in 4 patients treated with 200 mg/m(2) fludarabine, the dose was reduced to 150 mg/m(2). Engraftment was rapid with a median time to >500 granulocytes/microL of 12 (range, 10-21) days, >20,000 platelets/microL of 11 (range, 7-38) days and full donor chimerism after 2-4 weeks in all patients. Incidence of grade II-IV degrees GVHD was 48% with grade II degrees =10, III degrees =2 and IV degrees =2. One patient, who received the highest T-cell dose, developed lethal grade IV GVHD. TRM in the first 100 days was 6/29 (20%) with deaths due to idiopathic pneumonia syndrome (n=1), mucormycosis (n=1), pneumonia (n=3) or GVHD (n=1). Overall survival is 9/29 patients (31%) with deaths due to infections (n=7), GVHD (n=1) and relapse (n=12) with a median follow-up of 241 days (range, 112-1271). In conclusion, this regimen is promising in high risk patients lacking a suitable donor, and a prospective phase I/II study is ongoing.

Haploidentical allogeneic hematopoietic cell transplantation in adults with reduced-intensity conditioning and CD3/CD19 depletion: Fast engraftment and low toxicity

OBJECTIVE

CD3/CD19 depletion may improve engraftment and immune reconstitution after haploidentical hematopoietic cell transplantation (HHCT) as grafts not only contain CD34+ stem cells but also CD34- progenitors and natural killer, dendritic, and facilitating cells.

PATIENTS AND METHODS

Ten consecutive patients received HHCT with CD3/CD19-depleted grafts. Reduced-intensity conditioning was performed with fludarabine (150-200 mg/m2), thiotepa (10 mg/kg), melphalan (120 mg/m2), and OKT-3 (5 mg/day, day -5 to +14) without additional posttransplant immunosuppression. Diagnoses were AML (n = 4), ALL (n = 3), NHL (n = 2), and multiple myeloma (n = 1). All patients were "high risk" with refractory disease or relapse after preceding HCT. The CD3/CD19-depleted haploidentical grafts contained a median of 7.8 x 10(6) (range, 5.2-17 x 10(6)) CD34+ cells/kg, 5.5 x 10(7) (range, 0.02-8.6 x 10(7)) CD56+ cells/kg, and 2.0 x 10(4) (range, 0.006-44 x 10(4)) CD3+ T cells/kg. Engraftment was rapid with median time to greater than 500 granulocytes/microL of 13 (range, 11-17) days, greater than 20,000 platelets/microL of 11 (range, 8-16) days, and full donor chimerism after 2 weeks in all patients. Six cases of grade II GVHD occurred. One patient, who received the highest T cell dose, developed lethal grade IV GVHD. Treatment-related mortality in the first 100 days was 3/10 (30%) with one death each due to idiopathic pneumonia syndrome, GVHD, and CMV disease. Two patients died after day 100, one due to relapse and one with systemic adenoviral infection. Overall survival is 5/10 patients (50%) with a median follow-up of 435 (range, 229-814) days.

CONCLUSION

This regimen is promising in high-risk patients lacking a suitable donor, and a prospective phase I/II study is ongoing.

Comparison of two immunomagnetic separation technologies to deplete T cells from human blood samples

The objective of this study was to compare the performance of two immunomagnetic separation technologies to deplete T cells from buffy coats of human blood. Specifically, two versions of the commercial MACS(R) Technology: MiniMACS and SuperMACS, and a prototype, flow-through system, the QMS, were evaluated. Peripheral blood mononuclear leukocytes (PBL) were isolated from buffy coats and an immunomagnetic separation of CD3(+) cells was conducted using company and optimized labeling protocols. To mimic peripheral blood containing bone marrow purged hematopoietic stem cells, HSC, CD34 expressing-cells (KG1a) were spiked into PBL prior to T-cell depletion once optimized depletion conditions were determined. Once the labeling protocol was optimized, the MiniMACS system performed well by producing a highly enriched CD3(+) fraction, and a respectable level of depletion of T cells and recovery of KG1a cells in the depleted fraction; an average log(10) depletion of T cells of 2.88 +/- 0.17 and an average recovery of the KG1a cells of 60.8 +/- 5.94% (n = 14). The performance of the SuperMACS system was very similar with an average log(10) depletion of T cells of 2.89 +/- 0.22 and an average recovery of KG1a of 63.1 +/- 8.55% (n = 10). In contrast, the QMS system produced an average log(10) depletion of T cells of 3.98 +/- 0.33 (n = 16) with a corresponding average recovery of 57.9 +/- 16.6% of the spiked CD34+ cells. The aforementioned QMS performance values were obtained using sorting speeds ranging from 2.5 x 10(4) to 1.7 x 10(5) cells per second. It is suggested that the lack of a 100% recovery of the unlabeled KG1a cells is the result of a previously reported "drafting" phenomena which pulls unlabeled cells in the direction of the magnetically labeled cells thereby resulting in loss of the unlabeled cells.

CD34+-selected stem cell boost for delayed or insufficient engraftment after allogeneic stem cell transplantation

BACKGROUND

Poor graft function without rejection may occur after stem cell transplantation (SCT). CD34(+) stem cell boost (SCB) can restore marrow function but may induce or exacerbate GvHD. We therefore investigated the feasibility and efficacy of CD34(+)-selected SCB in some patients with poor graft function. We present the results for eight patients (median age 46 years) transplanted initially for myelofibrosis, acute leukemia, myeloma and NHL. Six patients had received HLA-matched and two mismatched grafts (PB, BM; n=5, 3). After a median of 128 days post-transplant, the median leukocyte and platelet counts were, respectively, 2.05/nL and 18/nL. None had achieved platelet counts >50/nL even though donor chimerism was >95% in seven recipients.

METHODS

Positive selection of CD34(+) stem cells was performed on a CliniMACS device, observing GMP and achieving a median of 98.5% purity. The patients received a median of 1.7 x 10(6)/kg CD34(+) cells and 2.5 x 10(3)/kg CD3(+) T lymphocytes.

RESULTS

Hemograms at days +30, +60 and +90, respectively, showed steadily increasing median leukocyte (2.55, 3.15 and 4.20/nL) and platelet (29, 39 and 95/nL) counts. After a median follow-up of 144 days, five patients remained alive. No patient had developed acute or chronic GvHD. One patient died of leukemic relapse and two others of systemic mycosis.

DISCUSSION

These preliminary results point to the possibility of safely improving graft function using CD34(+) positively selected stem cells without necessarily increasing the incidence of GvHD in patients with poor graft function post-SCT. Experience with more patients and longer follow-up should clarify the optimal role for this procedure.

Long-term outcome after haploidentical stem cell transplantation in children

We present an update of our results with transplantation of highly purified stem cells from one to three loci mismatched parental donors. Sixty-three pediatric patients with acute lymphoblastic leukemias (n = 32), acute myeloid, chronic myeloid and myelomonocytic leukemias (n = 13), myelodysplastic syndromes (n = 4), lymphomas (n = 4), and various nonmalignant diseases (n = 10) underwent transplantation. Mobilized peripheral-blood stem cells were selected with either anti-CD34- or anti-CD133-coated microbeads. Patients received a median of 19.5 x 10(6) purified cells and <25,000 CD3+ T lymphocytes per kilogram, with no regular posttransplant pharmacological immunosuppression. Engraftment occurred in 98% of patients (primary sustained engraftment, 83%; engraftment after reconditioning/stem cell boosts, 15%). Moreover, all survivors but one had a stable three-lineage engraftment with a median follow up of 4.1 years (range 0.6-8 years). Primary acute graft-versus-host disease (GvHD) grade II was seen in only 7% of patients. No severe primary acute GvHD grades III-IV occurred. Thirteen percent of the patients developed transient chronic GvHD. Probability of disease-free survival (DFS) at 3 years was 60% for patients with nonmalignant diseases and 48% for patients with acute lymphatic leukemia (ALL)/non-Hodgkin lymphoma (NHL) in complete remission (CR)1-3. None of the ALL/NHL patients with active disease survived. Children with acute and chronic myeloid leukemias had a poorer outcome (3-year DFS = 18%), whereas two of four patients with myelodysplastic syndrome (MDS) are alive. Relapse probability of the whole group was not significantly increased when compared to a historical control group. The incidence of lethal viral infections was 18% between 1995 and 2002 and has since been reduced to 8% by the introduction of new therapeutic strategies. In summary, the use of stem cells from haploidentical parental donors should be strongly considered in all children who need transplantation but lack an identical donor.

Haploidentical transplantation for acute lymphoblastic leukemia in childhood

Haploidentical transplantation in childhood acute lymphoblastic leukemia (ALL) is a promising option for children lacking a suitable donor. We have updated our series of patients with ALL and report the results. Additionally, we reviewed the literature and try to embed our own experiences in the published results. We performed HLA-mismatched stem cell transplantations with megadoses of purified positively selected mobilized peripheral blood CD34+ progenitor cells (PBPC) from adult donors in 27 children with acute lymphoblastic leukemia (ALL) in first (CR1 n = 7), second (CR2 n = 10), or third (CR3 n = 4) complete remission, and in refractory state (NR n = 6). The patients received a mean number of 19.1+/-11.3 x 10(6)/kg purified CD34+ and a mean number of 15.5+/-24.2 x 10(3)/kg CD3+ T-cells. No additional graft-versus-host disease (GVHD) prophylaxis was used, except as short-term CSA in the first 3 patients. The myeloablative treatment was based on busulfan in 12 and on TBI in 14 patients. One patient was grafted with a non-myeloablative approach. Engraftment was rapid in 26 patients, with two patients suffering from a rejection. These two and one patient with initial non-engraftment had been successfully regrafted. The probability of survival of the total group is 0.34+/-0.09; the 12 patients transplanted in remission showed a probability of survival of 0.44+/-0.11. None of the patients transplanted in non-remission survived. There was no statistical difference in survival for patients with a 1, 2 or 3 antigen mismatched donor (out of 6 HLA antigens) or for patients in 1st, 2nd or 3rd remission. Causes of death were relapses in 10 patients, veno-occlusive disease (VOD) in 1, multi-organ failure (MOF) in 2 and infections in 4 patients. 3/24 evaluable patients without any additional GVHD-prophylaxis developed grade 1 or 2 GVHD. Ten patients were treated with additional donor lymphocyte infusion (DLI), from which 4 developed a maximum grade 3 GVHD. We conclude that the HLA barrier can be overcome by transplantation of megadoses of highly purified CD34+ PBPC and GVHD can effectively be prevented. This approach offers a promising treatment option for patients with acute lymphoblastic leukemia needing urgently transplantation but lacking a suitable donor.

Clinical strategies for expansion of haematopoietic stem cells

Haematopoietic stem cells (HSCs) give rise to all blood and immune cells and are used in clinical transplantation protocols to treat a wide variety of diseases. The ability to increase the number of HSCs either in vivo or in vitro would provide new treatment options, but the amplification of HSCs has been difficult to achieve. Recent insights into the mechanisms of HSC self-renewal now make the amplification of HSCs a plausible clinical goal. This article reviews the molecular mechanisms that control HSC numbers and discusses how these can be modulated to increase the number of HSCs. Clinical applications of HSC expansion are then discussed for their potential to address the current limitations of HSC transplantation.

Clinical relevance of serial quantitative analysis of hematopoietic chimerism after allogeneic stem cell transplantation in children for severe aplastic anemia

Allogeneic stem cell transplantation (allo-SCT) is a well-established treatment modality for children with severe aplastic anemia (SAA). Treatment failures are rare and mostly caused by graft rejection. Increasing mixed chimerism represents a stage at the very beginning of graft rejection, where immunological intervention might be an effective prophylactic approach. To substantiate this, we: (1) monitored peripheral blood cells from children with SAA after allo-SCT and performed pre-emptive immunotherapy in patients with increasing MC. In all, 23/34 courses of 32 children with SAA after allo-SCT showed a complete chimerism (CC) throughout and 10/34 developed different types of mixed chimerism (MC). Altogether, 4/10 with MC spontaneously developed decreasing MC, 2/10 courses persisted with low proportions of autologous cells below 30% (stable-MC), 4/10 developed increasing MC and one patient showed an autologous recovery. All patients with CC, decreasing MC or stable MC remained in continuous complete remission (CCR). In all, 2/4 patients with increasing MC developed graft rejection. Based on these observations, 2/4 new patients with increasing MC received low-dose DLIs prophylactically, and remained in CCR without any GVHD. These results substantiate that low-dose DLI in children with SAA and increasing MC can prevent graft rejection with a calculable risk to induce severe GVHD.

Transplantation of highly purified peripheral-blood CD34+ progenitor cells from related and unrelated donors in children with nonmalignant diseases

Transplantation of allogeneic stem cells is currently the only curative treatment for some nonmalignant pediatric diseases. We investigated whether transplantation of purified CD34(+) stem cells prevents acute and chronic GvHD and reduces transplant-related mortality. A total of 25 pediatric patients with nonmalignant diseases underwent allogeneic transplantation from 26 donors (matched related n=4, matched or partially matched unrelated n=14, mismatched related n=8). All grafts were purified peripheral-blood CD34(+) stem cells mobilized with G-CSF. Patients received a median of 12.9 x 10(6) CD34(+) progenitor cells with a median of 6.1 x 10(3) contaminating T-lymphocytes per kilogram of body weight. No post transplant immunosuppressive drugs were given for prophylaxis of GvHD. Engraftment was seen in 21 patients. Three patients engrafted after a second transplant and one patient failed to engraft. Two patients had autologous reconstitution 1.5 years post transplant and one of them was successfully retransplanted. No acute GvHD >grade II was seen, and only two patients developed limited, chronic GvHD. In all, 22 patients (88%) are alive with a median follow-up of 3.7 years. In total, 19 patients (76%) are free of disease or of progression. Transplantation of highly purified peripheral-blood CD34(+) stem cells is associated with low toxicity in patients with nonmalignant diseases.

Megadose transplantation of highly purified haploidentical stem cells: current results and future prospects

The transplantation of megadoses of haploidentical hematopoietic stem cells is for a number of children with malignant or nonmalignant diseases the only curative approach. In order to prevent severe GvHD, the removal of T lymphocytes from the stem cell graft either by positive selection of CD34+ stem cells or by negative depletion of CD3+ T lymphocytes is necessary. We present the results obtained so far by CD34+ positive selection and discuss new techniques of graft engineering which might hopefully further improve the outcome of haploidentical stem cell transplantation.

Transplantation of highly purified CD34+ progenitor cells from unrelated donors in pediatric leukemia

Unrelated donors are commonly used for hematopoietic stem cell transplants, but graft-versus-host disease (GVHD) is a major problem. We investigated whether transplantation of purified mobilized peripheral-blood CD34(+) stem cells from unrelated donors would prevent acute and chronic GVHD in pediatric patients with leukemia and avert the need for pharmacologic immunosuppression. Thirty-one pediatric patients with acute lymphoblastic leukemia (ALL, n = 16), acute myeloid (n = 7), chronic myeloid (n = 6), or juvenile myelomonocytic leukemia (n = 2) underwent transplantation. The median purity of CD34(+) cells after positive magnet-activated cell sorting was 98.5%. Patients received a median of 8.0 x 10(6) CD34(+) cells and 6 x 10(3) CD3(+) T lymphocytes per kilogram, with no posttransplantation pharmacologic immunosuppression. Primary acute GVHD > or = grade II was seen in only 10% of patients (n = 3) and occurred only after human herpesvirus 6 (HHV 6) infection. Two patients had limited chronic GVHD. Engraftment occurred in all patients (primary engraftment, n = 26; engraftment after reconditioning, n = 5). The 2-year survival estimate was 38% for all patients and 63% for patients with ALL in complete remission. Patients with myeloid malignancies had a poor outcome. In comparison to a historical control group who received unmanipulated bone marrow, our patients had a lower incidence of GVHD (P <.001). No difference was observed in the probability of relapse or survival. Study patients with ALL in remission showed a trend toward better survival (P =.07). Transplantation of purified peripheral-blood CD34(+) cells from unrelated donors effectively minimizes GVHD and may be a good therapeutic option for patients with relapsed ALL.

Hypoplastic myelodysplastic syndromes can be distinguished from acquired aplastic anaemia by bone marrow stem cell expression of the tumour necrosis factor receptor

It is often difficult to distinguish hypoplastic myelodysplastic syndrome (h-MDS) from acquired aplastic anaemia (AA), because of the considerable clinical, cytological and histological similarities between these two disorders. The distinction between AA and h-MDS is important because there is a higher risk of progression to acute leukaemia in patients with h-MDS compared with AA. Recent studies suggest that tumour necrosis factor-alpha (TNF-alpha) plays an important role in the development of AA. In order to determine the potential importance of TNF-alpha in the differential diagnosis of hypoplastic bone marrow (BM) disorders, we examined whether analysis ofTNF-receptor expression could be used as a tool to differentiate AA from h-MDS. Flow cytometric analysis revealed that BM stem cells (CD34+) from AA patients have markedly greater TNF receptor (R) 1 and TNFR2 expression than those from patients with MDS and h-MDS. We suggest that the BM stem cells with a high expression of TNFR in patients with AA may be potently sensitive to TNF-alpha stimulation of differentiation. Thus, we propose that quantification of TNFR expression in BM stem cellsmay be a useful method to distinguish AA from h-MDS.

Isolation and transplantation of highly purified autologous peripheral CD34(+) progenitor cells: purging efficacy, hematopoietic reconstitution and long-term outcome in children with high-risk neuroblastoma

We have investigated the purging efficacy of positive selection of autologous mobilized CD34(+) peripheral stem cells in 22 children with high-risk neuroblastoma. CD34(+) cell selection was performed using the method of magnetic-activated cell sorting (MACS). The median purity of the CD34(+) cells post selection was 97.6% (range 81.7-99.7). For detection of contaminating neuroblastoma cells before and after CD34(+) selection, the chimeric anti-disialoganglioside GD2 antibody delta ch 14.18 was used. Prior to positive selection, various numbers of contaminating neuroblastoma cells were found in 17 patients. After positive CD34(+) cell selection, low numbers of neuroblastoma cells were only detectable in four patients. In 18 patients, high-dose chemotherapy was performed and the isolated CD34(+) cells were reinfused. In all patients, a rapid neutrophil recovery was seen with a median time to reach 0.5 x 10(9)/l neutrophils of 12 days (range 8-24 days). Nine of the 18 patients are free of progression with a median follow-up of 55 months (range 45-70 months). Two patients are alive with relapse, six patients died due to progression or relapse and one patient died due to secondary AML 10 months after transplant while in remission from neuroblastoma. In summary, we show that, through a highly effective positive selection method, a high purging efficacy can be obtained without compromising the hematopoietic reconstitution capacity of the graft.

Antibody and pre- plus post-transplant prednisone treatments support T cell-depleted stem cell engraftment without drug-induced morbidity

Rigorous T cell depletion methods can now be used to reduce the risk of graft-versus-host disease (GVHD) associated with allogeneic, hematopoietic stem cell transplantation (HSCT). However, full T cell depletion is also associated with a significant risk of graft failure. Here we hypothesize that engraftment failures after T cell-depleted HSCT may be due, in part, to the absence of GVHD prophylaxis. To test this hypothesis, we used a haploidentical mouse model to systematically measure the effects of immunosuppressive drug treatments and anti-T cell antibodies on engraftment. Results showed that engraftment was supported in all animals when hosts were pre-treated with anti-T cell antibodies, but donor chimerism was significantly improved when hosts were also treated with prednisone. Interestingly, when hosts received only pre-HSCT prednisone treatments, engraftment was not improved; when hosts received only post-HSCT prednisone (initiated near the time of irradiation), the animals became extremely ill. Results therefore demonstrated the need for both pre- and post-HSCT prednisone treatments as a means to ensure engraftment without morbidity in all host animals.

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.

Variables to predict engraftment of umbilical cord blood into immunodeficient mice: usefulness of the non-obese diabetic--severe combined immunodeficient assay

Umbilical cord blood is an alternative stem cell source for patients without matched family donors. In this study, we examined several parameters that have not been studied in detail -- radiation dose, cell dose, age of mice, and maternal and neonatal characteristics of the cord blood donor -- that affect engraftment of cord blood in non-obese diabetic-severe combined immunodeficient (NOD--scid) mice. Engraftment, measured using flow cytometry analyses of human CD45(+) cells, was highest in 400 cGy-treated mice. Successful engraftment was demonstrated up to 6 months, with a mean engraftment of 31% (range 0--67%) of human cells in recipient bone marrow. Engraftment was skewed to B lymphocytes. The radiation dose of 350 cGy resulted in superior survival of the murine recipients compared with 400 cGy (P = 0.03). The sex of the NOD--scid recipients had a significant effect on survival (female superior to male, P = 0.01), but not on engraftment. There were high levels of variability among different cord units and among animals injected with the same cord unit. This variability may limit the clinical usefulness of the NOD--scid mice as hosts for the quantification of human stem cells.

Immunological aspects of haploidentical stem cell transplantation in children

Thirty-eight children with high-risk hematological malignancies underwent transplantation with megadoses of peripheral mobilized CD34+ cells from haploidentical parents (n = 24) or from matched unrelated donors (n = 14). The CD34+ cells were isolated to a purity of > 98% using magnetic-activated cell sorting. This high purity was associated with an almost complete depletion of T lymphocytes. No pharmacological prophylaxis for graft-versus-host disease (GvHD) was used, and significant primary GvHD was not seen. A final engraftment was seen in all patients. Sixteen patients are alive and disease-free with a median follow-up of 24 months. The immunological reconstitution was faster in the patients transplanted with CD34+ stem cells from the haploidentical donors compared to the matched unrelated donors, and the transplantation of large numbers of haploidentical CD34+ stem cells seems to be superior to that of the matched unrelated donors. The phenotypical and functional analysis of the immune reconstitution provided some insights into the biology of transplantation of highly purified CD34+ cells. In this article, we summarize our current results with the transplantation of highly purified stem cells and discuss possible implications for further antileukemic post-transplant therapeutic strategies.

Allogeneic hematopoietic transplantation of CD34+ selected cells from an HLA haplo-identical related donor. A long-term follow-up of 135 patients and a comparison of stem cell source between the bone marrow and the peripheral blood

We studied the outcome of allogeneic transplants in 135 patients who received selected BM and/or PBSC CD34+ cells from HLA haplo-identical related donors. Donor engraftment was achieved in 108 of 128 evaluable transplants. Engraftment failure occurred more often in non-malignant than in malignant diseases (10 of 25 vs 17 of 103, P = 0.010). The CD34+ cell dose was associated with the speed of neutrophil and platelet recovery, but the cell source was not. Acute GVHD (> or = grade II) developed in 21.0 +/- 3.7%. Chronic GVHD occurred more frequently in malignancies than in non-malignancies (44.1 +/- 7.6% vs 0.0%, P = 0.0075), and more in PBSC recipients than in BM recipients (53.6 +/- 9.4% vs 17.4 +/- 9.3%, P = 0.0054). Relapse rate was higher in high risk patients than in standard risk patients (78.7 +/- 7.1% vs 22.1 +/- 10.0%, P = 0.0001). Probabilities of disease-free survival (DFS) were 14.2 +/- 3.5% in malignancies and 25.7 +/- 9.2% in non-malignancies. Probabilities of DFS in standard and high risk patients were 39.4 +/- 9.2% and 5.7 +/- 2.8% (P = 0.0001). A high incidence of graft failure, infection and relapse was observed and resulted in high mortality.

Overview of autologous stem cell transplantation

There has been a dramatic increase in the number of autologous peripheral blood stem cell transplants over the last decade. Faster recovery of cell counts, lesser transplant morbidity, shorter hospital stay and reduced cost compared with marrow autografts have been the main advantages of autologous peripheral blood cell over marrow transplants. In this paper we attempt to review the advances in the biology and mobilization of stem cells, and focus on clinical results of autologous peripheral stem cell and marrow transplants for disease specific sites such as breast cancer, myeloma, autoimmune diseases, germ cell tumors, the acute and chronic leukemias, the non-Hodgkin's lymphomas and Hodgkin's disease. We also discuss transplant related complications, gene therapy and the different methods of purging. This review was intended for autologous peripheral stem cell transplants, however, unavoidably, it also discusses autologous marrow transplantation and aspects common to both procedures.

Large scale purification of human blood CD34+ cells from cryopreserved peripheral blood stem cells, using a nylon-fiber syringe system and immunomagnetic microspheres

Isolation of large numbers of human peripheral blood CD34+ cells could lead to therapeutic applications, including purging of malignant cells from blood cell transplantations, purging of T cells from allogeneic bone marrow, and even blood cell transplantation. This procedure has limitations if there are not sufficient numbers of progenitor cells in the leukapheresis concentrates available for selection after detection of tumor cells in apheresis products. Use of frozen/thawed peripheral blood mononuclear cell (PBMC) samples would make feasible pooling of two or even more stem cell harvests collected at different time points and the total number of CD34+ progenitor cells available would increase. We established an efficient method for purification of CD34+ cells from cryopreserved apheresis products, using a nylon-fiber syringe system and immunomagnetic microspheres. We compared purity, recovery rate and clonogenicity of CD34+ cells purified from fresh (n = 22) and cryopreserved apheresis products (n = 14), using a nylon-fiber syringe system and immunomagnetic microspheres. The purity of CD34+ cells from cryopreserved products was less than that from fresh products (85.9 +/- 14.4% vs 94.6 +/- 10.0%), but the recovery rate of CD34+ cells and colony-forming cells was comparable between fresh and cryopreserved products. One patient underwent grafting with peripheral blood CD34+ cells selected after freezing, with good success. Therefore, these cells are capable of rapidly reconstituting hematopoiesis after high-dose chemotherapy. Bone Marrow Transplantation (2000) 26, 787-793.

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

Recently, a number of devices have been developed for the positive selection of CD34(+) peripheral blood progenitor cells (PBPC) for clinical use in autologous or allogeneic transplantation. The rationale for CD34(+) selection is based on clinical studies showing a two- to five-log reduction of contaminating tumor cells in patients with breast cancer, multiple myeloma and low-grade lymphoma. In addition, a three- to five-log reduction of T cells can be obtained by CD34(+) selection in both autologous grafts for patients with autoimmune disease resistant to conventional therapy and allogeneic grafts to reduce the incidence and severity of acute graft-versus-host disease. Transplantation of positively selected autologous CD34(+) PBPC results in a rapid and stable neutrophil and platelet engraftment in patients who received an infused dose of at least 2.0 x 10(6) CD34(+) cells/kg. Results from randomized trials suggest that time to engraftment is not different compared to unmanipulated PBPC autografts. However, close monitoring for infectious complications (e.g., cytomegalovirus disease) is required. Allogeneic CD34(+) PBPC have also been successfully transplanted and, using novel technologies, megadoses of purified CD34(+) PBPC can be obtained and used to overcome histocompatibility differences betweeen allogeneic donor and patient resulting in stable engraftment, even in a haploidentical setting. Additional randomized phase III trials are required to determine whether tumor cell purging or lymphocyte depletion by CD34(+) cell selection will have a significant impact on progression-free and overall survival in both autologous and allogeneic transplantation.