Thrombotic and Cardiovascular Events and Treatment Patterns Among Patients Hospitalized with COVID-19 in Japan: An Analysis of a Nationwide Medical Claims Database.

INTRODUCTION: Limited data are available regarding the prevalence of thrombotic/cardiovascular disease and treatment patterns for patients with coronavirus disease 2019 (COVID-19) in Japan. In this study we describe patients hospitalized for COVID-19 in Japan. METHODS: This retrospective database study analyzed the Japan Medical Data Vision database (416 acute care hospitals) for patients hospitalized for COVID-19 during the identification period from 1 January 1 to 30 September 2020. RESULTS: Among 9282 eligible patients, 832 (9%) had developed thrombotic disease including myocardial infarction, ischemic stroke, deep vein thromboembolism and pulmonary embolism. Intriguingly, 171(1.8%) had two thrombotic events and 25 (0.3%) had three or four thrombotic events at the same time. The data also showed that arterial thrombotic events accounted for 77% of total thrombotic events. Anticoagulant and/or antiplatelet medication was provided to 3312 patients. Even with antithrombotic medication, 21.2% of patients suffered from thrombotic diseases. CONCLUSIONS: Patients with COVID-19 could experience thrombotic complications in every blood vessel. Further optimization of medication is crucial for preventing thrombotic complications and improving prognosis.

Alternating bortezomib-dexamethasone and lenalidomide-dexamethasone in patients with newly diagnosed multiple myeloma aged over 75 years.

More than 40% of Japanese patients with multiple myeloma (MM) are over 75 years of age at diagnosis. Regardless of the treatment benefits, complications and relapses obstruct long-term survival. We conducted a phase II, open-label, single-arm, multicenter clinical trial to assess the efficacy and safety of alternating bortezomib-dexamethasone (Bd) and lenalidomide-dexamethasone (Ld) (Bd/Ld) treatment in MM patients aged over 75 years (MARBLE trial). Patients received Bd therapy from days 1 to 35 and Ld therapy from days 36 to 63. For Bd therapy, patients were administered bortezomib 1.3 mg/m2 and oral dexamethasone 20 mg on days 1, 8, 15, and 22. For Ld therapy, they were administered lenalidomide 15 mg from days 36 to 56 and dexamethasone 10 mg on days 36, 43, 50, and 57. They underwent six treatment cycles in total, each consisting of a 63-day regimen. In total, 10 patients were enrolled, with a median age of 81 years. Efficacy was not evaluated because the patients were fewer than planned. The overall response rate was 80.0% and complete response rate 40.0%. Seventy percent of patients completed the study treatment. Progression-free survival and overall survival at 2 years were 40.0% and 80.0%, respectively. Adverse events of grade 3 or higher, including anemia, decreased lymphocyte count, neutropenia, and hypokalemia, were observed in eight patients. Alternating chemotherapy with Bd/Ld might be feasible, but its efficacy should be verified further.

Current Status, Challenges, and Future Perspectives of Real-World Data and Real-World Evidence in Japan.

The aim of this article is to help develop a common understanding of the current status, challenges, and future perspectives of real-world data (RWD) and real-world evidence (RWE) in Japan. RWD and RWE are very widely used terms, but standardized definitions are lacking. Given broad and growing applications of RWD/RWE from the perspective of clinical development and medical affairs, the PhRMA Japan Medical Affairs Committee Working Group 1 have proposed the following definitions: "RWD are the data relating to patient health status and/or the delivery of health care routinely collected from a variety of sources" and "RWE is the evidence derived from analysis of RWD." The key challenges for RWD and RWE in Japan include restricted access and linkage of RWD, as well as a lack of universally accepted methodological approaches, which reduces the potential for patient and healthcare benefits. These challenges for RWD/RWE are by no means unique to Japan and similar challenges exist for countries in Europe and the USA. The quality of data and analysis, study design, and the transparency of reporting should be discussed more to ensure credibility and acceptance by decision-makers as the demand for RWD and RWE increases. The future developments around Japan's RWD and RWE are expected to include improved RWD access, data linkage, and increased acceptance by decision-makers, all supported by innovative technology. Improvements in RWD access and database linkage will enable both public and private sectors to assemble more comprehensive health information in Japan.

Intravenous itraconazole compared with liposomal amphotericin B as empirical antifungal therapy in patients with neutropaenia and persistent fever.

BACKGROUND: Fungal infections are a major complication of neutropaenia following chemotherapy. Their early diagnosis is difficult, and empirical antifungal treatment is widely used, and uses of less toxic drugs that reduce breakthrough infection are required. OBJECTIVE: We conducted a multicentre, open-label, randomised, non-inferiority trial to compare the safety and efficacy of intravenous itraconazole (ivITCZ) and liposomal amphotericin B (LAmB) as empirical antifungal therapy in patients with haematological malignancies with neutropaenia and persistent fever. METHODS: Patients with haematological malignancies who developed fever refractory to broad-spectrum antibacterial agents under neutropaenia conditions were enrolled. Patients were randomised for treatment with LAmB (3.0 mg/kg/d) or ivITCZ (induction: 400 mg/d, maintenance: 200 mg/d). RESULTS: Observed overall favourable response rates of 17/52 (32.7%) and 18/50 (36.0%) in the LAmB and ivITCZ groups, with a model-based estimate of a 4% difference (90% CI, -12% to 20%), did not fulfil the statistical non-inferiority criterion. In the LAmB group, there were two cases of breakthrough infection and five cases of probable invasive fungal disease, whereas in the itraconazole group, neither breakthrough infection nor probable invasive fungal disease occurred. Patients in the ivITCZ group had significantly fewer grade 3-4 hypokalaemia-related events than LAmB group patients (P < .01). The overall incidence of adverse events tended to be lower in the ivITCZ group (P = .07). CONCLUSION: ivITCZ showed similar efficacy and safety as LAmB as empirical antifungal therapy in haematological malignancy patients with febrile neutropaenia, although the small sample size and various limitations prevented demonstration of its non-inferiority.

Rituximab-Mediated Complement-Dependent Cytotoxicity Enhanced by Gemcitabine in Older Patients with Previously Rituximab-Treated Diffuse Large B-Cell Lymphoma: Study Protocol.

High-dose chemotherapy and autologous stem cell transplantation is too toxic for elderly patients with relapsed or refractory (DLBCL). Therefore, tolerable and efficient salvage regimens for elderly patients are greatly needed. In this study, therapy with rituximab, gemcitabine, dexamethasone, and cisplatin (R-GDP) will be performed every 4 weeks, and an interim evaluation will be performed after the completion of the 3rd course. If a complete response (CR) is achieved at the time of interim evaluation, 1 course of R-GDP therapy and 2 courses of monotherapy with rituximab will be additionally performed. If a partial response (PR) is achieved, 3 courses of R-GDP therapy will be additionally conducted. In patients without a PR or CR by the time of the interim evaluation, treatment will be discontinued. Treatment will also be discontinued at any point if disease progression is observed during protocol treatment. After the completion of the final course of R-GDP therapy, final effects of the regimen will be evaluated. A primary endpoint is the efficacy of R-GDP therapy (CR and response rates). This is the first multicenter phase II clinical study of R-GDP therapy to examine post-treatment activities of daily living in addition to the safety and efficacy of treatment in elderly patients with relapsed or refractory transplantineligible DLBCL.

Acute Promyelocytic Leukemia and HIV: Case Reports and a Review of the Literature.

Acute promyelocytic leukemia (APL) in human immunodeficiency virus (HIV)-infected individuals is very rare. There is currently no consensus regarding the use of anti-cancer drugs with highly active anti-retroviral therapy (ART) in these patients due to their small number. We herein report two cases of APL with HIV-infected patients. Both cases received all-trans-retinoic acid-containing chemotherapies and achieved complete remission. ART was continued throughout the treatment course. The clinical course of these cases suggests that it is preferable to perform standard chemotherapy for APL with ART if patients have an adequate performance status.

R-mini CHP in ≥80-year-old Patients with Diffuse Large B-cell Lymphoma: A Multicenter, Open-label, Single-arm Phase II Trial Protocol.

In very-elderly diffuse large B-cell lymphoma (DLBCL) patients, treatment intensities must be lowered due to the risks of comorbidities and organ function deterioration, and treatment outcomes are worse compared to younger patients. Very-elderly patients are often excluded from DLBCL clinical trials, and optimal treatments and dosages are not established. In this clinical trial, we examined the efficacy and safety of 6 courses of R-mini CHP therapy (cf., CHOP [cyclophosphamide, doxorubicin, vincristine, and prednisone]) in which vincristine is omitted to avoid the peripheral neuropathy that reduces elderly patients' quality of life, as remission induction therapy in DLBCL patients aged≥80 years.

Deeper molecular response is a predictive factor for treatment-free remission after imatinib discontinuation in patients with chronic phase chronic myeloid leukemia: the JALSG-STIM213 study.

The objective of this prospective clinical trial (JALSG-STIM213, UMIN000011971) was to evaluate treatment-free remission (TFR) rates after discontinuation of imatinib in chronic myeloid leukemia (CML). CML patients who received imatinib treatment for at least 3 years and sustained deep molecular response for at least 2 years were eligible. Molecular recurrence was defined as loss of major molecular response (MMR). Of the 68 eligible patients, 38.2% were women, the median age was 55.0 years, and the median duration of imatinib treatment was 97.5 months. The 12-month TFR rate was 67.6%. Patients who lost MMR were immediately treated with imatinib again; all re-achieved MMR. Three-year treatment-free survival (TFS) was estimated as 64.6% using the Kaplan-Meier method. Undetectable molecular residual disease (UMRD) was defined as no BCR-ABL1 in > 100,000 ABL1 control genes using international scale polymerase chain reaction. UMRD at the study baseline was found to be predictive of continuation of TFR. Our findings suggest that CML patients who meet all the eligibility criteria that have commonly been used in the TFR trials are able to discontinue imatinib use safely. TFR may thus be valuable as a new goal for CML treatment in Japan.

EBV-positive Reactive Hyperplasia Progressed into EBV-positive Diffuse Large B-cell Lymphoma of the Elderly over a 6-year Period.

A 70-year-old woman with lymphadenopathy was admitted to hospital in 2008. Lymph node biopsy showed reactive lymphoid hyperplasia (RH) with monoclonal proliferation of Epstein-Barr virus (EBV). Her lymphadenopathy regressed without treatment. In 2014, the patient presented with nasal obstruction because of a left nasal mass. She was diagnosed with EBV-positive diffuse large B-cell lymphoma (DLBCL) of the elderly based on the examination of a biopsy specimen of the mass. The IgH rearrangement in the specimens from the 2008 and the 2014 revealed that they were genetically identical. This is the first report of RH progressing to DLBCL, and suggests that EBV-positive B-cells in RH lymph nodes predict the evolution to DLBCL.

Efficacy and safety of autologous peripheral blood stem cell transplantation for Philadelphia chromosome-positive acute lymphoblastic leukemia: A study protocol for a multicenter exploratory prospective study (Auto-Ph17 study).

INTRODUCTION: The prognosis of Philadelphia chromosome positive acute lymphoblastic leukemia (Ph + ALL) has been dramatically improved since the introduction of tyrosine kinase inhibitors (TKIs). Although allogeneic hematopoietic cell transplantation (allo-HCT) is a major treatment option, the role of autologous peripheral blood stem cell transplantation (auto-PBSCT) has been reconsidered, especially in patients who achieved early molecular remission. METHODS AND ANALYSIS: This is a multicenter exploratory study for Ph + ALL patients aged between 55 and 70 years who achieved complete molecular remission within 3 cycles of chemotherapy. The target sample size is 5, and the registration period is 2 years. The primary endpoint is Day100- mortality after transplantation, and the secondary endpoints are survival, relapse rate, nonrelapse mortality, and adverse events.This study is divided into 3 phases: peripheral blood stem cell harvest, transplantation, and maintenance. Chemomobilization is performed using a combination of cyclophosphamide (CPM), doxorubicin, vincristine (VCR), and prednisolone (PSL). As a preparative regimen, the LEED regimen is used, which consists of melphalan, CPM, etoposide, and dexamethasone. Twelve cycles of maintenance therapy using a combination of VCR, PSL, and dasatinib are performed.In association with relapse, the minimal residual disease (MRD) of BCR-ABL chimeric gene and T-cell subsets are analyzed both before and after auto-PBSCT. ETHICS AND DISSEMINATION: The protocol was approved by the institutional review board of Nagoya University Hospital and all the participating hospitals. Written informed consent was obtained from all patients before registration, in accordance with the Declaration of Helsinki. Results of the study will be disseminated via publications in peer-reviewed journals. TRIAL REGISTRATION: Trial registration number UMIN000026445.

Fibroblast Growth Factor-2 facilitates the growth and chemo-resistance of leukemia cells in the bone marrow by modulating osteoblast functions.

Stromal cells and osteoblasts play major roles in forming and modulating the bone marrow (BM) hematopoietic microenvironment. We have reported that FGF2 compromises stromal cell support of normal hematopoiesis. Here, we examined the effects of FGF2 on the leukemia microenvironment. In vitro, FGF2 significantly decreased the number of stromal-dependent and stromal-independent G0-leukemia cells in the stromal layers. Accordingly, CML cells placed on FGF2-treated stromal layers were more sensitive to imatinib. Conversely, FGF2 increased the proliferation of osteoblasts via FGFR1 IIIc, but its effects on osteoblast support of leukemia cell growth were limited. We next treated a human leukemia mouse model with Ara-C with/without systemic FGF2 administration. BM sections from FGF2-treated mice had thickened bone trabeculae and increased numbers of leukemia cells compared to controls. Leukemia cell density was increased, especially in the endosteal region in FGF2/Ara-C -treated mice compared to mice treated with Ara-C only. Interestingly, FGF2 did not promote leukemia cell survival in Ara-C treated spleen. Microarray analysis showed that FGF2 did not alter expression of many genes linked to hematopoiesis in osteoblasts, but modulated regulatory networks involved in angiogenesis and osteoblastic differentiation. These observations suggest that FGF2 promotes leukemia cell growth in the BM by modulating osteoblast functions.

A new diagnostic kit, ODK-1201, for the quantitation of low major BCR-ABL mRNA level in chronic myeloid leukemia: correlation of quantitation with major BCR-ABL mRNA kits.

The current first-line therapy of chronic myeloid leukemia (CML) is based on tyrosine kinase inhibitors. Diagnostic kits that are capable of identifying at least a 4.5 log reduction in the international scale % BCR-ABL/ABL (IS % BCR-ABL/ABL) are needed for use in the clinical evaluation of deeper molecular response to treatment and to determine the timing of dose selection or treatment interruption during the course of treatment. In this study, we evaluated the performance of a new diagnostic kit, ODK-1201, designed to be capable of performing reverse transcription and quantitative PCR in a single tube for the quantitation of major BCR-ABL mRNA. The kit demonstrated excellent assay performance (limit of detection 0.0007 %) and a broader detection range of BCR-ABL mRNA in peripheral blood compared to a commercially available kit for CML (Amp-CML). ODK-1201 was also shown to be as sensitive as Ipsogen and Molecular MD kits in the same assay. Results obtained in this study indicate evidences that ODK-1201 was capable of identifying at least a 4.5 log reduction in the IS % BCR-ABL/ABL.

The synergistic effect of BCR signaling inhibitors combined with an HDAC inhibitor on cell death in a mantle cell lymphoma cell line.

Mantle cell lymphoma (MCL) is a B cell malignancy characterized by aberrant expression of cyclin D1 due to a t(11;14) translocation. MCL is refractory to conventional chemotherapy, and treatment remains challenging. We investigated the efficacy of the histone deacetylase (HDAC) inhibitor vorinostat combined with one of several B-cell receptor (BCR) signaling inhibitors on MCL cell death and the underlying mechanisms, using MCL cell lines. The Bruton's tyrosine kinase inhibitor PCI-32765 and the spleen tyrosine kinase inhibitor R406 showed synergistic effects with vorinostat on growth inhibition. Treatment with PCI-32765 or R406 alone induced 27.3 ± 2.1 or 25.1 ± 3.2% apoptosis. When combined with vorinostat, these apoptotic fractions significantly increased to 50.8 ± 4.9 and 63.1 ± 5.0%, respectively. Activation of caspase-3 and poly-(ADP-ribose) polymerase cleavage were markedly increased. We performed gene expression profiling following treatment with the combination of vorinostat and individual BCR signaling inhibitors using a microarray, and differentially expressed genes were identified. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis showed that the nuclear factor (NF)-κB signaling pathway was significantly enriched following treatment with the combination of vorinostat and R406. Protein expression analysis confirmed the down-regulation of NF-κB1/p105 and cyclin D1, suggesting inhibition of the NF-κB pathway. Taken together, the combination of an HDAC inhibitor and a BCR signaling inhibitor may be a novel therapeutic strategy for MCL.

Acute thrombotic thrombocytopenic purpura after pneumococcal vaccination.

We report the case of a 68-year-old woman with acute thrombotic thrombocytopenic purpura (TTP) that developed after pneumococcal vaccination. She was found in a confusional state with high fever 15 days after vaccination. Laboratory data showed hemolytic anemia and thrombocytopenia, and blood smear showed fragmented erythrocytes. TTP was diagnosed based on the clinical presentation, and was subsequently confirmed by the absence of ADAMTS13 activity and the presence of inhibitor against ADAMTS13 in serum. She was successfully treated using plasma exchange and corticosteroids, and no recurrence has been identified. This appears to represent the first report of TTP following pneumococcal vaccination.

Phase I study of clofarabine in adult patients with acute myeloid leukemia in Japan.

OBJECTIVE: There are limited treatment options for relapsed/refractory acute myeloid leukemia patients or previously untreated elderly (≥60 years) patients with acute myeloid leukemia. In Phase II studies from the USA and Europe, single-agent clofarabine demonstrated activity and acceptable toxicity in elderly patients with previously untreated acute myeloid leukemia. This Phase I, multicenter study assessed the maximum-tolerated dose, safety, pharmacokinetics and efficacy of clofarabine in Japanese adults with acute myeloid leukemia. METHODS: Intravenous clofarabine (20, 30 and 40 mg/m(2)/day) was administered for 5 days to Japanese adult patients with relapsed or refractory acute myeloid leukemia or elderly patients with newly diagnosed acute myeloid leukemia. RESULTS: Fourteen patients, median age of 67.5 (59-72) years, were enrolled in this study. Eleven out of 14 patients had relapsed/refractory acute myeloid leukemia. Three patients received clofarabine at 20 mg/m(2), six at 30 mg/m(2) and five at 40 mg/m(2). Frequently reported treatment-related adverse events included thrombocytopenia (100%), anemia (93%), neutropenia (86%), nausea (86%), alanine aminotransferase increase (71%), headache (71%) and febrile neutropenia (57%). Three patients experienced reversible dose-limiting toxicities; two had increased alanine aminotransferase with 30 and 40 mg/m(2) and one had Grade 3 elevation of serum amylase with 40 mg/m(2). The maximum-tolerated dose was 30 mg/m(2)/day. Cmax and exposure area under the curve0-24h increased with increasing dose and were proportional to dose through the tested dose range. Among the 14 assessable patients, four (29%) achieved complete remission and two (14%) complete remission without platelet recovery. The overall remission rate was 43%. CONCLUSIONS: These results demonstrate safety and preliminary, promising activity of clofarabine in Japanese patients with acute myeloid leukemia. Further investigation is warranted.

Akt phosphorylates the transcriptional repressor bmi1 to block its effects on the tumor-suppressing ink4a-arf locus.

The Polycomb group protein Bmi1 is a transcriptional silencer of the Ink4a-Arf locus, which encodes the cell cycle regulator p16(Ink4a) and the tumor suppressor p19(Arf). Bmi1 plays a key role in oncogenesis and stem cell self-renewal. We report that phosphorylation of human Bmi1 at Ser³¹6 by Akt impaired its function by triggering its dissociation from the Ink4a-Arf locus, which resulted in decreased ubiquitylation of histone H2A and the inability of Bmi1 to promote cellular proliferation and tumor growth. Moreover, Akt-mediated phosphorylation of Bmi1 also inhibited its ability to promote self-renewal of hematopoietic stem and progenitor cells. Our study provides a mechanism for the increased abundance of p16(Ink4a) and p19(Arf) seen in cancer cells with an activated phosphoinositide 3-kinase to Akt signaling pathway and identifies crosstalk between phosphorylation events and chromatin structure.

PROX1 overexpression inhibits protein kinase C beta II transcription through promoter DNA methylation.

Prospero-related homeobox 1 (PROX1) is important for embryonic organ formation and differentiation, and changes in PROX1 activity were recently associated with cancer. To address the PROX1 roles in tumorigenesis, we established cells stably overexpressing PROX1 using the human cervical cancer cell line, HeLa. Overexpression of PROX1 reduced cell proliferation and the rate of tumor formation as compared with controls. Comparison of gene expression profiles between PROX1-overexpressing and mock-transfected cells revealed that the expression of protein kinase C ßII (PRKCB2) is down-regulated in PROX1-overexpressing cells. A PRKCB inhibitor suppressed cell growth of control cells more than PROX1-expressing cells. Analysis of the 5'-promoter of PRKCB revealed that a region between -110 bp and the first exon contains two Sp1 binding sites and is important for transcriptional regulation of PRKCB. The inhibition of Sp1 transcription factor resulted in down-regulation of PRKCB2 protein levels. Treatment with a demethylating agent, 5-aza-2'-deoxycytidine, restored PRKCB2 mRNA expression in PROX1-expressing cells, suggesting that the 5'-promoter of PRKCB is methylated in these cells. Actually, it was found that a CpG island in this region, in particular a CpG site overlapping with the distal Sp1 site, was hypermethylated and direct Sp1 binding to this region was inhibited in PROX1-overexpressing cells. Thus, the suppressive effect of PROX1 on cell growth and tumor formation might be partially mediated by PRKCB2 via altered methylation of its promoter.

Mesenchymal stem cells stably transduced with a dominant-negative inhibitor of CCL2 greatly attenuate bleomycin-induced lung damage.

Acute respiratory distress syndrome (ARDS) is a crippling disease with no effective therapy characterized by progressive dyspnea. Mesenchymal stem cells (MSCs) have emerged as a new therapeutic modality for ARDS because MSCs can attenuate inflammation and repair the damaged tissue by differentiating into several cell types. Macrophages participate in the development of ARDS; however, MSCs only weakly modulate macrophage function. The chemokine CCL2 is a potent inducer of macrophage recruitment and activation, and its expression is elevated in patients with ARDS. We established MSCs that are stably transduced by a lentiviral vector expressing 7ND, a dominant-negative inhibitor of CCL2, to enhance the therapeutic function of MSCs. 7ND-MSCs retained the innate properties of MSCs and produced a large amount of 7ND. Many 7ND-MSCs were detected in bleomycin-treated lungs (immunostaining 24 hours after injection), suggesting that MSCs could work as a drug delivery tool. Mice treated with 7ND-MSCs showed significantly milder weight loss, lung injury, collagen content, accumulation of inflammatory cells and inflammatory mediators that were induced by bleomycin, and subsequent survival benefit. No evidence of 7ND-MSC-induced toxicity was observed during or after treatment. Thus, inhibiting the effects of macrophages may greatly enhance the ability of MSCs to effect lung repair in ARDS.

Adipose tissue-derived mesenchymal stem cells facilitate hematopoiesis in vitro and in vivo: advantages over bone marrow-derived mesenchymal stem cells.

Mesenchymal stem cells (MSCs) have emerged as a new therapeutic modality for reconstituting the hematopoietic microenvironment by improving engraftment in stem cell transplantation. However, the availability of conventional bone marrow (BM)-derived MSCs (BMSCs) is limited. Recent studies showed that a large number of MSCs can be easily isolated from fat tissue (adipose tissue-derived MSCs [ADSCs]). In this study, we extensively evaluated the hematopoiesis-supporting properties of ADSCs, which are largely unknown. In vitro coculture and progenitor assays showed that ADSCs generated significantly more granulocytes and progenitor cells from human hematopoietic stem cells (HSCs) than BMSCs. We found that ADSCs express the chemokine CXCL12, a critical regulator of hematopoiesis, at levels that are three fold higher than those with BMSCs. The addition of a CXCL12 receptor antagonist resulted in a lower yield of granulocytes from ADSC layers, whereas the addition of recombinant CXCL12 to BMSC cocultures promoted the growth of granulocytes. In vivo cell homing assays showed that ADSCs facilitated the homing of mouse HSCs to the BM better than BMSCs. ADSCs injected into the BM cavity of fatally irradiated mice reconstituted hematopoiesis more promptly than BMSCs and subsequently rescued mice that had received a low number of HSCs. Secondary transplantation experiments showed that ADSCs exerted favorable effects on long-term HSCs. These results suggest that ADSCs can be a promising therapeutic alternative to BMSCs.

Irrespective of CD34 expression, lineage-committed cell fraction reconstitutes and re-establishes transformed Philadelphia chromosome-positive leukemia in NOD/SCID/IL-2Rgammac-/- mice.

Stem cells of acute myeloid leukemia (AML) have been identified as immunodeficient mouse-repopulating cells with a Lin(-)CD34(+)38(-) phenotype similar to normal hematopoietic stem cells. To identify the leukemia-propagating stem cell fraction of Philadelphia chromosome-positive (Ph(+)) leukemia, we serially transplanted human leukemia cells from patients with chronic myeloid leukemia blast crisis (n = 3) or Ph(+) acute lymphoblastic leukemia (n = 3) into NOD/SCID/IL-2Rgammac(-/-) mice. Engrafted cells were almost identical to the original leukemia cells as to phenotypes, IGH rearrangements, and karyotypes. CD34(+)CD38(-)CD19(+), CD34(+)38(+)CD19(+), and CD34(-)CD38(+)CD19(+) fractions could self-renew and transfer the leukemia, whereas the CD34(-)CD38(+)CD19(+) fraction did not stably propagate in NOD/SCID mice. These findings suggest that leukemia-repopulating cells in transformed Ph(+) leukemia are included in a lineage-committed but multilayered fraction, and that CD34(+) leukemia cells potentially emerge from CD34(-) populations.