Katsuhiro Togami

Myelodysplastic syndromes are induced by histone methylation–altering ASXL1 mutations

Recurrent mutations in the gene encoding additional sex combs-like 1 (ASXL1) are found in various hematologic malignancies and associated with poor prognosis. In particular, ASXL1 mutations are common in patients with hematologic malignancies associated with myelodysplasia, including myelodysplastic syndromes (MDSs), and chronic myelomonocytic leukemia. Although loss-of-function ASXL1 mutations promote myeloid transformation, a large subset of ASXL1 mutations is thought to result in stable truncation of ASXL1. Here we demonstrate that C-terminal–truncating Asxl1 mutations (ASXL1-MTs) inhibited myeloid differentiation and induced MDS-like disease in mice. ASXL1-MT mice displayed features of human-associated MDS, including multi-lineage myelodysplasia, pancytopenia, and occasional progression to overt leukemia. ASXL1-MT resulted in derepression of homeobox A9 (Hoxa9) and microRNA-125a (miR-125a) expression through inhibition of polycomb repressive complex 2–mediated (PRC2-mediated) methylation of histone H3K27. miR-125a reduced expression of C-type lectin domain family 5, member a (Clec5a), which is involved in myeloid differentiation. In addition, HOXA9 expression was high in MDS patients with ASXL1-MT, while CLEC5A expression was generally low. Thus, ASXL1-MT–induced MDS-like disease in mice is associated with derepression of Hoxa9 and miR-125a and with Clec5a dysregulation. Our data provide evidence for an axis of MDS pathogenesis that implicates both ASXL1 mutations and miR-125a as therapeutic targets in MDS.

Two types of C/EBPα mutations play distinct but collaborative roles in leukemogenesis: Lessons from clinical data and BMT models

Two types of mutations of a transcription factor CCAAT-enhancer binding protein α (C/EBPα) are found in leukemic cells of 5%-14% of acute myeloid leukemia (AML) patients: N-terminal mutations expressing dominant negative p30 and C-terminal mutations in the basic leucine zipper domain. Our results showed that a mutation of C/EBPα in one allele was observed in AML after myelodysplastic syndrome, while the 2 alleles are mutated in de novo AML. Unlike an N-terminal frame-shift mutant (C/EBPα-N(m))-transduced cells, a C-terminal mutant (C/EBPα-C(m))-transduced cells alone induced AML with leukopenia in mice 4-12 months after bone marrow transplantation. Coexpression of both mutants induced AML with marked leukocytosis with shorter latencies. Interestingly, C/EBPα-C(m) collaborated with an Flt3-activating mutant Flt3-ITD in inducing AML. Moreover, C/EBPα-C(m) strongly blocked myeloid differentiation of 32Dcl3 cells, suggesting its class II mutation-like role in leukemogenesis. Although C/EBPα-C(m) failed to inhibit transcriptional activity of wild-type C/EBPα, it suppressed the synergistic effect between C/EBPα and PU.1. On the other hand, C/EBPα-N(m) inhibited C/EBPα activation in the absence of PU.1, despite low expression levels of p30 protein generated by C/EBPα-N(m). Thus, 2 types of C/EBPα mutations are implicated in leukemo-genesis, involving different and cooperating molecular mechanisms.

A novel cell-cycle-indicator, mVenus-p27K-, identifies quiescent cells and visualizes G0-G1 transition

The quiescent (G0) phase of the cell cycle is the reversible phase from which the cells exit from the cell cycle. Due to the difficulty of defining the G0 phase, quiescent cells have not been well characterized. In this study, a fusion protein consisting of mVenus and a defective mutant of CDK inhibitor, p27 (p27K−) was shown to be able to identify and isolate a population of quiescent cells and to effectively visualize the G0 to G1 transition. By comparing the expression profiles of the G0 and G1 cells defined by mVenus-p27K−, we have identified molecular features of quiescent cells. Quiescence is also an important feature of many types of stem cells, and mVenus-p27K−-transgenic mice enabled the detection of the quiescent cells with muscle stem cell markers in muscle in vivo. The mVenus-p27K− probe could be useful in investigating stem cells as well as quiescent cells.

SETBP1 Mutations Drive Leukemic Transformation in ASXL1-Mutated MDS

Mutations in ASXL1 are frequent in patients with myelodysplastic syndrome (MDS) and are associated with adverse survival, yet the molecular pathogenesis of ASXL1 mutations (ASXL1-MT) is not fully understood. Recently, it has been found that deletion of Asxl1 or expression of C-terminal-truncating ASXL1-MTs inhibit myeloid differentiation and induce MDS-like disease in mice. Here, we find that SET-binding protein 1 (SETBP1) mutations (SETBP1-MT) are enriched among ASXL1-mutated MDS patients and associated with increased incidence of leukemic transformation, as well as shorter survival, suggesting that SETBP1-MT play a critical role in leukemic transformation of MDS. We identify that SETBP1-MT inhibit ubiquitination and subsequent degradation of SETBP1, resulting in increased expression. Expression of SETBP1-MT, in turn, inhibited protein phosphatase 2A activity, leading to Akt activation and enhanced expression of posterior Hoxa genes in ASXL1-mutant cells. Biologically, SETBP1-MT augmented ASXL1-MT-induced differentiation block, inhibited apoptosis and enhanced myeloid colony output. SETBP1-MT collaborated with ASXL1-MT in inducing acute myeloid leukemia in vivo. The combination of ASXL1-MT and SETBP1-MT activated a stem cell signature and repressed the tumor growth factor-β signaling pathway, in contrast to the ASXL1-MT-induced MDS model. These data reveal that SETBP1-MT are critical drivers of ASXL1-mutated MDS and identify several deregulated pathways as potential therapeutic targets in high-risk MDS.

Blastic Plasmacytoid Dendritic Cell Neoplasm Is Dependent on BCL2 and Sensitive to Venetoclax

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is an aggressive hematologic malignancy with dismal outcomes for which no standard therapy exists. We found that primary BPDCN cells were dependent on the antiapoptotic protein BCL2 and were uniformly sensitive to the BCL2 inhibitor venetoclax, as measured by direct cytotoxicity, apoptosis assays, and dynamic BH3 profiling. Animals bearing BPDCN patient-derived xenografts had disease responses and improved survival after venetoclax treatment in vivo Finally, we report on 2 patients with relapsed/refractory BPDCN who received venetoclax off-label and experienced significant disease responses. We propose that venetoclax or other BCL2 inhibitors undergo expedited clinical evaluation in BPDCN, alone or in combination with other therapies. In addition, these data illustrate an example of precision medicine to predict treatment response using ex vivo functional assessment of primary tumor tissue, without requiring a genetic biomarker. SIGNIFICANCE Therapy for BPDCN is inadequate, and survival in patients with the disease is poor. We used primary tumor cell functional profiling to predict BCL2 antagonist sensitivity as a common feature of BPDCN, and demonstrated in vivo clinical activity of venetoclax in patient-derived xenografts and in 2 patients with relapsed chemotherapy-refractory disease. Cancer Discov; 7(2); 156-64. ©2016 AACR.This article is highlighted in the In This Issue feature, p. 115.

Fulminant sepsis caused by Bacillus cereus in patients with hematologic malignancies: analysis of its prognosis and risk factors.

Bacillus cereus is a growing concern as a cause of life-threatening infections in patients with hematologic malignancies. However, the risk factors for patients with unfavorable outcomes have not been fully elucidated. At our institution, we observed the growth of B. cereus in blood culture in 68 patients with (23) or without (45) hematologic malignancies treated from September 2002 to November 2009. We defined a case as having sepsis when more than two blood culture sets were positive for B. cereus or only a single set was positive in the absence of other microorganisms in patients who had definite infectious lesions. We determined 12 of 23 patients with hematologic malignancies as having sepsis, as well as 10 of 45 patients without hematologic malignancies (p = 0.012). Of the 12 patients with hematologic malignancies, four patients with acute leukemia died of B. cereus sepsis within a few days. In our cohort, risk factor analysis demonstrated that a neutrophil count of 0/mm3, central venous (CV) catheter insertion, and the presence of central nervous system (CNS) symptoms were significantly associated with a fatal prognosis (p = 0.010, 0.010, and 0.010, respectively). Analysis of data from our cohort in conjunction with those from 46 previously reported patients with B. cereus sepsis identified similar risk factors, that is, acute leukemia, extremely low neutrophil count, and CNS symptoms (p = 0.044, 0.004, and 0.002, respectively). These results indicate that appropriate prophylaxis and early therapeutic intervention against possible B. cereus sepsis are crucially important in the treatment of hematologic malignancies.

A Soluble Form of LMIR5/CD300b Amplifies Lipopolysaccharide-Induced Lethal Inflammation in Sepsis

Leukocyte mono-Ig–like receptor 5 (LMIR5, also called CD300b) is an activating receptor expressed in myeloid cells. We have previously demonstrated that T cell Ig mucin 1 works as a ligand for LMIR5 in mouse ischemia/reperfusion injury of the kidneys. In this article, we show that LMIR5 is implicated in LPS-induced sepsis in mice. Notably, neutrophils constitutively released a soluble form of LMIR5 (sLMIR5) through proteolytic cleavage of surface LMIR5. Stimulation with TLR agonists augmented the release of sLMIR5. LPS administration or peritonitis induction increased serum levels of sLMIR5 in mice, which was substantially inhibited by neutrophil depletion. Thus, neutrophils were the main source of LPS-induced sLMIR5 in vivo. On the other hand, i.p. administration of LMIR5-Fc, a surrogate of sLMIR5, bound to resident macrophages (Mϕ) and stimulated transient inflammation in mice. Consistently, LMIR5-Fc induced in vitro cytokine production of peritoneal Mϕ via its unknown ligand. Interestingly, LMIR5 deficiency profoundly reduced systemic cytokine production and septic mortality in LPS-administered mice, although it did not affect in vitro cytokine production of LPS-stimulated peritoneal Mϕ. Importantly, the resistance of LMIR5-deficient mice to LPS- or peritonitis-induced septic death was decreased by LMIR5-Fc administration, implicating sLMIR5 in LPS responses in vivo. Collectively, neutrophil-derived sLMIR5 amplifies LPS-induced lethal inflammation.

Feasibility of Reduced-Intensity Cord Blood Transplantation as Salvage Therapy for Graft Failure: Results of a Nationwide Survey of Adult Patients

To evaluate whether rescue with cord blood transplantation (CBT) could improve the poor survival after graft failure (GF), we surveyed the data of 80 adult patients (median age, 51 years) who received CBT within 3 months of GF (primary 64, secondary 16), with fludarabine-based reduced-intensity regimens with or without melphalan, busulfan, cyclophosphamide, and/or 2-4 Gy total-body irradiation (TBI). A median number of 2.4 × 10(7)/kg total nucleated cells (TNC) were infused, and among the 61 evaluable patients who survived for more than 28 days, 45 (74%) engrafted. The median follow-up of surviving patients was 325 days, and the 1-year overall survival rate was 33% despite poor performance status (2-4, 60%), carryover organ toxicities (grade 3/4, 14%), and infections (82%) prior to CBT. Day 100 transplantation-related mortality was 45%, with 60% related to infectious complications. Multivariate analysis showed that the infusion of TNC ≥2.5 × 10(7)/kg and an alkylating agent-containing regimen were associated with a higher probability of engraftment, and that high risk-status at the preceding transplantation and grade 3/4 organ toxicities before CBT were associated with an increased risk of mortality. In conclusion, in an older population of patients, our data support the feasibility of CBT with a reduced-intensity conditioning regimen for GF.

Chronic eosinophilic Leukemia with the fip1l1-pdgfr± fusion gene in a patient with a history of combination chemotherapy

Hypereosinophilic syndrome (HES) was diagnosed in December 2000 in a 43-year-old man on the basis of persistent eosinophilia (11.7 x 109/L) and a normal karyotype of the bone marrow cells. He had developed intra-abdominal non-Hodgkin’s lymphoma and in 1992 had received 3 courses of combination chemotherapy with doxorubicin (Adriamycin), cyclophosphamide, vincristine, methotrexate, bleomycin, and prednisolone. The patient was orally given prednisolone (10 mg/day) and cyclophosphamide (50 mg/day) as HES treatment without a subsequent improvement of the eosinophilia. In May 2003, anemia (hemoglobin, 7.9 g/dL) and thrombocytopenia (65 x 109/L) manifested with progressive eosinophilia (21.0 ×109/L) and a small number of blasts. The patient became febrile and was admitted in July 2003. Cytogenetic reexamination of the bone marrow cells disclosed the deletion of 4q12, indicating the presence of a fusion of the Fip1-like 1 (FIP1L1) gene to the plateletderived growth factor receptor α (PDGFRα) gene and consequently the clonal nature of his hematopoietic cells. DNA sequence analysis demonstrated that the breakpoints of the FIP1L1 and PDGFRα genes were present in exon 9 and exon 12, respectively. Treatment with imatinib mesylate (300 mg/day) promptly brought about complete remission. Although a number of similar eosinophilic cases have been reported, our patient may be the first such patient with a history of chemotherapy.

Successful allogeneic bone marrow transplantation for myelodysplastic syndrome complicated by severe pulmonary alveolar proteinosis

Pulmonary alveolar proteinosis (PAP) is a rare disorder characterized by the abnormal accumulation of alveolar surfactant protein in alveolar spaces. We report herein a rare case of myelodysplastic syndrome (MDS-RAEB) complicated by severe PAP, and successful allogeneic bone marrow transplantation (BMT) for both disorders. An unrelated BMT was planned for a 48-year-old male with advanced MDS-RAEB. Just before the initiation of the conditioning regimen for unrelated BMT in March 2007, he developed dyspnea. A diagnosis of PAP was made based on findings of chest X-ray, CT scanning, and the fluid obtained by bronchoalveolar lavage. To improve his dyspnea and improve BMT safety, whole lung lavage (WLL) was performed twice, with the partial improvement of PAP. Unrelated allogeneic BMT was performed in September 2007. We had to perform a third WLL because of the worsening of PAP on day 26 after BMT. Despite many infectious complications after BMT, GVHD was relatively mild. PAP had almost disappeared 6 months after BMT. He was well with favorable hematopoiesis 20 months after the BMT without any specific treatment. There has been no report of an MDS patient with PAP in whom 3 WLL procedures were performed before and after allogeneic BMT.