ALBERT

Description: Most B cell precursor acute lymphoblastic leukemia (BCP ALL) can be classified into known major genetic subtypes, while a substantial proportion of BCP ALL remains poorly characterized in relation to its underlying genomic abnormalities. We therefore initiated a large-scale international study to reanalyze and delineate the transcriptome landscape of 1,223 BCP ALL cases using RNA sequencing. Fourteen BCP ALL gene expression subgroups (G1 to G14) were identified. Apart from extending eight previously described subgroups (G1 to G8 associated with MEF2D fusions, TCF3–PBX1 fusions, ETV6–RUNX1–positive/ETV6–RUNX1–like, DUX4 fusions, ZNF384 fusions, BCR–ABL1/Ph–like, high hyperdiploidy, and KMT2A fusions), we defined six additional gene expression subgroups: G9 was associated with both PAX5 and CRLF2 fusions; G10 and G11 with mutations in PAX5 (p.P80R) and IKZF1 (p.N159Y), respectively; G12 with IGH–CEBPE fusion and mutations in ZEB2 (p.H1038R); and G13 and G14 with TCF3/4–HLF and NUTM1 fusions, respectively. In pediatric BCP ALL, subgroups G2 to G5 and G7 (51 to 65/67 chromosomes) were associated with low-risk, G7 (with ≤50 chromosomes) and G9 were intermediate-risk, whereas G1, G6, and G8 were defined as high-risk subgroups. In adult BCP ALL, G1, G2, G6, and G8 were associated with high risk, while G4, G5, and G7 had relatively favorable outcomes. This large-scale transcriptome sequence analysis of BCP ALL revealed distinct molecular subgroups that reflect discrete pathways of BCP ALL, informing disease classification and prognostic stratification. The combined results strongly advocate that RNA sequencing be introduced into the clinical diagnostic workup of BCP ALL.

Description: Background: Pretreatment status assessment at diagnosis in patients with chronic myeloid leukemia in chronic phase (CML-CP) is more important for successful treatment in the tyrosine kinase inhibitors (TKIs) era. For instance, the Charlson comorbidity index (CCI) score is considered the useful tool for predicting overall survival (OS) in patients with CML treated with imatinib (IM) (Saussele S et al., 2015). However, the effect of CCI in patients with CML treated with second-generation TKI (2nd TKI) and clinical practice setting was unknown. This study aimed to evaluate the effect of pretreatment statuses, including CCI, on OS of participants of the New TARGET observational study 1 conducted by the Japanese Society of Hematology (JSH). Methods: Patients newly diagnosed with CML-CP were registered to the New TARGET observational study 1 from April 2010 to March 2013. They were treated with TKIs (IM, nilotinib [NIL], or dasatinib [DAS]) after registration. Exclusion criteria were defined as follows: (1) accelerated phase/blast crisis (AP/BC) CML and (2) pretreatment with interferon-alfa, any TKIs, or hydroxyurea for more than 3 months, or allogeneic hematopoietic stem cell transplantation before registration. Other details of the protocol were previously reported (Kizaki et al., 2019). Patients were classified into CCI risk groups of 2, 3, and ≥4 for analysis. The New TARGET observational study 1 was supported by research fundings from Novartis Pharmaceuticals and Bristol-Myers Squibb to JSH. This subgroup analysis was approved by the institutional review board of the Hamamatsu University School of Medicine. The chi-square test was used to compare clinical characteristics for categoricaldata and the Wilcoxon rank-sum test for continuous data. OS was calculated using the Kaplan-Meier method and compared by the log-rank test. Gray's test was used to compare cumulative incidence curves. Cox proportional hazard analyses were performed to determine prognostic indicators of OS. The Wald test was used to assess the prognostic significance of a candidate variable. Statistical analyses were performed using EZR, a graphical user interface for R (Kanda Y, 2013). Results: Among 506 enrolled patients, 475 with a median age of 56 years were assessable. The median follow-up period was 5.4 years. In total, 103 patients (21.7%) had various types of comorbidities, with diabetes mellitus, mild liver disease, peripheral vascular disease, myocardial infarction, renal disease, and peptic ulcer disease (7.3%, 4.1%, 3.2%, 2.6%, 2.2%, and 2.2%, respectively) as the most common. The lowest CCI score was 2 owing to CML. CCI scores were stratified as follows: 2, 372 patients (78%); 3, 74 patients (16%); and ≥4, 29 patients (6%). Higher CCI scores were significantly associated with older age (P

Description: Background: Bosutinib, a Src/Abl tyrosine kinase inhibitor, is approved at a starting dose of 500 mg once daily (QD) in many countries, including Japan, for patients with Philadelphia chromosome-positive (Ph+) chronic phase (CP), accelerated phase (AP), or blast phase (BP) chronic myeloid leukemia (CML) after prior therapy. The indication for bosutinib was expanded to patients with newly diagnosed CP CML, at a starting dose of 400 mg QD, in 2017 by the US Food and Drug Administration and in 2018 by the European Medicines Agency. Approval of first-line bosutinib for CP CML was based on data from the global phase 3 BFORE trial, which demonstrated a significantly higher major molecular response (MMR) rate at Month 12 with bosutinib vs imatinib in patients with Ph+ CP CML and e13a2/e14a2 transcripts (primary endpoint; 47.2% vs 36.9%; 2-sided P=0.02). We conducted a phase 2 study to evaluate the efficacy, safety, and pharmacokinetics (PK) of bosutinib in Japanese patients with newly diagnosed CP CML. Methods: In this open-label, single-arm study (NCT03128411), Japanese patients ≥20 years of age with a molecular diagnosis of CP CML within 6 months, Eastern Cooperative Oncology Group performance status 0 or 1, adequate renal and hepatic function, and no prior treatment for CML (hydroxyurea within 6 months permitted) received bosutinib at a starting dose of 400 mg QD. The primary endpoint was MMR at Month 12 in the modified as-treated population, which included patients who were Ph+ and had e13a2/e14a2 transcripts. A total of 60 patients was required in the modified as-treated population for the study to have 〉82% power to reject the null hypothesis (25% MMR rate at Month 12) and accept the alternative hypothesis (40% MMR rate at Month 12) with a 1-sided ∝-level of 5%. Secondary endpoints included MMR and complete cytogenetic response (CCyR) by Month 12, event-free survival (EFS), overall survival, safety, and PK. Results: In all, 60 Japanese patients with CP CML were treated with bosutinib; all patients were Ph+ and had e13a2/e14a2 transcripts and were included in the modified as-treated population analyzed for efficacy. Median age was 55 years (range 20-83), 60.0% of patients were male, and 45.0%, 43.3%, and 11.7% had low-, intermediate-, and high-risk Sokal scores, respectively. Median duration of follow-up was 16.6 months (range 11.1-21.9), and median duration of bosutinib treatment was 15.3 months (range 0.3-21.9). After 12 months of follow-up, 42 (70.0%) patients remained on bosutinib; 17 (28.3%) discontinued due to adverse events (AEs) and 1 (1.7%) due to physician decision. Median dose intensity was 354.7 mg/day (range 95.3-494.1). The MMR rate at Month 12 was 55.0% (2-sided 90% confidence interval [CI] 44.4-65.6); the test of the null hypothesis was rejected (1-sided P

Description: Introduction: Romiplostim is a thrombopoietin mimetic protein that increases platelet production. Romiplostim has already been approved in numerous countries for treatment of immune thrombocytopenia. We previously reported a clinical trial to identify the dosage of romiplostim in aplastic anemia (AA) patients with thrombocytopenia refractory to immunosuppressive therapy (IST). Platelet, erythroid, and neutrophil responses were achieved at high rates with the initial dose at 10 μg/kg in the previous studies (Lee JW et al, ASH2016, 2017). Based on these findings, we conducted a Phase 2/3 clinical study in Japan and Korea for the purpose of evaluating the efficacy and safety of romiplostim in patients with AA who were ineligible or refractory to IST. This abstract shows the efficacy and safety results as of cut-off date (17 Nov 2017), which will be updated with 1-year follow-up result on the ASH2018 annual meeting. Methods: This study was a multi-center, open-label, intra-individual dose adjustment study in adult AA patients in Japan and Korea (NCT02773290). Patients with AA who were ineligible or refractory to IST and having thrombocytopenia with platelet count equal to or less than 30×109/L were enrolled in this study. The dosage of romiplostim was set at the initial level of 10 μg/kg and fixed for the first 4 weeks. The dose was adjusted from 5 to 20 μg/kg according to dose adjustment procedure. Patients who did not achieve a platelet response after the treatment with 20 μg/kg during 8 consecutive weeks were withdrawn from the study. The primary endpoint was the proportion of patients achieving a hematological response (any of the platelet, erythroid, and neutrophil response) at Week 27. Each response was defined as Table1. The secondary endpoints included the proportion of patients achieving hematological response at Week 53; and the time from the first romiplostim administration to hematological response; and the proportion of patients with transfusion independence or decreased platelet transfusion requirement among patients receiving platelet transfusion within 8 weeks prior to the first romiplostim administration. The bone marrow and cytogenetic analyses were performed prior to enrollment and every 6 months after treatment. Results: Of 46 patients with screening, a total of 31 patients (24 Japanese patients, and 7 Korean patients) were enrolled in this study. The median age was 46.0 years old (range: 20-78 years old). All patients had received at least 1 AA treatment, most of which were antithymocyte globulin (71.0%) and cyclosporin (96.8%). As of cut-off date (17 Nov 2017), 28 patients completed assessment of Week 27, and 18 patients completed assessment of Week 53. Three patients discontinued before Week 27, and 1 patient discontinued after Week 27 but before Week 53. In total (31 patients), 26 patients (83.9% [95% CI; 66.3%, 94.5%]) achieved any hematological response at Week 27. Eight patients (25.8%) achieved tri-lineage hematological response at Week 27. The median days to reach any hematological response were 37.0 [95% CI; 36.0, 44.0] days. Of the patients who depended on platelet transfusion before romiplostim administration (15 patients), 12 patients (80.0%) achieved transfusion independence or showed a reduction of transfusion requirements until Week 53. The frequently reported adverse events (AEs) were nasopharyngitis (38.7%) followed by upper respiratory tract infection (22.6%); pyrexia (19.4%); headache (16.1%); and diarrhoea (12.9%). The frequently reported drug-related AEs were headache (12.9%) followed by muscle spasms (9.7%); and alanine aminotransferase increased, fibrin D dimer increased, malaise, and pain in extremity (each 6.5%). In bone marrow test, 2 patients showed abnormality in karyotypes after romiplostim dosing. Monosomy 7 was shown at Week16 in 1 patient who had been receiving granulocyte-colony stimulating factor prior to the start of romiplostim. This patient did not show the transformation into acute myeloblastic leukemia and/or myelodysplastic syndrome. The other patient showed the gains of chromosomes 3, 4, 14, 16, 17, 19 and 21 at Week 27, but did not show any abnormality at Week 53. None of patient discontinued the study because of AE or karyotype abnormality. Conclusion: These results demonstrate that romiplostim is quite effective and well-tolerated in adult patients with AA ineligible or refractory to IST. Disclosures Tomiyama: Sysmex Corporation: Consultancy; Kyowa Hakko Kirin Co., Ltd.: Honoraria; Chugai Pharmaceutical Co., Ltd.: Honoraria; Novartis Pharma Co., Ltd.: Honoraria, Membership on an entity's Board of Directors or advisory committees. Lee:Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria, Research Funding. Miyazaki:Kyowa Hakko Kirin Co., Ltd.: Honoraria, Research Funding; Novartis Pharma Co., Ltd.: Honoraria. Usuki:Novartis: Speakers Bureau; Ono Pharmaceutical: Speakers Bureau; Chugai Pharmaceutical: Speakers Bureau; Takeda Pharmaceutical: Speakers Bureau; Janssen Pharmaceutical K.K: Research Funding; Pfizer Japan: Research Funding, Speakers Bureau; Boehringer-Ingelheim Japan: Research Funding; Sumitomo Dainippon Pharma: Research Funding, Speakers Bureau; Daiichi Sankyo: Research Funding; Celgene Corporation: Research Funding, Speakers Bureau; SymBio Pharmaceuticals Limited.: Research Funding; Shire Japan: Research Funding; Sanofi K.K.: Research Funding; GlaxoSmithKline K.K.: Research Funding; Kyowa Hakko Kirin Co., Ltd.: Research Funding; Otsuka Pharmaceutical Co., Ltd.: Research Funding; Astellas Pharma Inc.: Research Funding; Nippon Shinyaku: Speakers Bureau; Mochida Pharmaceutical: Speakers Bureau; MSD K.K.: Speakers Bureau. Kizaki:Nippon Shinyaku,: Research Funding, Speakers Bureau; Celgene: Research Funding, Speakers Bureau; Bristol-Myers Squibb: Research Funding, Speakers Bureau; Novartis: Speakers Bureau. Sawa:Celgene Corporation: Honoraria; Takeda Pharmaceutical Company Limited: Honoraria; Bristol-Myers Squibb: Honoraria; Novartis International AG: Honoraria; CHUGAI PHARMACEUTICAL CO., LTD.: Honoraria; Mundipharma K.K.: Honoraria. Yonemura:Alexion Pharma: Honoraria, Research Funding. Keta:Kyowa Hakko Kirin Co., Ltd.: Employment. Matsuda:Novartis Pharma K. K.: Honoraria; GlaxoSmithKline K.K.: Honoraria; Chugai Pharmaceutical Co, Ltd.: Honoraria; Kyowa Hakko Kirin Co, Ltd.: Honoraria; Sumitomo Dainippon Pharma Co., Ltd.: Honoraria; Nippon Shinyaku Co., Ltd.: Honoraria; Celgene Corporation: Honoraria; Alexion Pharmaceuticals, Inc.: Honoraria; Sanofi K.K.: Honoraria; Beckman Coulter K.K.: Honoraria. Mitani:Kyowa Hakko Kirin Co., Ltd.: Consultancy, Research Funding, Speakers Bureau; Bristol-Myesr Squibb: Research Funding, Speakers Bureau; Celgene: Speakers Bureau; Chugai: Research Funding; Astellas: Research Funding; Sumitomo Dainippon: Research Funding; Novartis: Research Funding; Toyama Chemical: Research Funding. Nakao:Novartis: Honoraria; Kyowa Hakko Kirin Co., Ltd.: Honoraria; Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria.

Description: It has long been known that lymphopoiesis is transiently suppressed during pregnancy, and that this can be experimentally simulated by treatment with estrogen. Indeed, sensitivity to estrogen made it possible to identify very primitive lymphoid cells in the Lin- c-kitHi Sca-1+ fraction that is enriched with hematopoietic stem cells (HSC) and multipotent progenitors of mouse bone marrow. However, analyses showing how the earliest events in lymphopoiesis is suppressed in those circumstances have not been performed. Hematopoietic and environmental cells are both potential hormone targets and, because of this complexity, very little has been known regarding mechanisms. In the present study, we performed high resolution analysis using RAG-1/GFP reporter mice and confirmed that early lymphoid progenitors (ELP) in the Lin-c-kitHi Sca-1+ fraction are particularly depressed in pregnancy or after estrogen injection. The Lin- c-kitLo fraction containing common lymphoid progenitors (CLP)/pro-lymphocytes was very sensitive to estrogen in stroma-free serum-free culture, but earlier stages of lymphopoiesis seemed to be blocked in vivo. Thus, we focused on identifying mechanisms involving bone marrow environment. Two independent strategies with macroarrays or differential display-PCR were used to isolate stromal cell genes that were both estrogen regulated and associated with inability to support B lymphopoiesis. We have identified secreted frizzled related protein 1 (sFRP1) as an estrogen inducible gene, and its expression corresponded to inability to support lymphopoiesis. This member of the complex Wnt family has been previously described as both an agonist and an antagonist of canonical, β-catenin dependent signaling. We found that sFRP1, like recombinant Wnt3a, stimulated the canonical pathway in the Lin- c-kitHi Sca-1+ fraction, and blocked progression in the B lymphocyte lineage even when exogenous Wnt ligands were not provided. The suppressive effects of sFRP1 and Wnt3a on B lymphopoiesis were canceled out when both were present simultaneously. To better understand the vulnerability of early progenitors to the Wnt signaling, we examined the expression pattern of Frizzled receptors. Interestingly, the HSC-enriched fraction (Lin- c-kitHi Sca-1+ IL-7Rα-RAG-1/GFP-) highly expressed 7 out of 9 Frizzled receptors, which markedly declined as they differentiated to ELP (Lin- c-kitHi Sca-1+ IL-7Rα- RAG-1/GFP+) and CLP (Lin- c-kitLo Sca-1Lo/- IL-7Rα+). Myelo-erythroid progenitors were less affected by sFRP1 in culture, suggesting that it is similar to estrogen with respect to lineage specificity. Bone-lining stromal cells express sFRP1 and the transcripts were elevated in bone marrow by pregnancy or estrogen injection. In summary, these observations implicate sFRP1 as a possible mediator in hormone regulation of the earliest events in lymphopoiesis.

Description: Substitution of valine (Val) for aspartic acid (Asp) at codon 814 constitutively activates murine c-kit receptor tyrosine kinase (KIT), and Asp816Val mutation, corresponding to murine Asp814Val mutation, is found in patients with mastocytosis and acute myelocytic leukemia. However, the signal transduction pathways responsible for oncogenesis by the Asp814Val mutant (KITVal814) are not fully understood. To examine the oncogenic signal transduction of KITVal814, we converted 20 tyrosine (Tyr) residues to phenylalanine (Phe) in the cytoplasmic domain of KITVal814 or deleted the C-terminal region containing 2 other tyrosine residues (Del). Among various KITVal814- derived mutants, KITVal814-Tyr719Phe and KITVal814-Delseverely impaired receptor tyrosine phosphorylation and association with the p85 subunit of phosphatidylinositol 3′-kinase (p85PI3-K). Moreover, KITVal814-Tyr719Pheand KITVal814-Del failed to induce ligand-independent growth in Ba/F3 cells, indicating that Tyr719, the binding site for p85PI3-K, and the C-terminal region are indispensable for factor-independent growth by KITVal814. Although the C-terminal region was also required for ligand-dependent growth by wild-type KIT (KITWT), the Tyr719Phe substitution had negligible effects on ligand-dependent growth by KITWT. Furthermore, dominant-negative PI3-K significantly inhibited ligand-independent growth by KITVal814. These results demonstrate that Tyr719 is crucial for constitutive activation of KITVal814, but not for the ligand-induced activation of KITWT, and that the downstream signaling of PI3-K plays an important role in ligand-independent growth and tumorigenicity by KITVal814, thereby suggesting that KITVal814 is a unique activating mutation that leads to a distinguishable function from the effects of KITWT.

Description: Promyelocytic leukemia protein PML acts as a tumor suppressor, whereas its chimeric mutant promyelocytic leukemia/retinoic acid receptorα (PML/RARα) causes acute promyelocytic leukemia (APL). Because PML has been shown to form transcription-regulatory complexes with various molecules, we speculated that PML and/or PML/RARα might affect signal transducer and activator of transcription 3 (STAT3) activity, which plays a crucial role in granulocyte colony-stimulating factor (G-CSF)–induced growth and survival of myeloid cells. In luciferase assays, PML inhibited STAT3 activity in NIH3T3, 293T, HepG2, and 32D cells. PML formed a complex with STAT3 through B-box and COOH terminal regions in vitro and in vivo, thereby inhibiting its DNA binding activity. Although PML/RARα did not interact with STAT3, it dissociated PML from STAT3 and restored its activity suppressed by PML. To assess the biologic significance of these findings, we introduced PML and PML/RARα into interleukin-3 (IL-3)–dependent Ba/F3 cells expressing the chimeric receptor composed of extracellular domain of G-CSF-R and cytoplasmic domain of gp130, in which gp130-mediated growth is essentially dependent on STAT3 activity. Neither PML nor PML/RARα affected IL-3–dependent growth of these clones. By contrast, gp130-mediated growth was abrogated by PML, whereas it was enhanced by PML/RARα. These results reveal new functions of PML and PML/RARα and suggest that dysregulated STAT3 activity by PML/RARα may participate in the pathogenesis of APL.

Description: Abstract 3899 DCs play important roles in tumor immunology. In patients with myeloid neoplasm such as AML, CML, and MDS, there are spontaneously-differentiated DCs in vivo from leukemic cells (in vivo leukemic DCs), which are thought to retain leukemia-associated antigens (LAAs). Therefore it is postulated that in vivo leukemic DCs affect host immune responses in a LAA-specific manner. However, there have been only a few concise examinations about their subsets, maturation state, or function. DC differentiation is crucially regulated by STAT3/5 and in part associated with myeloid differentiation. Myeloid neoplasm develops from hematopoietic stem/progenitors cells (HSCs/HPCs) bearing various gene abnormalities, named class I and class II mutations, which contribute to growth augmentation and myeloid differentiation block, respectively. Therefore, this study tested the hypothesis that myeloid neoplasm-related gene abnormalities may affect steady-state DC differentiation from HSCs/HPCs. We first established an efficient and reproducible in vitro FLT3-ligand (FL)-mediated DC (FL-DC) differentiation system from murine HSCs/HPCs-rich population, lineage-, Sca-I+, c-Kithigh cells (LSKs). After 9 days of culture, the proportion of whole FL-DCs (CD11c+ cells), pDCs (CD11c+B220+ cells) and cDCs (CD11c+B220- cells) were reproducibly constant (whole FL-DCs; 87.5 ± 0.9 %, pDCs; 30.4 ± 6.4 %, cDCs; 57.1 ± 6.4 %, pDCs/cDCs ratio; 0.55 ± 0.19). FL-DCs from LSKs efficiently stimulated allogeneic CD4+ T cells. FL-DCs from LSKs yielded high amount of type I interferon by CpG-stimulation. These results indicated that our culture method efficiently and reproducibly induced functionally competent FL-DCs from LSKs. Next, we transduced various myeloid neoplasm-related gene abnormalities, named class I and II mutations, into LSKs, and then analyzed their effects on FL-DC differentiation from LSKs. We selected FLT3-ITD, FLT3-TKD, constitutive active (CA)-N-Ras, c-Kit-TKD, TEL/PDGFRβ, and FIP1L1/PDGFRα as representative of class I mutations, and AML1/ETO, PML/RARα, CBFβ/MYH11, and AML1dC as representative of class II mutations, respectively (Table). All class II mutations consistently showed mild impairment of FL-DCs keeping comparable pDCs/cDCs ratio with control. In contrast, class I mutations induced the heterogeneous impairment of FL-DCs. Both FLT3-ITD and FLT3-TKD showed a mild decrease in whole FL-DCs retaining comparable pDCs/cDCs ratio with control. CA-N-Ras showed the mild impairment of whole FL-DCs with a severe decrease in pDCs/cDCs ratio. c-Kit-TKD, TEL/PDGFRβ, and FIP1L1/PDGFRα displayed a severe decrease in both whole FL-DCs and their pDCs/cDCs ratio. whole FL-DCs (%) pDCs/cDCs ratio mock 85.4 ± 3.0 0.50 ± 0.21 FLT3-WT 46.1 ± 5.7 0.42 ± 0.19 FLT3-ITD 30.6 ± 14.5 0.60 ± 0.23 FLT3-TKD 29.4 ± 10.0 0.82 ± 0.48 CA-N-Ras 55.2 ± 6.3 0.02 ± 0.01 c-Kit-TKD 9.4 ± 5.7 0.19 ± 0.10 TEL/PDGFRβ 13.3 ± 2.9 0.05 ± 0.04 FIP1L1/PDGFRα 14.8 ± 4.7 0.03 ± 0.04 AML1/ETO 51.6 ± 8.4 0.63 ± 0.11 PML/RARα 35.6 ± 3.0 0.60 ± 0.30 CBFβ/MYH11 40.9 ± 17.3 0.48 ± 0.27 AML1dC 55.8 ± 7.9 0.29 ± 0.15 Time course study showed that each differentiation pattern of CA-N-Ras, c-Kit-TKD, TEL/PDGFRβ, or FIP1L1/PDGFRα was quite different from that of control. The analysis of the effects of signal transduction molecules revealed that CA-STAT5 and CA-MEK1, but not CA-STAT3 and CA-PI3 kinase, severely inhibited pDC differentiation. These data suggested that class I mutations differentially regulated FL-DC differentiation, possibly via their individual sets and magnitude of each constitutive active signal transduction pathway. We next investigated whether this DC differentiation heterogeneity seen in class I mutations influence on DC maturation. Overall, surface expressions of MHC II, CD80, and CD86 on whole FL-DCs induced by class I mutations were higher than those induced by control. FLT3-ITD-expressing FL-DCs, showing relatively immature phenotype among class I mutations, stimulated allogeneic CD4+ T cells comparably with control. CA-N-Ras-expressing FL-DCs, showing relatively mature phenotype among class I mutations, more efficiently stimulated allogeneic CD4+ T cells. These data suggested that class I mutations caused heterogeneous maturation and function of FL-DC. In conclusion, FL-DC differentiation from LSKs, its maturation, and function were affected in a myeloid neoplasm-related gene abnormality-specific manner. Disclosures: No relevant conflicts of interest to declare.

Description: Cell migration requires a dynamic interaction between the cell, its substrate, and the cytoskeleton-associated motile apparatus. Integrin-associated protein (IAP)/CD47 is a 50-kd cell surface protein that is physically associated with β3 integrins and that modulates the functions of β3 integrins in various cells. However, in B-lymphocytes that express β1 integrins but few β3 integrins, the roles of IAP/CD47 remain to be determined. Cross-linking of IAP/CD47 by the immobilized anti-IAP/CD47 monoclonal antibody (mAb) B6H12, but not 2D3, produced signals to promote polarization with lamellipodia, a characteristic morphology during leukocyte migration, in pre-B and mature B-cell lines (BALL, Nalm6, ONHL-1, Daudi), but not in myeloma cell lines (RPMI8226, OPM-2). In the presence of the immobilized fibronectin (FN), soluble B6H12 could increase the rate of the polarization and activate migratory activity of BALL cells to FN in a transwell filter assay. Furthermore, the dominant-negative form of CDC42 completely blocked B6H12-induced morphologic and functional changes without inhibiting phorbol 12-myristate 13-acetate–induced spreading on FN in BALL cells, whereas the dominant-negative form of Rac1 inhibited all these changes. These findings demonstrate that in B-lymphocytes, IAP/CD47 may transduce the signals to activate the migratory activity, in which CDC42 may be specifically involved, and that IAP/CD47 shows synergistic effect with 4β1 on B-cell migration. These findings would provide new insight into the role of IAP/CD47 on B-cell function.