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Expression of the tumor suppressor gene NR4A3 is silenced in the blasts of acute myeloid leukemia (AML), irrespective of the karyotype. Although the transcriptional reactivation of NR4A3 is considered to have a broad-spectrum anti-leukemic effect, the therapeutic modalities targeting this gene have been hindered by our minimal understanding of the transcriptional mechanisms regulating its expression, particularly in human AML. Here we show the role of intragenic DNA hypermethylation in reducing the expression of NR4A3 in AML. Bisulfite sequencing analysis revealed that CpG sites at the intragenic region encompassing exon 3 of NR4A3, but not the promoter region, are hypermethylated in AML cell lines and primary AML cells. A DNA methyltransferase inhibitor restored the expression of NR4A3 following a reduction in DNA methylation levels at intragenic CpG sites. The in silico data revealed an enrichment of H3K4me1 and H2A.Z at exon 3 of NR4A3 in human non-malignant cells but that was excluded specifically in leukemia cells with CpG hypermethylation. This suggests that exon 3 represents a functional regulatory element involved in the transcriptional regulation of NR4A3. Our findings improve the current understanding of the mechanism underlying NR4A3 silencing and facilitate the development of NR4A3-targeted therapy.

TO THE EDITOR: Polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes (POEMS) syndrome is a rare plasma cell disorder additionally characterized by extravascular volume overload, sclerotic bone lesions, and plasmacytomas. Although high-dose melphalan followed by

Polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes (POEMS) syndrome is a rare plasma cell dyscrasia characterized by polyneuropathy, organomegaly, endocrinopathy, extravascular fluid overload, M protein, and a myriad of skin changes. The pathogenesis is poorly understood, but monoclonal plasma cells are λ-restricted and these immunoglobulin λ light chain variable (IGLV) region genes are derived from only two germlines, either IGLV1-44 or 1-40. Here we analyzed the clonal IGLV gene rearrangements of genomic DNA samples of bone marrow mononuclear cells using next-generation sequencing (NGS) to understand the clonal composition of IGLV genes in patients with POEMS syndrome (n = 30). The dominant IGLV gene rearrangement of POEMS syndrome-specific germline sequences were significantly increased in 11 POEMS patients (36.7%; IGLV1-44: n = 9, IGLV1-40: n = 2). In some cases, IGLV gene rearrangement clone was not detected as significant increase but was detected using cDNA samples by heteroduplex (HD) analysis and Sanger sequencing, suggesting that the quite small number of monoclonal plasma cells may produce large quantity of mRNA of monoclonal proteins. However, significant increase of dominant clone sizes was not directly linked to the initial disease status. On the other hand, in cases with significantly increased dominant clones, they decreased and increased accompanying with disease remission and relapse. These data demonstrate that monoclonal plasma cells are related to the pathogenesis of POEMS syndrome.

Severe acute lung injury is a rare but life-threatening complication associated with bortezomib. We report a patient with multiple myeloma who developed a severe diffuse alveolar hemorrhage (DAH) immediately after the first bortezomib administration. The patient was suspected to have pulmonary involvement of myeloma, which caused DAH after rapidly eradicating myeloma cells in the lungs with bortezomib. Rechallenge with bortezomib was performed without recurrent DAH. In patients with multiple myeloma who manifest abnormal pulmonary shadow, we should be aware of early-onset severe DAH after bortezomib administration, which might be due to pulmonary involvement of myeloma cells.

Thrombopoietin-receptor agonists have been recently introduced for a second-line treatment of immune thrombocytopenia (ITP). Splenectomy has tended to be avoided because of its complications, but the response rate of splenectomy is 60–80% and it has still been considered for steroid-refractory ITP. We performed partial splenic embolization (PSE) as an alternative to splenectomy. Between 1988 and 2013, 91 patients with steroid-resistant ITP underwent PSE at our hospital, and we retrospectively analyzed the efficacy and long-term outcomes of PSE. The complete response rate (CR, platelets > 100 × 109/L) was 51% (n = 46), and the overall response rate (CR plus response (R), > 30 × 109/L) was 84% (n = 76). One year after PSE, 70% of patients remained CR and R. The group with peak platelet count after PSE ≥ 300 × 109/L (n = 29) exhibited a significantly higher platelet count than the group with platelet count

Myeloid sarcoma (MS) is an extramedullary myeloid tumor that sometimes presents with antedating systemic leukemia, leading physicians to the misdiagnosis of lymphoma. CD25 is expressed in 13% of patients with acute myeloid leukemia (AML), and its expression is associated with FLT3-ITD mutations, an elevated serum soluble interleukin 2 receptor (sIL-2R) level and a lower survival rate. However, there are no reports concerning the relationship between MS and the CD25 expression. We herein report a case of AML accompanied by thoracic epidural MS with a high CD25 expression, the FLT3-ITD mutation and an extremely elevated serum sIL-2R level in a 59-year-old man who presented with paraplegia.

Imatinib mesylate has revolutionized the treatment of chronic myeloid leukemia (CML) by providing excellent disease control and showing satisfactory tolerance. Despite the achievement of complete s...

Infections of the central nervous system (CNS) with varicella zoster virus (VZV) is a rare occurrence after allogeneic hematopoietic stem cell transplantation. We herein report a case of VZV meningitis, radiculitis and myelitis that developed 8 months after cord blood transplantation, shortly after the cessation of cyclosporine and low-dose acyclovir. Although treatment with acyclovir did not achieve a satisfactory response, the patient was successfully treated with foscarnet. Our report indicates that VZV infection should be considered in allo-hematopoietic stem cell transplantation (HSCT) patients with CNS symptoms and that foscarnet may be effective for the treatment of acyclovir-resistant VZV infections of the CNS. The development of optimal prophylactic strategies and vaccination schedules may eradicate post-transplant VZV disease.

Although autologous stem cell transplantation can achieve excellent responses in patients with POEMS syndrome, the optimal regimen for peripheral blood stem cell (PBSC) collection is still controversial. We retrospectively investigated the safety and efficacy of 41 PBSC collecting procedures in 37 patients with POEMS syndrome. PBSC mobilization was performed using cyclophosphamide + granulocyte colony–stimulating factor (G-CSF) (CG, n = 14) or G-CSF alone (G, n = 27). Twelve (85.7%) patients in the CG group and all (100%) patients in the G group received induction chemotherapy before PBSC collection. The proportions of good mobilizers (≥2.0 × 106 CD34+ cells/kg) were comparable between the 2 groups (CG versus G: 78.6% versus 70.4%, P = .71). Two (14.3%) patients in the CG group developed severe capillary leak symptoms during the PBSC mobilization period, whereas no patient in the G group experienced severe adverse events. Appropriate induction therapies followed by the G-CSF monotherapy compose an optimal strategy for PBSC collection.

A 34-year-old man who had been referred to our hospital was diagnosed with acute promyelocytic leukemia (APL). All-trans retinoic acid (ATRA), oral administration, was initiated. On day 25, he developed fever and respiratory distress with bilateral pulmonary infiltrates, suggesting differentiation syndrome (DS) caused by ATRA. These symptoms showed amelioration after discontinuing ATRA and initiating methylprednisolone. ATRA was re-started on day 29 at half the original dose because of residual APL blasts. The patient subsequently developed fever, severe stomatitis, and oropharyngeal ulcers, which persisted even after discontinuing ATRA. On day 48, he suddenly developed severe abdominal pain with free air, observable on an abdominal X-ray, and underwent emergency ileocecal resection. Pathological examination of the resected ileocecal intestines revealed multiple ulcers and perforations. No leukemic cell infiltration was observed. In this case, only ATRA was administered for APL treatment. These findings suggest that ileocecal ulcerations and perforations, as well as oropharyngeal ulcers, might have been caused by DS or ATRA. Furthermore, DNA typing of the HLA-B locus revealed that the patient had HLA-B51 associated with Behçet's disease. Therefore, hypercytokinemia with DS might have induced Behçet's disease-like symptoms, including stomatitis and ileocecal perforation, complications that are particularly observed in patients with HLA-B51.

Although tyrosine kinase inhibitors (TKIs) have significantly improved the prognosis of chronic myeloid leukemia (CML), the ability of TKIs to eradicate CML remains uncertain and patients must continue TKI therapy for indefinite periods. In this study, we performed whole-exome sequencing to identify somatic mutations in 24 patients with newly diagnosed chronic phase CML who were registered in the JALSG CML212 study. We identified 191 somatic mutations other than the BCR-ABL1 fusion gene (median 8, range 1–17). Age, hemoglobin concentration and white blood cell counts were correlated with the number of mutations. Patients with mutations ⩾6 showed higher rate of achieving major molecular response than thoseP=0.0381). Mutations in epigenetic regulator, ASXL1, TET2, TET3, KDM1A and MSH6 were found in 25% of patients. TET2 or TET3, AKT1 and RUNX1 were mutated in one patient each. ASXL1 was mutated within exon 12 in three cases. Mutated genes were significantly enriched with cell signaling and cell division pathways. Furthermore, DNA copy number analysis showed that 2 of 24 patients had uniparental disomy of chromosome 1p or 3q, which disappeared major molecular response was achieved. These mutations may play significant roles in CML pathogenesis in addition to the strong driver mutation BCR-ABL1.

Th e prognosis of t(9;22), Philadelphia chromosome-positive, acute lymphoblastic leukemia (Ph ALL) is poor. Despite high complete response (CR) rates with intensive chemo- therapy (Cx) regimens, the response is only transient. Th is is attributed to the requirement for administering allogeneic hematopoietic stem cell transplant (HCT) (1). Concurrently, the prognosis is very poor for patients with no indications for transplant, particularly the elderly. Th e relatively recent introduction of the selective tyrosine kinase inhibitor (TKI) imatinib mesylate (IM) for Cx has signifi cantly improved the prognosis of patients with Ph ALL (2,3), and has improved outcomes after allogeneic HCT (4,5). However, we are aware of only one report that compares prognosis between adult patients treated with intensive Cx followed by HCT and those treated with Cx alone (3). Th erefore, we retrospectively analyzed patients with Ph ALL treated with IM at our institution and compared treatment outcomes between HCT and Cx alone. Twenty-two patients with Ph ALL treated with IM- combined Cx in our institution from March 2002 to June 2011 were retrospectively evaluated. Patient characteristics are summarized in Table I. Twenty-one patients received intensive Cx according to the protocol of hyper-CVAD (hyperfractionated cyclophosphamide, vincristine, doxo- rubicin, dexamethasone) combined with IM (2) and one patient was treated with the Japan Adult Leukemia Study Group (JALSG) IM-combined regimen Ph ALL202 (3). All patients received IM at a dose of 600 mg orally per day. Patients aged more than 60 years were administered doses of cytotoxic agents reduced by 20 - 30%. Allogeneic HCT was administered to 13 patients (HCT cohort), and nine patients received Cx alone (Cx cohort). All patients in the HCT cohort received a transplant during their fi rst CR. IM or other TKI therapy was not administered after transplant. To quantify the levels of minor and major BCR - ABL mRNA transcripts (encoding p190 and p210 oncoproteins, respectively), real-time quantitative polymerase chain reac- tion (PCR) analysis was used to diagnose Ph ALL. Th e copy number of BCR - ABL mRNA transcripts was normalized to that of GAPDH (glyceraldehyde 3-phosphate dehydroge- nase) and converted to molecules/ μ g RNA. Th e detection threshold for quantifi cation was 50 copies/ μ g RNA, which corresponded to a minimal sensitivity of 10 5 (6). Survival of the patients was determined on 31 December 2012 and analyzed using the Kaplan - Meier method. Statistical tests for diff erences in survival were based on the log-rank test. Overall survival (OS) and event-free survival (EFS) were calculated from the date of diagnosis to the date of death by any cause or according to the last known date of follow-up, and to the date of hematological or molecu- lar relapse or death by any cause or the last known date of follow-up, respectively. Th e cumulative incidence of relapse and treatment-related mortality (TRM) were estimated after adjusting for the competing risk of patient death using Gray ' s method (7). Diff erences in variables were compared using independent t -tests. Fisher ' s exact test was performed when appropriate. All statistical analyses were performed with EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), which is a graphical user interface for R (Th e R Foundation for Statistical Computing, Vienna, Austria; version 1.6-3) (8). Despite a higher median age of the Cx cohort compared with the HCT cohort (60 vs. 39 years of age, p 0.001, Table I), there were no signifi cant diff erences between the progno- ses of the Cx and HCT cohorts (5-year OS, 50.8% vs. 48.4%, p 0.76 (Figure 1(A)), 5-year EFS 38.1% vs. 50.5%, p 0.97). We considered that allogeneic HCT should be given to those patients with Ph ALL who would tolerate it well, explaining the advanced median age in the Cx cohort. Th e 5-year prob- abilities of relapse for the Cx and HCT cohorts were 61.1% and 15.4% ( p 0.07, data not shown), respectively, and the 5-year probabilities of TRM were 0% and 34.1% for the Cx and HCT cohorts ( p 0.07, data not shown), respectively. Th ere were no signifi cant diff erences between white blood cell (WBC) counts and levels of BCR - ABL mRNA transcripts at diagnosis between both cohorts (Table I).

[Backgrounds] POEMS syndrome is a rare plasma cell dyscrasia and its pathogenesis including the significance of monoclonal plasma cells in disease progression is poorly understood. Monoclonal plasma cells only produce λ immunoglobulins, and genes encoding immunoglobulin λ light chain (IGL) V regions are derived from IGLV1-44 or IGLV1-40 germline sequences. Here we analyzed the clonality in IGLV gene rearrangements using next generation sequencing (NGS) to evaluate the significance of monoclonal plasma cell clone size and follow its changes in clinical course to understand the pathogenesis of POEMS syndrome. [Methods] Patients who were diagnosed with POEMS syndrome between November 2006 and October 2015 at Chiba University Hospital were included in the study. As positive controls, 3 multiple myeloma (MM) patients with λ-type monoclonal light chain, and 9 negative control patients were also analyzed. NGS libraries were constructed from genomic DNA samples, extracted from bone marrow mononuclear cells. The IGLV1 and IGLV2 genes were amplified by polymerase chain reaction (PCR) using a 5' primer for the IGLV1/2 framework 3 (FR3) region and 3ʹ consensus primers for the IGLJ1/2/3 joining regions. Multiple samples were pooled, and paired-end 2 × 250 base pair sequencing reactions were carried out using an Illumina MiSeq sequencer. The closest matched germline sequences were determined using the ImMunoGeneTics database. Subsequently, frequencies of each clonotype that were characterized by a unique V-J rearrangement, conserved complementarity determining region 3 (CDR3) anchors and a unique CDR3 amino acid sequence, were calculated. [Results] Twenty-eight patients with POEMS syndrome were enrolled. All the patients had λ-type M protein. The median follow up time of the patients was 24.4 months (range, 3.7 - 113.9). Firstly we analyzed the usage of IGLV germline genes in each case. In 8 cases, the POEMS syndrome-specific germline sequences, IGLV1-40 or IGLV1-44, were dominant; accounting for more than 40% of all germline sequence usage. However, other samples showed minimal or no differences from controls, indicating that the clonal expansion of monoclonal plasma cells is generally low in patients with POEMS syndrome. Analyzing frequencies of the most dominant rearrangement in each germline, the clonal IGLV gene rearrangements of POEMS syndrome-specific germline sequences were significantly increased in 10 POEMS patients (35.7%; IGLV1-44: n = 8, IGLV1-40: n = 2). Significant increase of clone sizes were not directly linked to the initial disease status (vascular endothelial growth factor [VEGF] level and percentage of plasma cells in the bone marrow), overall survival and progression-free survival of POEMS patients. In 12 patients that we were able to follow their clinical courses, the clone size of IGLVgene rearrangements correlated with disease course assessed with serum VEGF level in most cases (n = 8), as they decreased with serum VEGF levels in disease remission and increased with re-elevation of serum VEGF in relapse cases. Clone sizes without significant increase at diagnosis were constantly flat even after achieving disease remission (n = 3). In one case, clone size with significant increase at diagnosis was unchanged even after serum VEGF level decreased (n = 1). Further observation is needed in this case. [Discussion] Considering the cases with significant increase of IGLV rearrangement clones, it was confirmed that clonal light chain gene expression is restricted to the IGLV1-44 and IGLV1-40 germline sequences, as previously reported. IGLV gene rearrangement clone was not detected as significant increase in some cases. Therefore, we speculated that there are certain numbers of patients with POEMS syndrome with extremely low frequency of clone cells. On the other hand, significant increase of clone size did not reflect disease status, suggesting that disease status is not regulated by tumor burden alone. By contrast, in cases with significantly increased clones, clone sizes changed dependiing on the disease status. These data do demonstrate that monoclonal plasma cells are related to the pathogenesis of POEMS syndrome. [Conclusions] Our analysis of IGLV gene rearrangements has demonstrated the association between the size of IGLV gene rearrangement clones and the clinical courses in POEMS syndrome. Disclosures No relevant conflicts of interest to declare.

The expression of NR4A3, which is a member of the gene encoding NR4A orphan nuclear receptor subfamily, has been reported to be commonly silenced in blasts of patients with acute myeloid leukemia (AML), irrespective of karyotype. In line with this finding, Nr4a1-/-/Nr4a3-/- mice rapidly develop AML within one month following birth (Mullican et al., 2007). In addition, Nr4a1+/-/Nr4a3-/- and Nr4a1-/-/Nr4a3+/- mice show myelodysplastic/myeloproliferative neoplasms (Ramirez-Herrick et al., 2011), suggesting that NR4A3 functions as a tumor suppressor gene in myeloid malignancies. The extremely short latency of AML development in Nr4a1-/-/Nr4a3+/- mice indicates that silencing these tumor suppressors is sufficient to induce AML and that NR4A3 has a crucial role in the pathogenesis of AML. Thus, unveiling the molecular mechanism that regulates NR4A3 expression in AML would facilitate the development of novel therapies, including transcriptional reactivation of the gene. However, the therapeutic modalities targeting NR4A3 have been hindered by our minimal understanding of the mechanism underlying reduced NR4A3 expression, particularly in human AML cells. Abnormal epigenetic regulation is a common mechanism in the pathogenesis of several types of cancers. For instance, the expression of several tumor suppressor genes, such as p16 and MLH1, is repressed due to DNA hypermethylation at their promoter regions. Given that loss-of-function mutations in NR4A3 have not been reported in AML to date, we hypothesized that DNA hypermethylation contributes to a reduction in NR4A3 expression in AML. To test our hypothesis, we analyzed DNA methylation status of NR4A3 in human AML cells. We first compared the level of NR4A3 expression in eight human AML cell lines and two human primary AML samples, with that in CD34+ mononuclear bone marrow (BM) cells from healthy human controls. As expected, the expression of NR4A3 was markedly reduced in all of the AML cell lines and primary AML cells compared with that in the cells of the healthy controls. To evaluate the function of NR4A3 in human AML cells, we ectopically overexpressed NR4A3 in a human AML cell line (NB4 cells). The growth of NR4A3 -overexpressing NB4 cells was remarkably compromised compared with that of the controls, suggesting a tumor suppressive function of NR4A3 in both human AML and murine cells. To investigate the DNA methylation status of NR4A3, we performed bisulfite sequencing assays using eight human AML cell lines (HL60, NB4, Kasumi, TF1, U937, K562, MOLM13, and THP1) as well as CD34+ BM cells from healthy controls. Unexpectedly, a hypermethylated CpG site in the promoter region was not detected in any of the cell lines. However, the drastically or mildly methylated region including twenty eight CpGs was identified approximately 3 kb downstream of the transcription start site in six AML cell lines (97.5%, 78.3%, 77.1%, 89.9%, 95.2%, and 86.9% in HL60, NB4, Kasumi, TF1, U937, and K562, respectively) and two mixed lineage leukemia-related cell lines (31.0% and 53.6% in MOLM13 and THP1, respectively), whereas this site was hypomethylated in the controls (n = 2; mean, 12.7%; range, 7.1%-18.2%). To evaluate the contribution of this hypermethylated region to reduced NR4A3 expression, the six AML cell lines with heavily hypermethylated CpGs at NR4A3 and two human primary AML cell samples were treated with a DNA methyltransferase inhibitor (decitabine; DAC) for three or five days. DAC exposure inhibited cell growth and restored the expression of NR4A3 in all AML cell lines and primary cells in a dose- and time-dependent manner. Next, we examined the status of DNA methylation at the CpG site following DAC treatment with bisulfite sequencing assays. The frequencies of methylated CpG in HL60, NB4, and K562 cells was reduced from 97.5% to 53.6%, 78.3% to 68.5%, and 86.9% to 67.5% after DAC treatment, respectively. In contrast, the methylation status in Kasumi, TF1, and U937 cells did not significantly changed after DAC treatment. Our findings in the present study suggest that DNA hypermethylation may partially account for the transcriptional inactivation of NR4A3 in AML. However, the mechanism of reduced NR4A3 expression is complex and variable depending on the genetic background. We are currently working on a more detailed analysis of DNA methylation using human primary cells, by extending the regions for investigation, such as enhancer regions. Disclosures Nakaseko: Novartis: Honoraria, Research Funding, Speakers Bureau; Otsuka: Honoraria, Research Funding; BMS: Honoraria, Research Funding, Speakers Bureau; Pfizer: Honoraria, Research Funding, Speakers Bureau.

Recently, novel agents such as bortezomib and lenalidomide have been introduced for multiple myeloma (MM) treatment and have improved patients' survival drastically. However, dexamethasone remains a mainstay in the treatment of MM. Dexamethasone effectively induces tumor cell death when used for the initial treatment of MM. In addition, dexamethasone has a synergistic effect with novel agents and is hence used in combination with such agents. However, prolonged dexamethasone exposure may lead to drug resistance. To elucidate the mechanism of dexamethasone resistance, we generated a dexamethasone-resistant subline of the MM cell line RPMI8226. We cultured RPMI8226 cells with 1 µM dexamethasone for 7 weeks and established the dexamethasone-resistant cell line Dex-R. This cell line showed no difference in survival in the presence or absence of 1 µM dexamethasone. We then examined differences in gene expression between RPMI8226 and Dex-R cells using cDNA microarray. Expression of the FARP1 gene, which is a transforming growth factor beta (TGF-b) target gene in myeloma cells, was increased approximately 50-fold in Dex-R cells compared to that in RPMI8226 cells. In some myeloma patients who become chemoresistant, myeloma cells show high levels of FARP1 expression at the initial stage. FARP1 has a Rho-GEF domain and can associate with proteins on the cell membrane through the FERM domain. In the nervous system, FARP1 is involved in synaptogenesis via the activation of Rac1. Based on these observations, we hypothesize that Dex-R cells acquires dexamethasone resistance with an increase in the level of FARP1 expression via the activation of Rac1. To verify this hypothesis, we established inducible FARP1 knockdown Dex-R cells using the TET-ON lentiviral system. We cultivated these cells for 24 h with doxycycline and added 1 µM dexamethasone. A total of 48 h after adding dexamethasone, we measured cell viability using the MTS assay. We cultured Dex-R cells with a Rac1 inhibitor (NSC23766) and added dexamethasone 12 h later. FARP1 expression decreased to approximately 10% in FARP1 knockdown cells 24 h after the addition of doxycycline. Without dexamethasone, there was no difference in survival in the presence or absence of doxycycline. However, when cells were cultured with dexamethasone, the growth of FARP1 knockdown Dex-R cells was significantly inhibited compared with that of the control (Fig 1). Next, we examined the change in dexamethasone resistance on the addition of the Rac1 inhibitor. The number of cells increased after 96 h without dexamethasone. On the other hand, the number of cells significantly decreased when cultured with dexamethasone (Fig 2). These data suggest that resistance to dexamethasone in Dex-R cells was mitigated by the inhibition of Rac1. We conclude that the activation of Rac1 through FARP1 is one mechanism of dexamethasone resistance in MM. Disclosures No relevant conflicts of interest to declare.

LR11, also known as SorLA or SORL1, is a type-I membrane protein from which a large extracellular part, soluble LR11 (sLR11), is released by proteolytic shedding on cleavage with a disintegrin and metalloproteinase 17 (ADAM17). A shedding mechanism is presumed to have a key role in the functions of LR11, but the evidence for this has not yet been demonstrated. Tetraspanin CD9 has been recently shown to regulate the ADAM17-mediated shedding of tumor necrosis factor-α and intercellular adhesion molecule-1 on the cell surface. Here, we investigated the role of CD9 on the shedding of LR11 in leukocytes. LR11 was not expressed in THP-1 monocytes, but it was expressed and released in phorbol 12-myristate 13-acetate (PMA)-induced THP-1 macrophages (PMA/THP-1). Confocal microscopy showed colocalization of LR11 and CD9 proteins on the cell surface of PMA/THP-1. Ectopic neo-expression of CD9 in CCRF-SB cells, which are LR11-positive and CD9-negative, reduced the amount of sLR11 released from the cells. In contrast, incubation of LR11-transfected THP-1 cells with neutralizing anti-CD9 monoclonal antibodies increased the amount of sLR11 released from the cells. Likewise, the PMA-stimulated release of sLR11 increased in THP-1 cells transfected with CD9-targeted shRNAs, which was negated by treatment with the metalloproteinase inhibitor GM6001. These results suggest that the tetraspanin CD9 modulates the ADAM17-mediated shedding of LR11 in various leukemia cell lines and that the association between LR11 and CD9 on the cell surface has an important role in the ADAM17-mediated shedding mechanism.

Introduction LR11, which is also known as SorLA or SORL1, is a type-I membrane protein from which a large extracellular part, soluble LR11 (sLR11), is released by proteolytic shedding. We have demonstrated that serum sLR11 levels are significantly elevated in patients with acute leukemia and that sLR11 levels are associated with the peripheral blast percentage (Sakai et al. Clin Chim Acta. 2012). In addition, we found that high sLR11 levels have a significant negative prognostic impact on progression-free survival in patients with follicular lymphoma (FL; Kawaguchi et al. Br J Haematol. 2013). In this FL analysis, the immunohistological intensity of LR11 in lymph nodes of FL patients did not show a significant association with serum sLR11 levels. Therefore, a shedding mechanism is presumed to play a key role in the functions of LR11. A disintegrin and metalloproteinase 17 [ADAM17, also known as tumor necrosis factor (TNF)-α converting enzyme (TACE)] has been identified as the enzyme that cleaves TNF-α from its transmembrane precursor form, and it has been found to cleave the ectodomains of other cell surface proteins. LR11 is also shed by ADAM17. Tetraspanin CD9 has been recently shown to inhibit the shedding activity of ADAM17. Therefore, we investigated the role of CD9 in sLR11 release. Materials and methods First, we examined the gene expression levels of LR11 by quantitative real-time PCR and the cell surface expression of LR11 and CD9 by flow cytometric analysis in normal human peripheral-blood mononuclear cells (PBMCs). Second, we investigated the cellular expression and the released levels of LR11 and cellular CD9 in THP-1 monocytes, phorbol 12-myristate-13-acetate (PMA)-induced THP-1 macrophages (PMA/THP-1), and the B lymphoblastoid cell line CCRF-SB by immunoblot analysis. Furthermore, to assess the relationship between LR11 and CD9 in PMA/THP-1, we performed double immunofluorescence staining of these molecules followed by confocal microscopy analysis. Third, we examined the effects of ectopic neoexpression of CD9, anti-CD9 mAbs, and CD9 silencing. THP-1 cells stably interfered with CD9 were generated by the transfection of the shRNA expression vector that is specific for CD9. Results The gene expression levels of LR11 were significantly higher in CD3+ T cells than in CD14+ monocytes, and there was no difference between monocytes and CD19+ B cells. However, LR11 was only expressed on the cell surface of monocytes in normal PBMCs. CD9 was broadly expressed on the cell surface of every PBMCs. Because it has been reported that CD9 associates with ADAM-17 on the cell surface, we hypothesized that CD9 associates with the shedding of LR11 on the cell surface. To verify this hypothesis, we chose the monocytic cell line THP-1 because monocytes have both LR11 and CD9 on their surface. In addition, because the gene expression levels of LR11 were significantly higher in human monocyte-derived macrophages than that in monocytes, we investigated the levels in PMA/THP-1. LR11 was not expressed or released in undifferentiated THP-1 cells, but it was expressed or released in differentiated PMA/THP-1. CD9 was poorly expressed in THP-1 cells, and the CD9 expression levels were increased in PMA/THP-1. The confocal microscopy analysis showed colocalization of LR11 and CD9 proteins in PMA/THP-1. We next investigated the effects of ectopic neoexpression of CD9 in CD9-negative cells, neutralizing anti-CD9 mAbs (clone ALB-6) in CD9-positive cells, and CD9 silencing in THP-1 on the shedding of LR11. When CCRF-SB, LR11-positive and CD9-negative cells were transiently overexpressed with CD9, the amount of sLR11 released from CD9-overexpressing cells was decreased compared with that from control cells. The amount of sLR11 released from LR11-transfected THP-1 cells that were cultured with ALB-6 was significantly increased compared with that cultured with an isotypic control antibody. The PMA-stimulated release of sLR11 was significantly increased in CD9 shRNA-interfered THP-1 cells compared with cells that were transduced with the control shRNA. The increase in CD9 shRNA-interfered THP-1 was nullified by treatment with the metalloproteinase inhibitor GM6001 (Figure 1). Conclusion These results suggested that the tetraspanin CD9 inhibits ADAM17-mediated LR11 shedding in leukemia cells and that it may have a role in controlling the function of LR11. Disclosures: No relevant conflicts of interest to declare.

Introduction Although thrombopoietin-receptor agonists have recently been introduced for the treatment of refractory immune thrombocytopenia (ITP), splenectomy is still the standard treatment option for patients with steroid-refractory ITP. However, open and laparoscopic splenectomy is associated with a mortality rate of 1.0% and 0.2%, respectively, and the major known long-term risk of splenectomy is severe bacterial sepsis. Partial splenic embolization (PSE) is an alternative to splenectomy for patients with steroid-refractory (Kimura et al., AJR 2002). PSE does not require general anesthesia and has not been associated with severe complications. In this study, we analyzed the efficacy and long-term outcomes of PSE in steroid-refractory ITP patients. Patients and Methods Between 1988 and 2009, 77 patients with chronic ITP [30 men and 47 women, 16.5–80.9 years old (median age, 46.5 years)] underwent PSE at Chiba University Hospital. Almost all patients did not respond to steroid treatment or other therapies including Helicobacter pylori eradication and immunosuppressive drugs. A 5-French catheter was introduced via the femoral artery to the middle splenic artery and a 0.089-cm guidewire was inserted coaxially. Embolization of intrasplenic arterial branches was performed by the injection of 2 x 2 mm fragments of Gelfoam and an antibiotic solution. Splenic embolization was monitored angiographically during the procedure, and embolization was stopped after 70% of the splenic parenchyma had been ablated. The therapeutic response to PSE was evaluated on the basis of the platelet (PLT) count at 1 year after PSE: a complete response (CR) was defined as PLT count of more than 10 x 1010/L without any medication and a partial response (PR) was defined as PLT count = 5–10 x 1010/L without any medication. Patients who required medication to maintain a PLT count of more than 5 x 1010/L or patients with a PLT count of less than 5 x1010/L were considered to have no response (NR). Results The average PLT count prior to PSE was 2.7 ± 2.4 x 1010/L. The mean time to achieve the peak PLT count was 10.2 ± 5.2 days after PSE. The PLT count was 11.1 ±10.3 x 1010/L (n = 74), 9.8 ± 8.3 x 1010/L (n = 70), 9.1 ± 8.2 x 1010/L (n = 65), and 9.1 ± 7.5 x 1010/L (n = 69) at 1 month, 3 months, 6 months, and 1 year, respectively. One year post PSE, CR or PR was obtained in 33 (58%) of the evaluable 57 patients and 24 patients (42%) had NR. The group in which the peak PLT count after PSE was over 30.0 x 1010/L showed a significantly higher PLT count than the group in which the peak count was under 30.0 x 1010/L after PSE treatment (Figure 1). The peak PLT count was significantly higher in CR and PR groups (37.4 x 1010/L) than in the NR group (15.0 x 1010/L) (p = 0.041). In addition, 52% patients did not require additional treatment for 10 years after PSE (Figure 2); in 16 patients, PSE was performed for the second time after recurrence; and CR or PR was obtained in 5 patients (31%). There were no severe PSE-related complications such as splenic abscess and no PSE-related deaths. Conclusions PSE might be a safe and effective alternative therapy to splenectomy for patients with steroid-refractory ITP as it generates long-term durable responses. Disclosures: No relevant conflicts of interest to declare.