ALBERT

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 Patients who did not achieve a platelet response after the treatment with 20 μg/kg during 8 consecutive weeks were withdrawn from the study.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: Immune thrombocytopenic purpura (ITP) is an autoimmune disorder, and eradication of Helicobacter pylori (HP) has been demonstrated to be an effective and tolerable firstline treatment for the patients infected with HP in Japan. However the mechanism has still remained to be uncovered. Recently CD4+CD25high+Foxp3+ regulatory T cells (Tregs), which regulate autoreactive T cells, have been identified, and suggested to play an important role in pathogenesis of ITP, as well as other autoimmune disorders. It has been shown that Tregs are reduced and suppressed in the ITP patients. And a recent report has demonstrated that the defective Tregs are restored upon the rituximab treatment. However, the effects of HP eradication therapy on Tregs have not been determined. The aim of this study is to investigate the circulating Tregs in ITP patients treated with HP eradication. And we also attempted to elucidate the mechanisms of the treatment. The peripheral blood CD4+CD25high+ Tregs were measured by flow cytometry before and after the treatment in 21 Japanese adults with HP-positive chronic ITP. We also confirmed the expression of Foxp3 in this cellular population with the permeabilized mononuclear cells. Among 21 patients, the platelet counts increased in 13 cases (responders), but not in 9 cases (non-responders). In responders the numbers of Tregs have been restored, but not in non-responders after the treatment. It is interesting here that the amounts of Tregs were still transiently elevated in an early phase (2–3weeks) after the treatment in some non-responders without recovery of the platelet counts. Furthermore, in three cases, who failed in pylorus elimination, Tregs were also transiently increased in number associated with brief recovery of the platelet counts, and reduced to the initial level in about two months. After the successful re-eradication, the numbers of Tregs and platelets have been restored. From these results it is shown that HP eradication can modulate Tregs to increase the platelet counts for ITP patients. We also demonstrate that the increase of Tregs by HP eradication was more rapid than that by rituximab, which required about three months. Further, it might be suggested that there are two phases of the therapy with HP eradication for ITP. In an initial stage, the therapy itself could have an effect modulating the immune systems to potentiate Tregs. Some drugs, such as macrolide antibiotics including clarithromycin have been demonstrated to be a potent immunomodulator. However, this phase is not sufficient for the successful treatment, as shown in the cases of failure in HP elimination. In a retentive stage, extermination of HP is also necessary for sustainment of restored Tregs.

Description: Abstract 5088 Aim: With the exception of CD5, the clinical implications of aberrant T-cell antigen expression on B cells in diffuse large B cell lymphoma (DLBCL) have not been well studied. The present retrospective study aimed to determine associations between T cell antigen expression and patients′ characteristics and prognosis Patients, Material and Methods: 249 cases with B-cell lymphoma (BCL) newly-diagnosed in our Institute between January 2002 and August 2009 were biopsied and also analyzed by flow cytometry. Biopsy specimens were fixed in formalin, stained with Hematoxylin-Eosin, and also immunostained. Histological subtypes were defined according to the World Health Organization Classification Version 3. Flow cytometric (F/C) analysis was performed following standard methods. The aberrant expression of one or more T cell surface antigens on B cells (CD2, 3, 4, 7, 8) was assessed. Statistical analysis was conducted to seek associations between aberrant positive and negative cases and patients′ background laboratory data, and prognosis. This study was approved by the Ethics Committee of Kitasato University School of Medicine. Results: 150 DLBCL, 68 Follicular lymphoma (FL), 17 Marginal zone lymphoma (MZL), 6 MCL and 4 CLL patients were tested. Of the DLBCL cases, 12 (8%) showed aberrant T cell antigen expression with 4, 1, 5, 1 and 1 patients′ B cells positive for CD2, CD4, CD7, CD8 and CD7 + 8 respectively. Aberrant expression among the FL, MCL, MZL and CLL cases was seen in 0, 1, 1 and 1 patient, respectively. Among the DLBCL patients, T antigen-negative cases tended to have higher WBC counts and greater CD20 expression by F/C analysis. No statistically significant associations with gender, age, IPI, clinical stage, laboratory data, expression of CD5 and other markers, ABC/GCB, or karyotype were observed between the positive and negative groups. 96 of the 150 DLBCL patients received rituximab-chemotherapy. Again, there were no statistically significant differences between the two groups in overall survival and response to treatment. Discussion: 1) CD2 and CD7 are relatively common among aberrant T cell antigen- positive DLBCL. 2) No statistically significant differences were observed between the two groups in terms of background and prognosis. 3) Both CD8-positive DLBCL patients experienced a very aggressive clinical course and rapidly succumbed to their disease. CD8-positive DLBCL cases may in general have poorer survival. 4) Further analysis will be necessary to confirm these results. Disclosures: No relevant conflicts of interest to declare.

Description: Abstract 3704 Introduction: Chronic immune thrombocytopenia (ITP) is an autoimmune disorder characterized by both increased platelet destruction and decreased platelet production. Romiplostim increases platelet counts by binding and activating the thrombopoietin receptor. Romiplostim has been approved for the treatment of adult ITP in the United States, Europe, Canada, and Australia. This study evaluated dosing, efficacy, and safety in a Japanese population of adults with ITP. Methods: This phase 3 study was placebo-controlled, double-blind, and randomized 2:1 (romiplostim:placebo). Patients were eligible for the study if they were Japanese patients with ITP diagnosed at least 6 months before the initial screening, were aged ≥ 20 years, and were H pylori negative or had received at least 1 treatment for H pylori eradication. Patients were stratified by splenectomy status (yes or no). After a 3-week evaluation period, patients were treated for 12 weeks with a weekly subcutaneous injection of either romiplostim or placebo. The starting dose was 3 mcg/kg with dose adjustments to a maximum of 10 mcg/kg to achieve a platelet count within the target range of ≥ 50 to ≤ 200 × 109/L. Patients were monitored posttreatment until their platelet count dropped to ≤ 50 × 109/L or for a maximum of 12 weeks. The primary endpoint was number of weeks with platelet response (platelet count ≥ 50 × 109/L). Results: Thirty-four patients enrolled (22 romiplostim, 12 placebo), 24 (71%) were female, the median (range) age was 55 (44 - 64) years, and the median (range) baseline platelet count was 19 (3 – 32) × 109/L. Patients had received a median of 4 (1 – 19) prior ITP therapies, and 15 (44%) had previously undergone a splenectomy; 23 (68%) patients were receiving concurrent ITP therapy at baseline. All patients completed the study. Romiplostim demonstrated superiority to placebo on weekly platelet response, incidence of increase in platelet count ≥ 20 × 109/L from baseline, change from baseline in mean of last 4 platelet counts during week 2 to week 13, and number of weeks with platelet counts within the target range (Table 1), and 16 (73%) romiplostim patients had platelet counts ≥ 200 × 109/L. Twenty-one (95%) patients in the romiplostim group had a platelet response with a median time of 1 week until first response. Results for weekly platelet response were comparable irrespective of splenectomy status and baseline concurrent ITP therapy. Two (17%) patients in the placebo group achieved a platelet response. In romiplostim-treated patients, posttreatment platelet counts remained 〉 50 × 109/L for 8 weeks in one and for 12 weeks in another. The mean weekly dose of romiplostim for the study was 2.6 mcg/kg compared with the dose range of 3–4 mcg/kg in prior phase 3 studies (Kuter et al. Lancet. 2008;371:395–403). There was a low incidence of rescue medication use in the study (Table 1). The adverse events profile was comparable to that seen in non-Japanese studies. Patients in both treatment groups experienced similar proportions of adverse events (91% romiplostim, 92% placebo). Adverse events with 〉 10% higher frequency in the romiplostim group than placebo group) were (romiplostim, placebo) nasopharyngitis (41%, 17%), headache (32%, 17%), peripheral edema (18%, 0%), back pain (14%, 0%), and pain in extremity (14%, 0%). Significant (≥ grade 3) bleeding events occurred in 1 patient in the romiplostim group (subarachnoid hemorrhage) and 1 patient in the placebo group (subarachnoid hemorrhage, cerebral hemorrhage, and gastrointestinal hemorrhage). There were no adverse events of bone marrow reticulin, thrombosis, or detection of neutralizing antibodies. Conclusion: Romiplostim significantly increased and maintained platelet counts and was well-tolerated in a Japanese ITP population. Disclosures: Tomiyama: Kyowa Hakko Kirin Co.: Speakers Bureau; GlaxoSmithKline: Speakers Bureau. Kurokawa:Novartis: Consultancy; Shionogi & Co., Ltd.: Consultancy. Wei:Amgen Inc.: Employment, Equity Ownership. Lizambri:Amgen Inc.: Employment, Equity Ownership.

Description: Abstract 1097 The immature platelet fraction (IPF) is a useful parameter indicating thrombopoietic activity to differentiate the causes of thrombocytopenia. We previously reported that the percentage of IPF (%IPF) is negatively correlated to the platelet count among ITP patients, and not among myelodysplastic syndrome (MDS) patients. We also noticed that some MDS patients exhibited extremely high %IPF values, which were dissociated from the percentages of reticulated platelets (%RP) measured by flow cytometry. Such discrepancies were also observed in hereditary macrothrombocytopenias, which are sometimes difficult to be distinguished from ITP, because ITP also exhibits increased number of reticulated platelets in a slightly larger size. Once misdiagnosed, a hereditary macrothrombocytopenia patient might be subjected to an invasive treatment such as splenectomy. In order to avoid such mistreatments, a clear marker to differentiate macrothrombocytopenia is desperately needed. In this study, we investigated the IPF values of 16 individuals from 12 families with various hereditary macrothrombocytopenia in order to clarify whether the IPF could be a useful marker to distinguish macrothrombocytopenia from ITP, and examined the IPF during EDTA aggregation and cold-storage to elucidate how platelet size may affect the IPF value. The IPF values were about 5 times higher in MYH9 disorders (%IPF 48.0 ± 1.8) and about 1.5 times higher in other macrothrombocytopenias (%IPF 17.0 ± 2.2) than immune thrombocytopenic patients with similar platelet counts (%IPF 9.3 ± 0.4). These results suggested that the platelet size can affect the IPF value. However it still remains the possibility that some factors specific to these macrothrombocytopenias other than the platelet size might make an influence on the IPF, because the characteristic of large platelets in hereditary macrothrombocytopenia has not been fully understood, and no one knows whether large platelets are functionally identical to normal platelets except for the size. In order to exclude the possibility, we next examined the changes of IPF values during EDTA aggregation and cold-storage. The IPF was significantly increased during storage in a time dependent manner along with forming platelet clumps. The IPF was strongly influenced by a few tiny platelet aggregates rather than other platelet indices, such as mean platelet volume (MPV), platelet-large cell ratio (P-LCR) and platelet distribution width (PDW). In conclusion, the IPF is susceptible to the platelet size, and could be a useful parameter for screening of macrothrombocytopenia from ITP. Disclosures: No relevant conflicts of interest to declare.

Description: Abstract 5000 AIM The anti-CD20 antibody Rituximab has improved the disease-free survival and overall survival of patients with several types of B-cell lymphoma, in which CD20 is expressed on the cell surface and in the cytoplasm. Flow cytometry indicated that CD20 expression varies from null, weak to strong. Despite its clinical importance, the influence of CD20 expression levels on lymphoma therapy has not been well elucidated. Patients, Material and Methods 214 cases were analyzed, all newly diagnosed with B-cell lymphoma at our institute from January in 2002 to April in 2009. All were biopsied and analyzed by flow cytometry. The biopsy specimens were fixed in formalin and stained with Hematoxylin-Eosin; they were also immunostained. Histological subtypes were defined according to the World Health Organization Classification Ver. 3. The mean florescence intensities of CD20 and CD19 were determined by flow cytometry, and cytoplasmic expression of CD20 was determined by immunohistochemistry. 1) The cases were categorized as follows: A: CD20-negative, B: CD20/19 less than 20%, C: CD20/19 20-50% and D: CD20/19 more than 50%. Patients' backgrounds, pathological diagnoses, primary lesions, etc. were also analyzed. 2) Among DLBCL cases, 76 treated with R-chemo were selected and analyzed with respect to treatment response and overall survival. Results 1) Diagnoses: DLBCL 128, Follicular lymphoma 58, MALT 7, CLL 4 and so on. Among the DLBCL cases, immunohistochemistry indicated six (4%) were CD20-negative and three were CD20-positive; the ages in the CD20-negative DLBCL group tended to be high (74.28 vs 64.36, p=0.06, t-test). Weak CD20 expression was observed in 15 cases (B: 4, C:11). No statistically significant differences were seen with respect to gender, IPI, clinical stage, biopsy lesion, CD5 expression or Karyotype. No FL cases were CD20-negative, but two ( 3.4%) showed low CD20 expression. 2) Kaplan-Meier analysis of 76 cases of DLBCL treated with R-Chemo showed a significantly lower overall survival for Group A, (CD20-negative) while there was no significant difference in overall survival of Groups B+C(CD20-weak) and D(CD20-normal). Our results indicate that even patients with lower levels of CD20 expression in B-cell lymphoma may respond favorably to anti-CD20 therapy. Further studies will be necessary to explore this possibility. Disclosures No relevant conflicts of interest to declare.

Description: Abstract 4925 [Introduction] Normal T lymphocytes express CD3 protein, major component of T-cell receptor, in the cytoplasm membrane. However, CD3 expression is suppressed in malignant T cells. The mechanism of suppression of CD3 expression remains unknown. We previously reported the cloning of three isoforms of non-muscle myosin light chain, including MYL9 (transcript variant 1). MYL9 mRNA was expressed in monocyte-macrophage cell lines, but not in lymphoid cell lines (J. Smooth Muscle Res.44: 29–40, 2008). We report here some evidence, suggesting the prerequisite role of MYL9 (transcript variant 1) in the process of CD3 expression in cytoplasm membrane. [Materials and Methods] Leukemic cell lines were cultured in RPMI1640 plus 10% FCS. mRNA contents were measured with RT-PCR. CD3 expression was measured using FACScan FITC-labeled or PE-labeled second antibody. Whole CD3 contents were measured using IntraPrep™ (Beckman Coulter). Transfection of MYL9(transcript variant 1)gene into Jurkat cell (wild-type) was performed using Trans Fasc Reagent (Promega). In the process of screening the change the percentage of surface marker, we found that some clones showed the CD3 positive, and Jurkat (clone I), which expresses CD3 (85∼90%) in the cytoplasm membrane, was selected. We also used Jurkat, Clone E6-1(TIB-152)(ATCC®), strong positive in CD3 (90∼95%) in cytoplasm membrane. [Results] 1) CD3 were negative in Jurkat cell (wild-type), and highly positive in both clone I and clone E6-1. 2) Whole CD3 (cytosole and cytoplasm membrane) were positive in these three cells, suggesting that transportation of CD3 protein from cytosole to cytoplasm membrane is suppressed in Jurkat cell (wild-type). 3) Long term culture (i.e. 30∼60 days) induced, although weakly, both MYL9 mRNA and CD3 of cytoplasm membrane in Jurkat cell (wild-type). 4) Clone E6-1 shows positive in MYL9 mRNA. 5) In Jurkat cell (wild-type), PMA induced CD3 expression in cytoplasm membrane, but not MYL9 mRNA. Pre-treatment with staurosporine showed partial inhibitory effect on PMA-induced CD3 expression. 6) Neither concanavalin A nor A23187 induced CD3 expression in both clone I and Jurkat cell (wild-type). [Discussion] These results suggest that MYL9 is prerequisite for the CD3 expression in cytoplasm membrane of normal T lymphocytes. However, in T-cell malignant cells, MYL9 gene is suppressed by unknown mechanism. Our data show that CD3 expression in cytoplasm membrane may be regulated by MYL9-dependent and MYL9-independent fashions. Disclosures: No relevant conflicts of interest to declare.

Description: Background: Immune thrombocytopenia (ITP) is an autoimmune disease characterized by the presence of autoantibodies against platelet membrane glycoproteins, which cause the autoantibody-mediated destruction of platelets and impaired platelet production. Thrombopoietin (TPO) binds to its receptor on the surface of hematopoietic stem cells and megakaryocytes and induces their maturation and proliferation. Patients with thrombocytopenia due to aplastic anemia have drastically elevated plasma levels of TPO, whereas patients with ITP have normal or slightly elevated plasma levels of TPO despite their low platelet count. Furthermore, based on the existence of a multitude of autoantibody reactivities in ITP, including antibodies against platelets and TPO receptors, the presence of anti-TPO antibodies in patients with ITP may be suspected. Objective: We developed assay systems to detect plasma anti-TPO antibodies and screen patients with ITP. We examined the clinical characteristics associated with anti-TPO antibodies and their pathogenic roles in patients with ITP. Methods: Plasma anti-TPO antibodies from 101 patients with ITP and 72 healthy controls were measured by enzyme-linked immunosorbent assay (ELISA) using recombinant human TPO (rhTPO) as an antigen. The specificity of anti-TPO antibody reactivity was confirmed by ELISA competition assay. The presence of anti-TPO antibodies was further examined using immunoprecipitation and immunoblotting using rhTPO. To investigate whether anti-TPO antibodies inhibited functional interactions between TPO and TPO receptors, we examined extracellular signal-regulated kinases (ERKs), downstream signals induced by TPO. The binding of TPO to TPO receptors induced the phosphorylation of ERK in TPO receptor-expressing UT-7/TPO cells. Results: The level of anti-TPO antibodies measured by ELISA was significantly greater in the samples from patients with ITP than in those from healthy controls (2.91 ± 3.64 units versus 1.45 ± 0.67 units, P 〈 0.001). Samples were classified as positive or negative for anti-TPO antibody, as determined by immunoprecipitation and immunoblotting. Thus, the ELISA positive-cutoff value was considered to be the mean plus 3.5 standard deviation (SD) of 72 healthy control plasma samples. Plasma anti-TPO antibodies were detected in twenty-four ITP patients (23.8%), but in none of the healthy controls. By ELISA competition assay, anti-TPO antibody reactivity was inhibited dose-dependently by preincubation of patient plasma with rhTPO. In addition, anti-TPO antibody-positive plasma samples inhibited the phosphorylation of ERK in UT-7/TPO cells. In contrast, healthy control plasma had no inhibitory effect. Furthermore, the number of megakaryocytes was decreased relatively in the anti-TPO antibody-positive ITP patients. There was no difference in the TPO levels in plasma between ITP patients with anti-TPO antibodies and patients without anti-TPO antibodies (63.6 ± 79.7 pg/ml versus 45.2 ± 49.3 pg/ml). Conclusion: Our results have thus demonstrated the presence of anti-TPO autoantibodies in patients with ITP. The ELISA using rhTPO was specific for the detection of anti-TPO antibodies and thus allows their easy and rapid measurement in clinical settings. These findings suggest that functional anti-TPO antibodies cause impaired megakaryocyte proliferation and platelet production in patients with ITP. Disclosures Higashihara: Bristol-Myers Squibb: Research Funding; Baxter: Research Funding; Teijin: Research Funding; Pfizer: Research Funding; Astellas: Research Funding; Yakurt: Honoraria; KyowaHakkoKirin: Honoraria, Research Funding; Chugai: Honoraria, Research Funding; Eisai: Honoraria; GlaxoSmithKline: Honoraria, Research Funding; Nippon Shinyaku: Research Funding; Shionogi: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Celgene: Honoraria; Takeda: Honoraria; Janssen　pharma: Honoraria, Research Funding; Alexion: Honoraria; Dainippon Sumitomo: Research Funding; Taisho Tomiyama: Research Funding.

Description: It is sometimes confusing to distinguish idiopathic thrombocytopenic purpura (ITP) from thrombocytopenia due to dysmegakaryopoiesis, as seen in myelodysplastic syndrome (MDS) patients, especially MDS with isolated thrombocytopenia. In this study, we investigated the useful parameters for the different diagnosis of thrombocytopenia. The number of reticulated platelets reflects the rate of thrombopoiesis, and this clinical utility has been established in the laboratory diagnosis of thrombocytopenia due to increased peripheral platelet destruction, such as autoimmune thrombocytopenic purpura (AITP). However, the number of reticulated platelets has not been well investigated in the patients with myelodysplatsic syndrome (MDS), while some of them are misdiagnosed as ITP. The aim of this study is to evaluate the diagnostic utility of the measurements of reticulated platelets as well as other parameters of platelets, such as MPV (mean platelet volume), P-LCR (platelet larger cell ratio) and PDW (platelet distribution width). The reticulated platelets, expressed as the immature platelet fraction (IPF) were determined in 108 ITP and 57 MDS patients using the Sysmex XE-2100 blood cell counter with upgraded software (Sysmex, Kobe, Japan). This system enabled rapid, inexpensive, automated, stable measurements of reticulated platelets compared with the flow cytometry system, of which consensus method has not yet been identified to provide acceptable intra- and inter-laboratory results. The platelet counts in ITP and MDS patients were equivalent (ITP, 7.99 ± 0.40 × 104/μL; MDS, 8.05 ± 0.57× 104/μL). The IPF values in ITP patients (10.4 ± 0.61%) were significantly higher than those in MDS (5.82 ± 0.63%), and the inverse correlation between the IPF and the platelet counts was observed among the ITP patients, but not among the MDS. Both MPV and PDW in MDS (10.6 +/− 0.15 fL and 12.2+/−0.41 fL, respectively) were significantly higher than in ITP (7.7 +/− 0.38 fL and 9.4 +/− 0.48 fL, respectively), while P-LCR in MDS (28.7 +/− 1.2%) and ITP (23.6 +/− 1.3%) were not significantly different. Although MPV was correlated with IPF among either group, the correlation between IPF and either PDW or P-LCR was weak among MDS (IPF × PDW, r=0.673; IPF × P-LCR, r=0.660) compared with ITP (IPF × PDW, r=0.779; IPF × P-LCR, r=0.803). Next we precisely investigated the clinical features of the minor population of MDS with higher IPF. Most of these patients revealed the significantly higher values of PAIgG (Platelet-associated IgG) and/or poor response to the blood transfusion, suggesting the possibility of associated autoimmune mechanisms. The patients of MDS in overt leukemic stage also recorded higher IPF even if they had no or few blood transfusion. The IPF would be a useful parameter to distinguish ITP from MDS with isolated thrombocytopenia, which has been shown to have a favorable prognosis.