ALBERT

Description: [Background] Paroxysmal nocturnal hemoglobinuria (PNH) is a hematopoietic　stem cell disorder derived from an acquired mutation of the phosphatidylinositol glycan class A (PIGA) gene in the hematopoietic stem cells which results in the expansion of glycosylphospatidylinositol-anchored protein (GPI-AP)-deficient (PNH-type) hematopoietic cells. PNH-type blood cells are also observed in patients with bone marrow failure (BMF). PNH is conventionally diagnosed when patients have 〉1% of GPI-AP-deficient erythrocytes and granulocytes determined by flow cytometry. Analyses with high resolution flow cytometry by several different groups have shown that patients with aplastic anemia (AA) or low-risk types of myelodysplastic syndromes (MDS) have small percentages of PNH-type erythrocytes, granulocytes, and/or other lineages of blood cells and that these patients respond better to immunosuppressive therapies compared with BMF patients lacking PNH-type cells. In order to determine the prevalence and clinical significance of PNH-type cells in BMF patients, we conducted a nationwide multi-center prospective observational investigation, the OPTIMA study. [Methods] From July 2011, Japanese patients with PNH, AA, MDS or BMF of uncertain origin have been prospectively enrolled into the study. Six laboratories in different cities in Japan were assigned as regional analyzing centers and measured the percentages of PNH-type cells in the study population as well as collecting clinical and laboratory data. The high-resolution flow cytometry assessments used a liquid fluorescein-labeled proaerolysin (FLAER) method and a cocktail method with anti-CD55 and anti-CD59 antibodies for the detection of PNH-type granulocytes and erythrocytes, respectively. Periodic blind cross validation tests using a standard blood sample containing 0.01% PNH-type cells and a normal control were conducted to minimize inter-laboratory variations. From analysis of 68 healthy individuals 〉0.003% of PNH-type granulocytes and 〉0.005% of PNH-type erythrocytes were considered to be abnormal (Sugimori et al, Blood, 2006). [Results] As of May 2014, flow cytometry data have been collected from 1685 patients and are included in this interim analysis. Of these patients, 65 (4%) were diagnosed with PNH, 523 (31%) with AA, 459 (27%) with MDS, and 638 (38%) with BMF of unknown etiology. Overall, 154 (9%) patients had ≥1% of both PNH-type erythrocytes and granulocytes: 63 (97%) patients with PNH; 57 (11%) with AA; 18 (4%) with MDS; and 16 (3%) with BMF of unknown etiology. In total, 545 (32%) patients had ≥0.005% PNH-type erythrocytes and ≥0.003% PNH-type granulocytes. These consisted of the followings; all 65 (100%) patients with PNH; 264 (51%) with AA; 76 (17%) with MDS; and 140 (22%) with BMF of unknown origin. Lactate dehydrogenase (LDH) levels ≥1.5 × upper limit of normal range were seen in 14/329 (4%) patients with 0.005-1% PNH-type erythrocytes, 23/62 (37%) patients with 1-10% PNH-type erythrocytes, and 69/71 (97%) patients with ≥10% PNH-type erythrocytes. Periodic blind validation tests revealed that inter-laboratory differences in absolute measurements of PNH-type cells were always within 0.02%. [Conclusion] A high-resolution flow cytometry-based method, based on the Kanazawa method, that enables the detection of very low percentages of PNH-type cells was successfully transferred to 6 laboratories across Japan. Our results demonstrated that the proportion of patients identified as having small percentages of PNH-type cells differed depending on diagnosis (PNH, AA, MDS, or unknown BMF) and that elevated LDH levels (〉1.5 x upper limits of normal range) were more frequently associated with higher percentages of PNH-type erythrocytes. Our findings suggest that the high resolution method is helpful as a diagnostic tool in BMF syndromes, including AA, MDS, and PNH, and may prove useful in understanding the pathophysiology of these disorders. Disclosures Noji: Alexion Pharma: Honoraria. Shichishima:Alexion Pharmaceuticals, Inc; and Medical Review Company: Honoraria, Research Funding. Obara:Alexion Pharma: Research Funding. Chiba:Alexion Pharma: Research Funding. Ando:Alexion Pharma: Research Funding. Hayashi:Alexion Pharma: Research Funding. Yonemura:Alexion Pharma: Research Funding. Kawaguchi:Alexion Pharma: Honoraria. Ninomiya:Alexion Pharma: Honoraria, Research Funding. Nishimura:Alexion Pharma: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Kanakura:Alexion Pharma: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau.

Description: Background: Acquired aplastic anemia (AA), the prototypical bone marrow failure syndrome, is inferred to result from immune-mediated destruction of hematopoietic progenitors, as most patients respond to immunosuppressive therapies. Clonal hematopoiesis in AA is evident in the presence of paroxysmal nocturnal hemoglobinuria (PNH) cells in as many as half of patients and by identification of uniparental disomies involving 6p (6pUPD) chromosome in 13% of cases. In addition, "clonal transformation", as defined by the development of myelodysplastic syndromes (MDS) or acute myelogenous leukemia (AML) is a serious long-term complication in 10-15% AA patients. Methods: We performed targeted deep sequencing and SNP array-based copy number (CN) analysis of peripheral blood- or granulocyte-derived DNA from 439 patients with AA (280 from US and 159 from Japanese cohorts) for a panel of 103 candidate genes, chosen because they are known to be frequently mutated in myeloid neoplasms. Germline DNA was available for 288 out of 439 patients and was used to confirm the somatic origin of mutations. Whole exome sequencing (WES) was performed in 52 cases. Where serial samples were available, the chronology of detected mutations was also investigated. Results: Targeted deep sequencing provided highly concordant results between the US and Japanese cohorts; approximately one third of AA patients had mutations in genes commonly affected in myeloid neoplasms, and about one third of patients in whom mutations were identified had multiple mutations. Multi-lineage involvement of mutations was confirmed in 6 cases using flow-sorted bone marrow samples. However, compared to myeloid neoplasms, mutations in AA were at much lower variant allele frequencies (VAFs) (

Description: Abstract 1976 Background: Heme oxygenase-1 (HO-1) is the rate-limiting enzyme in the first step of heme degradation to biliverdin, free iron, and carbon monoxide. Aside from heme degradation, HO-1 has been attributed several regulatory functions in tissue inflammation and protection against stress-induced apoptosis. Inducibility of HO-1 is moderated by a single nucleotide polymorphism (SNP) A -413 T in the promoter. It has been reported that the A-allele of this SNP is associated with higher promoter activity than T-allele. Additionally, there have been several reports on the involvement of polymorphism within the promoter region of the human HO-1 gene in various diseases of the vascular systems. Recently, the polymorphism in the HO-1 gene has been reportedly associated with the graft survival after liver transplantation. In this study we analyzed the impact of HO-1 polymorphism on transplant outcomes in patients undergoing unrelated HLA-fully-matched bone marrow transplantation (BMT) through the Japan Marrow Donation Program. Methods and Results: The SNP A -413 T was analyzed using the TaqMan system (Applied Biosystems). The HO-1 polymorphisms were retrospectively analyzed in a cohort of 259 pairs of patients with hematologic malignancies and their unrelated donors. The genotype frequencies of A/A, A/T and T/T were 22%, 48% and 38% in recipients and 20%, 53% and 27% in donors (P=0.41). The donor A/A or A/T genotype, a genotype expected to induce higher activity of the HO-1 gene, was associated with a better overall survival (OS) than the donor T/T genotype (55% vs. 38% @5-yr, P=0.002; Fig 1A) as well as trend toward reduced transplant-related mortality (TRM; 18% vs. 27% @5-yr, P=0.08; Fig 1B), while no significant differences between the A/A genotype and A/T genotype were noted. The beneficial effects of the donor A/A or A/T genotype were also found to be consistent on the multivariate analysis for OS (hazard ratio [HR], 0.64; 95% confidence interval [CI], 0.44 to 0.93; P=0.02) and TRM (HR, 0.59; 95% CI, 0.32 to 1.06; P=0.08). Furthermore, in the multivariate analysis the donor A/A or A/T genotype showed a tendency to a lower incidence of grades II-IV acute graft-versus-host disease (GVHD; HR, 0.68; 95% CI, 0.43 to 1.06; P=0.09). The recipient HO-1 genotypes did not significantly influence the transplant outcomes. Conclusions: These results suggest an association of the donor HO-1 genotype with overall survival after unrelated BMT, and may substantiate that the higher HO-1 activity by donors with the HO-1 A allele likely accounts for a reduced risk for TRM and acute GVHD in their recipients. These could therefore be useful in selecting the donor and creating therapeutic strategies for improving the final outcome of allogeneic BMT. Disclosures: No relevant conflicts of interest to declare.

Description: [Introduction] Recent data suggest that monocytes are the dominant effector cells during immunotherapy using the anti-CD20 monoclonal antibody rituximab, depleting B cells through FcγR-dependent pathways. Because monocyte colony-stimulating factor (M-CSF) enhances the antibody-dependent cellular cytotoxicity (ADCC) of monocytes, the clinical efficacy of rituximab might be improved by the addition of M-CSF. We have studied the effect of M-CSF in the enhancement of rituximab-mediated ADCC against B-cell lymphoma. [Methods] Monocytes were isolated by negative selection of PBMCs from healthy individuals for the absence of T-cell, B-cell, and NK-cell markers. Cytotoxicity was determined by a flow cytometry using two fluorescent dyes, calcein-AM and ethidium homodimer to specifically stain living and dead cells respectively. Monocytes were cultured for 48 hours in the presence or absence of human recombinant M-CSF (66 ng/ml). The B-cell lymphoma cell line Daudi was used as target in the presence of rituximab (5 μg/ml) or human IgG1 as control for 30 min at room temperature. Effector cells and target cells were incubated at different ratios ranging from 1:1 to 15:1 for 4 hours at 37°C. The expression of FcγRl, FcγRII, and FcγRIII on monocytes was determined using a flow cytometry. [Results] Monocytes treated with M-CSF showed a significant increase in rituximab-mediated cytotoxicity against B lymphoma cells: specific lysis at an E:T ratio of 15:1 was 39% ± 7% (mean ± SD) vs. 21% ± 5%, M-CSF-treated monocytes vs. non-treated monocytes. Lysis of lymphoma cells treated with rituximab alone was 8% ± 4%. Treatment with M-CSF led to a 1.5- to 2.0-fold increase of FcγRI and FcγRIII expression in monocytes, while FcγRII expression remained unchanged. [Conclusion] Pretreatment of monocytes with M-CSF enhances their rituximab-mediated ADCC against B-cell lymphoma, which may partly result from increasing expression of FcγRI and FcγRIII on monocytes via M-CSF stimulation. These in vitro results may provide a new approach to improve the therapeutic activity of rituximab.

Description: Introduction Ravulizumab, an innovative complement C5 inhibitor given every 8 weeks (q8w), was recently demonstrated in a large phase 3 study of patients (pts) with paroxysmal nocturnal hemoglobinuria (PNH) and naïve to complement inhibitor therapy to be non-inferior to eculizumab given every 2 weeks (q2w) across all endpoints that measured different aspects of PNH disease (transfusion avoidance [TA], lactate dehydrogenase normalization [LDH-N], percent LDH reduction, breakthrough hemolysis [BTH], Functional Assessment of Chronic Illness Therapy [FACIT]-Fatigue, and hemoglobin stabilization [HGB-S]) (Lee JW et al. EHA Learning Center, Jun 17, 2018; LB2603). PNH pts currently receiving eculizumab may experience treatment burden associated with the q2w dosing regimen. With the development of ravulizumab, PNH pts on prior eculizumab therapy can potentially switch to ravulizumab without interruption of treatment. The primary objective of this study was to assess the noninferiority of ravulizumab compared to eculizumab in adult PNH pts who were clinically stable after having been treated with eculizumab for at least 6 months. Methods In this phase 3, open-label, multicenter study (NCT03056040), adult pts with a documented diagnosis of PNH who were treated with labelled-dose eculizumab for 〉6 months having LDH levels ≤1.5 times the upper limit of normal at screening were randomly assigned 1:1 to continue eculizumab or switch to ravulizumab. Pts randomized to ravulizumab received weight-based loading [day 1]/maintenance doses [day 15 and q8w thereafter]: ≥40 to

Description: 【Background】The use of novel agents with different mechanisms of action has resulted in high complete response (CR) rates and improved the survival of patients with multiple myeloma (MM). Obtaining minimal residual disease (MRD) negativity following treatment is an important determinant for longer survival in patients with MM. The EuroFlow MM-MRD panel (EuroFlow panel) using the Infinicyt software (Cytognos, Salamanca, Spain) is a two-tube six-color antibody panel. By the addition of two drop-in antibodies (CD138, CD27; vendor of user's choice) into both tubes, an eight-color configuration, which has been validated by the EuroFlow consortium is obtained. The DuraClone RE PC kit (DuraClone panel) is a recently developed one-tube eight-color dry antibody panel using the Kaluza software (Beckman Coulter, Miami, USA) for manual identification of abnormal plasma cells (PCs) to detect MRD in MM. Although both methods are available, a comparison between them has yet to be performed. This study aimed to compare the EuroFlow panel and the DuraClone panel analysis of residual abnormal plasma cells by eight-color flow cytometry. 【Methods】Patients with International Myeloma Working Group defined symptomatic MM treated at Kanazawa University Hospital and Kameda Medical Center in Japan from January 2017 to July 2018 were included. Bone marrow samples were obtained as part of routine clinical practice for evaluating treatment response when appropriate. Bone marrow aspirates (4 mL; first pull of bone marrow aspiration) anti-coagulated with ethylenediamine tetraacetic acid were evenly split (2 mL each) for the EuroFlow panel and the DuraClone panel. PC quantification by the EuroFlow panel was performed at Kanazawa University Hospital and the DuraClone panel was performed at Kameda Medical Center. The monoclonal antibodies used in the EuroFlow and the DuraClone panels are detailed in Table 1. Identification of neoplastic PCs required ≥ 20 cells. Sample processing and measurement of PCs were performed within 48 hours of collection. The correlation of total leukocyte acquisition, total plasma cells and MRD were analyzed for both methods. Qualitative comparison of MRD negativity was also performed. Spearman's correlation coefficient was used for evaluating the correlation of paired data. The Bland-Altman plot was used for detection of fixed bias and proportional bias. 【Results】A total of 79 samples were analyzed. We first assessed the number of total leukocytes using the EuroFlow panel and the DuraClone panel. The median number of total leukocytes acquired with the EuroFlow panel was significantly higher than with the DuraClone panel (median: 8,505,172 cells, interquartile range [IQR]: 6,164,094 - 9,105,097 cells and median: 2,858,026 cells, IQR: 1,466,004 - 4,284,926 cells, respectively; p 〈 0.01), but the percentage of total plasma cells showed good concordance between both methods (regression coefficient = 0.91, p 〈 0.01). The median percentage of abnormal plasma cells was 0.0035% (IQR: 0.0005 - 0.05) and 0.0046% (IQR: 0.0005 - 0.05) using the EuroFlow panel and the DuraClone panel, respectively. Figure 1A shows scatter plots comparing the percentage of abnormal cells analyzed using the EuroFlow panel and the DuraClone panel. Both methods showed a high degree of concordance (regression coefficient = 0.90, p 〈 0.01). Bland-Altman plots also showed good agreement between both methods. There was no statistically significant fixed bias with a mean difference of 10% (95% confidence interval [CI]: -12~14%). In addition, no significant proportional bias was detected between the two methods (regression coefficient: -0.01, p = 0.85; Figure 1B). Qualitative analysis of MRD negativity also showed substantial agreement between the two methods (kappa = 0.7); 11 of 79 (13.9 %) samples showed discrepancy for determination of MRD negativity (〈 1 × 10-5). Nine of these samples were MRD negative by the EuroFlow panel, but MRD positive by the DuraClone panel, and two samples were MRD positive by the EuroFlow panel, but MRD negative by the DuraClone panel. However, all discrepancies occurred near the limit of detection of both methods (1.0 × 10-5). 【Conclusion】Our findings indicate that the DuraClone panel has good overall concordance with the EuroFlow panel for the detection of abnormal PCs in MM samples. The one-tube DuraClone panel enables to reduce processing time and test cost compared with the two-tube EuroFlow panel. Disclosures Takamatsu: Celgene: Honoraria, Research Funding; Janssen: Honoraria; Bristol-Myers Squibb: Research Funding; Ono: Research Funding. Nakao:Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria; Kyowa Hakko Kirin Co., Ltd.: Honoraria; Novartis: Honoraria.

Description: [Background] In cases of immune-mediated bone marrow (BM) failure, such as acquired aplastic anemia (AA) and AA/PNH, aberrant hematopoietic stem progenitor cells (HSPCs) that acquire resistance to immune attack are thought to survive and support hematopoiesis in convalescent patients. Two representative progenies of such "escape" HSPC clones are HLA class I allele-lacking (HLA[-]) leukocytes and glycosylphosphatidylinositol-anchored protein-deficient (GPI[-]) cells. The mechanism underlying the immune selection of HLA(-) HSPCs is the failure of cytotoxic T lymphocyte (CTL) to recognize target antigens that are presented by particular HLA class I alleles of HSPCs. However, the mechanisms underlying the immune selection of GPI(-) HSPCs remain unclear. In addition, whether or not immune pressure that persists after immunosuppressive therapy (IST) contributes to the development and maintenance of clonal hematopoiesis by HLA(-) or GPI(-) HSPCs that are often seen in patients in long-term remission is also unknown. Phenotypical analyses of HSPCs that can be obtained from peripheral blood (PB) of AA patients who possess HLA(-) or GPI(-) leukocytes may provide a hint to elucidate these unsolved issues. [Objectives/Methods] We analyzed PB lineage-CD45dimCD34+CD38+ HSPCs of 15 AA patients who had 1%-99% HLA-A2(-) or HLA-A24(-) granulocytes (Gs) using flow cytometry (FCM). PB samples from 1 patient with severe AA were obtained before IST while the other 14 patients were in remission at the time of sampling; 10 were on cyclosporin (CsA) and eltrombopag (EPAG) (n=1), CsA and anabolic steroids (n=3), CyA (n=4), anabolic steroids (n=1) and EPAG alone (n=1); and 4 were free of therapy. We also determined the percentages of HLA(-) cells in different CD34+ subsets of BM, including HSCs (CD38-CD90+CD45RA-), MPPs, CMPs, GMPs, MEPs and CLPs for patients whose BM cells were available. Six AA/PNH patients whose GPI(-) Gs were 4-99% of the total Gs were subjected to the same PB HSPC analysis. For a separate group of seven AA patients who responded to CsA and had both HLA(-) and GPI(-) G populations, the percentages of each population were serially determined over one to 12 years. [Results] FCM identified 0.01%-0.4% (median 0.01%) CD45dimCD34+CD38+ HSPCs in the mononuclear cell population of the 15 AA patients, values that were significantly lower than those of seven healthy volunteers (0.19-0.78%, median 0.58%, P

Description: Administration of the immunosuppressive drug cyclosporine A (CsA) following autologous stem cell transplantation paradoxically elicits a systemic autoimmune syndrome resembling graft-versus-host disease (GVHD). This syndrome, termed autologous GVHD, is associated with autoreactive CD8+ T cells that recognize major histocompatibility complex (MHC) class II determinants in association with a peptide from the invariant chain. To investigate the potential role of cytokines and chemokines in autologous GVHD, interleukin 2 (IL-2), IL-4, IL-10, interferon γ (IFN-γ), and macrophage inflammatory protein-1α (MIP-1α) gene expression in peripheral blood mononuclear cells (PBMCs) was determined in 36 patients treated with CsA following transplantation and correlated with the induction of cytolytic activity against autologous phytohemagglutinin-stimulated lymphocytes (PHA-blasts) and the breast cancer cell line (T47D). The determination of gene expression by real-time polymerase chain reaction (PCR) revealed that IL-10 mRNA levels by PBMCs in patients with autologous GVHD were 29-fold higher than in healthy individuals. IFN-γ (4-fold), IL-2 (3-fold), and MIP-1α (44-fold) mRNA levels were also increased in GVHD-induced patients compared with healthy individuals. The ability of PBMCs to lyse autologous PHA-blasts and T47D tumor cells exhibited an identical temporal relationship with expression of IL-10 and IFN-γ during autologous GVHD. Moreover, the susceptibility to autologous GVHD as assessed in 75 patients was significantly associated with the IL-10−1082 G/G polymorphic alleles, allelic variants in the promoter region that govern IL-10 production. These findings indicate that IL-10 may play an unexpected but critical role in autologous GVHD and could be utilized to enhance a graft-versus-tumor effect after transplantation. Interestingly, polymorphisms in the IL-10 promoter region may also explain differences in the susceptibility of patients to autologous GVHD induction.

Description: [Background] Hematopoietic stem progenitor cells (HSPCs) with PIGA mutations are thought to acquire a survival advantage over normal HSPCs under immune attack against HSPCs and produce glycosylphosphatidylinositol-anchored protein-deficient (GPI[-]) cells in patients with acquired aplastic anemia (AA). Various underlying mechanisms of the survival advantage of PIGA-mutated HSPCs have been proposed; however, it remains still unclear how PIGA-mutated HSPCs are immunologically selected in AA. Approximately 15% of AA patients with increased GPI(-) cells possess another aberrant leukocyte subset that lacks the expression of the HLA-class I allele due to a copy number-neutral loss of heterozygosity of the HLA haplotype, which occurs in the short arm of chromosome 6 (6pLOH) as a result of uniparental disomy, or HLA allelic mutations. The presence of HLA-class I allele-lacking leukocytes (HLA-LLs) is considered to be the most compelling evidence to support the involvement of cytotoxic T lymphocytes (CTLs) in the development of bone marrow failure. Charactering GPI(-) leukocytes and platelets in AA patients with HLA-LLs may provide an insight into the mechanism underlying the immune selection of PIGA-mutated HSPCs. [Patients and Methods] We investigated the presence of GPI(-) leukocytes, erythrocytes, and platelets in 63 patients with AA using high-sensitivity flow cytometry (FCM). For the platelet analysis, platelet rich plasma (PRP) was obtained by centrifuging anticoagulated blood at 1000 rpm for 7 minutes with the brake turned off. Thirty microliters of PRP was incubated with monoclonal antibodies specific to CD55-PE, CD59-PE, CD41a-APC and HLA-A2 or A24-FITC for 20 minutes at room temperature in the dark. To prevent doublets, samples were diluted 1 to 100 in PBS and filtered with mesh immediately before the FCM analysis. Thirty of the 63 patients were heterozygous for the HLA-A allele with A24 and A2, and thus the presence of both HLA-LLs and HLA-A allele-lacking platelets could be evaluated by FCM. The lack of the HLA-A allele due to 6pLOH or allelic mutations in all HLA-LL(+) patients was confirmed by a droplet digital PCR or deep sequencing. [Results] Increased GPI(-) granulocytes, which accounted for 0.01-99.8% of the total granulocytes, were detected in 37 (58.7%) patients while HLA-A24 or A2-lacking granulocytes accounted for 0.39-98.3% of the total granulocytes in 20 (66.7%) of the 30 patients. Eight patients possessed both GPI(-) cells and HLA-LLs. In all 8 of these patients, the two aberrant cell populations were mutually exclusive. The analyses of different cell lineages revealed HLA-A allele-lacking cells in all lineages of cells, including granulocytes (Gs), monocytes (Ms), T cells (Ts), B cells (Bs), NK cells (NKs), and platelets (Ps) in 7 of the 8 patients; the remaining one patient had the GMTP pattern. In contrast, the lineage diversity of GPI(-) in the 8 patients was more restricted; GMTBNKP was only detected in 2 patients; the combinations in the other 6 patients were GT (n=1), GMBNKP (n=2), GMTNKP (n= 1) and GMTBP (n= 2). In Case 1, GPI(-) cells were not detected in T cells while HLA-A24(-) cells were detected in all lineages of cells including T cells (Figure 1). The limited lineage diversity of GPI(-) cells was also evident in 6 patients who did not possess HLA-LLs (GMP, GMBP, GMBNKP, GMTNKP, GMTBP) with GPI(-) granulocytes〉10% while the GMTBNKP pattern was common in 10 HLA-LL(+) patients who did not possess GPI(-) cells, regardless of their percentage of HLA-A allele-lacking granulocytes. Longitudinal follow-up of 5 patients over a period of 8-27 years showed a decline in the percentage of GPI(-) granulocytes (39.2 to 0.00%, 11.4 to 0.04%, 3.50 to 0.30%, 1.77 to 0.00% and 0.79 to 0.11%) and a reciprocal increase in the percentage of HLA-A allele-lacking granulocytes (80.0 to 95.2%, 92.0 to 99.1%, 24.0 to 24.4%) in 3 patients who had been placed under observation; in two patients (Cases 2 and 3) whose GPI(-) granulocyte percentages had been 〉10%, the PNH clones were completely replaced by HLA-LL clones during 6 and 8 years, respectively (Figure 2). [Conclusions] The limited diversity of the blood cell lineage and spontaneous decline of GPI(-) cells that coexisted with HLA-LLs suggest that GPI(-) cells are derived from the PIGA-mutated hematopoietic progenitor cells that were allowed to proliferate as a bystander in the environment where the CTL attack against HSPCs is taking place. Disclosures Nakao: Novartis: Honoraria; Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria; Kyowa Hakko Kirin Co., Ltd.: Honoraria.