Abstract: Treatment-free remission (TFR) has become a therapeutic goal in chronic myeloid leukemia (CML), and approximately half of the patients with chronic phase-CML (CML-CP) with deep molecular remission (DMR) by tyrosine-kinase inhibitors (TKIs) have achieved TFR. However, the mechanism of continuous TFR is still unclear, as there are “fluctuate” patients who have BCR–ABL-positive leukemia cells but do not observe obvious relapse. We focused on the immune response and conducted an immune analysis using clinical samples from the imatinib discontinuation study, JALSG-STIM213. The results showed that, in the group that maintained TFR for 3 years, changes in regulatory T (Treg) cells were observed early after stopping imatinib treatment. The effector Treg (eTreg) cells increased transiently at 1 month after stopping imatinib and then returned to baseline at 3 months after stopping imatinib treatment. There was no difference in the Treg phenotype, and CD8+ T cells in the TFR group were relatively activated. High concentrations of imatinib before stopping were negatively correlated with eTreg cells after stopping imatinib. These data suggest immunological involvement in the maintenance of the TFR, and that Treg cells after stopping imatinib might be a biomarker for TFR. Furthermore, high imatinib exposure may have a negative immunological impact on the continuous TFR.

Abstract: While unrelated bone marrow transplantation ( UBMT ) has been widely used as alternative donor transplantation, the use of umbilical cord blood transplantation ( UCBT ) is increasing recently. Methods We conducted a decision analysis to address which transplantation procedure should be prioritized for younger patients with acute myeloid leukemia ( AML ) harboring high‐ or intermediate‐risk cytogenetics in first complete remission ( CR 1), when they lack a matched related donor but have immediate access to a suitable umbilical cord blood unit. Main sources for our analysis comprised the data from three phase III trials for a chemotherapy cohort ( n = 907) and the registry data for a transplantation cohort ( n = 752). Results The baseline analysis showed that when the 8/8 match was considered for UBMT , the expected 5‐year survival rate was higher for UBMT than for UCBT (58.1% vs. 51.8%). This ranking did not change even when the 7/8 match was considered for UBMT . Sensitivity analysis showed consistent superiority of UBMT over UCBT when the time elapsed between CR 1 and UBMT was varied within a plausible range of 3–9 months. Conclusions These results suggest that 8/8 or 7/8 UBMT is a better transplantation option than UCBT even after allowing time required for donor coordination.

Abstract: Background: The Japan Adult Leukemia Study Group (JALSG) conducted the Ph+ALL202 and Ph+ALL208 studies for newly diagnosed (ND) Philadelphia-chromosome (Ph)-positive acute lymphoblastic leukemia (ALL), and successfully introduced imatinib into intensive chemotherapy followed by allogeneic hematopoietic cell transplantation (alloHCT). However, 30-40% of patients could not undergo alloHCT at CR1 because of older age, early relapse, or therapy-related death. We report the outcome of the Ph+ALL213 study, which introduced dasatinib (DA) to improve the efficacy and two-step combination to minimize the toxicity of treatments prior to alloHCT. Methods: The Ph+ALL213 study was a single-arm, multicenter phase II study for ND Ph+ALL. The protocol was reviewed and approved by the institutional review board of each hospital and registered in the UMIN Clinical Trials Registry (#UMIN000012173) and the Japan Registry of Clinical Trials (#jRCTs041180136). Patients with ND BCR/ABL1-positive ALL aged 16-64 years with PS 0-3 and sufficient organ function were included. All patients provided written informed consent before enrollment. The first step of treatment was induction (IND) targeting hematological complete remission (HCR) by 28 days of 140-mg DA and 14 days of 60-mg/m2 prednisone (PSL). IND was preceded by 7 days of PSL pre-phase treatment, during which BCR/ABL1 was confirmed by multiplex RQ-PCR. The second step was intensive consolidation (IC) targeting molecular CR (MCR), which was defined as no BCR/ABL1 signal by RQ-PCR, by 28 days of 100-mg DA in combination with CALGB BFM-like intensive chemotherapy. Consolidation comprised 4 cycles alternating between two regimens: high-dose methotrexate/cytarabine followed by 21 days of 100-mg DA (C1) and a CHOP-like regimen using vincristine (VCR)/cyclophosphamide/daunorubicin followed by 21 days of 100-mg DA (C2). The maintenance regimen was 12 cycles of 24 days of 100-mg DA with VCR /PSL. Patients who achieved HCR and had an appropriate donor proceeded to alloHCT after the first C1 consolidation (C1-1). DA was started after alloHCT only when the BCR/ABL1 signal was positive by RQ-PCR just before transplantation. The primary endpoint was event-free survival (EFS) from the induction at 3 years. Major secondary endpoints were hematological and molecular responses, adverse events (AEs), hematological relapse, non-relapse mortality (NRM), and overall survival (OS) from the induction at 3 years. Results: Of the 81 patients enrolled between Feb 2014 and April 2016 from 46 hospitals, 78 were evaluable, and the median age was 45 years (range, 16-64 years). Hematological response after IND were 73 (93.6%) CR, 4 (5.1%) CRi, and 1 (1.3%) PD, and 40 (56%) patients achieved MCR after IC. Grade 4 neutropenia/ thrombocytopenia in IND, IC, and C1-1 was reported in 51.3%/ 48.7%, 93.5%/ 5.2%, and 97.2%/ 70.8%, respectively, whereas grade 4 non-hematological AEs were noted in 2.6%, 9.1%, and 8.5%, respectively. No patients died during the course of IND, IC, or C1-1. All of 4 patients who relapsed before alloHCT had T315I mutations. One pt relapsed only in the CNS. Six patients completed the planned chemotherapy, and 8 patients discontinued the planned treatment because of AEs (4), physician's decision (2), and transfer (2) to non-registered hospitals. AlloHCT at CR1 was performed for 58 patients (74.4%). Forty-one patients (70.7%) had CMR just before transplantation. MAC and RIC conditioning was intensified for 69.0% and 31.0%, respectively, and the donor type was related, unrelated, and cord blood for 29.3%, 48.3%, and 20.7%, respectively. Eleven of 13 patients who discontinued the treatment underwent alloHCT afterwards. Three patients had NRM, but 7 patients survived with CR. At the median follow-up of 48.1 months, the 3-year EFS and OS were 67.2% (95%CI, 55.4-76.5%) and 82.8% (95%CI, 72.3-89.7%), respectively (figure 1). Of the patients who transplanted at CR1, the 3-year EFS and OS were 74.1% (95%CI, 60.8-83.5%) and 86.1% (95%CI, 74.2-92.8%), respectively. Among these patients, hematological relapse, relapse mortality, and NRM were noted in 10 (17.2%), 5 (8.6%), and 6 (10.3%), respectively. Conclusions: In this study, we reduced the relapse and toxicity before alloHCT, and improved the EFS and OS at 3 years. JALSG is starting a Ph+ALL219 phase II study to introduce ponatinib for patients who did not achieve CMR after INC following the schedule in the Ph+ALL213 study. Disclosures Kako: Pfizer Japan Inc.: Honoraria; Bristol-Myers Squibb: Honoraria. Yokoyama:Astellas: Other: Travel expenses. Onishi:Pfizer Japan Inc.: Honoraria; MSD: Honoraria, Research Funding; Novartis Pharma: Honoraria; Bristol-Myers Squibb: Honoraria, Research Funding; Janssen Pharmaceutical K.K.: Honoraria; Astellas Pharma Inc.: Honoraria; Celgene: Honoraria; ONO PHARMACEUTICAL CO., LTD.: Honoraria; Otsuka Pharmaceutical Co., Ltd.: Honoraria; Nippon Shinyaku: Honoraria; Takeda Pharmaceutical Co., Ltd.: Research Funding; Chugai Pharmaceutical Co., Ltd.: Honoraria; Sumitomo Dainippon Pharma: Honoraria; Kyowa-Hakko Kirin: Honoraria. Shiro:Bristol-Myers Squibb: Honoraria. Atsuta:CHUGAI PHARMACEUTICAL CO., LTD.: Honoraria; Kyowa Kirin Co., Ltd: Honoraria. Miyazaki:Chugai: Research Funding; Otsuka: Honoraria; Novartis: Honoraria; Nippon-Shinyaku: Honoraria; Dainippon-Sumitomo: Honoraria; Kyowa-Kirin: Honoraria.

Abstract: Background: Treatment-free remission (TFR) is a new therapeutic goal for chronic myeloid leukemia in chronic phase (CML-CP). Deep molecular response (DMR) is a prerequisite condition to discontinue a tyrosine kinase inhbitor (TKI). In ENESTnd and DASISION trials, both nilotinib and dasatinib achieved DMR more effectively than imatinib. However, there is no direct comparative study to determine which TKI is better to achieve DMR for de novo CML-CP. So, we conducted a randomized phase 3 JALSG CML212 study to compare the achievement of MR4.5 (BCR-ABL IS≤0.0032%) between nilotinib and dasatinib. Methods: The JALSG CML212 study is a multicentral open-labeled prospective randomized controlled phase 3 study for de novo CML-CP. This study was reviewed and approved by the institutional review board of each institute and registered in the UMIN Clinical Trials Registry (#UMIN000007909). All patients provided written informed consent before enrollment. Diagnosis of CML was done by a cytogenetic study (G-banding or FISH) and/or detection of BCR-ABL by RT-PCR. The primary endpoint is a rate of cumulative achievement of MR4.5 by 18 mon. Major secondary endpoints were safety, continuity, progression-free survival (PFS), event-free survival (EFS), overall survival (OS), and cytogenetic and molecular responses. A total of 461 patients were registered from 82 institutes and 454 patients were randomly assigned to the nilotinib arm or dasatinib arm (both, n=227) with Sokal risk scores as a stratification factor. Treatment doses were 300 mg, bid for nilotinib and 100 mg, qd for dasatinib. Treatment responses were evaluated by ELN2009. Patients were allowed to stop study treatment if judged as failure by ELN2009 or showed intolerance (repetitive ≥Grade 3 or continuous Grade 2 side effects) to the allocated TKI. BCR-ABL mRNA levels were monitored every three months with international scales using a MolecularMD, ODK-1201, or M135R kit with ≥MR4.5 sensitivities. Adverse events were evaluated by the CTCAE ver 4.0. Results: The median age of the patients was 53 years old in both arms. The proportions of Sokal low, intermediate, and high risk groups were 44.1%, 37.0%, and 18.9% in the nilotinib arm and 44.5%, 37.0%, and 18.5% in the dasatinib arm, respectively, without a significant difference. Also, there was no significant difference in ECOG PS, EUTOS risk groups, complications, or frequencies of additional chromosomal abnormalities in both arms. In the ITT population, the cumulative achievement rates of MR4.5 by 18 mon were 33.0% (75/227) (95% CI:27.0-39.6%) in the nilotinib arm and 30.8% (70/227) (95% CI: 24.9-37.3%) in the dasatinib arm with no significant difference with a CMH test (p=0.62). This finding was also confirmed in the per-protocol (PP) population (33.5% in the nilotinib arm and 31.8% in the dasatinib arm, p=0.72). At 18 mon, 75.9% and 79.6% of the patients continued the allocated TKI in the nilotinib and dasatinib arms, respectively (p=0.36) (in the PP population).There was no significant difference in PFS, EFS, or OS between two arms by log-rank tests (the estimated rates at 36 mon: 98.8%, 67.2%, and 98.8% in the nilotinib arm; 99.0%, 65.4%, and 99.0% in the dasatinib arm). In addition, PFS, EFS and OS didn't differ between both arms regardless of Sokal and EUTOS risk groups. The cumulative CCyR rates by 12, 18, 24, and 36 mon were 77.1%, 78.0%, 78.4%, and 78.4% in the nilotinib arm and 78.4%, 78.9%, 78.9%, and 78.9% in the dasatinib arm, respectively without no significant difference. The MMR rates by 12, 18, 24, and 36 mon were 62.6%, 67.0%, 72.3%, and 73.1% in the nilotinib arm and 68.7%, 73.1%, 75.3%, and 77.1% in the dasatinib arm, respectively, without no significant difference. The MR4.5 rates by 12, 24, and 36 mon were 25.6%, 37.4%, and 40.5% in the nilotinib arm and 23.4%, 36.6%, and 44.5% in the dasatinib arm, respectively, with no significant difference. In the safety population, Grade 3/4 adverse events observed with ≥10% frequencies were lipase elevation (11.5%) in the nilotinib arm and neutropenia (12.8%) and thrombocytopenia (16.8%) in the dasatinib arm. Any new safety issue was observed in neither of the arms. Conclusions: Based on these results, we consider that nilotinib and dasatinib are equally effective for de novo CML-CP patients in achieving MR4.5 as well as in achieving CCyR and MMR in terms of both frequencies and times to achievement with similar continuity. Figure Disclosures Matsumura: Kyowa Kirin Co., Ltd.: Research Funding; Sumitomo Dainippon Pharma Co., Ltd.: Research Funding; Shionogi & Co., Ltd.: Research Funding; Janssen Pharmaceutical K.K: Speakers Bureau; Amgen K.K.: Speakers Bureau; DAIICHI SANKYO COMPANY, LIMITED.: Speakers Bureau; Astellas Pharma Inc.: Speakers Bureau; Otsuka Pharmaceutical Co., Ltd.: Speakers Bureau; ONO PHARMACEUTICAL CO., LTD.: Research Funding; Chugai Pharmaceutical Co., Ltd.: Research Funding; Eisai Co., Ltd.: Research Funding; Bristol-Myers Squibb Company: Speakers Bureau; Pfizer Japan Inc.: Speakers Bureau; Novartis Pharma KK: Speakers Bureau. Minami:Pfizer Japan Inc.: Honoraria; Novartis Pharma KK: Honoraria; Bristol-Myers Squibb Company: Honoraria; Takeda: Honoraria. Takahashi:Bristol-Myers Squibb Company: Honoraria; Pfizer Japan Inc.: Honoraria, Research Funding; Novartis Pharma KK: Honoraria, Research Funding. Nakaseko:Novartis Pharma KK: Speakers Bureau; Pfizer Japan Inc.: Speakers Bureau. Iriyama:Bristol-Myers Squibb Company: Speakers Bureau; Novartis Pharma KK: Speakers Bureau; Pfizer Japan Inc.: Speakers Bureau; Otsuka Pharmaceutical: Speakers Bureau. ONO:Mundipharma K.K.: Honoraria; Janssen Pharmaceutical K.K: Honoraria; Eisai Co., Ltd.: Honoraria; Astellas Pharma Inc.: Honoraria; TAIHO PHARMACEUTICAL CO., LTD.: Research Funding; Takeda Pharmaceutical Company Limited.: Honoraria; ONO PHARMACEUTICAL CO., LTD.: Honoraria, Research Funding; Otsuka Pharmaceutical Co., Ltd.: Honoraria; Pfizer Japan Inc.: Honoraria; Bristol-Myers Squibb Company: Honoraria; Novartis Pharma KK: Honoraria; Chugai Pharmaceutical Co., Ltd.: Honoraria, Research Funding; Kyowa Kirin Co., Ltd.: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; DAIICHI SANKYO COMPANY, LIMITED.: Honoraria. Fujisawa:Janssen Pharmaceutical K.K: Speakers Bureau; Celgene: Speakers Bureau; Novartis Pharma KK: Research Funding, Speakers Bureau; Bristol-Myers Squibb Company: Speakers Bureau; Pfizer Japan Inc.: Research Funding, Speakers Bureau; Otsuka Pharmaceutical: Speakers Bureau; Astellas Pharma Inc.: Research Funding, Speakers Bureau; Takeda Pharmaceutical Company Limited.: Speakers Bureau; NIPPON SHINYAKU CO.,LTD.: Research Funding. Kobayashi:Pfizer Japan Inc.: Research Funding, Speakers Bureau; Astellas Pharma Inc.: Speakers Bureau; SymBio Pharmaceuticals Limited.: Consultancy. Asou:Fuji Pharma Co.,Ltd.: Speakers Bureau; Sumitomo Dainippon Pharma Co., Ltd.: Research Funding; Eisai Co., Ltd.: Research Funding; NIPPON SHINYAKU CO.,LTD.: Honoraria, Speakers Bureau; Astellas Pharma Inc.: Research Funding; Chugai Pharmaceutical Co., Ltd.: Research Funding; Novartis Pharma KK: Honoraria; Asahi Kasei Pharma.: Speakers Bureau. Kiyoi:Celgene Corporation: Research Funding; Bristol-Myers Squibb Company: Speakers Bureau; Astellas Pharma Inc.: Consultancy, Research Funding, Speakers Bureau; Chugai Pharmaceutical Co., Ltd.: Research Funding; Novartis Pharma KK: Research Funding, Speakers Bureau; Sumitomo Dainippon Pharma Co., Ltd.: Research Funding; Otsuka Pharmaceutical Co., Ltd.: Research Funding; NIPPON SHINYAKU CO.,LTD.: Research Funding; Amgen Astellas BioPharma K.K.: Consultancy; Kyowa Kirin Co., Ltd.: Research Funding; Zenyaku Kogyo Co., Ltd.: Research Funding; FUJIFILM Corporation: Research Funding; Daiichi Sankyo Co., Ltd.: Consultancy, Research Funding; Eisai Co., Ltd.: Research Funding; Pfizer Japan Inc.: Research Funding; Takeda Pharmaceutical Co., Ltd.: Research Funding; Sanofi K.K.: Research Funding; Perseus Proteomics Inc.: Research Funding. Miyazaki:NIPPON SHINYAKU CO.,LTD.: Honoraria; Otsuka Pharmaceutical: Honoraria; Novartis Pharma KK: Honoraria; Chugai Pharmaceutical Co., Ltd.: Honoraria; Kyowa Kirin Co., Ltd.: Honoraria; Astellas Pharma Inc.: Honoraria; Celgene: Honoraria; Sumitomo Dainippon Pharma Co., Ltd.: Honoraria. Naoe:Sysmex co.: Speakers Bureau; NIPPON SHINYAKU CO.,LTD.: Speakers Bureau; Eisai Co., Ltd.: Speakers Bureau; Astellas Pharma Inc.: Speakers Bureau; Bristol-Myers Squibb Company: Speakers Bureau.

Abstract: Background: After long-term analysis of the JALSG-APL204 study we recently reported that maintenance therapy with tamibarotene was more effective than all-trans retinoic acid (ATRA) by reducing relapse in APL patients. Here, the clinical significance of other important prognostic factors was evaluated with multivariate analyses. Patients and Methods: Newly diagnosed acute promyelocytic leukemia (APL) patients were registered with the study. Induction was composed of ATRA and chemotherapy. Patients who achieved molecular remission after consolidation were randomly assigned to maintenance with tamibarotene or ATRA. Results: Of the 344 eligible patients, 319 (93%) achieved complete remission (CR). After completing consolidation, 269 patients underwent maintenance random assignment—135 to ATRA, and 134 to tamibarotene. By multivariate analysis, overexpression of CD56 in blast was an independent unfavorable prognostic factor for relapse-free survival (RFS) (p = 0.006) together with more than 10.0 × 109/L WBC counts (p = 0.001) and the ATRA arm in maintenance (p = 0.028). Of all phenotypes, CD56 was related most clearly to an unfavorable prognosis. The CR rate, mortality rate during induction and overall survival of CD56+ APL were not significantly different compared with CD56− APL. CD56 is continuously an independent unfavorable prognostic factor for RFS in APL patients treated with ATRA and chemotherapy followed by ATRA or tamibarotene maintenance therapy.

Abstract: Background: Tamibarotene, a new synthetic retinoid, displays (i) approximately 10-fold increased potency over ATRA at inducing in vitro differentiation of NB-4 cells (ii) enhanced chemical stability compared with ATRA (iii) low affinity for cellular RA-binding protein. The clinical efficacy of tamibarotene for the treatment of acute promyelocytic leukemia (APL) has also been reported. A prospective randomized controlled study to evaluate tamibarotene by comparison to ATRA was carried out for maintenance therapy of APL in JALSG APL204 (Shinagawa et al, 2014). The 4-year-relapse free survival (RFS) did not differ between patients treated with ATRA or tamibarotene. However, an improved efficacy of tamibarotene in high-risk patients was suggested, which warrants further investigation. Here, we evaluate the long-term outcome of the study. Patients and Methods: Patients enrolled in this study were newly diagnosed with APL and documented cytogenetic and/or molecular evidence of t(15;17)/ PML-RARA . The age of the patients ranged between 15 and 70 years and the ECOG performance status was between 0 and 3. For remission induction therapy, ATRA was administered to all patients at a daily dose of 45 mg/m2 until complete remission (CR). The chemotherapy protocol varied depending on the initial leukocyte count and blast count in the peripheral blood. In brief, patient groups were defined as: leukocytes & lt; 3,000/µl (Group A: ATRA alone), 3,000/µl ≤ leukocytes & lt; 10,000/µl (Group B: ATRA plus IDA/Ara-C: 2+5), and leukocytes ≥ 10,000/µl (Group C: ATRA plus IDA/Ara-C: 3+5). Those patients who experienced leukocytosis received additional chemotherapy (Group D). Patients who achieved molecular remission after consolidation chemotherapy were randomly assigned to 2 groups of maintenance therapy, and administered tamibarotene at a daily dose of 6 mg/m2 divided into 2 doses for 14 days or ATRA at a daily dose of 45 mg/m2 divided into 3 doses for 14 days. Each cycle of treatment was repeated every 3 months for 2 years. The primary endpoint was hematological or molecular relapse-free survival (RFS) during the maintenance and follow up period. This study is registered at the University Hospital Medical Information Network Clinical Trials Registry as C000000154. Results: A total of 347 patients were enrolled in the study. Of the 344 eligible patients, 319 (93%) achieved CR. After completing three courses of consolidation therapy, 269 patients underwent maintenance random assignment; 135 patients were assigned to ATRA, and 134 patients were assigned to tamibarotene. The mean follow-up of patients alive and relapse-free at the date of last contact was 7 years. The 7-year RFS rate was 84% for the ATRA arm and 93% for the tamibarotene arm (p=0.031) (Fig.1). When the analysis was restricted to 52 high-risk patients with an initial leukocyte count ≥ 10,000/µl, the difference was more prominent (62% vs 89%, p=0.034) (Fig.2). The 7-year RFS of induction treatment for Group A (92 cases) was 91%, Group B (38 cases) 92%, Group C (52 cases) 75% and Group D (87 cases) 91% (p=0.005). Both treatments were generally well tolerated. Secondary hematopoietic disorders were observed in 12 cases, malignancies in 9 cases, late cardiac complications (grade 3 or more) in 5 cases. However, there was no significant difference in terms of these complications between the two treatment groups. Conclusions: Maintenance therapy with tamibarotene was effective at decreasing the relapse rate in APL patients by comparison to ATRA at the 7-year observation point. In particular, tamibarotene was significantly more effective than ATRA for high risk patients with leukocytes ≧10,000/μl. These results could lead to a new strategy for the treatment of high risk patients, which is one of the recent priority issues in the treatment of APL. Disclosures Takeshita: Chugai Pharmaceutical Co., Ltd.: Research Funding; Astellas Pharma Inc.: Research Funding; Phizer Japan Inc.: Research Funding; Takeda Pharmaceutical Co Ltd: Research Funding. Asou: Chugai Pharmaceutical Co., Ltd.: Research Funding; Astellas Pharma Inc.: Research Funding. Ueda: KAINOS LABORATORIES INC: Membership on an entity's Board of Directors or advisory committees; Abrynx nv: Membership on an entity's Board of Directors or advisory committees; Elli LiLLY Japan KK: Other: Clinical Trial; Takeda PharmaceuticalCompany Limited: Other: Clinical TRial; Otsuka Pharmaceutical Co Ltd: Other: Clinical Trial; Celgene KK: Other: Clinical Trial; Symbio Pharmaceutical Limited: Other: Clinical Trial; AstellasPharma Inc: Other: Clinical Trial; Eisai Co. Ltd: Other: Clinical Trial. Fujita: Chugai Pharmaceutical: Honoraria. Usui: Nippon Shinyaku Pharmaceutical Co: Research Funding. Kobayashi: Pfizer, Ohtsuka, Astellas, Ariad: Research Funding. Kiyoi: Kyowa Hakko Kirin Co., Ltd.: Research Funding; Nippon Shinyaku Co., Ltd.: Research Funding; ONO Pharmaceutical Co., Ltd.: Research Funding; Takeda Pharmaceutical Co., Ltd.: Research Funding; Nippon Boehringer Ingelheim Co., Ltd.: Research Funding; Meiji Seika Pharma Co.,Ltd.: Research Funding; FUJIFILM Corporation: Patents & Royalties, Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding; Eisai Co., Ltd.: Research Funding; Celgene Corporation: Consultancy, Research Funding; Chugai Pharmaceutical Co., Ltd.: Research Funding; Astellas Pharma Inc.: Consultancy, Research Funding; Zenyaku Kogyo Co., Ltd.: Research Funding; Phizer Japan Inc.: Honoraria, Research Funding; MSD K.K.: Research Funding; Novartis Pharma K.K.: Research Funding; Sumitomo Dainippon Pharma Co., Ltd.: Research Funding; JCR Pharmaceuticals Co.,Ltd.: Research Funding. Atsuta: Otsuka Pharmaceutical Co., Ltd.: Honoraria. Naoe: Otsuka Pharmaceutical Co.,Ltd.: Honoraria, Research Funding; Nippon Boehringer Ingelheim Co.: Honoraria, Research Funding; Fujifilm Corporation: Patents & Royalties, Research Funding; Dainippon Sumitomo Pharma Co.,LTD.: Research Funding; Astellas Pharma Inc.: Research Funding; Toyama Chemikal Co.,Ltd.: Research Funding. Miyazaki: Nippon Shinyaku: Honoraria.

Abstract: Introduction: Tyrosine kinase inhibitor (TKI) has dramatically improved the prognosis of chronic myeloid leukemia (CML) patients. Recently, many trials of TKI discontinuation revealed that approximately 40% to 60% of CML patients who received long time TKI therapy reached the treatment-free remission (TFR), thus now TFR is proposed as one of the goals in CML treatment. Achieving deep molecular response (DMR) by TKI therapy is a minimum requirement of a challenge to TKI discontinuation in CML patient, actually CML patients with molecular residual disease (MRD) showed worse consequence than undetectable MRD (IJH, 2017). On the other hand, it has been known that some patients sustain a molecular response for a long time despite BCR-ABL fusion gene positivity in their peripheral blood. We hypothesized that the residual malignant cells were eliminated by host immune systems in the patients with continuous TFR. Practically, we obtained the data that the immune responses of the patients with continuous TFR were more activated than relapsed patients in the discontinuation trial of imatinib (ASH, 2019). Here, we reported immune effects before and after TFR phase in two Japanese discontinuation trials of second-generation TKIs (JALSG N-STOP216 and D-STOP216). Methods: Japanese patients with CML-CP treated with nilotinib or dasatinib as the first line for at least three years and confirmed in DMR for at least two years were eligible. Patients who received other TKI or stem cell transplantations were excluded. Patients were re-confirmed in MR4.5 before discontinuing TKI and they were sampled peripheral blood at pre- and 1, 3 months after stopping TKIs and after retreatment (figure 1). Peripheral blood mononuclear cells (PBMCs) were subjected to staining with immune markers and analyzed by flow cytometry. Results: 51 patients treated with nilotinib and 49 patients treated with dasatinib were assessed clinical outcomes. At 12 months, 39/51 patients (76.5%) and 27/49 patients (55.1%) remained TFR in N-STOP216 and D-STOP216 respectively (EHA, 2021). For immunological analysis, 48 patients and 43 patients were analyzed by flowcytometry. We classified the patient of each trial into two groups (TFR group and Retreatment (RET) group) (figure 1). The frequency of CD4 + T cells and CD8 + T cells in CD3 + T cells was not different between both groups in each trial. The frequency of FoxP3 +CD4 + regulatory T (Treg) cells were not different between both groups in each trial. However, the kinetics of Treg cells, especially effector Treg (eTreg; FoxP3 hiCD45RA -) cells from Pre-stopping dasatinib to 1 month after stopping dasatinib, significantly increased in TFR groups but not in RET group (figure 2). This difference in kinetics of eTreg cells was not observed in nilotinib discontinuation trial (figure 2). In N-STOP216 trial, there were no differences between TFR and RET groups in the immuno-phenotype of CD8 + T cells, NK cells, or B cells, while granulocytic myeloid-derived suppressor cells (G-MDSCs) increased at 1 month after stopping nilotinib in RET group (0.27% in RET group vs. 0.08% in TFR group, P=0.011) (figure 3). On the other hand, in D-STOP216, CD8 + T cells from the patients with continuous TFR showed less exhausted phenotype (PD-1 +CD8 +T cells 37.4% in RET group vs. 49.8% in TFR group, p=0.018) and more proliferative activity (Ki67+CD8 cells 5.03% in RET group vs. 8.91% in TFR group, p=0.043) compared with RET group at 1 month after stopping dasatinib (figure 4). There were no differences in NK cells, B cells, and MDSCs between TFR and RET groups in D-STOP216. Conclusion: We found that each TKI evoked different immune responses after stopping TKI. Nilotinib has been developed as higher specific for BCR-ABL, therefore immune cells were not affected because of its narrower off-target effect. MDSCs developed by hematopoietic stem cells with BCR-ABL were decreased by the direct effect of nilotinib in the patients with continuous TFR. Antitumor immune responses might be diminished by residual MDSCs in RET group consequently it would be a molecular relapse. On the other hand, dasatinib has different immune effects probably due to its broad-spectrum kinase inhibitory effects. T cell immune responses might be exhausted by long term exposure to dasatinib in RET group. This study showed the possibility of different mechanisms of relapse caused by distinct immune effects. Figure 1 Figure 1. Disclosures Takahashi: Kyowahakko-Kirin: Research Funding; Ono: Research Funding; Asahikasei: Research Funding; Toyamakagaku: Research Funding; Eizai: Research Funding; Chugai: Research Funding; Otsuka Pharmaceutical: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Atsuta: Astellas Pharma Inc.: Speakers Bureau; Mochida Pharmaceutical Co., Ltd.: Speakers Bureau; Meiji Seika Pharma Co, Ltd.: Honoraria; AbbVie GK: Speakers Bureau; Kyowa Kirin Co., Ltd: Honoraria. Minami: Bristol-Myers Squibb Company: Honoraria; Novartis Pharma KK: Honoraria; Pfizer Japan Inc.: Honoraria; Takeda: Honoraria; Astellas: Honoraria; Ono: Research Funding; CMIC: Research Funding. Iriyama: Bristol Myers Squibb: Honoraria, Speakers Bureau; Novartis: Honoraria, Speakers Bureau; Pfizer: Honoraria, Speakers Bureau; Otsuka: Honoraria, Speakers Bureau. Kiyoi: Kyowa Kirin: Honoraria; Fijifilm: Honoraria; Eisai: Honoraria; Dainippon Sumitomo: Honoraria; Daiichi Sankyo: Honoraria; celgene: Honoraria; Astellas: Honoraria; Otsuka: Honoraria; Perseus Proteomics: Honoraria; Pfizer: Honoraria; Pfizer: Honoraria; Sanofi: Honoraria; Takeda: Honoraria; Zenyaku Kogyo: Honoraria. Miyazaki: Novartis: Honoraria; Abbvie: Honoraria; Kyowa-Kirin: Honoraria; Nippon-Shinyaku: Honoraria; Chugai: Honoraria; Bristol-Myers Squibb: Honoraria; Pfizer: Honoraria; Sumitomo-Dainippon: Honoraria, Research Funding; Janssen: Honoraria; Eisai: Honoraria; Daiichi-Sankyo: Honoraria; Astellas: Honoraria; Takeda: Honoraria; Sanofi: Honoraria. Matsumura: Ono: Research Funding; Otsuka: Consultancy, Research Funding, Speakers Bureau; Pfizer: Research Funding, Speakers Bureau; Shionogi: Research Funding; Taiho: Research Funding; Takeda: Research Funding; Sumitomo Dainippon: Research Funding; Nihon Pharmaceutical: Research Funding; Daiichi Sankyo: Research Funding, Speakers Bureau; Japan Blood Products Organization: Research Funding; Mundipharma: Research Funding; AYUMI Pharmaceutical: Research Funding; Eli Lilly Japan: Research Funding; Novartis: Research Funding, Speakers Bureau; Nippon Shinyaku: Research Funding; MSD: Research Funding; Mitsubishi Tanabe: Research Funding; Amgen: Speakers Bureau; Bristol-Myers Squibb: Speakers Bureau; Janssen: Speakers Bureau; Kyowa Kirin: Research Funding; Eisai: Research Funding; Chugai: Research Funding; Astellas: Speakers Bureau; Asahi Kasei: Research Funding; Addvie: Research Funding.

Abstract: [Background] We previously demonstrated that allogeneic hematopoietic stem cell transplantation (HSCT) in the first complete remission (CR1) was recommended for adult patients wih Philadelphia chromosome (Ph)-negative acute lymphoblastic leukemia (ALL) who have a human leukocyte antigen (HLA)-matched related (Leukemia 2011;25:259-265) or unrelated donor (Bone Marrow Transplant 2013;48:1077-1083). However, pediatric-inspired high-intensity chemotherapy dramatically improved the prognosis of adult patients with Ph-negative ALL. Therefore, the optimal treatment strategy for Ph-negative ALL in CR1 has not been established in the era of high-intensity chemotherapy. [Methods] Outcomes of patients with Ph-negative ALL who underwent HSCT from HLA-matched related or unrelated donor in CR1 performed between 2002 and 2011 (HSCT-MRD group and HSCT-MUD group, respectively) were obtained from the Transplant Registry Unified Management Program (TRUMP), which is the registry database of the Japanese Society for Hematopoietic Cell Transplantation (JSHCT). Patients aged between 16 and 24 and between 25 and 65 were analyzed separately, and their outcomes were compared with those of patients who did not receive HSCT in CR1 in clinical studies by Japan Adult Leukemia Study Group (JALSG), ALL-202U study in which patients received chemotherapy designed for pediatric patients (Blood Cancer J 2014;4:e252)(202U group) and ALL-202O study in which patients were randomly assigned to receive adult-type chemotherapy with high-dose or intermediate-dose methotrexate (MTX) therapy (Leukemia 2018;32:626-632)(202O group), respectively. Median durations between diagnosis to HSCT were obtained from the TRUMP data, and only patients who were disease-free more than each median duration were included from the JALSG studies. Risk stratifications were performed based on the white blood cell (WBC) count and cytogenetics. [Results] In patients aged less than 25 who underwent HSCT from related donor, the median duration between diagnosis to HSCT was 188 days. Overall survival (OS) in 202U group (N = 93) was significantly superior compared with OS in HSCT-MRD group (N = 102) (OS at 5 years: 81.8% vs 67.8%, P = 0.016) (Figure 1(A)), and which was attributed to the higher non-relapse mortality in HSCT-MRD group (NRM at 5 years: 1.4% vs 9.5%, P = 0.015). Disease-free survival (DFS) and relapse rate (RR) were similar between two groups (DFS at 5 years: 70.2% vs 62.5%, P = 0.115, and RR at 5 years: 28.4% vs 28.4%, P = 0.689). Higher OS was preserved in younger ( 〈 21) and standard-risk patients. In patients aged less than 25 who underwent HSCT from unrelated donor, the median duration between diagnosis to HSCT was 246 days. OS in 202U group (N = 92) was similar with OS in HSCT-MUD group (N = 51) (OS at 5 years: 81.6% vs 82.7%, P = 0.772). RR in HSCT-MUD group was lower (RR at 5 years: 16.7%) than that in HSCT-MRD group. In patients aged more than 24 who underwent HSCT from related donor, the median duration between diagnosis to HSCT was 158 days. OS rate was not different between 202O group (N = 147) and HSCT-MRD group (N = 152) (OS at 5 years: 57.0% vs 60.2%, P = 0.114) (Figure 1(B)). The lower RR was counterbalanced by the higher NRM in HSCT-MRD group (RR at 5 years: 51.6% vs 30.0%, P 〈 0.001, and NRM at 5 years: 4.1% vs 15.2%, P = 0.015). No difference in OS was demonstrated among any subgroups. Superior DFS in HSCT-MRD group was observed only in high-risk patients (DFS at 5 years: 26.5% vs 57.2%, P = 0.003), but it diminished when only patients who actually received high-dose MTX were included in 202O group (DFS at 5 years: 36.4% vs 57.2%, P = 0.092). In patients aged more than 24 who underwent HSCT from unrelated donor, the median duration between diagnosis to HSCT was 214 days. OS rate was not different between 202O group (N = 138) and HSCT-MUD group (N = 104) (OS at 5 years: 60.0% vs 65.8%, P = 0.563). Superior DFS in HSCT-MUD group was observed even in all patients (DFS at 5 years: 47.2% vs 64.2%, P = 0.029). RR in HSCT-MUD group was lower (RR at 5 years: 14.3%) than that in HSCT-MRD group. [Discussions & Conclusions] High-intensity chemotherapy may change the role of HSCT for Ph-nagative ALL. Improved outcomes in HSCT-MUD group were observed, and it was partially because patients who had long CR before HSCT could underwent HSCT from MUD in CR1. Disclosures Kako: Bristol-Myers Squibb: Honoraria; Pfizer Japan Inc.: Honoraria. Tanaka:Bristol-Myers Squibb: Research Funding. Ichinohe:JCR Pharmaceuticals: Honoraria; Celgene: Honoraria; Janssen Pharmaceutical K.K.: Honoraria; Astellas Pharma: Research Funding; Chugai Pharmaceutical Co.: Research Funding; CSL Behring: Research Funding; Eisai Co.: Research Funding; Kyowa Hakko Kirin Co.: Research Funding; Ono Pharmaceutical Co.: Research Funding; Pfizer: Research Funding; Nippon Shinyaku Co.: Research Funding; MSD: Research Funding; Otsuka Pharmaceutical Co.: Research Funding; Repertoire Genesis Inc.: Research Funding; Sumitomo Dainippon Pharma Co.: Research Funding; Taiho Pharmaceutical Co.: Research Funding; Takeda Pharmaceutical Co.: Research Funding; Zenyaku Kogyo Co.: Research Funding; Alexion Pharmaceuticals: Honoraria; Bristol-Myers Squibb: Honoraria; Mundipharma: Honoraria; Novartis: Honoraria. Kurahashi:Sumitomo Dainippon Pharma Co., Ltd.: Honoraria; Novartis Pharma Co., Ltd.: Honoraria; Takeda Pharmaceutical Co., Ltd: Honoraria; Bristol-Myers Squibb, Ltd.: Honoraria. Usui:Alexion Pharmaceuticals: Other: Personal Fees; Bristol-Myers Squibb: Other: Personal Fees, Research Funding; Kyowa-Hakko-Kirin Co.Ltd.: Other: Personal Fees; Astellas Pharma Inc.: Other: Personal Fees; Huya Bioscience International: Other: Personal Fees; Nippon Shinyaku Co.: Other: Personal Fees; SymBio Pharmaceuticals: Other: Personal Fees; Celgene Corporation: Other: Personal Fees; Pfizer: Other: Personal Fees, Research Funding; Takeda Pharmaceutical Co. Ltd: Other: Personal Fees; Cmic Co: Other: Personal Fees; Otsuka Pharmaceutical Co.Ltd.: Other: Personal Fees; AbbVie Inc: Other: Personal Fees. Kiyoi:Sumitomo Dainippon Pharma Co., Ltd.: Research Funding; Astellas Pharma Inc.: Honoraria, Research Funding; Kyowa Hakko Kirin Co., Ltd.: Research Funding; Eisai Co., Ltd.: Research Funding; Zenyaku Kogyo Co., Ltd.: Research Funding; Chugai Pharmaceutical Co., Ltd.: Research Funding; Pfizer Japan Inc.: Honoraria; Perseus Proteomics Inc.: Research Funding; Otsuka Pharmaceutical Co.,Ltd.: Research Funding; Bristol-Myers Squibb: Research Funding; Daiichi Sankyo Co., Ltd: Research Funding; Nippon Shinyaku Co., Ltd.: Research Funding; FUJIFILM Corporation: Research Funding; Takeda Pharmaceutical Co., Ltd.: Research Funding. Matsumura:Bristol-Myers Squibb: Speakers Bureau; Novartis: Speakers Bureau; Otsuka Pharmaceutical: Consultancy, Research Funding; Pfizer: Research Funding, Speakers Bureau. Miyazaki:Chugai: Research Funding; Otsuka: Honoraria; Novartis: Honoraria; Nippon-Shinyaku: Honoraria; Dainippon-Sumitomo: Honoraria; Kyowa-Kirin: Honoraria. Atsuta:CHUGAI PHARMACEUTICAL CO., LTD.: Honoraria; Kyowa Kirin Co., Ltd: Honoraria.