Abstract: Abstract 2554 Aims: Children with Ph+ALL generally have a poor prognosis when treated with chemotherapy alone. The timing and duration of the use of imatinib has not been determined. We investigated a role of imatinib immediately before HSCT. Methods: All the patients with ALL were screened for diagnosis of Ph+ALL using RT-PCR. Children with Ph+ALL were enrolled on JPLSG Ph+ALL04 Study within 1 week of initiation of treatment for ALL. Treatment regimen consisted of 5 therapeutic phases: Induction phase (5-drug induction), Intensification phase (high-dose cytarabine and BFM Ib), Re-induction phase (4-drug re-induction), 2 weeks of Imatinib monotherapy phase (23 weeks after diagnosis), and HSCT phase (Etoposide+CY+TBI conditioning). Before and after each phase, minimal residual disease (MRD), the amount of BCR-ABL transcripts, was measured with the real-time PCR method (cut-off 50 copies/microgram RNA). The study was registered in UMIN-CTR (Medical Information, University hospital Medical Information Network - Clinical Trials Registry): UMIN ID C000000290. Results: During the period 2004–08, 42 patients were registered in the Ph+ALL04 study. Out of 42 patients, 37 patients (88%) achieved CR and 7 of 37 patients also achieved MRD-negative after induction phase. There were 13 patients who had no MRD at the beginning of imatinib monotherapy phase, and 14 patients were MRD-negative after imatinib phase, consequently, 14 patients were MRD-negative at the time of HSCT. Six patients relapsed before HSCT. In total, 31 patients received HSCT in 1st CR. All the patients had engraftment and no patients died because of complications of HSCT. Five patients relapsed after HSCT and 4 of the 5 patients were MRD-negative before HSCT and the other patient had detectable MRD although it was less than 50 copies. Twenty-six patients continue to be in 1st CR and MRD-negative for median of 3 years after diagnosis. The 3-year event-free survival rate and over-all survival rate for all the patients was 57% and 80%, respectively (figure 1). Five patients did not achieve CR after induction phase and they were treated with imatinib-contained chemotherapy. Four of the 5 patients achieved CR. All of the 4 patients received cord blood transplantation and remains in continued CR. Interpretation: The chemotherapy we employed was based on the previous high-risk regimen of TCCSG (Tokyo Children's Cancer Study Group) L-99-15 Study. The chemotherapy was intensive enough to induce MRD-negative in 13 at the time of imatinib phase and 31 of 42 patients were in CR at the time of HSCT (around 25–28 weeks after diagnosis). We planned to assess the efficacy of imatinib immediately before HSCT but it was not possible because of the low amount of MRD in most patients at the beginning of imatinib phase. Conclusion: Although EFS and OS was excellent in this study, 88% of induction rate appeared unsatisfactory and relapse occurred before HSCT in 6 out of 37 patients who achieved CR after induction phase. Earlier and longer use of imatinib may improve EFS in children with Ph+ALL and HSCT may be omitted in a subset of patients who achieve an early and deep remission status. Disclosures: No relevant conflicts of interest to declare.

Abstract: IRF8 induces the Klf4 gene in myeloid progenitors; this transcription factor cascade is essential for Ly6C+ monocyte development. IRF8 binding to genomic targets promotes H3K4me1, a chromatin signature for promoter-distal enhancers, thereby inducing gene expression.

Abstract: [Background] Myelodysplastic syndrome is an intractable disorder characterized by ineffective hematopoiesis. Although allogeneic hematopoietic stem cell transplantation is the only curative therapy for eligible patients, hematopoiesis-supportive pharmacotherapy is practically important for transplant-ineligible patients to overcome transfusion dependency and infections. Vitamin K2 (VK2, menatetrenone) is a drug used to aim at improvement of hematopoiesis in MDS patients (Leukemia 14: 1156, 2000). However, the exact mechanism how VK2 improves hematopoiesis remains largely unknown. It was reported that VK2 induces MDS cells to undergo apoptosis (Leukemia 13: 1399, 1999). Here, we investigated our hypothesis that VK2 exerts its hematopoiesis-supportive effects through acting on mesenchymal stem/stromal cells (BM-MSCs) in the bone marrow microenvironment. [Methods] Normal bone marrow (BM) samples from healthy adult volunteers were purchased from AllCells (Emeryville, CA). BM-CD34+ cells were isolated from BM-mononuclear cells using anti-CD34 immunomagnetic microbeads (Miltenyi Biotec, Bergisch Gladbach, Germany). Human BM-MSCs were isolated according to our previously published methods (Stem Cells 32:2245, 2014). In co-culture experiments, BM-MSCs with or without VK2 treatment were seeded on a 24-well culture plate. BM-CD34+ cells were applied on the MSC-grown plate and co-cultured in SFEM (StemCell Technologies, Vancouver, Canada) supplemented with 100 ng/mL SCF, 100 ng/mL Flt-3 ligand, 50 ng/mL TPO and 20 ng/mL IL-3. After 10 days of co-culture, the number and surface marker expression of the expanded hematopoietic cells were examined by flow cytometric analysis. [Results] We first tested the direct effect of VK2 on BM-CD34+ cells. BM-CD34+ cells were treated with VK2 at various concentrations ranged from 0 µM to 10 µM for 24 hours and then cultured in SFEM in combinations with cytokines. Surprisingly, viable hematopoietic cells were hardly detected in the expansion culture of BM-CD34+ cells treated with 10 µM VK2. Even with 1 µM treatment, the number of CD45+ cells was decreased, as compared to that of expan sion culture of untreated BM-CD34+ cells. The apoptosis analysis showed that the percentage of AnnexinV+ PI+ cells in the expanded hematopoietic cells is increased by VK2 treatment. We next examined the effect of VK2 on the hematopoiesis-supportive capability of BM-MSCs. BM-MSCs were pretreated with VK2 at various concentrations and then co-cultured with BM-CD34+ cells. The numbers of CD34+ cells and CD45+ cells were increased in a VK2 dose-dependent manner. These results demonstrated that VK2 shows different effects on distinct stem/progenitor cells: the induction of apoptosis in BM-CD34+ cells and the enhancement of hematopoiesis-supportive capability of BM-MSCs. We then investigated whether apoptosis-related cell death of BM-CD34+ cells by VK2 treatment is ameliorated in the presence of BM-MSCs. Both BM-CD34+ cells and BM-MSCs were treated with VK2 for 24 hours, and then co-cultured. The number of CD34+ cells was not decreased significantly in contrast to its severe decrease in single culture of VK2-treated BM-CD34+ cells. We further analyzed the effect of VK2 on BM-MSCs. Subpopulation analysis in co-culture of CD34+ cells with VK2-treated BM-MSCs showed that the expansion efficacy of CD34+CD38+ cells is higher in comparison to that of CD34+CD38- cells. In addition, the percentages of CD34-CD33+ cells and CD34-CD13+ cells were higher than those in co-cultures with untreated BM-MSCs. Therefore, VK2-treated BM-MSCs supported the expanded CD34+ cells to skew their phenotype toward myeloid lineage. The presence of a transwell in the co-culture system was unrelated to the expansion pattern of CD34+ cells, which suggested the involvement of soluble factors with respect to the underlining mechanism. We therefore compared the levels of hematopoiesis-supporting cytokine mRNA expression in VK2-treated and untreated BM-MSCs: VK2-treated BM-MSCs showed lower expression of CXCL12/SDF-1 mRNA and a trend toward higher expression of GM-CSF mRNA. [Summary] VK2 acted on BM-MSCs to support their ability to enhance expansion and myeloid differentiation of BM-CD34+ cells probably via altered GM-CSF and CXCL12/SDF-1 expression in MSCs. These findings may help to identify the mechanisms of therapeutic effects of VK2 in patients with MDS (Figure). Disclosures No relevant conflicts of interest to declare.

Abstract: Abstract 2990 Introduction Transplantation of allogeneic hematopoietic progenitor cells (HPC) is an effective treatment for a variety of hematological diseases. Intravenous (IV) injection is the routine method for HPC transplantation, based on the concept of “homing” to the bone marrow. To date, intrabone (IB) HPC transplantation has largely been investigated in the preclinical setting with only limited application in humans. Furthermore, an optimized method for the direct IB infusion of HPC in humans which maximizes cellular retention in the bone has not yet been developed. In this study, we aimed to optimize the IB transplantation procedure using a large animal model with the goal of retaining HPCs within the pelvic bone and to explore the feasibility of radionuclide labeling to assess the trafficking of HPCs using PET/CT imaging early after IB transplantation. Methods HPC collection: a) Human HPCswere mobilized from healthy volunteers using G-CSF then were positively selected for CD34+ cells using immuno-magnetic beads (MiltenyiBiotec, MA) then were cryopreserved. b) Porcine bone marrow (BM) cells were aspirated (approximately 40 ml) from the iliac crest of swine then were filtered and mononuclear cells (MNCs) were isolated using Ficoll-Paque™ with density gradient separation. All animal procedures were conducted using domestic swine (Susscrofadomesticus) on NHLBI Animal Use Committee approved protocols. IB access in animals was initially achieved using the OnControl driver (Vidacare Corp. TX). To evaluate flow through the marrow and venous drainage, direct IB injection into the hemipelvis with iopamidol-370 contrast was performed under anesthesia with dynamic CT images acquired using a 320-detector row scanner (Aquilion One, Toshiba Medical, Japan). Human CD34+ and swine BM MNCs were labeled with Zirconium-89 (89Zr) then were assessed for viability, cell number, and the level of cellular radioactivity. Radiolabeled cells were then injected into pigs either IV or directly IB into the porcine pelvis at different infusion rates. Intramarrow(IM) pressures were measured continuously during IB injection using Millarcatheters and acquired simultaneously with intra-arterial pressure and electrocardiography on a PowerLab data acquisition system (ADInstruments, CO) and analyzed using LabChart 7. After injection of labeled cells, positron emission tomography (PET) images were acquired for up to 180 minutes with a clinical PET/CT system (Gemini TF, Philips Medical Systems, MA) to assess cellular distribution and homing. Results Peak IM pressures during bolus hand IB injection were high, substantially exceeding systemic systolic arterial pressures. In contrast, IM pressures during slow IB infusion were significantly lower, remaining well below diastolic arterial pressures. During manual sequential hand IB injection of 5 ml aliquots of contrast at two different sites in the ipsilateral iliac crest, dynamic CT images revealed leakage from the initial access site after the first injection as well as immediate drainage into the ipsilateral iliac vein. Following manual hand injection of 89Zr labeled human CD34+ cells (89Zr-hCD34+) given IV in swine via the external jugular vein, there was persistent PET activity noted in the lungs for up to 3 hrs. Bolus hand IB injection of 89Zr labeled swine BM MNCs or 89Zr-hCD34+ cells revealed PET activity in the iliac bone as well as activity in the lungs. Furthermore, PET activity following bolus hand IB injection was also noted in surrounding tissues outside the bone when more than a single ipsilateral injection site was used. In contrast, slow infusion of 89Zr labeled swine BMMNCs or 89Zr-hCD34+cells resulted in PET activity that was limited to the iliac bone, indicating retention of cells within the marrow space with no leakage of cells to the lungs. Conclusion Rapid hand infusion of HPCs into the pelvic bone results in cellular leakage out of the marrow space into the lungs. In contrast, slow IB infusion of HPCs localizes cells to the bone marrow without leakage to the lungs. These data suggest maintaining low IM pressures may be critical to maximize cellular trapping in the marrow space following IB HPC transplantation in humans. Further study will be required to determine whether this optimized IB transplantation approach can be used to improve engraftment in recipients of transplants containing low HPC numbers. Disclosures: No relevant conflicts of interest to declare.

Abstract: Mutations of CCAAT/enhancer–binding protein alpha (CEBPAmu) are found in 10% to 15% of de novo acute myeloid leukemia (AML) cases. Double-mutated CEBPA (CEBPAdm) is associated with a favorable prognosis; however, single-mutated CEBPA (CEBPAsm) does not seem to improve prognosis. We investigated CEBPAmu for prognosis in 1028 patients with AML, registered in the Multi-center Collaborative Program for Gene Sequencing of Japanese AML. It was found that CEBPAmu in the basic leucine zipper domain (bZIP) was strongly associated with a favorable prognosis, but CEBPAmu out of the bZIP domain was not. The presence of CEBPAmu in bZIP was a strong indicator of a higher chance of achieving complete remission (P & lt; .001), better overall survival (OS; P & lt; .001) and a lower risk of relapse (P & lt; .001). The prognostic significance of CEBPAmu in bZIP was also observed in the subgroup with CEBPAsm (all patients: OS, P = .008; the cumulative incidence of relapse, P = .063; patients aged ≤70 years and with intermediate-risk karyotype: OS, P = .008; cumulative incidence of relapse, P = .026). Multivariate analysis of 744 patients aged ≤70 years showed that CEBPAmu in bZIP was the most potent predictor of OS (hazard ratio, 0.3287; P & lt; .001). CEBPAdm was validated as a cofounding factor, which was overlapping with CEBPAmu in bZIP. In summary, these findings indicate that CEBPAmu in bZIP is a potent marker for AML prognosis. It holds potential in the refinement of treatment stratification and the development of targeted therapeutic approaches in CEBPA-mutated AML.

Abstract: Intrabone (IB) injection of umbilical cord blood has been proposed as a potential mechanism to improve transplant engraftment and prevent graft failure. However, conventional IB techniques produce low retention of transplanted cells in the marrow. To overcome this barrier, we developed an optimized IB (OIB) injection method using low-volume, computer-controlled slow infusion that promotes cellular retention in the marrow. Here, we compare engraftment of CD34+ cells transplanted in a myeloablative rhesus macaque (RM) model using the OIB method compared with IV delivery. RM CD34+ cells obtained by apheresis were split equally for transduction with lentiviral vectors encoding either green fluorescent protein or yellow fluorescent protein reporters. Following conditioning, one marked autologous population of CD34+ cells was injected directly IB using the OIB method and the other was injected via slow IV push into the same animal (n = 3). Daily flow cytometry of blood quantified the proportion of engrafting cells deriving from each source. Marrow retention was examined using positron emission tomography/computed tomography imaging of 89Zirconium (89Zr)-oxine–labeled CD34+ cells. CD34+ cells injected via the OIB method were retained in the marrow and engrafted in all 3 animals. However, OIB-transplanted progenitor cells did not engraft any faster than those delivered IV and contributed significantly less to hematopoiesis than IV-delivered cells at all time points. Rigorous testing of our OIB delivery system in a competitive RM myeloablative transplant model showed no engraftment advantage over conventional IV infusion. Given the increased complexity and potential risks of IB vs IV approaches, our data do not support IB transplantation as a strategy to improve hematopoietic engraftment.

Abstract: Introduction: Intravascular large B-cell lymphoma (IVLBCL) is a rare disease entity characterized by selective growth of lymphoma cells in the lumina of small vessels. IVLBCL has been listed in the WHO classification, which improves recognition of the disease. However, no standard therapy has been established based on the results of prospective studies. We previously reported promising efficacy of rituximab (R)-containing chemotherapy for IVLBCL (JCO 2008) and a high incidence of central nervous system (CNS) recurrence (25% at 3 y) after R-chemotherapy (Lancet Oncol 2009, Cancer Sci 2010). To explore a more effective first-line treatment, we conducted a phase 2 trial of R-CHOP combined with CNS prophylaxis including R-high-dose methotrexate (R-HDMTX) and intrathecal chemotherapy with MTX, cytarabine (Ara-C), and prednisolone (PSL) (IT). Methods: Major inclusion criteria were untreated, histologically confirmed IVLBCL, age 20-79 y, ECOG PS 0-3, and no apparent CNS involvement at diagnosis. Patients received 3 cycles of R-CHOP followed by 2 cycles of R-HDMTX (3.5 g/m2; 2 g/m2 for ≥70 y) every 2 weeks, and 3 additional cycles of R-CHOP. IT (MTX 15 mg, Ara-C 40 mg, PSL 10 mg) was performed twice during the first 3 cycles of R-CHOP and twice during the final 3 cycles of R-CHOP (4 times in total). If patients achieved complete response (CR), they were observed without any therapy until relapse or disease progression. The primary endpoint was 2-y progression-free survival (PFS), and secondary endpoints included 2-y overall survival (OS), CR rate, cumulative incidence of CNS recurrence at 2 y, patterns of progression, and adverse events. The threshold 2-y PFS was estimated to be 35%, with expected 2-y PFS estimated to be 60%. With a statistical power of 90% and a one-sided, type I error of 5%, a projected sample size of 37 was calculated in anticipation of 10% ineligible patients. The trial was registered in the UMIN Clinical Trials Registry (UMIN000005707). Results: 38 IVLBCL patients were enrolled between June 2011 and July 2016. One patient was found to be ineligible after completion of the protocol treatment due to a past history of lymphoma. The protocol treatment was completed in 34 (89%) of 38 patients. The diagnosis of IVLBCL was histologically confirmed by central pathological review in all enrolled patients. The baseline characteristics of the 37 eligible patients were: male sex, 16 (43%); median age, 66 (range 38-78) y; ECOG PS & gt;1, 15 (41%); stage IV, 37 (100%); serum LDH & gt;ULN, 36 (97%); WBC & lt;4,000/μL, 11 (30%); Hgb & lt;11g/dL, 30 (81%); PLT & lt;105/μL, 17 (46%); and IPI HI/H, 33 (89%) patients. The following clinical symptoms were observed before treatment initiation: B symptoms, 30 (81%); hypoxemia, 10 (27%); neurological symptoms, 3 (8%);exanthema, 4 (11%); hepatomegaly, 15 (40%); splenomegaly, 28 (76%); and hemophagocytosis, 8 (22%) patients. In the 37 eligible patients, the CR rate was 84% (95%CI: 68-94%). With a median follow-up of 3.9 (range, 2.0-6.6) y, 2-y PFS was 76% (95%CI: 59-87%), 2-y OS was 92% (95%CI: 77-97%), and the cumulative incidence of CNS recurrence at 2 y was 2.7% (95%CI: 0.2-12%) (Fig. 1). Only one patient had CNS relapse during follow-up. Of all 38 enrolled pts, there were no treatment-related deaths. G4 non-hematological adverse events were febrile neutropenia, hypokalemia, and low blood pressure in one patient each. Major G3 non-hematological toxicities were febrile neutropenia (32%) and hypokalemia (26%). G3 and G4 lymphocytopenia were observed in 95% and 50% and thrombocytopenia in 40% and 24% of patients, respectively. All toxicities were manageable. Conclusion: This phase 2 trial met its primary endpoint and showed favorable outcomes with a low cumulative incidence of CNS recurrence and acceptable toxicity profiles. These results indicate that R-CHOP combined with CNS prophylaxis including R-HDMTX and IT could be a reasonable treatment option for untreated IVLBCL without apparent CNS involvement at diagnosis. Disclosures Shimada: Takeda Pharmaceutical: Honoraria; MSD: Research Funding; Otsuka Pharmaceutical: Research Funding; Janssen Pharmaceutical: Honoraria; Bristol-Myers Squibb: Honoraria; Celgene: Honoraria; Eisai: Honoraria, Research Funding; Chugai Pharmaceutical: Consultancy, Honoraria; Kyowa Kirin: Honoraria, Research Funding; AstraZeneca: Honoraria. Yamaguchi:Ono Pharmaceutical: Research Funding; Teijin Pharma: Honoraria; MSD: Honoraria; Astrazeneca: Membership on an entity's Board of Directors or advisory committees; Sumitomo Dainippon Pharma: Honoraria; Janssen: Honoraria; Takeda: Honoraria; Astellas Pharma: Research Funding; Sorrento: Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria; Meiji Seika Kaisha: Honoraria; Kyowa Hakko Kirin: Honoraria, Research Funding; Eisai: Honoraria; Chugai: Honoraria, Research Funding. Atsuta:Chugai Pharmaceutical Co., Ltd.: Honoraria; Kyowa Kirin Co., Ltd: Honoraria; Mochida Pharmaceutical Co. Ltd: Honoraria; Janssen Paharmaceutical K.K.: Honoraria. Matsue:Celgene: Honoraria; Takeda Pharmaceutical Company Limited: Honoraria; Ono Pharmaceutical: Honoraria; Novartis Pharma K.K: Honoraria; Janssen Pharmaceutical K.K.: Honoraria. Kusumoto:Chugai Pharmaceutical Co., Ltd.: Consultancy, Honoraria, Research Funding; Kyowa Kirin Co., Ltd.: Honoraria, Research Funding. Nagai:Eisai: Honoraria, Research Funding; HUYA Bioscience International: Research Funding; AstraZeneca: Honoraria, Research Funding; Takeda Pharmaceutical: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Janssen Pharmaceutical: Honoraria, Research Funding; Ono Pharmaceutical: Honoraria, Research Funding; Zenyaku Kogyo: Honoraria, Research Funding; Sanofi: Honoraria; Otsuka Pharmaceutical: Research Funding; SymBio Pharmaceuticals Limited: Honoraria, Research Funding; Solasia Pharma K.K.: Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding; Kyowa Kirin: Honoraria, Research Funding; IQVIA: Research Funding; Chugai Pharmaceutical: Honoraria, Research Funding; MSD: Honoraria; Novartis Pharma: Honoraria; Mundi Pharma: Honoraria, Research Funding; Bayer Pharma: Honoraria, Research Funding; AbbVie: Research Funding. Fukuhara:Mundi: Honoraria; Celgene Corporation: Honoraria, Research Funding; Chugai Pharmaceutical Co., Ltd.: Honoraria; Eisai: Honoraria, Research Funding; Janssen Pharma: Honoraria; Kyowa-Hakko Kirin: Honoraria; Mochida: Honoraria; Nippon Shinkyaku: Honoraria; Ono Pharmaceutical Co., Ltd.: Honoraria; Takeda Pharmaceutical Co., Ltd.: Honoraria, Research Funding; Zenyaku: Honoraria; AbbVie: Research Funding; Bayer: Research Funding; Gilead: Research Funding; Solasia Pharma: Research Funding. Miyazaki:Eisai: Honoraria; Chugai: Honoraria; Kyowa Hakko Kirin: Honoraria, Research Funding; Celgene: Honoraria; Ono Pharmaceutical: Research Funding; Astellas Pharma: Research Funding; Takeda: Honoraria; SymBio Pharmaceuticals: Honoraria; Nippon Shinyaku: Honoraria; Janssen Pharmaceutical: Honoraria. Okamoto:Kyowa Kirin Co., Ltd.: Other: Scholarship donation; Chugai Pharmaceutical Co., Ltd.: Other: Scholarship donation; Takeda Pharmaceutical Co., Ltd.: Other: Scholarship donation; Taiho Pharmaceutical Co., Ltd.: Other: Scholarship donation. Uchida:Eisai: Honoraria. Tsukasaki:Daiichi Sankyo: Consultancy; Kyowa Kirin: Honoraria; Huya: Consultancy, Honoraria, Research Funding; Byer: Research Funding; Mundi Pharma: Honoraria; Ono Pharmaceutical: Consultancy; Eisai: Research Funding; Chugai Pharmaceutical: Honoraria, Research Funding; Celgene: Honoraria, Research Funding. Masaki:Tanabe Mitsubishi: Research Funding; Taiho: Research Funding; Kyowa Kirin: Research Funding; Astellas Pharma: Research Funding; Chugai Pharmaceutical: Research Funding; Ono Pharmaceutical: Research Funding; Pfizer: Research Funding; Eisai: Research Funding; Taisho Toyama: Research Funding; Daiichi Sankyo: Research Funding; Teijin: Research Funding; Takeda Pharmaceutical: Research Funding. Kiyoi:Sumitomo Dainippon Pharma Co., Ltd.: Research Funding; Bristol-Myers Squibb: Research Funding; Chugai Pharmaceutical Co., Ltd.: Research Funding; Astellas Pharma Inc.: Honoraria, Research Funding; Takeda Pharmaceutical Co., Ltd.: Research Funding; Zenyaku Kogyo Co., Ltd.: Research Funding; Kyowa Hakko Kirin Co., Ltd.: Research Funding; Otsuka Pharmaceutical Co.,Ltd.: Research Funding; FUJIFILM Corporation: Research Funding; Eisai Co., Ltd.: Research Funding; Nippon Shinyaku Co., Ltd.: Research Funding; Pfizer Japan Inc.: Honoraria; Perseus Proteomics Inc.: Research Funding; Daiichi Sankyo Co., Ltd: Research Funding. Suzuki:Chugai Pharmaceutical Co.,Ltd.: Honoraria; Meiji Seika: Honoraria; Merck Sharp & Dohme: Honoraria; Takeda Pharmaceutical Co., Ltd.: Honoraria; Bristol-Myers Squibb: Honoraria; Kyowa Hakko Kirin: Honoraria; Celgene: Honoraria; Eisai: Honoraria; ONO Pharmaceutical Co., Ltd.: Honoraria; Janssen: Honoraria; AbbVie: Honoraria; Novartis: Honoraria.

Abstract: Introduction: Umbilical cord blood (UCB) grafts are the only option for a significant minority of patients who require hematopoietic stem cell transplantation (HSCT) but lack a suitable related or unrelated donor. While UCB can serve as a suitable 'off the shelf' graft for many patients, units with the best HLA match often contain low and sometimes insufficient numbers of CD34+ cells for use in transplantation, particularly for adult patients. Furthermore, UCB grafts contain lower CD34+ cells number compared to BM or PBSC grafts, which leads to longer engraftment times and a higher risk of graft failure. BM and PBSC grafts are usually injected intravenously, homing to the bone marrow after several hours in the circulation. During this time, CD34+ cells are lost in the lungs, liver and spleen with typically 〈 20% making it to the bone marrow.1 Investigators have sought to overcome the limitation of low cell dose in UCB grafts and loss of CD34+ cells in the circulation by injecting CD34+ cells directly into the bone marrow space. However, we have recently shown that conventional intrabone delivery methods used in investigational trials to transplant UCB, result in low-level retention of hematopoietic progenitor cells in the intrabone space. Recently, we developed an optimized intrabone (OIB) transplant method using computer controlled low pressure and low volume injection (controlled infusion rate 〈 0.2ml/min, total volume 〈 5ml) under CT guidance. Utilizing porcine and rhesus macaque models, we have shown that OIB delivery of CD34+ cells improves intrabone retention, preventing circulation of CD34+ cells through the lungs, which is observed with conventional non-optimized intrabone methods.2 Here we conducted experiments using an autologous myeloablative transplant model in rhesus macaques comparing engraftment of gene-marked CD34+ cells transplanted intravenously, with cells transplanted using OIB delivery. Methods: Rhesus macaques received GCSF and plerixafor mobilization prior to apheresis. Products were CD34+ selected using Miltenyi beads. CD34+ cells were split equally for transduction with lentiviral vectors encoding the reporters GFP and YFP. After myeloablative conditioning with 10Gy total body irradiation, half the graft was injected directly intra-bone using the OIB method, with the other half of the autograft simultaneously being injected intravenously via slow iv push. Peripheral blood samples were measured daily by flow cytometry to assess the proportion of engrafting cells deriving from each source. To address whether OIB transplantation could allow engraftment of low CD34+ cell numbers, as found in UCB units, the cell doses transplanted in one rhesus macaque recipient were reduced to only 0.5 x 106CD34+ cells/kg. Results: CD34+ cells injected intrabone utilizing the OIB method engrafted in all 3 animals. However, flow cytometric analysis gating on GFP vs YFP positive neutrophils showed CD34+ cells injected utilizing OIB delivery did not engraft quicker than IV transplanted cells. Sequential monitoring of neutrophils over 30 days showed the contribution to hematopoiesis of OIB delivered cells was significantly lower than the cells injected IV (Table 1.) Conclusions: We developed a novel intrabone delivery system that optimizes the retention of CD34+ cells into the bone marrow space. Although autologous CD34+ cells injected using this OIB transplant method were capable of engrafting in rhesus macaques that had undergone myeloablative conditioning, they did not engraft faster and contributed less to hematopoiesis than CD34+ cells simultaneously transplanted using conventional IV infusion. These data raise questions over whether intrabone delivery, even when using techniques to optimize intrabone retention, has utility in improving CD34+ cell engraftment. References: 1. Van der Loo JC et al. Marrow and spleen seeding efficiencies of all murine hematopoietic stem cell subsets are de- creased by preincubation with hematopoietic growth factors. Blood. 1995; 85:2598-2606 2. Pantin et. al. Optimization of intrabone delivery of hematopoietic progenitor cells in a swine model using cell radiolabeling with 89zirconium. American J Transplant. 2015 Mar;15(3):606-17. Disclosures Davidson: Macrogenics: Employment. Pantin:NIH: Patents & Royalties: a patent application for an intrabone delivery device. Dunbar:National Institute of Health: Research Funding.

Abstract: Interleukin 15 (IL-15) is a critical factor for the proliferation and activation of natural killer (NK) and CD8 T cells. Recently, we demonstrated that IL-15Rα expressed on monocytes/dendritic cells captures and presents IL-15 to neighboring cells in trans (trans-presentation of IL-15) through cell-cell contact. In the current study, we provide evidence that the IL-15 presented in trans, but not soluble IL-15 at physiologic concentrations, augments the killing activity mediated by NK cells in vitro. In addition, transfection of IL-15Rα into a colon carcinoma cell line (MC38) enabled these cells to present IL-15 in trans to NK cells and augmented their killing activity, resulting in the efficient lysis of MC38 cells by NK cells in vitro. Furthermore, these transfected MC38 cells no longer form fatal pulmonary metastases in mice. It was also shown that NK cells play an important role in the rejection of MC38 cells under these circumstances. These results collectively suggest that the IL-15 trans-presentation mechanism operates in vivo to augment the tumor immune surveillance mechanism. Furthermore, our observation provides the scientific basis for a novel strategy to prevent cancer development/metastasis.

Abstract: Mesenchymal stromal/stem cells (MSCs) are a major source of cell for cell therapy. MSCs derived from bone marrow (BMMSCs) have been mostly used in clinical applications. BMMSCs can be easily isolated as a cell population that adheres to plastic culture dishes within 1 week of culture. A recent report has demonstrated that cells that remain in suspension and fail to form adherent colonies contain a fraction of late adherent cells that resembles BMMSCs (Biomed Res Int, 2013; 2013: 790842). Umbilical cord blood (UCB) is as accessible as bone marrow for the isolation of MSCs. In this study, we identified a late adherent subpopulation in UCB and determined its hematopoiesis-supporting activity. Forty-five UCB units, which were not matched to the eligibility criterion defined in the Japan UCB donation program, were collected after delivery of placenta. Written informed consent was obtained before delivery from all pregnant women who participated in the study. The study protocol was approved by the ethics committee of the Kyoto University Graduate School of Medicine. Mononuclear cells were isolated from UCB by the density gradient centrifugation method with (n = 19) and without (n = 18) subsequent separation of CD34 negative cells using anti-CD34 immunomagnetic microbeads (Miltenyi Biotec, Bergisch Gladbach, Germany). Nucleated cells were separated by the hydroxyethyl starch sedimentation method from the other eight UCB units. The cells were then seeded into a culture flask and cultured in alpha minimal essential medium supplemented with 15% FBS (Culture 1; C1). After 1 week of culture, non-adherent cells in C1 supernatant were collected and re-seeded into a new flask (C2). The attached cells in C1 were cultured until adherent colonies emerged, after which they were detached using trypsin/EDTA and twice passaged to obtain a sufficient number of cells (C1 cells). In the same way, after 1 week of culture, non-adherent cells in C2 supernatant were collected and re-seeded into a new flask (C3). The attached cells in C2 were cultured to obtain C2 cells. Afterwards, re-seeding and culture (C4, C5c) were repeated until no new colonies were formed. Collected cells were cryopreserved and thawed when required in experiments. BMMSCs were isolated from human bone marrow cells purchased from AllCells (Emeryville, CA). C1 cells, the so-called UCBMSCs, were successfully isolated from 18 units (40 %). Adherent cells isolated from C2 and later were defined as elate adherent cellsf and, were obtained from 9 units: these cells were referred to as C2 cells (from 9 units), C3 cells (from 9 units), C4 cells (from 6 units) and C5 cells (from 2 units). The interval from seeding to the first colony formation in C1 was shorter in these 9 units than that in the other 9 units that contained only C1 cells: 10.8 } 1.4 vs 15.9 } 4.5 days, p 〈 0.01. The volume of the former 9 units tended to be large compared to the latter 9 units: 49.6 } 10.5 vs 33.7 } 21.0 mL, p = 0.07. These findings indicated that UCB containing late adherent cells was suitable for a cell source of MSCs. Next, we examined whether these late adherent cells (C2 and C3 cells) had properties consistent with those of MSCs. Both C2 and C3 cells showed spindle-shaped fibroblast-like morphology and the same immunophenotype as C1 cells: positive for CD73, CD90 and CD105, and negative for CD34, CD45 and HLA-DR. They had osteogenic, adipogenic and chondrogenic differentiation potentials in vitro. These findings are the minimal criteria for MSCs (Cytotherapy, 2006; 8:315). Finally, we evaluated the hematopoiesis-supporting activity of these cells in vitro and in vivo. CD45-positive hematopoietic cells were expanded when co-cultured of CD34-positive hematopoietic progenitor cells (6 ~ 102 cells) with C2 or C3 cells (2 ~ 104 cells) in vitro as much as when co-cultured with C1 cells (Figure A). In vivo analysis was conducted by using subcutaneous transplantation of MSCs on NOD/SCID mice (Int J Hematol, 2015; 102: 218). C2 cells induced trabecular bone formation and bone marrow hematopoiesis as well as C1 cells, however, C3 cells did not induce hematopoiesis (Figure B). In conclusion, we demonstrated that UCB contains a late adherent cell subpopulation with the same characteristics and hematopoiesis-supporting activity as those of UCBMSCs isolated using the conventional method. The continuance of cell culture without discarding suspension cells could improve the efficiency of isolation of MSCs from UCB. Disclosures Hirai: Kyowa Hakko Kirin: Research Funding; Novartis Pharma: Research Funding. Maekawa:Bristol-Myers K.K.: Research Funding.