Abstract: UCB is an attractive source for unrelated HSCT of benign indications; however, cell dosage is a critical factor for UCB HSCT. The red cell depletion (RD) and post-thaw wash techniques that are widely used incur significant nucleated cell loss; therefore, two strategies to minimize cell loss are to deplete plasma, but not the red blood cells (PD) during processing and forego post-thaw wash. A retrospective audited analysis was performed on 61 patients with benign disorders who were transplanted with 68 PD UCB units (8 double cords) with 29 thalassemias, 8 AA, 5 WAS, 5 SCID, 2 osteoporosis, 2 sickle cell disease, 2 Hemophagocytic Lymphohistiocytosis, 2 Hurler Syndrome, 1 CGD, 1 Fanconi’s Anemia, 1 Leroy I-Cell Disease, 1 Lymphohistiocytosis, 1 OIMD, and 1 Alpha Mannosidosis. Transplant characteristics: patient median age 4.25 years old (range 0.3–39); median weight 17 kg (range 5–76); male 56%; median # HLA ABDR matches of 5.0 (12–6/6; 19–5/6; 23–4/6; 5–3/6, 1–2/6); median pre-freeze TNC dose 8.1 x 107/kg; median post-thaw TNC dose as reported by TC 7.7 x 107/kg; median pre-freeze CD34 dose 3.1 x 105/kg; transplants outside of U.S.− 32 (52%); non-myeloablative − 9; 44% post-thaw washed (W), 56% infused without post-thaw wash (NW). The Kaplan-Meier estimates of 3-month ANC500 and 6-month platelet 20K and 50K engraftment are 87±5%, 83±6%, and 84±6% respectively. The median time to engraftment for ANC 500, platelet 20K, and 50K are 20 days (range 11–64), 46 days (range 13–153), and 61 days (range 21–171) respectively. No major adverse event was observed in either the W or the NW group, and the median time to engraftment for ANC 500, platelet 20K and 50K for W vs. NW were 21 vs. 19 days, 55 vs. 44.5 days, and 76 vs. 59 days respectively. The incidence of reported grade II–IV acute GVHD was 29%, and 10% had grade III–IV acute GVHD. 33% developed limited chronic GVHD, and 15% developed extensive chronic GVHD. With a median follow-up of 219 days (range 4–1402 days), the Kaplan-Meier estimates of 1-year TRM, OS and disease-free survival were 20±6%, 78±6% and 72±6% respectively. These results demonstrate that HSCT using unrelated PD UCB can be performed safely with outstanding results in patients with benign disorders, and post-thaw washing may delay engraftment of HSCT using PD UCB.

Abstract: Cell dosage is a limiting factor for UCB HSCT, especially for adult patients. Most UCB banks practice red cell depletion (RCD) techniques to save storage space, which incur significant nucleated cell loss after processing. One method to minimize cell loss and still reduce volume after processing is to deplete plasma (PD), but not the red blood cells. Not washing UCB (NW) after thawing also minimizes cell loss. A large racially diverse PD UCB inventory of over 25,000 units is now available on stem cell registries. There were 70 ALL, 54 AML, 19 CML, and 45 others transplanted for malignant indications. A retrospective audited analysis was performed on 170 patients with engraftment and/or survival information. Of the ALL/AML/CML cases with available information, there were 32 1CR/CP, 33 2CR, and 13 3CR/CP. The median age of patients was 13 years old (range 05–59); median weight 50 kg (range 5–137); male 45%. Transplant characteristics indicated a median # HLA ABDR matches of 4.0; median pre-freeze TNC dose 4.1 × 107/kg; median post-thaw TNC dose as reported by TC 3.7 × 107/kg; median pre-freeze CD34 dose 1.4 × 105/kg; transplants outside of U.S. 34%; double unit transplant 30%; non-myeloablative 16%. Sixty-one percent of the transplanted UCB were washed post-thaw (W), 39% were infused without post-thaw wash (NW), with 20% of the units without available post-thaw data. Kaplan-Meier estimates of 3-month ANC500 and 6-month platelet 20K and 50K engraftment are 89±3%, 81±5%, and 73±5% respectively. Median time to engraftment for ANC 500, platelet 20K, and 50K were 22 days (range 7–69 days), 52.5 days (range 12–181 days), and 64 days (range 25–374 days) respectively. Median time to engraftment for post-thaw washed units (W) versus PD CBU not washed and infused directly after thawing (NW) were 24 vs. 22 days for ANC500, and 57 vs. 48 days for platelet 20K respectively. The incidence of reported grade II-IV and III-IV acute GVHD were 32% and 14% respectively. Twelve percent developed limited chronic GVHD and 14% developed extensive chronic GVHD. With a median follow-up of 170 days (range 4–1402 days), the Kaplan-Meier estimates of 1-year TRM, OS and relapse-free survival were 31±4%, 51±4% and 47±4% respectively. These results demonstrate that HSCT using unrelated PD UCB can be performed safely and effectively in patients with malignancies, and post-thaw wash may not be necessary.

Abstract: Background: Cord blood transplantations (CBT) are performed in transplant centers (TC) worldwide; however, conditions for TC located around the world may be quite different, in particular, few studies have focused on CBT outcome in Asian TC. Factors such as patient populations, experiences, disease indications, available resources, and protocols may affect outcome as some have suggested. Methods: In an effort to compare CBT performed by U.S. (n=129) and non-U.S. TC (n=63), a retrospective audited analysis was performed for all 192 patients with available engraftment and/or survival data using cord blood units (CBU) from a single source to minimize potential differences in quality. Results: Kaplan-Meier estimates of engraftment for ANC500, platelet 20K and 50K were 91±3%, 80±5% and 74±5% for U.S. respectively, and 81±5%, 85±6%, and 81±7% for non-U.S. TC respectively. The relapse rate for the U.S. and non-U.S. TC were 26±5% and 17±5% respectively. TRM were 31±4% for U.S. TC and 22±5% for non-U.S. TC. The 3-year OS and DFS were 51±5% and 41±7% for U.S. and 68±6% and 61±7% for non-U.S. centers respectively. Factors including recipient age, CD34+ cell dose, #HLA matches, malignancy and wash status of the CBU were taken into consideration in a multivariate analysis which will be presented. In this study, non-U.S. TC were more likely to forego post-thaw wash of CB and perform CBT for benign indications, which appeared to affect outcome. Upon closer inspection of the individual TC, it appeared that there may be more heterogeneity in the TC results overseas, and that centers in the U.S. produced more consistent outcome. While it is possible that, due to many complex reasons, outcome at some non-U.S. TC may be somewhat uneven, many including several in Asia, produced outstanding results that rival the best TC anywhere. Conclusion: It appears that many factors, including available resources, post-thaw wash, and CBT experience affect outcome, and outstanding outcome can be achieved, regardless of TC location.

Abstract: Background: Complications from chronic hepatitis C virus (HCV) infection are a major cause of morbidity and mortality among individuals with inherited blood disorders (IBLD). Inability to tolerate ribavirin and frequent comorbidities have limited HCV treatment options in these patients. The aim of the C-EDGE IBLD study was to evaluate the efficacy and safety of a once-daily, fixed-dose combination of elbasvir 50 mg (EBR, an NS5A inhibitor) and grazoprevir 100 mg (GZR, an NS3/4A protease inhibitor) in patients with HCV infection and IBLD, including those with hemoglobinopathies. Methods: C-EDGE-IBLD was a randomized, double-blind, placebo-controlled study of treatment-naïve and treatment-experienced patients with HCV genotype (GT)1, 4, or 6 infection and IBLD (hemophilia A/B, von Willebrand disease, β-thalassemia, or sickle cell anemia). Patients were randomized in a 2:1 ratio to an immediate-treatment group (ITG; 12 weeks of EBR/GZR) or deferred-treatment group (DTG; 12 weeks of placebo, followed by EBR/GZR for 12 weeks). Randomization was stratified according to the presence of cirrhosis and IBLD diagnosis. The primary endpoints were the proportion of patients in the ITG who achieved sustained virologic response (SVR12, HCV RNA 〈 15 IU/mL 12 weeks after completion of treatment) and a comparison of safety and tolerability between patients receiving EBR/GZR in the ITG vs those receiving placebo in the DTG. Results: One hundred fifty-nine patients were randomized (ITG, n = 107; DTG, n = 52). Three patients in the DTG did not commence deferred active treatment; therefore, 156 patients received ≥1 dose of EBR/GZR. Mean age was 44 years. Other baseline patient demographics were as follows: 75% male; 18% black; 41% GT1a-infected; 46% GT1b-infected; 11% GT4-infected; 24% cirrhotic; 6% HIV/HCV co-infected; 43% with hemophilia A/B or von Willebrand disease; 38% with β-thalassemia; 18% with sickle cell anemia. SVR12 was achieved by 92.9% (145/156) of patients receiving EBR/GZR (ITG 93.5% [100/107]; DTG 91.8% [45/49] ). Of the 11 patients who did not achieve SVR12, 2 discontinued treatment for reasons unrelated to study medication and 9 relapsed, including 7 who had NS5A resistance-associated variants present at baseline. One patient achieved SVR12 but relapsed between follow-up weeks 12 and 24. SVR12 was achieved by 90.8% (59/65), 95.7% (67/70), and 94.4% (17/18) of patients with HCV GT1a, GT1b, and GT4 infection, respectively (2 patients with GT1 non-a,b achieved SVR and the 1 patient with GT6 infection relapsed). SVR 12 was achieved by 96.3% (26/27) of patients with sickle cell anemia, 95% (57/60) with β-thalassemia, and 89.9% (62/69) with hemophilia A/B or von Willebrand disease. During the initial treatment period (EBR/GZR vs placebo), serious adverse events were reported in 3 (2.9%) patients in the ITG (1 drug-related, 2 related to IBLD) and 6 (11.5%) patients receiving placebo in the DTG (1 drug-related, 3 related to IBLD). In the DTG placebo phase, 1 patient discontinued treatment due to an adverse event and 1 patient withdrew consent. No patient in either arm discontinued treatment due to worsening of underlying IBLD. There was 1 hepatic event of clinical interest in each arm (ALT 〉 3× baseline and 〉 100 U/L). In the EBR/GZR treatment phase of the DTG (n = 49), 3 patients reported serious adverse events; none were drug-related and 2 were related to IBLD. Conclusions: Final data from the C-EDGE IBLD study indicate that EBR/GZR is well tolerated and effective in patients with HCV GT1 or 4 infection with IBLD. Disclosures Hézode: BMS: Consultancy; Janssen: Consultancy; MSD: Consultancy; AbbVie: Consultancy; Gilead: Consultancy. Fried:NIH: Research Funding; Gilead: Consultancy, Research Funding; TARGET PharmaSolutions: Equity Ownership; Merck: Consultancy, Research Funding; BMS: Consultancy, Research Funding; AbbVie: Consultancy, Research Funding. Colombo:Merck: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Bayer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead Science: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Tibotec: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Vertex: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen Cilag: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Achillion: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Lundbeck: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; GSK: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; GenSpera: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AlfaWasserman: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Jennerex: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Intercept: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Bourlière:MSD: Consultancy; AbbVie: Consultancy; Gilead: Consultancy; Janssen: Consultancy; GSK: Consultancy; BMS: Consultancy. Ben-Ari:Merck: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Strasser:MSD/Merck: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead Sciences: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Norgine: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Bayer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Astellas: Honoraria. Perumalswami:Merck: Research Funding; Gilead: Research Funding. Zamor:Gilead: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Merck: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Lee:Eli Lilly: Consultancy; BMS: Research Funding; Gilead: Research Funding; Sanofi: Consultancy; Merck: Research Funding; Novartis: Consultancy. Satoskar:Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Merck: Research Funding. Sherman:AbbVie: Research Funding; Gilead: Research Funding; BMS: Research Funding; Merck: Consultancy, Research Funding. Morgan:Merck & Co., Inc.: Employment, Equity Ownership. Qiu:Merck: Employment. Hwang:Merck: Employment, Equity Ownership. Robertson:Merck: Employment, Equity Ownership. Nguyen:Merck: Employment. Barr:Merck: Employment, Equity Ownership. Wahl:Merck: Employment. Haber:Merck: Employment. Chase:Merck: Employment. Talwani:Merck & Co., Inc: Employment. Di Marco:Gilead: Research Funding.

Abstract: Inborn errors of immunity (IEI) are a genetically heterogeneous group of disorders with a broad clinical spectrum. Identification of molecular and functional bases of these disorders is important for diagnosis, treatment, and an understanding of the human immune response. We identified 6 unrelated males with neutropenia, infections, lymphoproliferation, humoral immune defects, and in some cases bone marrow failure associated with 3 different variants in the X-linked gene TLR8, encoding the endosomal Toll-like receptor 8 (TLR8). Interestingly, 5 patients had somatic variants in TLR8 with & lt;30% mosaicism, suggesting a dominant mechanism responsible for the clinical phenotype. Mosaicism was also detected in skin-derived fibroblasts in 3 patients, demonstrating that mutations were not limited to the hematopoietic compartment. All patients had refractory chronic neutropenia, and 3 patients underwent allogeneic hematopoietic cell transplantation. All variants conferred gain of function to TLR8 protein, and immune phenotyping demonstrated a proinflammatory phenotype with activated T cells and elevated serum cytokines associated with impaired B-cell maturation. Differentiation of myeloid cells from patient-derived induced pluripotent stem cells demonstrated increased responsiveness to TLR8. Together, these findings demonstrate that gain-of-function variants in TLR8 lead to a novel childhood-onset IEI with lymphoproliferation, neutropenia, infectious susceptibility, B- and T-cell defects, and in some cases, bone marrow failure. Somatic mosaicism is a prominent molecular mechanism of this new disease.

Abstract: Sickle cell disease (SCD) is an autosomal recessive genetic disorder caused by a point mutation in the human β-globin gene. Patients harboring this mutation can exhibit long-chain polymers of hemoglobin and sickle-shaped red blood cells, and suffer from severe medical manifestations including hemolysis and vaso-occlusive crises. Multiple preclinical, clinical and epidemiologic studies have shown that the levels of unmutated fetal hemoglobin (HbF encoded by the γ-globin gene) correlate with less severe disease, validating HbF induction as a therapeutic approach in SCD. Treatment with hydroxyurea (HU), the only approved therapy for SCD, results in a variable induction of HbF and significant improvement in the frequency of pain crises. However, a significant percentage of patients treated with HU fail to exhibit durable benefit, necessitating the need for alternative therapeutic agents. The human γ-globin gene is repressed in the post-natal period by epigenetic mechanisms, and therefore may lend itself to pharmacological intervention aimed at derepressing gene expression. One of the most important of these epigenetic mechanisms is catalyzed by lysine-specific demethylase 1 (LSD1), a histone demethylase that removes mono-/dimethyl marks from the lysine 4 and 9 residues of histone H3 through an FAD-directed redox process. Here, we report the characterization of selective, potent, and orally bioavailable LSD1 inhibitors from two classes - FAD-directed inhibitors that achieve inhibitory activity through formation of covalent FAD-adducts and non-FAD-directed, reversible inhibitors - and demonstrate their ability to induce γ-globin gene expression in murine and primate preclinical models. In the Towne's SCD mouse model, oral administration of LSD1 inhibitors significantly increased HbF+ cell (F cell) production. Concurrent with the increase in F cells, sickle cell numbers, reticulocyte counts, and bilirubin levels were all markedly reduced, indicating an amelioration of several pathophysiological features of SCD. FAD- and non-FAD-directed LSD1 inhibitors were more effective than HU in increasing F cells production, and the combination of HU and suboptimal doses of LSD1 inhibitors resulted in a greater induction of F cells and more pronounced reductions in reticulocyte counts and bilirubin levels. In addition to the humanized SCD model, HbF induction in response to LSD1 inhibitor treatment was evaluated in non-anemic cynomolgus monkeys. Oral administration of LSD1 inhibitors significantly induced F cells and HbF in a dose-dependent manner and over a sustained period ( 〉 50 days) following the discontinuation of treatment. The percentage of induced F cells in total RBCs was linearly correlated with the percentage of HbF protein induced by LSD1 inhibition. Taken together, these results support the potential utility of LSD1 inhibition as a novel therapeutic approach to increase HbF production. Disclosures Lee: Incyte Corporation: Employment, Other: Stock. Soloviev:Incyte Corporation: Employment, Other: Stock. Zhang:Incyte Corporation: Employment, Other: Stock. Roman:Incyte Corporation: Employment, Other: Stock. Yang:Incyte Corporation: Employment, Other: Stock. Bowman:Incyte Corporation: Employment, Other: Stock. Burke:Incyte Corporation: Employment, Other: Stock. Margulis:Incyte Corporation: Employment, Other: Stock. O'Connor:Incyte Corporation: Employment, Other: Stock. Yang:Incyte Corporation: Employment, Other: Stock. Wu:Incyte Corporation: Employment, Other: Stock. Wynn:Incyte Corporation: Employment, Other: Stock. Burn:Incyte Corporation: Employment, Other: Stock. Shuey:Incyte Corporation: Employment, Other: stock. Diamond:Incyte Corporation: Employment, Other: Stock. Yao:Incyte Corporation: Employment, Other: Stock. Hollis:Incyte Corporation: Employment, Other: Stock. Yeleswaram:Incyte Corporation: Employment, Other: Stocks. Roberts:Incyte Corporation: Employment, Other: Stock. Huber:Incyte Corporation: Employment, Other: Stock. Scherle:Incyte Corporation: Employment, Other: Stock. Ruggeri:Incyte Corporation: Employment, Other: Stock.

Abstract: Introduction: Lenalidomide (len) is an immunomodulatory agent with single agent activity in relapsed and refractory peripheral T-cell lymphoma (PTCL). CHOEP (cyclophosphamide, doxorubicin, vincristine, etoposide, and prednisone) is a common initial regimen. Herein, we report the completed phase II results of the combination of len-CHOEP. Methods: Eligible patients (pts) had newly diagnosed PTCL, ANC ≥1000 cells/mm3, platelets ≥100 K/mm3, and adequate organ function. Based on phase I results [Lunning et al. T-cell Forum 2018] 10 mg of len was chosen for phase II. CHOEP was administered at standard doses with len given on days 1-10 of 21-day cycle for six planned cycles. Mandatory prophylaxis included aspirin (ASA) or alternative thromboprophylaxis and growth factor support per institutional guidelines with each cycle. A PET/CT after two cycles (PET-2) for interim response assessment was required per protocol. The primary endpoint was complete response (CR) by PET/CT after 6 cycles (PET-6) of len-CHOEP utilizing the revised Cheson 2007 criteria with secondary endpoints to include toxicity, overall response rate (ORR), progression free survival (PFS), 2-year PFS, and overall survival (OS). Pts who had CR or partial response (PR) at the end of therapy had the option of len maintenance (10 mg/day for 21 out of 28 days) for 1-year or consolidative autologous stem cell transplant (ASCT) without len maintenance. Per protocol pts dosed at 10 mg in phase I (N=8) were included in the phase II analysis. Results: Forty pts with PTCL-NOS (23), ALK negative ALCL (5) and AITL (12) enrolled into the phase II portion. Median age was 62 years (range 24-79) and 21 were male. Thirty (75%) pts completed all 6 cycles. Reasons for discontinuing len-CHOEP early were toxicity (n=6) and progressive disease (PD; n=4). PET-2 was not done in 4/40 pts (n=2 each either not performed or PD). In an intent to treat (ITT) analysis the CR rate at the end of treatment was 48% (19/40; 95CI-32-64%) with an ORR of 68%. In pts who completed 6 cycles (n=30) the CR/ORR rate was 63%/87% respectively. Seven pts (18%) experienced primary treatment failure. Of the 19 pts in CR at end of initial therapy, 14 were in a CR at PET-2 assessment. Two pts in a PET-2 CR discontinued prior to cycle 6 due to toxicity and have not progressed. Five pts converted from a PR to CR after PET-2, but 7 of 13 PRs remained PRs. Responding pts (CR/PR; n=30) proceeded either to an ASCT (n=18), len maintenance (n=10) or neither (investigator/pts preference; n=2). At a median follow up of 13 months (range: 4-23 months), the 1-year estimated PFS and OS is 68% [95% CI--50-80%] and 89% [95%CI--73-96%] respectively. There were five grade (G) 5 events including PD (n=1), secondary malignancy (n=1; AML), sepsis (n=2), and cardiac arrest (n=1). Serious or recurrent adverse events (SAEs or AEs) of interest occurring during any cycle included 38% G 3-4 febrile neutropenia despite mandated GCSF use, 43% G 3-4 anemia, 43% G 3-4 thrombocytopenia (without report of G 3-4 bleeding or bruising despite ASA use), 3% G3-4 rash (all G 23%), and 8% G 3-4 diarrhea (all G 43%). Conclusions: The phase II portion of the study in an ITT population noted an unexpectedly modest 48% CR rate and a high discontinuation rate (15%) due to AEs or SAE. The utility of response at PET-2 and post initial therapy strategy (len maintenance vs ASCT) continue to be monitored for PFS and OS in this limited cohort. Improving frontline outcomes for pts with PTCL remains an unmet need. Disclosures Lunning: Celgene: Consultancy; TG Therapeutics: Consultancy; Genentech: Consultancy; Bayer: Consultancy; AbbVie: Consultancy; Spectrum: Consultancy; Kite: Consultancy; Janssen: Consultancy; Gilead: Consultancy; Portola: Consultancy; Seattle Genetics: Consultancy; Astra-Zeneca: Consultancy; Genzyme: Consultancy; Juno: Consultancy; Genentech: Consultancy; Verastem: Consultancy. Horwitz:Millennium/Takeda: Consultancy, Research Funding; Trillium: Consultancy; Mundipharma: Consultancy; Kyowa-Hakka-Kirin: Consultancy, Research Funding; Portola: Consultancy; Aileron Therapeutics: Consultancy, Research Funding; Innate Pharma: Consultancy; Corvus: Consultancy; Spectrum: Research Funding; Seattle Genetics: Consultancy, Research Funding; Infinity/Verastem: Consultancy, Research Funding; ADC Therapeutics: Consultancy, Research Funding; Forty Seven: Consultancy, Research Funding; Celgene: Consultancy, Research Funding. Advani:Janssen Pharmaceutical: Other: Institutional Research Support; Cell Medica: Other: Consultancy/Advisory Role; Bayer Healthcare Pharmaceuticals: Other: Consultancy/Advisory Role; Merck: Other: Institutional Research Support; Forty Seven, Inc: Other: Institutional Research Support; Millenium: Other: Institutional Research Support; Roche/Genentech: Other: Consultancy/Advisory Role, Institutional Research Support; Pharmacyclics: Other: Institutional Research Support; Celgene: Other: Institutional Research Support; Regeneron Pharmaceuticals, Inc.: Other: Institutional Research Support; Kura: Other: Institutional Research Support; Infinity: Other: Institutional Research Support; Autolus: Other: Consultancy/Advisory Role; Kyowa: Other: Consulting/Advisory Role; Takeda: Other: Consultancy/Advisory Role; Bristol Myers Squibb: Other: Consultancy/Advisory role and Institutional Research Support; Agensys: Other: Institutional Research Support; Gilead/Kite: Other: Consultancy/Advisory Role; Seattle Genetics: Other: Consultancy/Advisory role, Institutional Research Support; AstraZeneca: Other: Consultancy/Advisory Role. Vose:Epizyme: Honoraria; Roche: Honoraria; Novartis: Honoraria, Research Funding; Celgene: Research Funding; Incyte Corp.: Research Funding; Legend Pharmaceuticals: Honoraria; Bristol Myers Squibb: Research Funding; Seattle Genetics, Inc.: Research Funding; Abbvie: Honoraria; Acerta Pharma: Research Funding; Kite Pharma: Research Funding; Merck Sharp & Dohme Corp.: Research Funding. Mehta-Shah:Verastem: Research Funding; Genetech: Research Funding; Celgene: Research Funding; Bristol-Myers Squibb: Research Funding; Spectrum: Consultancy. Haverkos:Viracta Therapeutics: Membership on an entity's Board of Directors or advisory committees. Moskowitz:ADC Therapeutics: Research Funding; Bristol Myers-Squibb: Consultancy, Research Funding; Merck: Research Funding; Incyte: Research Funding; Takeda: Honoraria; Seattle Genetics: Consultancy, Honoraria, Research Funding. Ansell:Merck & Co: Research Funding; Pfizer: Research Funding; Bristol-Myers Squibb: Research Funding; Seattle Genetics: Research Funding; Trillium: Research Funding; Takeda: Research Funding; LAM Therapeutics: Research Funding; Affimed: Research Funding; Celldex: Research Funding; Regeneron: Research Funding.

Abstract: In prior studies, we demonstrated that transplantation of major histocompatibility complex (MHC) matched and mismatched purified hematopoietic cells (HSCs) can block diabetes pathogenesis in pre-diabetic NOD mice. Here we applied this treatment to experimental allergic encephalomyelitis (EAE), an animal model for the human autoimmune disease multiple sclerosis (MS). C57BL/6 (B6) strains congenic for the CD45 locus were immunized with MOG 35–55 to induce disease. Similar to our studies in NOD mice we observed that disease response after transplantation of MHC-mismatched hematopoietic cells in EAE affected mice was superior to those that received congenic cells. Importantly, mice transplanted with MHC-matched HSC or BM showed no significant improvement in disease symptoms when compared with congenic recipients or disease controls. This result was markedly different from the positive response observed in NOD mice transplanted with MHC-matched HSC. We then sought to optimize translation of this approach by giving total lymphoid irradiation (TLI) plus anti-thymocyte globulin (ATG), a non-myeloablative regimen and permits allogeneic hematopoietic cell engraftment with significant protective effect against GVHD. We found that TLI/ATG treatment in wild type C57BL/6 mice permit engraftment of purified HSC isolated from MHC-matched AKR/B donors and improve disease severity significantly. The level of stable mixed chimerism correlated with the clinical score. While the prior studies demonstrated that a class of regulatory cells that express both nature killer cell and T cell markers (NK-T) are present at high levels in TLI/ATG treated mice, we determined that regulatory CD4+CD25+Foxp3+ cells are also present at a disproportionately high levels as compared to wild type animals. To study the role of regulatory T cell in disease protection, a flexible lentiviral vector platform supporting constitutive expression of a Tet-transactivating component with a selection marker and coordinated conditional expression of miR-shRNA targeting Foxp3 gene products in stem cells is being developed. The detailed mechanism will be discussed. We hope a MHC-matched hematopoietic graft in conjunction with TLI/ATG conditioning shown here to successfully ameliorate EAE can be translated to the treatment of human autoimmune disease.