ALBERT

Description: Background: Patients (pt) with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) who are elderly, or have secondary AML (sAML), or relapsed/refractory (R/R) disease have poor outcomes. Venetoclax (VEN), an oral BCL2 inhibitor, has shown activity in R/R AML as single-agent and in combination with hypomethylating agents (HMA) in newly diagnosed unfit AML. We designed a phase II trial to evaluate the safety and efficacy of VEN with 10-days (D) of decitabine (DEC) in AML and high risk MDS. Methods: Eligible AML pts included those who had failed prior therapy, or were newly diagnosed (ND) elderly pts (〉60 years), or had sAML. ECOG score ≤3, WBC count ≤10 x109/L, and adequate organ function were required. VEN was given on day 1-28 in cycle (cy) 1 and D1-21 in cy 2 onwards; and was interrupted on C1D21 if the 21D bone marrow showed clearance of blasts, until count recovery. VEN was dosed 200 mg PO daily (50% dose reduction) in pts needing CYP3A4 inhibitors. DEC was given 20 mg/m2 IVdaily on D1-10 until CR/CRi, followed by 5-day cycles. Hydroxyurea or ara-C could be used for cytoreduction prior to starting therapy. Prophylactic antimicrobials were used until neutrophil recovery. Tyrosine kinase inhibitors could be used in applicable patients. Primary objective was to determine overall response rate (ORR) including complete remission (CR), CR with incomplete blood count recovery (CRi), partial remission (PR), and morphologic leukemia-free state in pts with AML. Secondary objectives were to determine safety of the combination; duration of response (DOR), disease-free survival (DFS) and overall survival (OS). Results: 48 pts were enrolled between January and May 2018 (Table 1). 24 pts (50%) had ND AML, 7 pts (15%) had sAML, and 16 pts (33%) had R/R AML. Prior therapies are listed in Table 1. The overall CR/CRi rate was 71% (34/48). CR/CRi rate for ND, sAML and R/R AML were 92%, 71% and 44%, respectively (Table 2). Negative minimal residual disease (MRD-) by flow cytometry at the time of response was achieved in 16/33 responding pts (49%). CR/CRi with MRD- was achieved in 11/21 pts with ND AML (52%), 2/5 pts with sAML (40%), and 3/6 pts w R/R AML (50%). CR/CRi rate in TP53 mutated pts was 67% (8/12, Table 2). Additional therapies included ponatinib in 1 pt with AML and t(9;22) who achieved a CRi; and sorafenib in 5 pts (4 FLT3-ITD, 1 FLT3 S749L variant) of which 2 ITD pts achieved CRi and 3 pts did not respond. Median time to first response was 43D (range 20-110) with a median of 1 cy to best response (range 1-3). At a median follow-up of 2.3 months (mo; range 1.4-5.7), pts had received a median of 2 cy (range 2-5) and 32 pts continue on study. Reasons for discontinuation are shown in Table 3. Median OS has not been reached (NR) for ND and sAML pts (NR, range 1.8 mo-NR) and R/R AML (NR, range 0.4 mo-NR, Fig 1a). Median DFS (Fig 1b) and DOR for ND and sAML pts are also NR (range 0.9 mo-NR). Median DFS and DOR for R/R AML pts were 3.3 mo (range 0.5-NR). 10 pts received GCSF. 59 treatment-emergent adverse events (TEAE) occurred in 31 pts, out of which 48 were grade (gr) 3/4. The most frequent gr 3/4 TEAE were infections, with gr 3/4 neutropenia (53%), febrile neutropenia (14%), and tumor lysis syndrome (TLS, n=2, 4%). 1 pt with WBC count 12 x109/L developed TLS on C1D2 which resolved with rasburicase and holding VEN; another pt with WBC count 28 x109/L developed TLS on C1D2 needing hemodialysis for 12 days, prompting study amendment to the current baseline WBC≤10 x109/L. Time to blood count recovery are shown in Table 4. There were total 6 deaths, all in pts with R/R AML (n=5) and treated sAML (n=1), including 3 deaths in hospice, 2 early deaths in relapsed AML pts due to infection; and 1 early death in a relapsed MDS pt due to pneumonia and acute kidney injury unrelated to therapy. There were no deaths in the ND AML pts. 30D and 60D mortality rates were 8% and 10%, respectively. Preliminary BH3 profiling data in R/R cohort showed BCL-2 priming (by assessing cytochrome C release to recombinant BAD peptide and ABT-199) in 7/8 pts irrespective of their response; however, pts who failed to achieve CR/CRi demonstrated co-dependence on other anti-apoptotic proteins MCL-1, BCL-XL and A1 (Fig 2). Additional BH3 profiling and CyTOF analyses are ongoing. Conclusion: The DEC10-VEN regimen had an acceptable safety profile and excellent response rates with CR/CRi of 92% in ND AML, 71% in sAML, and 44% in R/R AML with MRD- in 52% of ND AML, 40% of sAML and 50% of R/R AML. Trial is continuing to accrue (NCT03404193). Disclosures Maiti: Celgene Corporation: Other: Research funding to the institution. DiNardo:AbbVie: Consultancy, Other: Advisory role; Agios: Consultancy, Other: Advisory role; Bayer: Other: Advisory role; Celgene: Other: Advisory role; Medimmune: Other: Advisory role; Karyopharm: Other: Advisory role. Cortes:Novartis: Consultancy, Research Funding; Arog: Research Funding; Daiichi Sankyo: Consultancy, Research Funding; Astellas Pharma: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding. Pemmaraju:plexxikon: Research Funding; novartis: Research Funding; Affymetrix: Research Funding; samus: Research Funding; cellectis: Research Funding; celgene: Consultancy, Honoraria; SagerStrong Foundation: Research Funding; abbvie: Research Funding; daiichi sankyo: Research Funding; stemline: Consultancy, Honoraria, Research Funding. Kadia:Celgene: Research Funding; Amgen: Consultancy, Research Funding; Jazz: Consultancy, Research Funding; Takeda: Consultancy; BMS: Research Funding; BMS: Research Funding; Pfizer: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Novartis: Consultancy; Celgene: Research Funding; Abbvie: Consultancy; Jazz: Consultancy, Research Funding; Abbvie: Consultancy; Novartis: Consultancy; Takeda: Consultancy; Pfizer: Consultancy, Research Funding. Ravandi:Amgen: Honoraria, Research Funding, Speakers Bureau; Abbvie: Research Funding; Bristol-Myers Squibb: Research Funding; Jazz: Honoraria; Sunesis: Honoraria; Abbvie: Research Funding; Xencor: Research Funding; Sunesis: Honoraria; Seattle Genetics: Research Funding; Seattle Genetics: Research Funding; Macrogenix: Honoraria, Research Funding; Orsenix: Honoraria; Astellas Pharmaceuticals: Consultancy, Honoraria; Xencor: Research Funding; Astellas Pharmaceuticals: Consultancy, Honoraria; Jazz: Honoraria; Bristol-Myers Squibb: Research Funding; Amgen: Honoraria, Research Funding, Speakers Bureau; Macrogenix: Honoraria, Research Funding; Orsenix: Honoraria. Short:Takeda Oncology: Consultancy. Daver:BMS: Research Funding; ImmunoGen: Consultancy; Incyte: Consultancy; Otsuka: Consultancy; Daiichi-Sankyo: Research Funding; Incyte: Research Funding; Novartis: Consultancy; Sunesis: Research Funding; Karyopharm: Research Funding; Pfizer: Research Funding; Alexion: Consultancy; Karyopharm: Consultancy; Pfizer: Consultancy; Sunesis: Consultancy; Kiromic: Research Funding; ARIAD: Research Funding; Novartis: Research Funding. Sasaki:Otsuka Pharmaceutical: Honoraria. Thompson:Gilead Sciences: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Research Funding; AbbVie: Honoraria, Research Funding; Pharmacyclics: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech: Honoraria, Membership on an entity's Board of Directors or advisory committees. Jain:Servier: Honoraria, Membership on an entity's Board of Directors or advisory committees; Servier: Research Funding; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Research Funding; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Research Funding; ADC Therapeutics: Research Funding; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Research Funding; ADC Therapeutics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Verastem: Honoraria, Membership on an entity's Board of Directors or advisory committees; Cellectis: Research Funding; Pharmacyclics: Research Funding; Novimmune: Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Research Funding; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Research Funding; Infinity: Research Funding; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novimmune: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologioes: Research Funding; Genentech: Research Funding; Verastem: Research Funding; Servier: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Research Funding; ADC Therapeutics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Astra Zeneca: Research Funding; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Research Funding; Verastem: Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Research Funding; Astra Zeneca: Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Research Funding; Abbvie: Honoraria, Membership on an entity's Board of Directors or advisory committees; ADC Therapeutics: Research Funding; Pharmacyclics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologioes: Research Funding; Pfizer: Research Funding; Cellectis: Research Funding; Verastem: Research Funding; BMS: Research Funding; Servier: Research Funding; Infinity: Research Funding; Astra Zeneca: Research Funding; Celgene: Research Funding; Genentech: Research Funding; Incyte: Research Funding; Abbvie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Astra Zeneca: Honoraria, Membership on an entity's Board of Directors or advisory committees. Jabbour:Pfizer: Consultancy, Research Funding; Novartis: Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; Abbvie: Research Funding. Andreeff:AstraZeneca: Research Funding. Konopleva:Stemline Therapeutics: Research Funding.

Description: Previous work from our group has demonstrated that the azurophil granule protease, neutrophil elastase (NE) can cleave PML-RARα (PR), the fusion protein that initiates acute promyelocytic leukemia; we identified valines 420 and 432 within the PML domain as the initial sites of NE cleavage. Furthermore, neutrophil elastase deficiency reduces the penetrance of leukemia in a knock-in model of APL in which the human PR cDNA is knocked into the 5′ untranslated region of the murine cathepsin G gene (Lane and Ley, Cell 2003) In this study, we demonstrate that mutation of residues V420 and V432 to arginine (2VR) confers resistance to proteolytic cleavage by NE. V420 and V432 are also cleaved using marrow extracts derived from NE deficient mice, indicating that other marrow-derived proteases can cleave PR at these two valines; the 2VR mutation confers resistance to these proteases as well. To determine the role that cleavage of PR plays in leukemogenesis, we generated protease-resistant PR mice by inserting the PR(2VR) allele into the murine cathepsin G locus via homologous recombination. Analysis of marrow from 6–8 week old preleukemic mice indicates that myeloid progenitors from PR(WT) and PR(2VR) mice both have increased replating efficiency in methocellulose cultures with a trend towards increased efficiency with PR(2VR)mice (WT=0%, PR(WT)=0.45%, PR(2VR)=1.65% at 4th replating, p=NS). Both PR(WT) and PR(2VR) mice develop a phenotypically identical, fatal myeloid leukemia characterized by splenic infiltration with blasts that co-express CD117 (c-kit) and Gr-1, and that are morphologically promyelocytes. A tumor watch revealed that PR(2VR) mice (n=89) demonstrated a shortened latency of leukemia development (274 days) compared to PR(WT) mice (n=41, 473 days, p=0.0003). These results indicate that resistance to proteolysis confers an increased leukemogenic potential to the PR fusion protein, which may be due to increased levels of full length PR in the myeloid progenitors of these mice. Based on these observations, we suggest NE-mediated cleavage of PR is not required for its activity. Therefore, the mechanism by which NE deficiency affects APL penetrance may be indirect.

Description: Despite advances in supportive care and post-remission therapy, the outcome of elderly and relapsed/refractory AML patients (pts) remains poor. These pts commonly present with high risk features including antecedent myelodysplastic syndrome and unfavorable cytogenetics. In addition, such pts are often unable to tolerate standard induction chemotherapy (IC) or myelotoxic salvage chemotherapy (SC), limiting clinical options. Between 1/2007 and 5/2008, we treated 24 pts with two cladribine based regiments designed to limit hematologic and non-hematologic toxicities, while maintaining cytotoxic activity. Treatment consisted of Cladribine (5 mg/m2 d1–5) and Cytarabine (2 g/m2 d1–5) in combination with G-CSF (300mcg sc d0–5) (CLAG) or mitoxantrone (10mg/m2 d1–3) (CLAM). IC pts had a median age of 63 (range 23–80). SC pts had a median age of 56 (range 25–68). No pt had favorable cytogenetics. 40% (IC) and 56% (SC) of patients had unfavorable cytogenetics. Prior anthracycline/topoisomerase inhibitor therapy, myelodysplastic syndrome or other antecedent hematologic disorder was common (53% IC and 11% SC) and prior remission had been brief among SC pts (median 165 days). Complete response occurred in 53% of IC and 44% of SC patients lasting a median of 73 days (IC) and 222 days (SC). The median duration of neutropenia and thrombocytopenia in IC pts (CLAG/CLAM) was 22 and 24 days, respectively. The median duration of neutropenia and thrombocytopenia in SC pts (CLAG/CLAM) was 25 days and 21 days, respectively. Neutropenia and thrombocytopenia contributed to significant rates of documented infection (53% IC and 78% SC) and severe bleeding (33% IC and 11% SC). Significant cardiac, hepatic or renal toxicities were not noted in any group. Examining subgroups, those that received IC CLAG were elderly (median age 70) and fared poorly (14%CR, 43%PD, 43%TRM). In contrast the younger IC CLAM cohort did well with 7/8 pts achieving CR with a median duration of 126 days despite poor risk features (38% high-risk cytogenetics/63% AHD). This is the first report of front-line CLAM in AML. Both CLAG and CLAM performed similar to other salvage regimens reported in the literature though in a less favorable population than has been previously reported with CLAG and CLAM (median age 45 and 17–25% unfavorable cytogenetics in the Polish experience compared to median age 56 and 56% unfavorable cytogenetics in this report) (Wierzbowska A et al. Eur J Haematol2007; 80: 115–26, Wrzesien-Kus A et al. Eur J Haematol2003; 71: 155–62). CLAM warrants further study, especially in the context of other agents as both induction and salvage therapy for high-risk AML. New Diagnosis Relapsed (xx/xx)=data from CLAG and CLAM, respectively. Patients (CLAG/CLAM) 15 (7/8) 9 (5/4) Median Age 63 (range 23–80) (70/56) 56 (range 25–68) (56/53) Median WBC count 18,000 (1000–157,600) 15,400 (200–83,000) Favorable cytogenetics 0% 0% High risk cytogenetics or FLT3-ITD positive 40% (43%/38%) 56% (60%/50%) Prior tAML, MDS or AHD 53% (43%/63%) 11% (20%/10%) Duration of first remission NA 165 days (30–263) CR 53% (14%/88%) 44% (40%/50%$) PD 27% (43%/12%) 56% (60%/50%) Death during aplasia 20% (43%/0%) 0% CLAG/CLAM Duration of CR (days) 73 (range 73)/126# (range 96–∞) 222 (range 219–224)/164 (range 61@-267) % of CR going on to receive allogeneic transplant 13% (0%/14%) 11% (20%/0%) Median duration of neutropenia

Description: Key Points Hematopoietic populations unrelated to the AML founding clone often expand after induction therapy, resulting in oligoclonal hematopoiesis.

Description: Hematopoietic cells from patients with myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) contain gene mutations that are variably distributed between the founding clone and daughter subclone(s). Traditional response criteria in MDS and AML are based on bone marrow morphology and may not accurately reflect antitumor activity and clinical benefit in patients treated with hypomethylating agents. We used digital sequencing of serial bone marrow samples to monitor tumor burden and to characterize the changes in the clonal structure of MDS and AML that occur during treatment with epigenetic therapy. We hypothesized that digital sequencing may provide an alternative measure of antitumor activity and identify the persistence or emergence of resistant clones during treatment which mediate disease relapse. We conducted a phase I/II study in older adults (age ≥ 60) with advanced MDS (IPSS ≥ 1.5) or AML. Subjects received a combination of decitabine 20 mg/m2 on d1-5 with the histone deacetylase inhibitor, panobinostat 10-40 mg po 3x/week every 28 days for up to 12 cycles. Serial bone marrow samples were collected for digital sequencing at baseline, after every 2 cycles of treatment and at the time of relapse. A total of 52 patients, 14 with MDS and 38 with AML were enrolled in this study. For AML patients, 10% achieved a complete remission (CR+CRi) with an additional 18% of patients achieving a morphologic leukemia-free state (mLFS) using IWG response criteria. For patients with MDS, 14% achieved a CR and 21% achieved a marrow CR. We identified 9 MDS and 16 AML patients that had banked, paired bone marrow and skin (as a source of normal DNA) samples and a somatic mutation in at least 1 of 54 recurrently mutated MDS/ AML genes. DNA was enriched for 285 genes commonly mutated in MDS and AML (n=24 patients) or whole exome probes spiked-in with the 285 genes (enhanced exome sequencing; EES) (n=7 patients), and sequenced on a HiSeq2000 instrument with 2x101bp reads. We detected an average of 4.9 SNVs and indels per patient (range 1-15) when only the 285 gene panel was used, compared to 27.4 mutations per patient (range 9-43) using EES. Ten genes were mutated in at least 3 pre-study samples. The presence of a TP53 mutation (N=8) was associated with a trend towards achieving a response (p=0.09). We then analyzed variant allele frequencies (VAF) of mutations in serial samples. We observed five distinct patterns that were associated with different clinical responses, including i) AML patients achieving a CR+CRi (n=2): mutation VAFs were undetectable by cycle 2 using standard sequencing, ii) AML with mLFS (n=2): mutation VAFs remained detectable but decreased to 30%. We observed responding patients can have persistent measurable clonal hematopoiesis for at least one year without disease progression. Sequencing also revealed selective AML subclone clearance in a patient with treatment failure, nominating a set of mutations that may mark super-responder clones. We observed that the blast percentage decreases prior to mutation VAFs in some patients, suggesting that the differentiation of blasts could falsely underestimate tumor burden. Finally, sequencing revealed that tumor burden can be measured even in patients achieving a CR. Using an ultra-sensitive barcode sequencing approach, we sequenced 1 MDS and 1 AML patient achieving a clinical and molecular CR (based on standard sequencing). We detected extremely rare TP53 mutations months to years prior to disease relapse (VAFs = 0.23% in MDS and 0.05% in AML during a CR - equivalent to a sensitivity of 1 in 2000 heterozygous mutant cells). While patients can live with persistent clonal hematopoiesis in a CR or stable disease, ultimately we find evidence that expansion of a rare subclone drives relapse or progression from MDS to secondary AML. Digital sequencing provides an alternative measure of disease response which may augment traditional clinical response criteria and should be explored in future clinical trials. Disclosures Uy: Novartis: Research Funding. Off Label Use: Panobinostat in MDS/AML. Duncavage:Cofactor Genomics: Consultancy; DI&P Consulting: Consultancy. Jacoby:Sunesis: Research Funding; Novo Nordisk: Consultancy. Abboud:Teva Phamaceutical: Research Funding.

Description: Abstract 2148 Introduction: Myelodysplastic syndrome (MDS) and Acute Myeloid Leukemia (AML) are hematological disorders that exist on a spectrum of ineffective and malignant hematopoiesis. Hypomethylating agents have been recently shown to result in clinical response and improved survival in patients with either disease, although only in a minority of patients. Arsenic trioxide too has shown limited single agent activity in patients with MDS and AML, and ascorbic acid improves response to arsenic trioxide in patients with multiple myeloma. We therefore sought to assess the tolerability of combination decitabine, arsenic and ascorbic acid in patients with MDS and AML. Study: The primary object of this single institution, dose-escalation study was to establish the maximum tolerated dose and dose-limiting toxicities during four cycles of therapy. Arsenic trioxide was administered in three dose cohorts of 3–6 patients each: 0.1 mg/kg, 0.2 mg/kg, and 0.3 mg/kg IV on days 1–5 followed by weekly administration for 15 weeks. All patients received decitabine 20 mg/m2 IV on days 1–5 every 28 days and ascorbic acid 1000 mg IV following every administration of arsenic trioxide. Secondary objectives were to establish overall response rates and effect of therapy on bone marrow angiogenesis. Results: Thirteen patients were enrolled in three dose cohorts [9 men, 4 women; median age: 67 (range 24 – 77); 5 MDS, 7 AML; ECOG 0 (46%), 1 (38%), 2 (15%)]. Most patients were transfusion dependent [RBC dependent: MDS 4/5, AML 4/7; platelet dependent: MDS 2/5, AML 4/7]. Most patients had received prior therapy [MDS 1/5; AML 7/7]. Ten patients received at least 2 cycles with four patients completing four cycles. Dose limiting toxicities were pneumonia/infection, which occurred in the third dosing cohort. Other grade 3–4 toxicities occurring during 4 cycles of treatment were: infection (46%), hypotension (15%), hypoxia/pneumonia (20%), anemia (53%), neutropenia (38%), QTc prolongation (15% - all asymptomatic), pericardial effusion (8%), pleural effusion (8%), hyperglycemia (20%), hypokalemia (8%). According to IWG response criteria, 2/5 MDS patients achieved stable disease, 2/5 developed progressive disease, and 1/5 withdrew prior to reevaluation. Similarly, 3/7 AML patients achieved stable disease, 2/7 progressive disease, and 2/7 died without repeat bone marrow evaluation. No transfusion dependent patients achieved transfusion independence. The median overall survival of these cohorts was 207 days and four patients remain alive with a median follow-up of 490 days. We did not observe a correlation between dosing cohort and response or survival. Because arsenic trioxide has been proposed to inhibit angiogenesis, we assessed bone marrow microvessel density (MVD) using CD34 immunohistochemistry by two binded, independent reviewers. Paired bone marrow samples from eight patients surprisingly revealed an increase in the number of vessels per high powered field during therapy [pre-treatment: (ave 10.3, stdev 5.2); after cycle 2: (ave 18.0, stdev 7.0, p = 0.06); after cycle 4: (ave 17.1, stdev 3.2, p = 0.05)]. Increased MVD occurred independent of response, disease or bone marrow cellularity. Conclusions: This study demonstrates that decitabine can be safely combined with arsenic trioxide and ascorbic acid in a heavily pre-treated population of MDS and AML patients. Our maximum tolerated dose of arsenic was observed in cohort 2: 0.2 mg/kg. Combination therapy resulted in increased bone marrow microvessel density, independent of response and bone marrow cellularity. Phase 2 studies will be required to assess the efficacy of combination therapy. Disclosures: Off Label Use: Decitabine, Arsenic and Ascorbic acid for the treatment of AML. Vij: Eisai: Speakers Bureau; Cephalon: Speakers Bureau.

Description: Background The negative impact of acute graft-versus-host disease (GvHD) on morbidity and mortality after allogeneic transplant is significant; thus, finding a means to harness the beneficial Graft versus tumor effect (GVT) while reducing or eliminating GvHD is a major goal of transplant trials. Alterations in immune subsets present after transplant can work to suppress allo-reactive T-cell responses by increasing regulatory T-cells and suppressing allo-reactive T-cell proliferation. Azacitidine (AZA) treatment in pre-clincal models resulted in an increase in regulatory T-cells, a decrease in allo-reactive T-cell proliferation and prevention of acute GvHD while preserving GVT effects. (Choi et al. Blood 2010). Based on these results a phase I/II study was designed to test the safety and efficacy of AZA administered shortly after transplant for the prevention/prophylaxis of acute GvHD and relapse in subjects receiving transplants from matched unrelated stem cell donors. We report the results for the Phase I portion of this trial. Methods Patients with hematologic malignancies in remission age 18 - 70 were eligible. Myeloablative or reduced intensity conditioning without antithymocyte globulin was used. All recipients were required to receive at least 2 x 106 CD34/kg and have at least 1 x 106 CD34/kg cryopreserved as back up in case of primary graft failure. AZA was administered intravenously on day +7 for five consecutive days and repeated every 28 days for a total of 4 cycles after allogeneic transplant from a 10/10 HLA matched unrelated donor. Standard GvHD prophylaxis with mini-methotrexate and tacrolimus was given. A Phase I, 3+3 dose escalation design of 4 cohorts (AZA dose levels 15, 30, 37.5, and 45 mg/m2) was used to determine toxicity and recommended phase II dose. The primary outcome for phase II is the rate of grade II - IV acute GvHD at day 180 after transplant. Results We have transplanted 16 subjects on trial, 15 have received study drug. Recipient characteristics include: median age 57, 67% male, and diagnoses of AML in CR (9), ALL in CR (2), or MDS (4). One DLT was observed in the final cohort of 6 subjects. The DLT experienced in the final cohort was primary graft failure. The subject had developed Clostridium difficile colitis during conditioning and fungemia shortly after transplant. A total CD34 dose of 2 x 106/kg was infused after myeloablative conditioning of Busulfan and Cytoxan. The subject received the cryopreserved back up donor leukocyte infusion at day +28 but died at day 29 of sepsis without evidence of neutrophil engraftment. Contributing causes to the DLT were thought to be the CD34 dose infused, sepsis, severe colitis and possibly AZA administration. For the remainder of subjects treated in phase I the median CD34 dose infused was 5 x 106/kg (range 2 - 5), median ANC engraftment was 14 days (range 10 - 22 days). Median platelet engraftment was 22 days (range 14 - 70). No grade III/IV acute GvHD has been observed. Grades 1 and 2 skin and gut GvHD have been observed, and all cases have responded to steroids except one case of steroid refractory GvHD in cohort 1 (15mg/m2 AZA). At the recommended phase 2 dose of 45mg/m2 AZA, 3 cases of skin GvHD were observed occurring just prior to or at the time of cycle 2 of treatment. All responded to steroids. With a median follow up of 233 days (range 29 - 784), only 2 subjects have relapsed and 11 (73%) remain alive. The most common non-hematologic grade 3 or 4 AEs were gastrointestinal toxicity (mucositis, nausea and diarrhea), electrolyte abnormalities, and infections. In conclusion, AZA can be given safely starting at day +7 after MUD transplant up to a dose of 45mg/m2 tested. Phase II is currently enrolling subjects. Because of the DLT experienced in phase I, the infused CD34 dose will be increased to a minimum of 4 x 106 CD34/kg with 1 x 106 CD34/kg cryopreserved in backup. Correlative studies from banked Phase I biospecimens evaluating dynamics of regulatory T-cells, T-cell subsets and methylation before and after treatment are being analyzed and will be reported. Disclosures Schroeder: Incyte: Consultancy; Celgene: Other: Azacitidine provided for this trial by Celgene. Off Label Use: Azacitidine for GVHD prophylaxis. Abboud:Gerson Lehman Group: Consultancy; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Novartis: Research Funding; Pfizer: Research Funding; Merck: Research Funding; Teva Pharmaceuticals: Research Funding. Vij:Onyx: Consultancy, Honoraria, Research Funding, Speakers Bureau; Millennium: Honoraria, Speakers Bureau; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau; BMS: Consultancy; Takeda: Consultancy, Research Funding; Novartis: Consultancy; Sanofi: Consultancy; Janssen: Consultancy; Merck: Consultancy.