ALBERT

Description: Multicenter large collaborative research groups have been the cornerstone for advances that have been made in multiple disciplines in medicine. These collaborative groups are specifically useful in situation where no single center based dataset is large enough to effectively address biological and clinical relevant questions that could advance the field. Most such collaborative groups exist in the developed countries and have contributed significantly to the development of the current standards of care in leukemia. The challenges in the developing countries or low middle income countries (LMIC) are distinctly different and often algorithms that have evolved in the developed world may not be applicable, relevant or accessible in the LMIC. It is imperative that these challenges be addressed through large multicenter studies that are located within the LMIC and appropriate local data driven solutions be implemented in response. The 'Hematological Cancer Consortium' is a collaborative group from India currently compromising twelve institutions spread across the country that have come together to collaborate in the field of leukemia. As an initial exercise, to establish denominators a retrospective data analysis was undertaken (Indian acute leukemia research database [INwARD]). Here we present the retrospective analysis of the acute myeloid leukemia (AML) data. Retrospective data from January 2013 to December 2017 was collected from 10 large tertiary centers from across the country (in one center data was available only from January 2017). A central online data capture and management system was in place which was independent of all the participating centers (Clinical Data Management Center [CDMC], Vellore, which is compliant with standard ICH-GCP regulations). In this initial phase some centers contributed data offline to the data management center. A total of 3848 were confirmed to have had a diagnosis of AML in this period of which it was noted that 1766 (46%) received definitive treatment (Fig 1 a). The median age of the patients was 40 years (range: 0-89) and there were 59% males. The age distribution of patients by each decade is illustrated in Fig 1b. 399 (10.4%) were ≤ 18 years). A sample for karyotyping was sent in 2609 (68%) however of these an evaluable karyotype was noted in only 1477 (57%) (Fig 1c), the reasons for lack of evaluable metaphases was not clear. A FLT3 and NPM1 mutation status was evaluated in 1338 (35%) and 1401 (36%) respectively. Of the evaluated patients 20.6% and 21.9% had FLT3-ITD and NPM1 mutated respectively (Fig 1d). Of the 1766 patients that were treated 858 (48.6%) received a conventional 7/3 induction, 170 (9.6%) received hypo-methylating agents while the rest received various abbreviated dose regimens and a small proportion (2.8%) received high dose cytosine based regimens as induction therapy. Antifungal prophylaxis was used by 82% of patients that received therapy. Of those that received induction therapy there were 18% induction deaths and 12.9% subsequently received an allogeneic SCT as part of their consolidation therapy (Fig 1a). The 5 year KM estimate for overall and event free survival for the patient that received treatment was 56.2±2.6% and 33.8±2.4% respectively. The data illustrates significant challenges and opportunities with the management of AML in India. A significant proportion of cases do not receive definitive therapy nor do they have conventional tests such as karyotyping or molecular tests done as part of the baseline diagnostic tests, various social and financial constraints could contribute to these and these need to be evaluated in more detail. Strategies to increase access to care and laboratory facilities along with an effort to reduce early induction deaths need relatively urgent attention. The relatively young age of the cohort and large number of cases would allow us to address relevant biological and clinically challenges effectively, in the future, in this cooperative setting. Disclosures No relevant conflicts of interest to declare.

Description: Significant strides have been made in the management of ALL and clinical outcomes have steadily improved over the last few decades. Many of these advances involve intensification of therapy, allogeneic SCT, improved molecular risk stratification and measurable residual disease (MRD) directed therapy. However in the developing world and low middle income countries (LMIC) there are significant challenges in implementing or access to such advances. Additionally, in the absence of large collaborative research groups in LMIC, as has been developed in most developed economies, it is difficult to get a handle of the magnitude of the problem and develop strategies to overcome them. The 'Hematological Cancer Consortium' is a collaborative group from India currently comprisingof twelve institutions spread across the country that have come together to collaborate in the field of leukemia. As an initial exercise to establish denominators a retrospective data analysis was undertaken (Indian acute leukemia research database [INwARD]). Here we present the retrospective analysis of the acute lymphoblastic leukemia (ALL) data. Retrospective data from January 2013 to December 2017 was collected from 7 large tertiary centers from across the country. A central online data capture and management system was in place which was independent of all the participating centers (Clinical Data Management Center [CDMC], Vellore, which is compliant with standard ICH-GCP regulations). In this initial phase some centers contributed data offline to the data management center. A total of 1631 patients were confirmed to have had a diagnosis of ALL in this period of which it was noted that 1217 (75%) received definitive treatment (Fig 1 a). The majority of treated cases were B ALL (73%) followed by T ALL (23%), MPAL was diagnosed in 11 cases (0.9%) (Fig 1b). Of the 1217 patients that received treatment a karyotype report was available in 81.6% (Fig 1c), while FISH/PCR data was available in 703 (58%) of cases. The median age of the patients was 16 years (range: 1-76) and there were 70% males. The age distribution of patients by each decade is illustrated in Fig 1d. Of the diagnosed cases 879 (54%) were ≤ 18 years of age. Following initial induction therapy 80% of patients achieved complete hematological remission (CR) and there were 6.6% induction deaths. Only 37 (3%) received an allogeneic SCT in CR1. The 5 year KM estimate for overall and event free survival for the entire cohort of patients that received treatment was 80.4±2% and 57.1±3.8% respectively. This retrospective data gives a snapshot of the status of treatment of ALL in India and illustrates the challenges. A significant proportion of cases due to various constraints abandon therapy and a significant proportion of treated cases do not have conventional karyotyping or molecular tests done prior to start of therapy which would be considered a deviation from the standard of care in the developed world. This collaborative group has the potential to evaluate and understand these challenges in greater depth over subsequent prospective studies and develop strategies to overcome them. Disclosures No relevant conflicts of interest to declare.

Description: Recent reports propose high-dose (HD) methotrexate (MTX)-based cytoreduction followed by consolidation with HD chemotherapy (HDC) with or without autologous stem-cell transplantation (ASCT) as first-line treatment for primary central nervous system lymphoma (PCNSL). The main rationale is that HDC-ASCT may improve disease control by achieving higher therapeutic concentrations of cytotoxic chemotherapy in the CNS, thus circumventing the blood-brain barrier (BBB). We have employed an alternative approach to treat PCNSL patients effectively. This first-line treatment enhances delivery of standard dose (SD) MTX-based chemotherapy administered intra-arterially (i.a.) with osmotic BBB opening plus the anti-CD20 monoclonal antibody (mAb) rituximab, followed in complete responders by anti-CD20 mAb maintenance immunotherapy. The main features that distinguish our approach from HDC-ASCT consolidation are to utilize BBB properties to maximize delivery of SD chemotherapy to the CNS sanctuary, and maintenance immunotherapy to delay recurrence. A multi-center study of 149 PCNSL patients (2,079 i.a. BBB treatments) resulted in one death within 48 hrs after treatment, from pulmonary embolism. Prior to routine use of granulocyte colony stimulating factor, granulocytopenic fever occurred in 3% of BBB treatments (Angelov, J Clin Oncol 2009). This contrasts with HDC-ASCT consolidation which carries substantial morbidity and treatment-related mortality (6% to 9%) (Ferrari, Lancet Hemat 2016; Omuro, Blood 2015). Further, HDC-ASCT is used primarily in younger PCNSL patients (〈 60-65 yrs) with good performance status and is not feasible in many PCNSL patients given the median age at diagnosis is 60-65 yrs. First-line enhanced BBB delivery of SD MTX-based chemotherapy in 149 patients provided an overall response rate (ORR) of 82% (58% CR rate) and median overall survival (OS) of 37 mo. In low risk patients (age 〈 60 yrs and KPS ≥ 70) median OS was approximately 14 yrs. Survivors in CR a minimum of 2 yrs after diagnosis (n = 24) were evaluated with standard neuropsychological tests. Median follow-up was 12 yrs (range 2 to 26 yrs) and results indicated long-term preserved or improved cognitive function (Doolittle, J Clin Oncol 2013). Recently we compared efficacy from two first-line MTX-based regimens: HD MTX (intravenous, 4gr/m2) (Thiel, Lancet Oncol 2010), and enhanced BBB delivery of MTX (i.a., 3.5gr/m2). After adjusting for patient characteristics, CR rate and progression free survival were higher in patients 〈 65 yrs treated with enhanced delivery of MTX (p 〈 0.001). When first-line rituximab was added to the i.a. enhanced delivery regimen in 24 patients (median age 64 yrs; median KPS 65), the ORR improved to 92% (75% CR) and OS to 61 mo. To prevent recurrence, Ney (Leuk Lymphoma 2009) treated a small group of patients in CR after standard PCNSL treatment, with maintenance rituximab. The addition of maintenance immunotherapy resulted in average disease control of 22 mo or longer. Consistent with the Ney report, we noted prolonged median CR duration of 38 mo (range: 10 to 85 mo) in a small subset treated with maintenance rituximab (n = 9). Increased survival was also seen in translational laboratory studies of a rodent model of intracerebrally implanted MC116 human B-cell lymphoma cells, using single agent rituximab, whether or not delivered with BBB disruption and whether or not MTX was included (Muldoon, Clin Cancer Res 2011). These results suggest that rituximab slowly leaked into main CNS tumor mass even in absence of BBB opening; and given the long half-life, was trapped by binding to CD20+ on tumor cells, attaining sufficient concentration for antitumor efficacy. Our goal is to maximize first-line enhanced BBB delivery of SD chemotherapy to enable less treatment-related morbidity and mortality than is associated with HDC-ASCT in PCNSL, and increase CR duration. Neurocognitive safety has been demonstrated in long-term survivors treated with BBB delivery. Based on the encouraging results from Ney et al, our pilot data using maintenance rituximab, and translational lab studies of mAb delivery to brain, a new randomized multi-center trial is underway to study the effect of maintenance obinutuzumab on CR duration, neurocognition and quality of life in PCNSL patients who achieve CR following first-line MTX-based chemotherapy (NCT02498951). A trial update will be presented during the ASH 2016 meeting. Disclosures No relevant conflicts of interest to declare.

Description: Introduction: Current advances in allogeneic hematopoietic cell transplant (alloHCT) may warrant a paradigm shift in managing children with sickle cell disease (SCD). This study characterizes the clinical outcomes and health care utilization (HCU) of alloHCT for pediatric SCD. We hypothesize that early alloHCT will have improved clinical outcomes, and decreased HCU. Methods: The Center for International Blood and Marrow Transplant Research database was used to identify children 21 years or less with alloHCT for SCD in the United States. Patient data included comprehensive research forms (CRF) from 2000-13 and transplant essential data (TED) forms from 2000-11. CRFs provided clinical risk factors associated with overall survival, graft failure, grade III-IV acute GVHD, and GVHD related event free survival (GREFS) - the survival free of graft failure, chronic GVHD, or death. Risk factors included age, gender, performance status, year of alloHCT, prior SCD complications and therapy, CMV status, donor type, conditioning regimen, and GVHD prophylaxis. Due to low event rates and sample size, only univariate analysis of risk factors was performed. TED data was merged with Pediatric Health Information System (PHIS) inpatient data using a probabilistic merging algorithm to determine risk factors and clinical outcomes associated with HCU. Available PHIS adjusted cost data was used to determine the total adjusted cost for all inpatient admissions per patient per hospital day. To standardize these costs, the total adjusted cost per 30 hospital days was calculated for each patient and used as the primary HCU outcome. HCU outcomes were analyzed for the alloHCT year, day 0 to day +365. Results: CRF data for 161 patients showed an overall survival at 2 years of 90% (95% confidence intervals [CI] 85-95%): 96% (95% CI 89-100%) for related and unrelated cord blood transplant (CBT), 94% (95% CI 86-98%) matched siblings (MSD), and 74% (95% CI 54-90%) matched unrelated donors (MUD, p=0.002). All deaths occurred among children with pre-alloHCT complications of SCD, and deaths were due to organ failure (37.5%), infections (25%), GVHD (6.25%). Risk of death was significantly higher for children ≥10 years old (HR 21, p=0.003) and MUD compared to MSD (HR 5.88, p=0.005) but lower with cyclosporine A (CSA) GVHD prophylaxis versus FK506 (HR 0.33, p=0.031). 75% of deaths occurred before day +42. Cumulative acute GVHD incidence at day 100 was 14% (95% CI 9-20%)and was associated with age ≥10yrs (HR 2.63, p=0.035). Chronic GVHD incidence was 31% (95% CI 23-38%) at 2yrs, and factors associated were age ≥10yrs (HR 1.92, p=0.034), MUD vs MSD (HR 2.53, p=0.017), and CSA vs FK506 prophylaxis (HR 0.48, p=0.018). Chronic GVHD risk increased significantly after 2006 (HR 2.81, p=0.018). The 2yr GREFS was 64% (95% CI 56-71%). Age ≥10yrs (HR 2.2, p=0.005), MUD (vs MSD, HR 3.00, p=0.002) and CSA prophylaxis (vs FK506, HR 0.49, p=0.011) were significantly associated with this outcome. Among the 175 patients with combined TED and PHIS data, the median total adjusted cost was $117,393 per 30 hospital days per patient (range: $36,244-$515,640) during the alloHCT year with a median of 53 hospital days per patient (range: 16-304). Age ≥10yrs and HCU were not significantly associated (p=0.775). MSD had the lowest HCU compared to CBT and unrelated transplants (p

Description: Among transplant related complications, graft versus host disease (GvHD) significantly affects survival among patients undergoing allogeneic hematopoietic stem cell transplantation (aHSCT). There is limited data on GvHD and its impact on outcomes of aHSCT in patients with thalassemia major (TM). We have reviewed the incidence and outcome of GVHD among patients with TM who underwent aHSCT at our center. All patients with TM undergoing their first aHSCT between January 2007 and December 2017 were included in this analysis. Till 2009, all patients received conditioning with busulfan (16mg/kg over 4 days) with cyclophosphamide (200mg/kg over 4 days). From 2010, most patients received treosulfan (42 G/m2 over 3 days) with thiotepa (8mg/Kg for one day) and fludarabine (160mg/m2over 4 days) based conditioning regimen. All patients receiving busulfan conditioning received bone marrow (BM) as the graft while most patients receiving treosulfan conditioning received mobilized peripheral blood stem cells (PBSC). GvHD prophylaxis was with short-course methotrexate (10mg/m2 on day +1, and 7mg/m2 on days 3, 6 and 11) with cyclosporine. Thymoglobulin was added for matched unrelated donors (MUD). GvHD was prospectively recorded and graded according to the Glucksberg classification. Between January 2007 and December 2017, 363 first transplants were done for patients with TM with HLA identical donors. There were 12(3.3%) class 1, 105(28.9%) class 2 and 246(67.8%) class 3 (Pesaro risk stratification), with 115(46.7%) of the latter being high risk (Vellore risk stratification - BBMT, 2007; 13: 889). The median age was 8 years (range: 1-25) with a male predominance (60%). 331 (91.2%) patients had matched related donors (MRD) and 32 (8.8%) had MUDs. Donor gender was mismatched in 207 (57%) of which 129 (35.5%) were female to male transplants. The graft was obtained from the bone marrow in 137 (37.7%) of whom 53 (38.7%) were class III, and from mobilized peripheral blood in 226 (62.3%) of whom 193 (85.4% were class III. 149 (41%) patients developed GvHD - acute GvHD (aGvHD) in 115 (31.7%) and chronic GvHD (cGvHD) in 80 (22%). aGvHD was grade I in 32 patients (27.8%), grade II in 36patients (31.3%), grade III in 16 patients (13.9%) and grade IV in 25 patients (21.7%), while 6 patients (5.2%) had features of overlap GvHD only (oral lichen planus). First line treatment was with steroids in all patients with grade II and above aGvHD (n=83) with 43 (51.8%) of them responding adequately. There were 37 patients (44.5%) who required various second line agents for aGvHD with 20 (24%) receiving more than one immunosuppressive agent. 20 patients (24%) with persistent aGvHD went on to develop cGvHD. Out of the total of 80 patients with cGvHD, 13 (16.3%) had limited and 67 (83.7%) had extensive cGvHD. 26 patients (32.5%) developed de novo cGvHD, 8 (10%) of them after donor lymphocyte infusion (DLI) for potential rejection. The other 46 patients (57.5%) had chronic overlap GvHD following previous aGvHD. Among the different variables evaluated for association with aGvHD (patient/donor age, gender mismatch, MUD vs MRD), none were significant. Among those with MRD, aGVHd occurred in 36/135 patients (26.7%) of patients receiving BM grafts compared to 65/196 patients (33.2%) who received PBSC grafts (p=ns). cGvHD occurred in 23/106 patients (21.7%) in those receiving BM grafts vs 52/171 patients (30.4%) receiving PBSC (p=ns). 30 patients (8.3%) persisted to have cGvHD at last follow-up but only 20 (5.2%) required treatment. Mortality of the whole cohort was 66 (18.2%), out of which 32 (8.8%) were related to GvHD - 24 (6.6%) due to aGvHD and 8 (2.2%) due to cGvHD. At a median follow up of 41 months (range: 0-148), the 5-year and 10-year overall survival (OS) was 81.1±2.1% each for the whole cohort. The 5-year OS of those with grade 2-4 aGvHD was significantly lower than those with grade 0/1 aGvHD (65.7±5.3% vs 85.7±2.2%, p=0.000) [figure 1]. The 5 year OS of those with cGvHD was 88.9% ± 3.8% as compared to those without cGVHD was 96.9% ± 1.2% (P=0.009) [figure 2]. There was no significant difference in OS among those with limited and extensive cGvHD (90.9±3.6% vs 88.4±4.2% (p=ns). Our data shows that, as expected, severe aGvHD and extensive cGvHD significantly lowers survival in patients with TM undergoing aHSCT. However, PBSC graft did not result in higher acute or chronic GVHD compared to BM. Disclosures No relevant conflicts of interest to declare.

Description: Introduction: Clinical Depression experienced in Chronic Myeloid Leukemia (CML) is common, with a prevalence of 15- 30%. Compliance to TKI therapy in CML is a crucial factor. However, the lifelong duration of treatment impacts overall health related Quality of Life (QoL) in CML. In the absence of TKI resistance and depression, there is a better prognosis of patients conferring a better QoL and response to therapy. Methods: 98 patients on first line Imatinib (n=81) and Nilotinib (n=17) with a minimum TKI duration of 6 months were prospectively recruited, including their data on baseline Sokal, Eutos and Hasford Scores. Measures of Depression, QoL and Adherence were evaluated using Patient Health Questionnaire 9 item (PHQ-9), Survey Form - Health Related Quality of Life 36 item (SF-36) and Medication Adherence Rating Scale (MARS), respectively. Correlation of Depressive scores with QoL and Adherence were analysed. Similarly, all three variables were studied for their impact on treatment response (assessed by RQ-PCR-BCR ABL). Results: Frequency of Depression reported in CML patients was no (n=4), minimal (n=22), mild (n=47), moderate (n=19), moderately-severe (n=5), severe depression (n=1). Adherence was found to be 86%. In our study, majority of our Depressive Scores negatively correlated with QoL domains and Adherence using Pearson Correlation co-efficient (p value

Description: Granulocytic sarcoma (GS) is a rare extra medullary manifestation of acute myeloid leukemia (AML). It may also represent blastic transformation of myelodysplastic syndromes or myeloproliferative neoplasms. Although usually seen in the context of advanced and poorly controlled disease, it may also present as the first manifestation of illness, without concurrent bone marrow or blood involvement. In the medical literature chloroma and GS are terms that have been used interchangeably with myeloid sarcoma. GS usually manifest as soft tissue or bony masses in several extra cranial sites such as bone, periosteum and lymph nodes; involvement of the head and neck region is uncommon. Herein, we report a case of a 63 yearr-old woman with insidious onset of progressive nasal congestion and diminished hearing who was diagnosed with an isolated GS of the nasopharynx. With involved field radiotherapy she achieved a complete remission of 12 months duration before being diagnosed with overt AML. Following induction and consolidation chemotherapy she has remained disease free for now greater than 18 months. Through a MEDLINE®/PubMed® search we identified an additional 13 cases of nasopharyngeal GC. The median age was 37 years (range, 1 to 81 years). The cases were equally distributed among the sexes. The most common presenting symptoms were conductive hearing loss and sino-nasal congestion. Isolated GC was identified in 6 cases and the median time from diagnosis of GS to AML was 12 months (range, 3 to 48 months). Treatment varied, but responses were seen in all patients who received chemotherapy with or without radiotherapy.REFERENCE (YEAR)AGE (YEARS), SEXCLINICAL FEATURESASSOCIATED DIAGNOSISCYTOGENETICSOUTCOMEBassichis et al. (2000)1, maleMasseter muscleSynchronous AMLNot reported (NR)Died during chemotherapy.Au WY et al. (2001)37, maleConductive hearing loss, infiltrative nasopharyngeal massSolitary site of GSNormalInvolved field radiotherapy (IFRT) and chemotherapy. Complete remission (CR) at 3 years.Nayak et al.(2001)24, femaleBilateral parotid and nasopharyngeal massSolitary site of GSNRpatient died on 17th day of chemotherapy due to systemic infectionGeisse et al. (2002)60, maleWaldeyer’s ring lymphadenopathySynchronous MDSNRDiagnosis made on autopsyPrades et al.(2002)20, femaleSino-nasal obstruction; right maxillary and sphenoid sinus massGS of the nasal cavity and paranasal sinust(19:1)Allogeneic hematopoietic stem cell transplant (AHSCT) following chemotherapy; CR at 18 monthsOzcelik et al. (2003)37, maleVocal cord paralysis, involvement of 9th, 10th, 12th cranial nervesAML (M0) 6 months earlier - treated with chemotherapy to CRNRTreated with chemotherapy with partial regression of the nasopharyngeal masses; patient died on 17th day of chemotherapy due to pulmonary infectionSugimoto et al.(2004)31, femaleNasopharynx, external acoustic meatusAML (M2) 3 months earlier - treated with chemotherapy to CRt(8;21)(q22;q22)Achieved CR2 with IFRT, re-induction chemotherapy, followed by AHSCT.Imamura et al.(2004)7, femaleWaldeyer’s ring and cervical lymphadenopathySynchronous juvenile myelomonocytic leukemiat(9;12) (p22;q24.1)AHSCT following chemotherapy; CR at 3 yearsFerri et al. (2005)72, femaleRight facial swelling and fever; maxillo-ethmoidal massAML (M0) 1 year earlier – treated with hydroxyurea.NRBest supportive care only; died after 10 days of hospitalization.Teramoto et al.(2006)81, femalenaso-pharyngeal massDeveloped AML (M2) 1 year later.Complex genomic defects on cDNA microarrayRadiation therapy only for GS; chemotherapy for AML; died 6 months after diagnosis of AML.Selvarajan et al. (2008)25, maleDysphagia, hoarseness, facial nerve palsyAML (M2) 4 years earlier – treated with chemotherapy to CR followed by AHSCTt(8:21)Treated with chemotherapy but had systemic relapse 1 year laterCho et al. (2011)18, maleConductive hearing loss, infiltrative nasopharyngeal massSynchronous AMLRUNX1-RUNX1T1Recurrence after 7 months of chemotherapy; achieved CR2 with re-induction chemotherapy, followed by AHSCT.Mei et al. (2013)56, femaleLeft maxillary sinusSolitary site of GSNRSurgical resection followed by chemotherapy; CR at 4 months(Current) case63, femaleConductive hearing loss, infiltrative nasopharyngeal massDeveloped AML one year later.NormalRadiation therapy only for GS; chemotherapy for AML; CR at 18 months Disclosures: No relevant conflicts of interest to declare.

Description: Introduction Immune thrombocytopenia (ITP) is an acquired disorder characterized by immune-mediated platelet destruction along with decreased platelet production. Adults with ITP are treated initially with glucocorticoids, intravenous immunoglobulin, and/or anti-D, but as many as 80% of patients (pts) will eventually relapse and become steroid-refractory. There is no universally agreed upon 2nd line therapy for ITP and consensus guidelines recommend either rituximab (R) or splenectomy (S) as acceptable, potentially curative options. Long-term responses to 2nd line S have been reported around 60%, and around 25% for R. It is unknown whether long-term outcome in the 3rd line setting is influenced by sequence of therapy. We evaluated the impact of sequence of 2nd and 3rdline therapy with R and/or S. Methods We identified all pts with ITP treated from 1990 through 2015 at the three Mayo Clinic (Arizona, Florida, and Minnesota) sites that were treated with R and/or S. Patients were excluded who were

Description: Haematopoietic stem and progenitor cells (HSPCs) develop through distinct waves at various anatomical sites during embryonic development. The in vitro differentiation of human pluripotent stem cells (hPSCs) is able to recapitulate some of these processes, however, it has proven difficult to generate functional haematopoietic stem cells (HSCs). To define the dynamics and heterogeneity of HSPCs that can be generated in vitro from hPSCs, we exploited single cell RNA sequencing (scRNAseq) in combination with single cell protein expression analysis. Bioinformatics analyses and functional validation defined the transcriptomes of naïve progenitors as well as erythroid, megakaryocyte and leukocyte-committed progenitors and we identified CD44, CD326, ICAM2/CD9 and CD18 as markers of these progenitors, respectively. Using an artificial neural network (ANN), that we trained on a scRNAseq derived from human fetal liver, we were able to identify a wide range of hPSCs-derived HPSC phenotypes, including a small group classified as HSCs. This transient HSC-like population decreased as differentiation proceeded and was completely missing in the dataset that had been generated using cells selected on the basis of CD43expression. By comparing the single cell transcriptome of in vitro-generated HSC-like cells with those generated within the fetal liver we identified transcription factors and molecular pathways that can be exploited in the future to improve the in vitro production of HSCs.

Description: Abstract 2818 Background: Pegylated interferon alpha-2a (Peg INF2a) has been demonstrated to be active therapy for high-risk essential thrombocythemia (ET) and polycythemia vera (PV), as well as treatment for early myelofibrosis (MF). We retrospectively analyzed the outcomes of Peg INF2a therapy in MPN patients treated outside the constraints of a clinical trial in the USA and EU. Methods: Clinical records of MPN patients treated at the participating centers, receiving Peg INF2a outside of the context of a clinical trial, were analyzed for response (ET and PV by ELN criteria; MF by EUNMET and IWG-MRT criteria), toxicity, and duration of response. Results: Patients: 115 patients were identified (54 PV (47%), 44 ET (38%), 17 MF (15%)) with a median age at diagnosis (48) and gender distribution (59% females) typical for the disorders. The patients had been diagnosed with the MPN a median of 44 months (0.0–312 months) prior to initiation of the Peg IFN2a and 64% harbored the JAK2-V617F mutation. The majority of patients (81%) had received at least one prior cytoreductive therapy for their disease (73 hydroxyurea, 39 anagrelide, 37 aspirin, 21 prior interferon (non pegylated), 3 phlebotomy alone). Therapy: Median starting dose of Peg INF2a was 45 micrograms/week (range: 22.5–180) with peak starting doses ranging from 30 to 300 micrograms/week. A total of 84 patients (73%) remain on Peg IFN2a with median duration of treatment of 17 months (range: 1.0–92). Toxicity: Overall the Peg INF2a was well tolerated. Hematological toxicity was Gr 3 or lower. There were 6 cases with anemia (5%), 10 with thrombocytopenia (9%) and 8 had leukopenia (7%). Most common non-hematologic toxicities were Gr 1–3 fatigue in 27 (23%), Gr 1 LFT elevation in 6 (5%), Gr 2–3 skin/allergic reaction in 6 (5%), Gr 1–2 nausea in 5 (4%), and Gr 2 mood disorder in 5 (4%) patients. Twenty patients (17%) discontinued therapy secondary to toxicity. Response: ET-PV: By ELN criteria, 30 PV patients achieved CR (55%), 17 achieved PR (31%), 4 achieved NR (7%), and 3 patients (5%) were lost to follow up or were too early to evaluate for response. In ET, the responses were CR in 27 (61%), PR in 7 (16%), NR in 4 (9%), and 6 patients (14%) were lost to follow up or were too early to evaluate for response. MF: The responses by IWG criteria were 1 CR (6%), 2 PR (12%), 2 CI (12%) and 9 SD (53%). By EUNMET, there were 2 CR (12%), 4 major responses (24%), 4 moderate responses (24%), 1 minor response (6%), 2 no response (12%), and 3 patients (17%) were lost to follow up or were too early to evaluate for response. Conclusions: Peg INF2a used at doses consistent with published clinical trials is active and well-tolerated when administered in a clinical setting outside of the support of a clinical trial. Given the majority of patients had previously failed cytoreductive therapy these results substantiate prior reports of efficacy of Peg INF2a in MPNs. Upcoming randomized clinical trials through the Myeloproliferative Disorders Research Consortium will help further define the role of Peg INF2a as first line therapy in high-risk MPNs. Disclosures: Mesa: Incyte: Research Funding; Lilly: Research Funding; SBio: Research Funding; Astra Zeneca: Research Funding; NS Pharma: Research Funding; Celgene: Research Funding.