ALBERT

Description: Aneuploidy causes a proliferative disadvantage, mitotic and proteotoxic stress in non-malignant cells ( Torres et al. Science 2007). Chromosome gain or loss, which is the hallmark of aneuploidy, is a relatively common event in Acute Myeloid Leukemia (AML). About 10% of adult AML display isolated trisomy 8, 11, 13, 21 (Farag et al. IJO 2002), or either an isolated autosomal monosomy or monosomal karyotype (Breems et al. JCO 2008). This evidence suggests that tumor-specific mechanisms cooperate to overcome the unfitness barrier and maintain aneuploidy. However, the molecular bases of aneuploid AML are incompletely understood. We analyzed a cohort of 166 cytogenetically-characterized AML patients (80 aneuploid (A-) and 86 euploid (E-)) treated at Seràgnoli Institute (Bologna). Aneuploidy was significantly associated with poor overall survival (median survival: 13 and 26 months in A-AML and E-AML respectively; p=.006, Fig.1). To identify AML-specific alterations having a causative and/or tolerogenic role towards aneuploidy, we integrated high-throughput genomic and transcriptomic analyses. We performed 100 bp paired-end whole exome sequencing (WES, Illumina Hiseq2000) of 70 samples from our A-AML and E-AML cohort of 166 patients. Variants where called with MuTect or GATK for single nucleotide variant and indels detection, respectively. AML samples were genotyped by CytoScan HD Array (Affymetrix). Gene expression profiling (GEP) was also conducted on bone marrow cells from 24 A-AML, 33 E-AML (≥80% blasts) and 7 healthy controls (HTA 2.0, Affymetrix). We detected a significantly higher mutation load in A-AML compared with E-AML (median number of variants: 31 and 15, p=.04) which was interestingly unrelated to patients' age (median age: 63.5 years in A-AML and 62 years in E-AML, Xie et al, Nat. Med. 2014). C〉A and C〉T substitutions, which are likely mediated by endogenous 5mCdeamination, were the most frequent alterations (Alexandrov et al. Nat. 2013). However, aneuploidy associated with an increased variability in terms of mutational signatures, with the majority of A-AML displaying 3 or more signatures compared to few E-AML cases (p=.04). WES analysis also revealed a specific pattern of somatic mutations in A-AML. A-AML had a lower number of mutations in signaling genes (p=.04), while being enriched for alterations in cell cycle genes (p=.01) compared with E-AML. The mutated genes were involved in different cell cycle phases, including DNA replication (MCM6, PURB, SSRP1), centrosome dynamics (CEP250, SAC3D1, HEPACAM2, CCP110), chromosome segregation (NUSAP1, ESPL1, TRIOBP), mitotic checkpoint (ANAPC7, FAM64A) and regulation (CDK9, MELK, ZBTB17, FOXN3, PPM1D, USP2). Moreover, genomic deletion of cell cycle-related genes was frequently detected in A-AML. Notably, ESPL1 which associated with aneuploidy, chromosome instability and DNA damage in mammary tumors (Mukherjee et al. Oncogene 2014) was mutated and also upregulated in A-AML compared with E-AML (p=.01), the latter showing expression levels comparable to controls. Among the top-ranked genes differentially expressed between A-AML and E-AML, we identified a specific signature characterized by increased CDC20 and UBE2C and reduced RAD50 and ATR in A-AML (p

Description: Introduction. Autologous Bone Marrow Transplantation (Auto-BMT) is currently rarely used in the treatment of Acute Myeloid Leukemia (AML). However, it may represent a good therapeutic option in a specific subset of patients, mainly in consolidation of both low risk (LR) and MRD negative AML without an available HLA matched donor. Aims. To review our database of AML patients who received Auto-BMT from 2005 to 2014 and who were referred to Bologna Institution, in order to assess the efficacy of the procedure in terms of Overall Survival (OS) and Disease Free Survival (DFS). Patients and methods: From 2005 to 2014, 98 AML patients underwent Auto-BMT in several Italian Institutions. 89/98 patients are evaluable for survival and outcome data. The 89 patients considered (42 female, 47 male), had a median age of 49 years (range 15-70). Cytogenetics was performed in all patients by conventional karyotype (22 patients were also analyzed by Single Nucleotide Polymorphisms Array); molecular analysis (FLT3 TKD and ITD, and NPM1 mutational analysis) was available for 51/89 patients. Molecular monitoring by specific fusion transcripts (CBF-MYH11 and AML1-ETO) was performed in CBF positive leukemias (inv(16) and t(8;21)) at the time of diagnosis, after induction, consolidation courses, and every 3 months in the first 2 years of follow-up. Based on this data, and according to ELN guidelines, a risk stratification identified 41 patients with a LR AML (t(8:21), inv(16) or NPM1+/FLT3- with normal karyotype), 4 patients with a high risk (HR) AML (complex karyotype or FLT3 ITD mutated or inv(3) or t(6;9)) and 44 patients with a standard risk (SR) AML (normal karyotype, other alterations). Results. All the patients received an induction chemotherapy treatment, as follows: a "3+7-like" course in 48 cases, a Fludarabine-based regimen in 20 patients and a Gemtuzumab-ozogamicin (GO)-based regimen in 21. 83/89 (93.3%) patients received a median of 2 consolidation courses of chemotherapy (range 1-4) before proceeding to Auto-BMT, performed in 1st CR. 6/89 (6.7%) patients received Auto-BMT in first relapse. 41 patients relapsed after auto-BMT and were treated with a re-induction chemotherapy, or were enrolled in clinical trials. 24 patients reached a 2nd complete remission, and 12 patients underwent an allogeneic BMT in 2nd CR. With a median follow up of 6 years, the median Overall Survival (OS) of the entire population was 64.3 months (range 5.8-294.2 months); the 1 year OS and the 5 years OS were, 97.1%, and 67.9%, respectively. The median Disease Free Survival (DFS) of the 83 patients treated with Auto-BMT in 1st CR was 36 months (range 1.3-293 months). The 1-year DFS and the 5-years DFS were 85% and 56.7%, respectively. Transplant related mortality (TRM, death in 100 days after BMT) was 1.2% for auto-BMT and 6.5% for allogeneic BMT. First, to assess the role of the number of consolidation courses we compared patients who received none or 1 consolidation course with patients who received 2 or more cycles, who showed a better OS (p= 0.0061, Figure 1). There was no statistical difference in terms of OS between young and elderly patients (cut off=65 years). Second, we compared patients who achieved a negative minimal residual disease status before auto-BMT (n=37) with patients who did not (n=9). MRD negativity offered a significantly better outcome in terms of 5-years OS (83.4% and 50% respectively); the median OS of MRD neg was not yet reached; the median OS of MRD pos was 27 months (p= 0.0130) (Figure 2). Conclusions: Auto-BMT offers a chance to achieve long-term DFS and OS if used as a consolidation therapy both in patients with LR and SR AML. The major role could be played in MRD negative patients, offering the best chances to achieve a long-term OS. Auto-BMT can be also a good choice as consolidation therapy for elderly patients, in which allo-BMT could induce high morbidity and mortality rates. The small patients cohort and the retrospective analysis don't allow us to define the best induction therapy to be used before auto-BMT. However, based on our findings we suggest a therapy schedule including two or more consolidation courses in patients who obtain a first CR, and to proceed then to auto-BMT. Acknowledgments: work supported by ELN, AIL, AIRC, Progetto Regione-Università 2010-12 (L.Bolondi), Fondazione del Monte di Bologna e Ravenna, FP7 NGS-PTL project. Figure 1. Figure 1. Figure 2. Figure 2. Disclosures Soverini: Novartis, Briston-Myers Squibb, ARIAD: Consultancy. Rodeghiero:Celgene Corporation: Honoraria, Research Funding. Cavo:Janssen-Cilag, Celgene, Amgen, BMS: Honoraria. Martinelli:AMGEN: Consultancy; Novartis: Consultancy, Speakers Bureau; Ariad: Consultancy; BMS: Consultancy, Speakers Bureau; ROCHE: Consultancy; Pfizer: Consultancy; MSD: Consultancy.

Description: The BCR-ABL1 fusion gene defines the subgroup of acute lymphoblastic leukemia (ALL) with the worst clinical prognosis. To identify oncogenic lesions that combine with BCR-ABL1 to cause ALL, we used Affymetrix Genome-Wide Human SNP arrays (250K NspI and SNP 6.0), fluorescence in situ hybridization, and genomic polymerase chain reaction to study 106 cases of adult BCR-ABL1–positive ALL. The most frequent somatic copy number alteration was a focal deletion on 7p12 of IKZF1, which encodes the transcription factor Ikaros and was identified in 80 (75%) of 106 patients. Different patterns of deletions occurred, but the most frequent were those characterized by a loss of exons 4 through 7 (Δ4-7) and by removal of exons 2 through 7 (Δ2-7). A variable number of nucleotides (patient specific) were inserted at the conjunction and maintained with fidelity at the time of relapse. The extent of the Δ4-7 deletion correlated with the expression of a dominant-negative isoform with cytoplasmic localization and oncogenic activity, whereas the Δ2-7 deletion resulted in a transcript lacking the translation start site. The IKZF1 deletion also was identified in the progression of chronic myeloid leukemia to lymphoid blast crisis (66%) but never in myeloid blast crisis or chronic-phase chronic myeloid leukemia or in patients with acute myeloid leukemia. Known DNA sequences and structural features were mapped along the breakpoint cluster regions, including heptamer recombination signal sequences recognized by RAG enzymes during V(D)J recombination, suggesting that IKZF1 deletions could arise from aberrant RAG-mediated recombination.

Description: Background: AML is a heterogeneous disease with various chromosomal aberrations. The karyotype at diagnosis provides important prognostic information that influences therapy and outcome, and patients (pts) with complex karyotype (CK) have generally a poor outcome. TP53 is the most frequently mutated gene in human tumors. The reported TP53 mutation rate in AML is low (2.1%). In contrast, the incidence of TP53 mutations in AML with a complex aberrant karyotype is higher (69-78%). Aims: To investigate the frequency, the types of mutations, the associated cytogenetic abnormalities and the prognostic role of TP53 mutations in adult AML pts, we focused the screening on subgroups of AML with chromosome abnormalities. Patients and Methods: 886 AML patients were analysed at the Seràgnoli Institute of Bologna between 2002 and 2013 for morphology, immunophenotype, cytogenetic and for a panel of genetic alterations (FLT3, NPM, WT1, CBF fusion transcripts, DNMT3A, IDH1, IDH2, etc). Of these, 172 adult AML pts were also examined for TP53 mutations using several methods, including Sanger sequencing, Next-Generation deep-Sequencing (Roche) and HiSeq 2000 (Illumina) platform (35/172 pts). 40 samples were genotyped with Genome-Wide Human SNP 6.0 arrays or with CytoScan HD Array (Affymetrix) and analysed by Nexus Copy Number™ v7.5 (BioDiscovery). Results: Of the 886 AML patients beforehand analysed, 172 pts were screened for TP53 mutations and were correlated with cytogenetic analysis (excluding 15 pts where the karyotype was not available). 1. Fifty-two pts (30,2%) have 3 or more chromosome abnormalities, i.e. complex karyotype; 2. 71 (41,3%) presented one or two cytogenetic abnormalities (other-AML) and 3. 34 pts (19,8%) have normal karyotype. Sanger sequencing analysis detected TP53 mutations on 29 patients with 36 different types of mutations; seven pts (4%) have 2 mutations. Mostly (23/29) of the TP53 mutated pts (79.3%) had complex karyotype while only 6/29 mutated pts have “no CK” (21% and 3% of the entire screened population). Overall, between pts with complex karyotype, TP53 frequency is 44.2%. Regarding the types of the TP53 alterations, 32 were deleterious point mutations (http://p53.iarc.fr/TP53GeneVariations.aspx) and 4 deletions. Forty pts were also analysed for Copy Number Alterations (CNAs) by Affymetrix SNP arrays: several CNAs were found ranged from loss or gain of complete chromosome (chr) arms to focal deletions and gains targeting one or few genes involving macroscopic (〉1.5 Mbps), submicroscopic genomic intervals (50 Kbps - 1.5 Mbps) and LOH (〉5 Mbps) events. Of relevance, gains located on chr 8 were statistically associated with TP53 mutations (p = 0.001). Seven genes are included in these regions (RGS20, TCEA1, LINC01299, ARMC1, MTFR1, RAD54B, KIAA1429). In addition to the trisomy of the chr 8, others CNAs, located on other chromosomes are significantly associated (p = 0.05) with TP53 mutations: loss of chr 5q, chr 3 (p22.3), chr 12 (p12.3) and the gain of chr 17 (p11.2), chr 16 (p11.2-11.3) and chr 14 (q32.33). The zinc finger gene ZNF705B, implicated in the regulation of transcription was the most differentially associated gene (gain). WES analysis was done in 37 pts, 32 TP53 were wt while 5 pts were TP53 mutated: of importance, CDC27, PLIN4 and MUC4 were found also mutated in 3 out of 5 TP53 mutated (60%). Clinical outcome: as previously reported, alterations of TP53 were significantly associated with poor outcome in terms of both overall survival and disease free-survival (P 〈 0.0001). Conclusions: Our data demonstrated that TP53 mutations occur in 16.86% of AML with a higher frequency in the subgroup of complex karyotype AML (p〈 0.0001–Fischer’s exact test). Since TP53 mutations have predicted to be deleterious and significantly correlated with prognosis, TP53 mutation screening should be recommended at least in complex karyotype AML pts. Furthermore, although further studies in larger numbers of patients are needed, the gain of chromosome 8 was observed to be significantly associated to TP53 mutations pts. Supported by: ELN, AIL, AIRC, PRIN, progetto Regione-Università 2010-12 (L. Bolondi), FP7 NGS-PTL project. Disclosures Martinelli: Novartis: Speakers Bureau; Bristol Mayers Squibb: Speakers Bureau; Pfizer: Speakers Bureau.

Description: Variant Philadelphia (Ph) chromosome translocations have been reported in 5%-10% of patients with newly diagnosed chronic myeloid leukemia (CML). Variant translocations may involve one or more chromosomes in addition to 9 and 22, and can be generated by 2 different mechanisms, 1-step and 2-step rearrangements, as revealed by fluorescence in situ hybridization. The prognostic significance of the occurrence of variant translocations has been discussed in previous studies. The European LeukemiaNet recommendations do not provide a “warning” for patients with variant translocations, but there is limited information about their outcome after therapy with tyrosine kinase inhibitors. To identify the role of variant translocations in early chronic phase (CP) CML patients treated with imatinib mesylate, we performed an analysis in a large series of 559 patients enrolled in 3 prospective imatinib trials of the Gruppo Italiano Malattie EMatologiche dell'Adulto (GIMEMA) Working Party on CML. Variant translocations occurred in 30 patients (5%). Our data show that the presence of variant translocations has no impact on the cytogenetic and molecular response or on outcome, regardless of the involvement of different mechanisms, the number of involved chromosomes, or the presence of deletions. Therefore, we suggest that patients with variant translocations do not constitute a “warning” category in the imatinib era. This study is registered at www.clinicaltrials.gov as NCT00514488 and NCT00510926.

Description: Background Ponatinib, a potent third generation pan BCR-ABL inhibitor, has recently shown relevant activity against native and mutant forms of BCR-ABL, including the TKI resistant T315I mutant. The aim of this compassionate protocol was to confirm and evaluate the efficacy and the safety of the compound in patients with advanced Ph+ ALL and CML. Design and Methods Ponatinib was obtained through a compassionate use named patient program, approved by ARIAD Pharmaceuticals and by the Bologna Ethical Committee. After informed consent was signed, 17 patients (M/F: 8/9) have been treated with Ponatinib (45 mg orally, once daily) between February 2012 and July 2013, including 14 Ph+ ALL (10 p190, 4 p210) and 3 blast phases of CML (2 Myeloid and 1 Lymphoid, p210). The median age of the patients was 64 years (range 23 -77). The median time from diagnosis was 754 days (range 46-2264). All the patients were resistant or intolerant to previous TKIs (median number of previous TKIs: 2; range 1-3). Standard chemotherapy was previously performed in 7/17 patients (41%). Four patients (23%) had previously received allogeneic stem cell transplantation. At the time of enrolment, median Hb, PLTs and WBC values were 10,9 g/dl (range 8.6-13.9), 139000/mmc (range 14000-325000) and 4300/mmc (range 1700-17000), respectively. In 6 out of 17 patients, additional cytogenetic alterations were revealed. Mutational analysis showed the presence of T315I mutation (9 pts), G250E (1 pt), T315I and Y253H (1 pt), T315I and Y253A (1 pt), V299L (1 pt). No mutations were detected in 4 patients. Results The median treatment duration was 139 days (range 14-540+). Causes of treatment stop were: progression disease (5 patients), savage allogenic stem cell transplantation (6 patients), drug intolerance (1 patient), consisting in grade III headache. With a median follow up of 284 days (range 8-540+), a maHR was obtained in 13/17 patients (76%). After one month of treatment, a reduction of BCR-ABL fusion transcript level was observed in 9/15 patients (60%). For two patients the follow up is too short to be evaluable. The level became undetectable in 4 patients (3 presenting with T315I mutation). After treatment, T315I mutation disappeared in 6 out of the 9 patients who showed this molecular alteration at the beginning of therapy. At the time of this report, 6/17 patients are still on study (35%). Five patients died due to progression disease. As expected, the drug was well tolerated. Non-hematologic adverse events were described in 7/17 patients (grade 〉III skin rash in 3 patients; grade〉II serum lipase increase in 2 patients; grade〉II myalgia in 1 patient; grade III headache). Conclusion In our experience, the activity of Ponatinib in advanced Ph+ leukemias, mainly in T315I mutated patients, was confirmed. No treatment-related deaths occurred. The understanding of molecular mechanisms responsible for resistance or lack of response to the drug will be necessary in order to identify patients early on who could take advantage of this treatment. Acknowledgments Work supported by European LeukemiaNet, AIRC, PRIN 2010-2011, University of Bologna and BolognAIL. Disclosures: Soverini: Novartis: Consultancy; Bristol-Myers Squibb: Consultancy; ARIAD: Consultancy. Martinelli:NOVARTIS: Consultancy, Speakers Bureau; BMS: Consultancy, Speakers Bureau; PFIZER: Consultancy; ARIAD: Consultancy.

Description: Abstract 2027 Poster Board II-4 Background. The prognosis of Ph+ adult ALL patients treated with standard therapies, including multi-agent chemotherapy, Imatinib, and allogeneic stem cell transplantation, is still dismal, due to a high risk of relapse. Dasatinib and Nilotinb are second generation TKIs developed to overcome the problem of resistance to Imatinib in relapsed Ph+ leukemias. Design and Methods. We retrospectively evaluated the single center experience on therapy efficacy of Dasatinib, Nilotinib, and experimental third generation TKIs, administered as second or subsequent line of therapy on 25 relapsed Ph+ adult ALL patients. All patients were previously treated with Imatinib. The median age at time of diagnosis was 50 years (range 18-74), 17 patients were male and 8 female. Ten patients presented a BCR-ABL P190 fusion protein and corresponding fusion transcript, the remaining a BCR-ABL P210. Nineteen patients received Dasatinib, 2 patients Nilotinib and the remaining 4 patients were treated with third generation TKIs. Fourteen patients (56%) were in first relapse, and 7 (28%), 3 (12%) and 1 (4%) were in second, third and fourth relapse, respectively. A mutational analysis was performed in all the patients before TKIs (9 wild type, 16 mutated, including T315I) and at the time of subsequent relapse; gene expression profiling, SNPArray (6.0 Affymetrix chip), and Ikaros deletions were also analyzed. Results. 13 out of 25 patients (52%) obtained a haematological response (HR) (11 patients treated with Dasatinib, 1 patient with Nilotinib and 1 patient with a third generation experimental TKI). 10 patients obtained also a cytogenetic response (CyR) and 6 patients a molecular response (MolR). With a median follow up of 10.8 months (range 2-29 months), median duration of HR, CyR and MolR were 117 days (range 14-385 days); progression free survival were 162 days with Dasatinib and 91 days with Nilotinib. Overall survival was 25.8 months. Interestingly, in 6 out of 9 wild-type patients, treated with Dasatinib, the mutational analysis showed the emergence of T315I or F317I mutation at the time of relapse. Conclusion. Second and third generation TKIs represent a valid approach in relapsed Ph+ adult ALL patients; the subsequent relapse is often associated to the emergence of mutation, conferring resistance to TKIs. Since TKIs are different and have different efficacy, pharmacokinetic, pharmacodynamic and toxicity profiles, and since are all effective, an alternative experimental option for the treatment of Ph+ ALL could be a combination or a rotation of two or more than two TKIs. Moreover, the addition of new promising targeted molecules, such as Aurora kinase or T315I inhibitors may contribute to overcome the problem of resistance to TKIs. Acknowledgments. Work supported by European LeukemiaNet, FIRB 2006, AIRC, AIL, COFIN, University of Bologna and BolognAIL. Disclosures: No relevant conflicts of interest to declare.

Description: Abstract 1118 Poster Board I-140 Background The median age of an unselected population of Ph+ CML patients is close to 60 years. In the prognostic classifications (Sokal, Blood 1984; Hasford, JNCI 1998) that were elaborated before the introduction of IM, age was a significant and important prognostic factor. The most recent IM studies have not clarified the prognostic importance of age and IM therapy is still denied to several elderly patients. Aim to asses the relationship between age (less and more than 65 years) and outcome, in CML patients treated front-line in early chronic phase (ECP). Methods We analyzed the data of 559 previously untreated ECP patients who were assigned to receive IM 400 mg daily (76%) or 800 mg daily (24%) in three controlled, prospective studies of GIMEMA (Clin Trials Gov. NCT00514488 and NCT00510926; and an observational study of IM 400 mg). The median follow-up is currently 42 (extremes 1 – 64) months. There were 115 patients more than 65 years old (median age 71 years), while 444 (79%) were less than 65 years (median age 46 years). The proportion of patients who were treated with IM 800 mg daily was the same in both age groups. Results The cumulative complete cytogenetic and major molecular response rates were identical in the two age groups (88% vs 88% and 82% vs 83%, respectively). However, overall survival (86% vs 93%, p = 0.01), failure-free survival (72% vs 81%, p=0.03) and particularly event-free survival (calculated based on the intention-to-treat principle, where events were any failure [according to the European LeukemiaNet criteria – Baccarani, Blood 2006] and treatment discontinuation for any cause) (60% vs 71%, p=0.006) were significantly inferior in the older age group. All these difference were mainly due to comorbidities leading to more deaths in CP (table). Conclusions/Methods These data show that response to IM was not affected by old age. Survival curves were affected because of age-related complications and comorbidities. Age should never be a contraindication to IM treatment. Acknowledgments: European LeukemiaNet, COFIN, University of Bologna and BolognAIL. Disclosures Saglio: Novartis: Honoraria. Baccarani:Novartis Pharma: Consultancy, Honoraria, Research Funding, Speakers Bureau; Bristol-Mayer Squibb: Consultancy, Honoraria, Research Funding, Speakers Bureau.

Description: Mesenchymal stromal cells (MSCs), an essential element of both normal and leukemic hematopoietic microenvironment, are multipotent cells with a unique immune-modulating ability. Thus, MSCs play a crucial role for both the proliferation and differentiation of hematopoietic stem cells (HSCs) and induce an immune-tolerant milieu. Indoleamine 2, 3-dioxygenase (IDO1 and IDO2) enzymes catabolize tryptophan to kynurenines and play a key role in the induction of immune tolerance in different settings, including acute myeloid leukemia (AML). Furthermore, IDO1/IDO2 pathway is a well described mechanism by which MSCs exert their mmunomodulatory properties. We hypothesized that: 1) MSC-dependent mechanisms are involved in leukemia initiation, maintenance and progression; 2) the expression of IDO1 and IDO2 by MSCs is part of a MSC-dependent mechanism able to create a tumor-supportive milieu. To this aim, we isolated MSCs from the bone marrow of AML patients (AML-MSCs) at diagnosis. We first analyzed their phenotypic and functional properties compared to that of healthy donor-derived MSCs (HD-MSCs). We found that AML-MSCs showed a reduced proliferative capacity but normal immunophenotype, differentiative and immunomodulatory capacity as compared to HD-MSCs. Furthermore, AML-MSCs did not show the chromosomal abnormalities identified in the primary blast counterpart (FISH analysis). We next investigated IDO1/2 expression and functions in MSCs. We demonstrated that IDO enzymes are expressed in AML-MSCs as well as in HD-MSCs. IDO1 is efficiently upregulated by different inflammatory stimuli, and IDO1 protein expression parallels mRNA in both HD-MSCs and AML-MSCs. Interestingly, IDO2 mRNA is expressed at low basal level in all analyzed conditions in HD-MSCs, while it is upregulated, in particular after IFN-gamma stimulation, in AML-MSCs, although the level of induction varies between different patients. When T-cell proliferation was tested in MSC co-cultures, w/or w/out IDO1/2 inhibitor, 1-methyltryptophan, we found that MSC immunomodulatory potential is IDO-dependent both in HD-MSCs and AML-MSCs. Finally, we found that in co-culture assay with primary AML blasts, MSCs stimulated blast proliferation and this effect is, at least in part, IDO-mediated. These data suggested that IDO enzymes, in particular IDO2, may be differentially expressed in AML-MSCs as compared to HD-MSCs and IDO inhibition has an impact on MSC/AML cell cross talk. These findings may help to discover novel niche-target prognostic/therapeutic factors and to provide novel applications for drugs already under active clinical investigation (i.e. IDO-inhibitors). Disclosures Cavo: Janssen-Cilag, Celgene, Amgen, BMS: Honoraria.