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Myelodysplastic syndromes with ring sideroblasts (MDS-RS) commonly originate from mutations in the splicing factorSF3B1(SF3B1mt).SF3B1mtcause RNA mis-splicing, mechanistically established as the major driver of RS development. However, little is known about RS fate and biology after their initial formation in the human bone marrow. We here achieve isolation of viable RS from patient samples, enabling the first complete investigation ofSF3B1mtdevelopment from stem cell to RS. We show that RS skew MACS-isolated CD34+data towards erythroid features not recapitulated in single-cell RNAseq. We demonstrate that RS divide, differentiate, enucleate and actively respond to mis-splicing/oxidative stress, decreasing wildtype stem cell fitness via GDF15 overproduction. We identify circulating RS as a uniform clinical feature associated with disease burden. Finally, we establish thatSF3B1mtmis-splicing intensifies during erythroid differentiation and demonstrate through combined transcriptomics/proteomics an uncoupling of RNA/protein biology in RS encompassing severe and dysfunctional mis-splicing of proapoptotic genes.Statement of significanceWe here combine a novel method for RS isolation with state-of-the-art multiomics to perform the first complete investigation ofSF3B1mtMDS-RS hematopoiesis from stem cell to RS. We identify the survival mechanisms underlyingSF3B1mterythropoiesis and establish an active role for erythroid differentiation and RS themselves inSF3B1mtMDS-RS pathogenesis.

Established cell culture systems have failed to accurately recapitulate key features of terminal erythroid maturation, hampering our ability to in vitro model and treat diseases with impaired erythropoiesis such as myelodysplastic syndromes with ring sideroblasts (MDS-RS). We developed an efficient and robust three-dimensional (3D) scaffold culture model supporting terminal erythroid differentiation from both mononuclear (MNC) or CD34+-enriched primary bone marrow cells from healthy donors and MDS-RS patients. While CD34+ cells did not proliferate beyond two weeks in 2D suspension cultures, the 3D scaffolds supported CD34+ and MNC erythroid proliferation over four weeks demonstrating the importance of the 3D environment. CD34+ cells cultured in 3D facilitated the highest expansion and maturation of erythroid cells, including generation of erythroblastic islands and enucleated erythrocytes, while MNCs supported multi-lineage hemopoietic differentiation and cytokine secretion relevant for MDS-RS. Importantly, MDS-RS 3D-cultures supported de novo generation of ring sideroblasts and maintenance of the mutated clone. The 3D cultures effectively model a clonal disease characterized by terminal erythroid failure and can be used to assess therapeutic compounds.

Transfer RNA-derived fragments (tRFs) are emerging small noncoding RNAs that, although commonly altered in cancer, have poorly defined roles in tumorigenesis1. Here we show that pseudouridylation (Ψ) of a stem cell-enriched tRF subtype2, mini tRFs containing a 5′ terminal oligoguanine (mTOG), selectively inhibits aberrant protein synthesis programmes, thereby promoting engraftment and differentiation of haematopoietic stem and progenitor cells (HSPCs) in patients with myelodysplastic syndrome (MDS). Building on evidence that mTOG-Ψ targets polyadenylate-binding protein cytoplasmic 1 (PABPC1), we employed isotope exchange proteomics to reveal critical interactions between mTOG and functional RNA-recognition motif (RRM) domains of PABPC1. Mechanistically, this hinders the recruitment of translational co-activator PABPC1-interacting protein 1 (PAIP1)3 and strongly represses the translation of transcripts sharing pyrimidine-enriched sequences (PES) at the 5′ untranslated region (UTR), including 5′ terminal oligopyrimidine tracts (TOP) that encode protein machinery components and are frequently altered in cancer4. Significantly, mTOG dysregulation leads to aberrantly increased translation of 5′ PES messenger RNA (mRNA) in malignant MDS-HSPCs and is clinically associated with leukaemic transformation and reduced patient survival. These findings define a critical role for tRFs and Ψ in difficult-to-treat subsets of MDS characterized by high risk of progression to acute myeloid leukaemia (AML).

Although copy number alterations (CNAs) and translocations constitute the backbone of the diagnosis and prognostication of acute myeloid leukemia (AML), techniques used for their assessment in routine diagnostics have not been reconsidered for decades. We used a combination of 2 next-generation sequencing–based techniques to challenge the currently recommended conventional cytogenetic analysis (CCA), comparing the approaches in a series of 281 intensively treated patients with AML. Shallow whole-genome sequencing (sWGS) outperformed CCA in detecting European Leukemia Net (ELN)–defining CNAs and showed that CCA overestimated monosomies and suboptimally reported karyotype complexity. Still, the concordance between CCA and sWGS for all ELN CNA–related criteria was 94%. Moreover, using in silico dilution, we showed that 1 million reads per patient would be enough to accurately assess ELN-defining CNAs. Total genomic loss, defined as a total loss ≥200 Mb by sWGS, was found to be a better marker for genetic complexity and poor prognosis compared with the CCA-based definition of complex karyotype. For fusion detection, the concordance between CCA and whole-transcriptome sequencing (WTS) was 99%. WTS had better sensitivity in identifying inv(16) and KMT2A rearrangements while showing limitations in detecting lowly expressed PML-RARA fusions. Ligation-dependent reverse transcription polymerase chain reaction was used for validation and was shown to be a fast and reliable method for fusion detection. We conclude that a next-generation sequencing–based approach can replace conventional CCA for karyotyping, provided that efforts are made to cover lowly expressed fusion transcripts.

Background and aims - The 2016 revised WHO classification incorporated somatic mutation in SF3B1 spliceosome gene within the diagnostic criteria of myelodysplastic syndrome (MDS) with ring sideroblasts (RS). However, SF3B1wt MDS-RS display significantly different clinical features and outcome from those of SF3B1mut MDS-RS. Recently, the recognition of SF3B1-mutant MDS as a distinct nosologic entity has been proposed to overcome this limitation. Methods - To evaluate the biological relevance of this proposal, we studied a consecutive cohort of 132 MDS with RS >5% using a pangenomic approach (targeted-DNA sequencing, genome-wide copy number variation analysis and bulk RNA-sequencing of CD34+ bone marrow mononuclear cells). 16 age-matched healthy individuals and 43 MDS-SLD/MLD negative for both splicing mutation and RS were included in this study as controls. Results - Unsupervised clustering analysis based on mutation profiles identified two major clusters predicted by SF3B1 mutation (87 MDS-RS-SF3B1mut and 45 MDS-RS-SF3B1wt). The most recurrently mutated genes in MDS-RS-SF3B1wt were TP53(40%), SRSF2(38%), TET2 (33%), ASXL1 (21%) and DNMT3A (12%). SRSF2 and TP53 mutations were found to be mutually exclusive with SF3B1 (p-value Differential gene expression analysis results were incorporated into a specific expression signature highly predictive of MDS-RS-SF3B1 mutand MDS-RS-SF3B1wt subgroups (Figure 1). The resulting gene clusters were classified in RS-specific genes (cluster 1 and 2) and SF3B1-specific genes (cluster 3 and 4). RS-specific genes comprising heme and hypoxia genes were enriched (Figure 2AB) and correlated with RS percentage (p Conclusions - This study contributes to unveil molecular features of SF3B1-mutant MDS and provides further evidence to support recognition of somatic SF3B1 mutation as a disease-defining genetic lesion. Disclosures Papaemmanuil: Isabl Technologies: Divested equity in a private or publicly-traded company in the past 24 months; Kyowa Hakko Kirin Pharma: Consultancy.

Myelodysplastic syndromes (MDS) constitute a heterogeneous group of clonal hematopoietic stem cell (HSC) disorders characterized by aberrant HSC differentiation, cytopenia, and an increased risk of progression to leukemia. The low-risk subtype MDS with ring sideroblasts (MDS-RS) is specifically characterized by expanded and ineffective erythropoiesis, with more than 80% of patients displaying mutations in the core spliceosome component SF3B1 (SF3B1 mt). A hallmark of the MDS-RS bone marrow (BM) is the progressive accumulation of ring sideroblasts (RS), erythroblasts displaying perinuclear mitochondria loaded with aberrant ferritin-iron complexes. Whilst several in vitro and in vivo model systems exist for studying the impact of SF3B1 mt on erythropoiesis and RS development, primary SF3B1 mt erythroid biology remains largely unexplored due to the inability to purify live SF3B1 mt cells or fully replicate BM conditions in vitro. To address this issue, we developed an innovative two-step method to isolate live ring sideroblasts from SF3B1 mt MDS-RS BM aspiration material with extremely high purity (as determined through droplet digital PCR-based genotyping [Fig. 1A] and morphology-based detection through Prussian blue staining [Fig. 1B,C]). Unexpectedly, evaluation of matching peripheral blood samples showed that circulating ring sideroblasts are strikingly common in MDS-RS (Fig. 1D), with their abundance being significantly positively associated with clinically-determined BM RS frequencies and serum erythropoietin levels, as well as negatively associated with hemoglobin levels. Through high-throughput Chromium 3'-based single-cell RNA sequencing (scRNAseq) analysis of purified RS, we then showed that these cells comprise a heterogeneous population encompassing all stages of the erythroid differentiation continuum, from early progenitors to orthochromatic erythroblasts (Fig. 1E). The RS transcriptome was shown to be dynamically regulated towards the maintenance of cell survival during late terminal erythroid differentiation (exemplified through parkin 1 [PINK1] expression), with SF3B1 K700E erythroblasts employing multiple strategies to preserve homeostasis despite undergoing extreme oxidative stress. These observations were confirmed through a parallel whole-transcript RNAseq investigation comprising CD34 + and GPA +-enriched samples obtained from normal bone marrow (NBM) donors and SF3B1 K700E MDS-RS patients, as well as purified RS samples. This bulk RNAseq experiment validated the RS transcriptomic signature observed in scRNAseq (Fig. 1F) and allowed for a detailed investigation of RNA splicing. SF3B1 K700E-associated alternative splicing in CD34 + and RS was consistent with previous literature, but also highly context-dependent and with substantial changes in scope and magnitude throughout erythroid differentiation (Fig. 1G-I). Finally, we substantiated these RNAseq results through Tandem Mass Tag-based semi-quantitative proteomic analysis of purified RS and GPA-enriched cells from NBM donors and MDS-RS patients. We confirmed that ring sideroblast survival is heavily dependent on redox balance modulation and suppression of ER stress via an increased dependence on glutamine, mirroring the molecular mechanisms observed in malignancy. Additionally, our data strongly indicate that the RS population is a major modulator of the MDS-RS BM microenvironment due to expression of stress factors (with particular emphasis on GDF15, erythroferrone and IL-18). In conclusion, our integrative analysis of primary RS constitutes a unique platform for the study of MDS-RS, with special interest for the investigation of potential drivers of disease severity or treatment avenues. Figure 1 Figure 1. Disclosures Kretzschmar: Vanadis Diagnostics, a PerkinElmer company.: Current Employment.

Mutations in the RNA splicing gene SF3B1 are found in >80% of patients with myelodysplastic syndrome with ring sideroblasts (MDS-RS). We investigated the origin of SF3B1 mutations within the bone marrow hematopoietic stem and progenitor cell compartments in patients with MDS-RS. Screening for recurrently mutated genes in the mononuclear cell fraction revealed mutations in SF3B1 in 39 of 40 cases (97.5%), combined with TET2 and DNMT3A in 11 (28%) and 6 (15%) patients, respectively. All recurrent mutations identified in mononuclear cells could be tracked back to the phenotypically defined hematopoietic stem cell (HSC) compartment in all investigated patients and were also present in downstream myeloid and erythroid progenitor cells. While in agreement with previous studies, little or no evidence for clonal (SF3B1 mutation) involvement could be found in mature B cells, consistent involvement at the pro-B-cell progenitor stage was established, providing definitive evidence for SF3B1 mutations targeting lymphomyeloid HSCs and compatible with mutated SF3B1 negatively affecting lymphoid development. Assessment of stem cell function in vitro as well as in vivo established that only HSCs and not investigated progenitor populations could propagate the SF3B1 mutated clone. Upon transplantation into immune-deficient mice, SF3B1 mutated MDS-RS HSCs differentiated into characteristic ring sideroblasts, the hallmark of MDS-RS. Our findings provide evidence of a multipotent lymphomyeloid HSC origin of SF3B1 mutations in MDS-RS patients and provide a novel in vivo platform for mechanistically and therapeutically exploring SF3B1 mutated MDS-RS.

The IMPOER project (implementation of open educational resources, OER) aimed to implement OER in a nursing programme at Dalarna University, Sweden. The university and its nursing programme have long engaged in e-learning, and the nursing programme has recently been awarded the European Association of Distance Teaching Universities E-xcellence Associates Quality Label. The quality award was based on the creation of a roadmap for the continuous development of e-learning and the implementation of OER. The results of the study illustrated that overall, the students and the educators were positive about using OER. They considered that this approach was a new way of learning, and they appreciated the fact that OER were free and easy to access. However, they felt overwhelmed by the amount of material that was available and they were concerned about quality. If the use of OER is to be sustainable, a change in attitudes and practices among students and teachers is likely needed regarding the use of resources on th...

Refractory anemia with ring sideroblasts (RARS) is a myelodysplastic syndrome (MDS) characterized by isolated erythroid dysplasia and 15% or more bone marrow ring sideroblasts. Ring sideroblasts are found also in other MDS subtypes, such as refractory cytopenia with multilineage dysplasia and ring sideroblasts (RCMD-RS). A high prevalence of somatic mutations of SF3B1 was reported in these conditions. To identify mutation patterns that affect disease phenotype and clinical outcome, we performed a comprehensive mutation analysis in 293 patients with myeloid neoplasm and 1% or more ring sideroblasts. SF3B1 mutations were detected in 129 of 159 cases (81%) of RARS or RCMD-RS. Among other patients with ring sideroblasts, lower prevalence of SF3B1 mutations and higher prevalence of mutations in other splicing factor genes were observed (P < .001). In multivariable analyses, patients with SF3B1 mutations showed significantly better overall survival (hazard ratio [HR], .37; P = .003) and lower cumulative incidence of disease progression (HR = 0.31; P = .018) compared with SF3B1-unmutated cases. The independent prognostic value of SF3B1 mutation was retained in MDS without excess blasts, as well as in sideroblastic categories (RARS and RCMD-RS). Among SF3B1-mutated patients, coexisting mutations in DNA methylation genes were associated with multilineage dysplasia (P = .015) but had no effect on clinical outcome. TP53 mutations were frequently detected in patients without SF3B1 mutation, and were associated with poor outcome. Thus, SF3B1 mutation identifies a distinct MDS subtype that is unlikely to develop detrimental subclonal mutations and is characterized by indolent clinical course and favorable outcome.

// Magnus Tobiasson 1, * , Hani Abdulkadir 1, * , Andreas Lennartsson 2 , Shintaro Katayama 2 , Francesco Marabita 3, 4 , Ayla De Paepe 1 , Mohsen Karimi 1 , Kaarel Krjutskov 2, 5, 6 , Elisabet Einarsdottir 2, 5 , Michael Grovdal 1 , Monika Jansson 1 , Asmaa Ben Azenkoud 1 , Lina Corddedu 2 , Soren Lehmann 1, 7 , Karl Ekwall 2 , Juha Kere 2, 5 , Eva Hellstrom-Lindberg 1, * and Johanna Ungerstedt 1, * 1 Center for Hematology and Regenerative Medicine, Department of Medicine Huddinge, Division of Hematology Karolinska Institutet, Karolinska University Hospital Huddinge, Huddinge, Sweden 2 Department of Biosciences and Nutrition, Karolinska Institutet, Stockholm, Sweden 3 Unit of Computational Medicine, Center for Molecular Medicine, Department of Medicine, Karolinska Institutet, Stockholm, Sweden 4 National Bioinformatics Infrastructure Sweden, Stockholm, Sweden 5 Molecular Neurology Research Program, University of Helsinki, and Folkhalsan Institute of Genetics, Helsinki, Finland 6 Competence Centre on Health Technologies, Tartu, Estonia 7 Department of Medical Sciences, Uppsala University, Uppsala, Sweden * These authors have contributed equally to this work Correspondence to: Magnus Tobiasson, email: johanna.ungerstedt@ki.se Keywords: MDS, azacitidine, epigenetics, DNA methylation, histone modifications Received: November 09, 2016 Accepted: February 01, 2017 Published: February 28, 2017 ABSTRACT Azacitidine (Aza) is first-line treatment for patients with high-risk myelodysplastic syndromes (MDS), although its precise mechanism of action is unknown. We performed the first study to globally evaluate the epigenetic effects of Aza on MDS bone marrow progenitor cells assessing gene expression (RNA seq), DNA methylation (Illumina 450k) and the histone modifications H3K18ac and H3K9me3 (ChIP seq). Aza induced a general increase in gene expression with 924 significantly upregulated genes but this increase showed no correlation with changes in DNA methylation or H3K18ac, and only a weak association with changes in H3K9me3. Interestingly, we observed activation of transcripts containing 15 endogenous retroviruses (ERVs) confirming previous cell line studies. DNA methylation decreased moderately in 99% of all genes, with a median β-value reduction of 0.018; the most pronounced effects seen in heterochromatin. Aza-induced hypomethylation correlated significantly with change in H3K9me3. The pattern of H3K18ac and H3K9me3 displayed large differences between patients and healthy controls without any consistent pattern induced by Aza. We conclude that the marked induction of gene expression only partly could be explained by epigenetic changes, and propose that activation of ERVs may contribute to the clinical effects of Aza in MDS.

Abstract 790 Lenalidomide has emerged as a very effective therapy for del(5q) myelodysplasia. Its mechanism of action, however, has hitherto remained elusive. Interestingly, the more primitive hematopoietic compartment seems to possess a clonal advantage where del(5q) HSC are able to outcompete remaining normal HSC. We have previously demonstrated that lenalidomide is able to abrogate this clonal advantage and found that lenalidomide restored expression of the matricellular protein SPARC, a gene located within the commonly deleted region on chromosome 5q. We hypothesized that the decreased expression of SPARC in del(5q) HSC leads to increased adhesion of HSC to their respective niche cells, translating to increased rates of proliferation, partly explaining the competitive advantage against non-del(5q) HSC. We conducted a prospective study analyzing the del(5q) HSC/progenitor compartment from 23 patients before, during and after (refractory phase) lenalidomide, in order to test whether a hematopoietic stem cell (HSC)-intrinsic decrease of SPARC explains the why and how a clone of cells inherently defective at spawning functioning cellular descendants is not selected against, but rather exhibits a clonal advantage. In addition, we studied whether treatment with lenalidomide induced changes in the microenvironment these cells reside in. We analyzed cell cycle distribution, frequency of apoptosis, and expression of adhesion markers on normal and del(5q) HSPC by multi-parameter flow cytometry. These experiments revealed a slight increase in proliferation of del(5q) versus normal HSC, as well as complex changes in the expression of adhesion markers in HSC of patients treated with lenalidomide. We studied the functional adhesion of normal and del(5q) HSPC to defined matrix components of the microenvironment and observed that HSPC from del(5q) patients exhibited stronger adhesion than normal bone marrow cells to fibronectin and VCAM-1. Recombinant SPARC protein abrogated adhesion to VCAM-1 specifically in a subset of patients, while having no significant effect on normal HSPC. To study whether SPARC plays a role in the clonal dominance, we used lentiviral transduction to overexpress SPARC in HSPC and found that increased expression of SPARC led to severely reduced engraftment in NSG-mice. We also analyzed how lenalidomide impacts the microenvironmental niche. To this end, we compared the gene expression profile of mesenchymal stem cells (MSC) obtained from del(5q) patients by DNA microarray and found only 36 genes to be differentially expressed by more than 2-fold, with 15 and 21 genes up- or downregulated in del(5q) MSC, respectively. Using longitudinal bone marrow biopsies from 5 patients on and off treatment, we analyzed whether lenalidomide induced changes in the frequency of candidate niche cells such as mesenchymal stem cells (MSC), macrophages, endothelium and megakaryocytes, by using immunohistochemical markers for the aforementioned cells. Lenalidomide induced no significant changes in the number of nestin+ MSC but seemed to decrease the number of Factor-VIII+ megakaryocytes. Taken together, these studies suggest that decreased expression of SPARC leads to increased adhesion of del(5q) HSC/progenitor cells to defined components of the microenvironment and may explain why del(5q) HSC are able to outcompete the remaining healthy HSC. Our studies implicate that lenalidomide is able to abrogate this clonal advantage partly via its increase in SPARC expression with a consecutive decrease in adhesion. Disclosures: No relevant conflicts of interest to declare.

Targeted Sequencing of A Cohort Of 385 Patients With Myelodysplastic Syndromes : A Multicenter, Population-Based Study From Sweden

Chromosomal aberrations are frequently found in multiple myeloma cells and play a major role in patient outcome and management of the disease. The most important chromosomal aberrations associated with poor outcome are del(17p), t(4;14), t(14;16) and t(14;20). Others that may be associated with adverse prognosis include amp(1)(q21), del(1p32), del(13), del(8p21) and hypodiploidy. Many chromosomal aberrations have no or uncertain impact; for example, t(11;14), t(8;14) and hyperdiploidy. Attempts have been made to overcome the negative prognostic impact of chromosomal aberrations using autologous or allogeneic transplantation or new immunomodulatory drugs such as thalidomide, lenalidomide and the proteasome inhibitor bortezomib, but the results are controversial. Data suggest that allogeneic transplantation and treatment with bortezomib or lenalidomide may help to overcome the negative effect of del(13) on prognosis, whereas bortezomib may have some influence on reducing the impact of del(17p), t(4;14) and t(14;16). Chromosome analysis should always be performed at diagnosis of multiple myeloma to improve the prediction of outcome and to aid treatment decision-making.

Conditioning regimens are an important issue determining the outcome of hematopoietic stem cell transplantation (HSCT). Less toxicity, early engraftment and no relapse are the aims of efficient conditioning. Our objective was to investigate the long-term effects of BU-CY and their administration order on the toxicity and chimerism in a mouse model of HSCT. Female BALB/c mice were treated with either BU (15 mg/kg/day x 4)-CY (100 mg/kg/day x 2) or CY-BU. Treated mice were transplanted with Sca-1+ cells from male BALB/c mice. Until 90 days after HSCT, the animals were monitored for body weight and analyzed for cellular phenotype of the thymus, spleen and BM, total chimerism, the spleen chimerism of DCs and T regulatory (Treg) cells, and hepatotoxicity. BU-CY and CY-BU treatments exerted comparable myeloablative and immunosuppressive effects. The long-term engraftment of donor cells in the BM and thymus regeneration showed the same features in both groups. However, the two regimens differed; in general, hepatotoxicity and chimerism of DC and Treg cells. In the long term, BU-CY, but not CY-BU caused a marked decrease in body weight and a significant increase in the activities of the liver enzymes, particularly aspartate amino transferase (AST). We conclude that the alteration of the administration order of BU-CY to CY-BU not only gives the same level of engraftment but also reduces the toxicity of the conditioning regimen that might be valuable specially in young patients who are undergoing HSCT.

The uterine endometrium is a highly dynamic, cyclically regenerating, richly vascularized tissue. The source of new endothelial cells (ECs) for vascular regrowth remains uncertain, and it is not clear whether endothelial progenitor cells (EPCs) derived from the bone marrow contribute to angiogenesis in the human endometrium. The rare occurrence of pregnancy and subsequent normal menstruation following bone marrow transplantation (BMT) provided an opportunity to explore the role of marrow-derived EPCs in endometrial angiogenesis. Endometrial biopsies were taken from a woman aged 30 with aplastic anemia following nonmyeloablative allogeneic BMT using a brother's cells, and also from 2 control women having cesarean section. The index patient menstruated normally, became pregnant 2 years after BMT, and had a cesarean section at 36 weeks' gestation. Biopsied tissue was examined immunohistochemically for CD34 and VEGFR2 antibodies for immunophenotyping of ECs, and FISH (fluorescence in situ hybridization) probes were used to detect donor cells. Chimerism was evaluated by the real-time polymerase chain reaction technique. A parallel study was carried out in female mice given a hematological stem cell transplant. At the time of cesarean section, an average of 14% of endometrial ECs were donor-derived. The figure 12 months later was 10%. Neither of the 2 nontransplanted female control women exhibited a mismatch in endometria at the time of cesarean section. In biopsies taken from female mice 40 days after stem cell transplantation, the average proportion of donor-derived ECs was 6%. The investigators conclude from these findings that, in the endometrium, bone marrow-derived EPCs contribute to the formation of new blood vessels. Endometrial biopsy is a feasible and cost-effective means of studying bone marrow-derived EPCs.

Early therapeutic decision-making is crucial in patients with higher-risk MDS where median survival is only around one year. Azacitidine prolongs survival for these patients (Fenaux et al, Lancet Oncology 2009) but clinically relevant biomarkers remain to be identified. We evaluated retrospectively, the impact of clinical parameters and mutational profiles in 134 consecutive patients treated with a median number of 7 cycles of Azacitidine (range 1-45), in accordance to European guidelines. The vast majority (n=114) had higher-risk disease i.e. MDS with IPSS int-2 or high, AML with multilinear dysplasia and 20-30% blasts or CMML-II. We combined an initial cohort from Karolinska University Hospital (n=89) with a validating cohort from King's College Hospital, London (n=45). Studied endpoints were response, as defined by the IWG criteria, and survival. Since prolonged survival is the main goal for this cohort of patients, we believe that survival is the most relevant endpoint, supported by the fact that even non-responding patients have a survival benefit from Azacitidine (Gore et al, Haematologica, 2013). While neither clinical parameters nor mutations had a significant impact on response rate, both karyotype and mutational profile were strongly associated with survival from the start of treatment, see Table 1 and Figure 1-2. IPSS high-risk cytogenetics was negatively associated with survival (median 20 vs 10 months; p Table 1. Variables associated with survival. Univariate analyses used the log-rank test. The cox model included all listed variables except response rate in a multivariate analyses. Estimated median survival (months) Univariate p-value Cox regression p-value Hazard ratio (95% CI) Response rate: CR / mCR vs PR/HI vs SD/PD 20 vs 20 vs 10 Figure 1. Kaplan-Meier estimated survival stratified for response and pre-treatment parameters Figure 1. Kaplan-Meier estimated survival stratified for response and pre-treatment parameters Figure 2. Forest plot indicating hazard ratio including confidence interval for all pre-treatment variables. The hazard ratios were retrieved using cox univariate regression models for each variable analyzed separately. Figure 2. Forest plot indicating hazard ratio including confidence interval for all pre-treatment variables. The hazard ratios were retrieved using cox univariate regression models for each variable analyzed separately. Figure 3. Kaplan-Meier estimated survival stratified for the two dominant predictors in the cox regression model: Adverse cytogenetics and histone modulator mutations Figure 3. Kaplan-Meier estimated survival stratified for the two dominant predictors in the cox regression model: Adverse cytogenetics and histone modulator mutations Disclosures McLornan: Novartis: Research Funding, Speakers Bureau. Jädersten:Celgene: Other: speakers fee. Kulasekararaj:Alexion: Consultancy. Mufti:Celgene: Consultancy, Other: Speakers fee. Hellström-Lindberg:Celgene Corporation: Research Funding.

During the past decades, several studies in animals have displayed the ability of cells from the bone marrow (BM) to participate in regeneration of various tissues including skeletal muscle tissue. Studies in mice have demonstrated that regular physical activity is sufficient to induce contribution of BM derived cells to the skeletal muscle tissue, suggesting that this is part of the physiological remodeling of skeletal muscle. To analyze whether BM-derived cells participate in skeletal muscle remodeling in human, we developed a protocol of immunofluorescence in combination with fluorescence in situ hybridization (FISH) that enables the detection of male donor bone marrow cell contribution to female skeletal muscle tissue.

Summary Refractory anaemia with ring sideroblasts (RARS) is distinguished by hyperplastic inefficient erythropoiesis, aberrant mitochondrial ferritin accumulation and anaemia. Heterozygous mutations in the spliceosome gene SF3B1 are found in a majority of RARS cases. To explore the link between SF3B1 mutations and anaemia, we studied mutated RARS CD34+ marrow cells with regard to transcriptome sequencing, splice patterns and mutational allele burden during erythroid differentiation. Transcriptome profiling during early erythroid differentiation revealed a marked up‐regulation of genes involved in haemoglobin synthesis and in the oxidative phosphorylation process, and down‐regulation of mitochondrial ABC transporters compared to normal bone marrow. Moreover, mis‐splicing of genes involved in transcription regulation, particularly haemoglobin synthesis, was confirmed, indicating a compromised haemoglobinization during RARS erythropoiesis. In order to define the phase during which erythroid maturation of SF3B1 mutated cells is most affected, we assessed allele burden during erythroid differentiation in vitro and in vivo and found that SF3B1 mutated erythroblasts showed stable expansion until late erythroblast stage but that terminal maturation to reticulocytes was significantly reduced. In conclusion, SF3B1 mutated RARS progenitors display impaired splicing with potential downstream consequences for genes of key importance for haemoglobin synthesis and terminal erythroid differentiation.

Mesenchymal stem cells (MSC) are progenitors of mesenchymal tissues such as bone, cartilage, and adipose. Adult human leukocyte antigen (HLA)-matched MSC have been used in cellular therapies of bone disorders such as osteogenesis imperfecta, with promising results.A female fetus with multiple intrauterine fractures, diagnosed as severe osteogenesis imperfecta, underwent transplantation with allogeneic HLA-mismatched male fetal MSC in the 32nd week of gestation. Engraftment analyses of donor cells, immunologic reaction against donor cells, and the well-being of the patient were assessed.At 9 months of age, on slides stained for osteocalcin or osteopontin, a centromeric XY-specific probe revealed 0.3% of XY-positive cells in a bone biopsy specimen. Whole Y genome fluorescent in situ hybridization staining showed a median of 7.4% Y-positive cells (range, 6.8%-16.6%). Bone histology showed regularly arranged and configurated bone trabeculae. Patient lymphocyte proliferation against donor MSC was not observed in co-culture experiments performed in vitro after MSC injection. Complementary bisphosphonate treatment was begun at 4 months. During the first 2 years of life, three fractures were noted. At 2 years of corrected age, psychomotor development was normal and growth followed the same channel, -5 SD.The authors' findings show that allogeneic fetal MSC can engraft and differentiate into bone in a human fetus even when the recipient is immunocompetent and HLA-incompatible.

Objective The present study was designed to investigate the influence of the administration sequence of busulphan (Bu) and cyclophosphamide (Cy) during conditioning regimen on myeloablative and immunosuppressive effects and on engraftment. Methods Female Balb/C mice were treated with either Bu-Cy or Cy-Bu (assigned order of administration). Bu was administered as 8.75 mg/kg/day × 4 and Cy as 100 mg/kg/day × 2. The control consisted of untreated animals. Bone marrow and spleen were harvested during the conditioning regimen and for up to 19 days after treatment. Colony-forming unit granulocyte macrophage assay was performed on marrow cells. Immunological analyses were performed using spleen cells. Liver status was determined using aspartate amino transferase (AST), alanine amino transferase (ALT), and bilirubin. Animals assigned for engraftment study were conditioned as above and transplanted using sca-1 cells from male Balb/C donors. Engraftment was followed using fluorescence in situ hybridization up to 30 days posttransplantation. Results No significant difference in myeloablative effect was observed between treatments. Immunosuppressive activity expressed as CD3 + /CD19 + and CD4 + /CD8 + was also similar. Levels of cytokines interleukin 2, tumor necrosis factor α, and interferon γ at the end of the conditioning regimen were lower in the Cy-Bu group, while liver enzymes were higher after the Bu-Cy regimen. Engraftment in bone marrow was reached faster within the first 20 days after conditioning with Cy-Bu compared to Bu-Cy. However, no difference in chimerism was observed at 30 days. Conclusion Cy-Bu treatment resulted in lower levels of cytokines, faster bone marrow engraftment, and lower values of liver enzymes compared to Bu-Cy regimen, which may benefit stem cell transplantation outcomes.

Karyotypical alteration of chromosome 5 and in particular band 5q13 is a frequent finding in hairy cell leukemia (HCL). We have previously identified a number of candidate genes localized in close proximity to a constitutional inv(5)(p13.1q13.3) breakpoint in one HCL patient. These included beta-hexosaminodase HEXB, frequently mutated in the lysosomal storage disorder Sandhoff disease. We now report that the 5q13.3 breakpoint disrupts a novel evolutionary conserved alternative isoform of HEXB. This isoform directly overlaps, in a cis-antisense fashion, exon 1 of the gene for ectodermal neuronal cortex 1 ENC-1, and was thus named ENC-1AS. ENC-1 has previously been shown to be overexpressed in several malignancies, and is believed to play a critical regulatory role in malignant transformation of various tumors. Importantly, subsequent analysis of ENC-1 in purified primary HCL tumor cells revealed a striking upregulation of ENC-1 in all 26 patients examined, compared with normal peripheral blood lymphocytes from healthy donors. Upon further analysis of the ENC-1/ENC-1AS locus, we identified a complex 5' regulatory mechanism involving an inverse expression of the ENC-1 sense and the ENC-1AS transcripts in several tissues supporting the hypothesis that expression of ENC-1AS regulates ENC-1 levels. In addition, we have also found tissue-specific methylation of a 1.2 kb segment encompassing the overlapping ENC-1/ENC-1AS 5' exons, adding to the complexity of the regulation of this locus. Altogether, these results suggest that upregulation of ENC-1 contributes to the development of HCL and provides new information on the possible dysregulation of ENC-1 including expression of a novel antisense gene, ENC-1AS.

During the past decades, several studies in animals have displayed the ability of cells from the bone marrow (BM) to participate in regeneration of various tissues including skeletal muscle tissue. Studies in mice have demonstrated that regular physical activity is sufficient to induce contribution of BM derived cells to the skeletal muscle tissue, suggesting that this is part of the physiological remodeling of skeletal muscle. To analyze whether BM-derived cells participate in skeletal muscle remodeling in human, we developed a protocol of immunofluorescence in combination with fluorescence in situ hybridization (FISH) that enables the detection of male donor bone marrow cell contribution to female skeletal muscle tissue.

The constitutional pericentric inversion on chromosome 3, inv(3), is rarely found in a normal population. The aim of our study was to investigate its possible link to hematologic malignancy. Chromosomes from bone marrow cells in 890 patients with hematologic disorders were analyzed with the Q-banding technique. Thirty-four patients had inv(3) (3.8%). In 241 patients with myelodysplastic syndromes the frequency was 6.2% as opposed to 2.9% in the remaining 649 patients (p = 0.02). The increased frequency of inv(3) in patients with myelodysplastic syndromes indicates that inv(3) could be a risk factor for the development of the disease.

The pathogenesis of hairy cell leukemia (HCL) remains largely unknown since no specific genetic lesion has been identified in this disease. Previous cytogenetic analysis from our group has shown that chromosome abnormalities involving the 5q13 band are common in HCL, occurring in approximately 1/3 of patients. The data suggest that the 5q13.3 band is likely to harbor a gene involved in the transformational events of this disease. We have recently found two cosmids flanking the 5q13.3 breakpoint in patients with HCL, and the distance between them is approximately 35 kb, as analyzed by fiber-FISH. The two cosmids have been located between the markers SGC34998 and WI-15505/WI-6897 by radiation hybrid mapping. Five of 11 patients with HCL had a hemizygous deletion of the two cosmids, indicating that the function of a tumor suppressor gene may be lost. With the aim of delineating the critical region of 5q13.3 loss in patients with HCL, we have constructed an integrated contig of YAC, BAC, PAC, P1, and cosmid clones that covers the region. Within this area, three expressed sequences were identified as candidates for the putative 5q13.3 tumor suppressor gene involved in the pathogenesis of HCL.

The most frequent structural chromosome abnormality in chronic lymphocytic leukaemia (CLL) is deletion at chromosome 13q14. Studies with Southern blot hybridisation have revealed deletions in the region located telomeric of the retinoblastoma gene in more than 40% of cases. The highest frequency of homozygous deletions has been found at the D13S319 locus and it is likely that a new tumour suppressor gene is located close to this region. We have analysed deletions in the D13S319 region in 20 selected CLL patients using conventional cytogenetic analysis, fluorescence in situ hybridisation (FISH) and Southern blot hybridisation. FISH and Southern hybridisation are equally efficient in detecting deleted clones in our study. However, FISH analysis indicate that subclones with different numbers of alleles in the D13S319 region can exist simultaneously. The cytogenetic analyses confirm that clones with different chromosomal abnormalities can occur in patients with CLL and that 13q14 deletions can be limited to one of these subclones. Furthermore, the FISH analyses show that trisomy 12 and deletion of 13q14 can occur in the same cell clone. Finally, our study confirms that mitogen stimulation of peripheral blood cells from CLL patients before FISH analysis may result in a sharp increase in normal appearing cells, which can hide leukaemic clones with deletions in the D13S319 region.

Azacitidine induces profound genome-wide hypomethylation in primary myelodysplastic bone marrow cultures but may also reduce histone acetylation

A high proportion of lower-risk del(5q) MDS patients will respond to treatment with lenalidomide. The estimated duration of transfusion-independence is 2 years including some long-lasting responses, but almost 40% of patients progress to acute leukemia by 5 years after start of treatment. As the molecular mechanisms underlying disease progression in del(5q) MDS remain to be elucidated, we do not know how to predict disease progression or how to monitor patients during lenalidomide treatment. We previously reported that small TP53 mutated subclones predict for an unfavorable outcome in del(5q) patients, and that these subclones expand with disease progression. However, whether or not other somatic mutations or factors related to the bone marrow microenvironment also contribute to disease progression has not been comprehensively assessed. We studied a longitudinal cohort of 35 low- and intermediate-1-risk del(5q) patients treated with lenalidomide (n=22), or other treatments including stem cell transplantation (n=13) by flow cytometric surveillance of hematopoietic stem and progenitor cells (HSPC) subsets, targeted sequencing of mutational patterns, and changes in the bone marrow microenvironment. In our cohort, 13 of 35 patients progressed to either higher-risk MDS (n=4) or leukemia (n=9), 12 of whom were treated with lenalidomide. Progression was associated with the detection of a restricted subset of new recurrent mutations, either alone or in combination: TP53 (n=9, p=0.0004), TET2 (n=6, p=0.006), RUNX1 (n=3, p=0.044), and PTPN11 (n=1). Regardless of whether the three mutations (TP53, TET2 and RUNX1) were present in the initial sample or whether they subsequently developed, testing positive for any of them carried a high probability (13/16, 81%) for predicting progression. For 11 out of 13 patients the new mutations were detected prior to the time point of clinical progression and the median time from detection of the mutation to clinical evidence of progression was 42 months (range 0-83.9). Thus, we were able to detect the mutation in the majority of cases well before clinical signs of disease progression. Seven of the nine patients who developed leukemia carried a TP53 mutation. Based on a median sequencing depth of 370 reads, the mutation was considered present pre-treatment in one of these patients and to have developed under treatment in the other six. Using flow cytometry for surveillance of HSPC subsets in lenalidomide-treated patients, we found that neither lenalidomide treatment nor the acquisition of additional mutations led to any uniform profound changes in the hematopoietic hierarchy unless the patient showed clinical signs of progression. Microarray analysis of mesenchymal stromal cells (MSC) exhibited an expression footprint consistent with MSC with high expression of typical MSC markers and absence of hematopoietic gene signatures. However, we observed only minor differences in gene expression between pre- treatment del(5q) and healthy MSC. In conclusion, while flow cytometric analysis of HSPC populations or analysis of the microenvironment had limited predictive value in this cohort of lower-risk del(5q) MDS, all patients who progressed to either higher-risk MDS or leukemia were identified by harboring recurrent mutations in a limited number of genes, i.e., TP53, RUNX1, TET2, and PTPN11. Based on our data, we advocate for conducting a prospective study aimed at investigating in a larger number of del(5q) MDS cases pre- and post-lenalidomide treatment, whether the detection of such mutations can guide clinical decision making, such as suggesting which patients should undergo hematopoietic cell transplantation. Disclosures No relevant conflicts of interest to declare.

This study was designed to analyze the effect of global and gene-specific DNA methylation patterns on the outcome of patients with acute myeloid leukemia (AML). Methylation of CDKN2B (p15), E-cadherin (CDH) and hypermethylated in cancer 1 (HIC1) promoters and global DNA methylation by luminometric methylation assay (LUMA) was analyzed in 107 AML patients and cytogenetic and molecular mutational analysis was performed. In addition, genome-wide promoter-associated methylation was assessed using the Illumina HumanMethylation27 array in a proportion of the patients. Promoter methylation was discovered in 66, 66 and 51% of the patients for p15, CDH and HIC1, respectively. In multivariate analysis, low global DNA methylation was associated with higher complete remission rate (hazard ratio (HR) 5.9, P=0.005) and p15 methylation was associated with better overall (HR 0.4, P=0.001) and disease-free survival (HR 0.4, P=0.016). CDH and HIC1 methylation were not associated with clinical outcome. Mutational status and karyotype were not significantly associated with gene-specific methylation or global methylation. Increased genome-wide promoter-associated methylation was associated with better overall and disease-free survival as well as with LUMA hypomethylation. We conclude that global and gene-specific methylation patterns are independently associated with the clinical outcome in AML patients.

High-dose therapy (HDT) followed by autologous stem cell transplantation (ASCT) is the most common treatment for patients under 65 years of age with multiple myeloma (MM). In this study, we present a retrospective analysis of the prognostic impact of different factors in patients who have received this treatment as first line therapy in our centre. Abnormalities in chromosome 13 were identified by fluorescence in situ hybridization at the time of diagnosis. The median overall survival (OS) and progression-free survival (PFS) from transplantation time in the whole group of 193 patients were 90 and 48 months respectively. The median follow-up was 65 months (range: 6-186 months). The complete remission (CR) rate in patients with and without del(13) was 31 and 40% respectively whereas the median OS in patients with del(13) was 58 months but not reached in patients without del(13) (p=0.006). The PFS was 26 months in patients with del(13) and 84 months in those without del(13) (p=0.001). The transplantation related mortality was 2.5% both in the absence and presence of del(13). Patients who achieved CR following ASCT had longer OS and PFS when compared to those who only achieved partial remission. Thus, this study confirms the role of del(13) as a marker of poor prognosis. Multivariate analysis showed that the existence of del(13) was the only single independent factor effecting survival (p=0.001). In patients without del(13), the prognostic impact was even stronger when combined with the plasma cell load in the bone marrow (p=0.020), whereas the plasma cell load had no effect on survival of patients with del(13). Overall, the absence of del(13) in combination with low plasma cell infiltration at diagnosis predicts the best survival.

Chromosomal aberrations are important prognostic parameters in acute myeloid leukemia (AML). Indicators of poor prognosis include del(5q)/-5, del(7q)/-7, abnormal 3q or complex karyotype. In recent years, it has become clear that aberrations in 17p represent one of the indicators of poor prognosis in haematological malignancies. In AML, deletions in 17p have been shown to indicate a dismal prognosis; genetic aberrations in 9p have also been discussed as influencing long-term survival in AML. In this study, we correlated genetic abnormalities in chromosomes 9 and 17 in patients with de novo AML to in vitro cytotoxicity of conventional anti-leukemic drugs, and long-term overall survival. Blast cells were isolated from 387 patients diagnosed with AML. Chromosomal analysis was successful in 336 cases. All samples were tested for in vitro cytotoxicity against fludarabine, amsacrine, mitoxantrone, etoposide, daunorubicin and Ara-C after being cultured for 4 days, using an ATP assay. Among the 336 patients, five main groups were identified. Abnormal chromosome 17 (n = 22), abnormal 9p (n = 13), monosomy 7 or deletion 7q (n = 35), complex karyotype (n = 52) and normal karyotype (n = 132). Patients with abnormalities of chromosome 17 showed significantly greater resistance to all drugs tested and significantly shorter overall survival compared with patients with normal and complex karyotypes (p = 0.0001 and 0.041, respectively). All patients with abnormalities of chromosome 17 died within 11 months of diagnosis. A tendency towards shorter overall survival and greater drug resistance was also noted when comparing chromosome 17 abnormalities with del(7q)/-7, but the differences did not reach statistical significance. Patients with abnormal 9p showed significantly shorter overall survival but did not differ significantly as regards in vitro drug resistance compared with patients presenting with a normal karyotype. Chromosomal abnormalities affecting the p53 pathway have a significant impact on cytostatic drug resistance and survival in AML. Developing new drugs targeting the p53 pathway could be a way to improve treatment of AML.

Background In the present investigation, we determined whether donor epithelial lung cells might be detected after allogeneic hematopoietic stem cell transplantation (HSCT). Methods Lung-tissue specimens were obtained at autopsy from four female patients, two with male donors, after nonmyeloablative HSCT. Immunohistochemical staining for cytokeratin was used to identify lung epithelial cells. The tissue sections were analyzed for the presence of donor-derived lung epithelial cells with the use of fluorescence in situ hybridization of XY-positive cells. Results All patients showed almost complete donor chimerism in all cell lineages after HSCT with polymerase chain reaction of minisatellites. In the two positive controls, between 2% and 6% Y-chromosome-positive epithelial lung cells were detected in each section. Surfactant-positive male epithelial cells were also detected, indicating engraftment of type II pneumocytes. In the two negative controls, no Y-chromosome-positive cells were detected. Conclusion Circulating donor stem cells may differentiate into lung epithelial cells after allogeneic HSCT.

Introduction: Azacytidine (Aza) is first-line treatment for patients with higher-risk MDS but only around 50% of patients respond to therapy. Overall survival for this patient group is short and clinical decision-making tools are highly warranted. As Aza may improve survival also in patients with hematologic improvement or stable disease, survival may be a better response predictor than response rate. Methods: We evaluated the impact of clinical parameters (n=134), mutations (n=90) and DNA methylation profiles (n=42) on response and survival in a cohort of consecutive patients with higher-risk MDS treated with Aza. Targeted sequencing of 42 genes involved in myeloid disease and Illumina 450 methylation arrays were applied for mutational assessment and methylation profiling, respectively. The IWG criteria were used for response scoring. Results: Patients were eligible for analysis if they had received ≥1 dose of Aza. Median number of cycles given was 6 (range 1-29). Responses were scored as CR (22%), mCR (11%), PR (3%), HI (13%), SD (27%) and PD (13%). Fifteen patients (11%) were not evaluated for response due to early death. Disease duration was negatively associated with both response (p=0.035) and survival (p=0.001). Adverse cytogenetics and high absolute neutrophil count was associated with shorter survival (p=0.03 and p=0.02) but not with response. No single mutation or group of mutations was associated with response although there was a weak positive trend for TET2 and ASXL1. When using survival as endpoint, ASXL1 showed a strong trend towards prolonged survival (median 29 vs 14 months, p=0.07) and, importantly, the group of patients with any mutation in histone modulators (ASXL1, EZH2, MLL) had a significant longer survival (median 28 vs 13 months, p=0.01). This remained significant in the cox regression model (HR 0.3223 (0.16-0.70 95% CI); p=0.002). No other mutations or group of mutations were associated with survival. Interestingly, previously reported negative prognostic factors including RUNX1 (p=0.82), TP53 (p=0.54), and the number of mutations (p=0.37), were not associated with survival in this Aza-treated cohort DNA methylation profiling identified 233 differentially methylated regions (DMRs) between responders and non-responders, corresponding to 200 genes, including six HOX-genes, which were highly enriched for gene ontology pathways involved in development and differentiation. High methylation of HOXA5, the most significant DMR, was associated with prolonged survival (22 vs 12 months, p=0.03). We also studied the methylation level of HOXA5 in CD34+ cells from patients with high-risk MDS and sorted compartments during myeloid differentiation in normal bone marrow. The methylation profile in responding patients was closer to that of differentiated cells while non-responding cells were closer to progenitor cells. Discussion: Single mutations have a limited impact on response rates. Howver, we demonstrate a clear survival benefit for patients with mutations in histone modulators, which previously have been reported as negative prognostic factors (Bejar, NEJM 2013; Haferlach, Leukemia 2014). Moreover, several negative risk factors, such as RUNX1, TP53, and the number of mutations were neutralized by Aza. Histone modulation mutations may therefore be used in the clinical decision-making for higher-risk MDS. We demonstrate for the first time that methylation profiles in genes involved in differentiation and development differ between responders and non-responders and that hypermethylation of HOXA5 is positively associated with survival (p=0.03). Since methylation pattern in HOXA5 is linked to differentiation status, we hypothesize that non-responding patients are skewed towards more immature differentiation. Figure 1: Survival curves Figure 1:. Survival curves Figure 2: DNA methylation levels at the HOXA5 locus. Squares represent gene location with light green=TSS-1500; Dark green=TSS-200; Red=Gene body; Magenta=1st Exon; Dark blue=5’UTR; Cyan=3’UTR and diamonds represent sample values. A=Median methylation level of responders illustrated with orange diamonds (MNCs) and non-responders with blue diamonds (MNCs). B=Added CD34+ cells with red diamonds. C=All patients. D=Normal bone marrow with PMN illustrated with brown diamonds and CMP with green diamonds. Figure 2:. DNA methylation levels at the HOXA5 locus. Squares represent gene location with light green=TSS-1500; Dark green=TSS-200; Red=Gene body; Magenta=1st Exon; Dark blue=5’UTR; Cyan=3’UTR and diamonds represent sample values. A=Median methylation level of responders illustrated with orange diamonds (MNCs) and non-responders with blue diamonds (MNCs). B=Added CD34+ cells with red diamonds. C=All patients. D=Normal bone marrow with PMN illustrated with brown diamonds and CMP with green diamonds. Figure 3 Figure 3. Disclosures No relevant conflicts of interest to declare.

Previous studies have indicated the presence of a putative tumor suppressor gene on human chromosome 13q14, commonly deleted in patients with B-cell chronic lymphocytic leukemia (B-CLL). We have recently identified a minimally deleted region encompassing parts of two adjacent genes, termed LEU1 and LEU2 (leukemia-associated genes 1 and 2), and several additional transcripts. In addition, 50 kb centromeric to this region we have identified another gene, LEU5/RFP2. To elucidate further the complex genomic organization of this region, we have identified, mapped, and sequenced the homologous region in the mouse. Fluorescence in situ hybridization analysis demonstrated that the region maps to mouse chromosome 14. The overall organization and gene order in this region were found to be highly conserved in the mouse. Sequence comparison between the human deletion hotspot region and its homologous mouse region revealed a high degree of sequence conservation with an overall score of 74%. However, our data also show that in terms of transcribed sequences, only two of those, human LEU2 and LEU5/RFP2, are clearly conserved, strengthening the case for these genes as putative candidate B-CLL tumor suppressor genes.