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Patient-derived xenograft (PDX) models have emerged as versatile preclinical platforms for investigation of functional pathomechanisms in myelodysplastic syndromes (MDS) and other myeloid neoplasms. However, despite increasingly improved methodology, engraftment efficiencies frequently remain low. Humanized three-dimensional scaffold models (ossicle xenotransplantation models) in immunocompromised mice have recently been found to enable improved engraftment rates of healthy and malignant human hematopoiesis. We therefore interrogated the feasibility of using four different three-dimensional ossicle-based PDX models for application with primary MDS samples. In a fully standardized comparison, we evaluated scaffold materials such as Gelfoam, extracellular matrix (ECM), and human or xenogenous bone substance in comparison to intrafemoral (IF) co-injection of bone marrow (BM)-derived mesenchymal stromal cells (MSCs) and CD34

Preclinical research of myelodysplastic syndromes (MDSs) is hampered by a lack of feasible disease models. Previously, we have established a robust patient-derived xenograft (PDX) model for MDS. Here we demonstrate for the first time that this model is applicable as a preclinical platform to address pending clinical questions by interrogating the efficacy and safety of the thrombopoietin receptor agonist eltrombopag. Our preclinical study included n = 49 xenografts generated from n = 9 MDS patient samples. Substance efficacy was evidenced by FACS-based human platelet quantification and clonal bone marrow evolution was reconstructed by serial whole-exome sequencing of the PDX samples. In contrast to clinical trials in humans, this experimental setup allowed vehicle- and replicate-controlled analyses on a patient–individual level deciphering substance-specific effects from natural disease progression. We found that eltrombopag effectively stimulated thrombopoiesis in MDS PDX without adversely affecting the patients’ clonal composition. In conclusion, our MDS PDX model is a useful tool for testing new therapeutic concepts in MDS preceding clinical trials.

Although acute promyelocytic leukemia (APL) has evolved to the AML entity with the best prognosis, typical 'early death' (ED) events still account for mortality rates of ∼20% in population-based studies. To investigate this poorly understood issue we performed whole transcriptome analysis of

The significance of clonal evolution in myelofibrosis (MF) relapse remains poorly understood. Here we performed panel sequencing in paired samples of 30 patients with MF who relapsed after undergoing allogeneic hematopoietic stem cell transplantation (alloSCT). We identified a median of 2 mutations (range, 0 to 12) in a median of 2 genes (range, 0 to 8) before allo-SCT, along with a median of 2 mutations (range, 0 to 12) in 2 genes (range, 0 to 6) at relapse. Additional whole-genome sequencing (n = 6) did not elucidate additional molecular changes. Taken together, our data provide further evidence, here on MF, that clonal evolution after alloSCT is limited and that instead, alloSCT selects specific (sub)clones.

Separase, a cysteine endopeptidase, is a key player in mitotic sister chromatid separation, replication fork dynamics, and DNA repair. Aberrant expression and/or altered separase proteolytic activity are associated with aneuploidy, tumorigenesis, and disease progression. Since genomic instability and clonal evolution are hallmarks of progressing chronic myeloid leukemia (CML), we have comparatively examined separase proteolytic activity in TKI-treated chronic phase CML. Separase proteolytic activity was analyzed on single cell level in 88 clinical samples and in 14 healthy controls by a flow cytometric assay. In parallel, BCR-ABL1 gene expression and replication fork velocity were measured by qRT-PCR and DNA fiber assays, respectively. The separase activity distribution (SAD) value indicating the occurrence of MNCs with elevated separase proteolytic activity within samples was found to positively correlate with BCR-ABL1 gene expression levels and loss of MMR (relapse) throughout routine BCR-ABL1 monitoring. Analyses of CD34+ cells and MNCs fractionized by flow cytometric cell sorting according to their separase activity levels (H- and L-fractions) revealed that CD34+ cells with elevated separase activity levels (H-fractions) displayed enhanced proliferation/viability when compared with cells with regular (L-fraction) separase activity (mean 3.3-fold, p = 0.0011). BCR-ABL1 gene expression positivity prevailed in MNC H-fractions over L-fractions (42% vs. 8%, respectively). Moreover, expanding CD34+ cells of H-fractions showed decreased replication fork velocity compared with cells of L-fractions (p BCR-ABL1 gene expression, and enhanced proliferative capacity in hematopoietic cells within the leukemic niche of TKI-treated chronic phase CML.

Autologous hematopoietic cell transplantation (HCT) is suitable for consolidation of favorable-/intermediate-risk AML patients in CR1. However, ~50% of AML patients relapse after autologous HCT, and efficacy of subsequent salvage strategies including allogeneic HCT remains unclear. We studied 123 consecutive patients with newly diagnosed AML undergoing high-dose chemotherapy (HDCT)/autologous HCT in CR1. In relapsing patients afterwards, we analyzed salvage treatments and outcomes focusing particularly on salvage allogeneic HCT. Of 123 patients, 64 (52%) relapsed after autologous HCT. Subsequently, 13 (21%) received palliative therapy, whereas 51 (79%) proceeded to salvage therapy with a curative intent. Of the 47 patients with a curative intent and who did not proceed directly to allogeneic HCT, 23 (49%) achieved CR2 or had ongoing hematologic CR1 despite molecular relapse. Finally, 30 patients (47%) received allogeneic HCT with estimated 3-year leukemia-free and overall survival rates of 33% and 43%. Hematologic remission at allogeneic HCT and lack of acute GvHD had a positive impact on OS and LFS (p

The bone marrow (BM) stroma in myeloid neoplasms is altered and it is hypothesized that this cell compartment may also harbor clonal somatically acquired mutations. By exome sequencing of in vitro expanded mesenchymal stromal cells (MSCs) from n = 98 patients with myelodysplastic syndrome (MDS) and n = 28 healthy controls we show that these cells accumulate recurrent mutations in genes such as ZFX (n = 8/98), RANK (n = 5/98), and others. MDS derived MSCs display higher mutational burdens, increased replicative stress, senescence, inflammatory gene expression, and distinct mutational signatures as compared to healthy MSCs. However, validation experiments in serial culture passages, chronological BM aspirations and backtracking of high confidence mutations by re-sequencing primary sorted MDS MSCs indicate that the discovered mutations are secondary to in vitro expansion but not present in primary BM. Thus, we here report that there is no evidence for clonal mutations in the BM stroma of MDS patients., Bone marrow-derived mesenchymal stroma cells (MSCs) in myeloid neoplasia have been hypothesized to carry somatic mutations and contribute to pathogenesis. Here the authors analyse ex-vivo cultures and primary MSCs derived from patients with myelodysplastic syndromes, finding functional alterations but no evidence of clonal mutations.

Autologous hematopoietic cell transplantation (HCT) is suitable for consolidation of favorable-/intermediate-risk AML patients in CR1. However, ~50% of AML patients relapse after autologous HCT, and efficacy of subsequent salvage strategies including allogeneic HCT remains unclear. We studied 123 consecutive patients with newly diagnosed AML undergoing high-dose chemotherapy (HDCT)/autologous HCT in CR1. In relapsing patients afterwards, we analyzed salvage treatments and outcomes focusing particularly on salvage allogeneic HCT. Of 123 patients, 64 (52%) relapsed after autologous HCT. Subsequently, 13 (21%) received palliative therapy, whereas 51 (79%) proceeded to salvage therapy with a curative intent. Of the 47 patients with a curative intent and who did not proceed directly to allogeneic HCT, 23 (49%) achieved CR2 or had ongoing hematologic CR1 despite molecular relapse. Finally, 30 patients (47%) received allogeneic HCT with estimated 3-year leukemia-free and overall survival rates of 33% and 43%. Hematologic remission at allogeneic HCT and lack of acute GvHD had a positive impact on OS and LFS (p 0.05). Our study suggests that almost 80% of AML patients can undergo salvage therapy following relapse after front-line HDCT/autologous HCT. Allogeneic HCT can provide cure in one third of patients relapsing after front-line HDCT/autologous HCT.

Ho et al. demonstrate that old HSCs are extremely resistant to bloodborne systemic rejuvenation approaches and long-term exposure to a young BM niche microenvironment, maintaining a cell-intrinsic aged state. They also show that young HSCs are not affected by old blood or blood-derived factors, an important finding for transplantations in older patients and other emerging anti-aging interventions., While young blood can restore many aged tissues, its effects on the aged blood system itself and old hematopoietic stem cells (HSCs) have not been determined. Here, we used transplantation, parabiosis, plasma transfer, exercise, calorie restriction, and aging mutant mice to understand the effects of age-regulated systemic factors on HSCs and their bone marrow (BM) niche. We found that neither exposure to young blood, nor long-term residence in young niches after parabiont separation, nor direct heterochronic transplantation had any observable rejuvenating effects on old HSCs. Likewise, exercise and calorie restriction did not improve old HSC function, nor old BM niches. Conversely, young HSCs were not affected by systemic pro-aging conditions, and HSC function was not impacted by mutations influencing organismal aging in established long-lived or progeroid genetic models. Therefore, the blood system that carries factors with either rejuvenating or pro-aging properties for many other tissues is itself refractory to those factors., Graphical Abstract

Non-targeted effects (NTE) of ionizing radiation may initiate myeloid neoplasms (MN). Here, protein mediators (I) in irradiated human mesenchymal stromal cells (MSC) as the NTE source, (II) in MSC conditioned supernatant and (III) in human bone marrow CD34+ cells undergoing genotoxic NTE were investigated. Healthy sublethal irradiated MSC showed significantly increased levels of reactive oxygen species. These cells responded by increasing intracellular abundance of proteins involved in proteasomal degradation, protein translation, cytoskeleton dynamics, nucleocytoplasmic shuttling, and those with antioxidant activity. Among the increased proteins were THY1 and GNA11/14, which are signaling proteins with hitherto unknown functions in the radiation response and NTE. In the corresponding MSC conditioned medium, the three chaperones GRP78, CALR, and PDIA3 were increased. Together with GPI, these were the only four altered proteins, which were associated with the observed genotoxic NTE. Healthy CD34+ cells cultured in MSC conditioned medium suffered from more than a six-fold increase in γH2AX focal staining, indicative for DNA double-strand breaks, as well as numerical and structural chromosomal aberrations within three days. At this stage, five proteins were altered, among them IQGAP1, HMGB1, and PA2G4, which are involved in malign development. In summary, our data provide novel insights into three sequential steps of genotoxic signaling from irradiated MSC to CD34+ cells, implicating that induced NTE might initiate the development of MN.

Radiation-induced bystander effects (RIBE) in human hematopoietic stem and progenitor cells may initiate myeloid neoplasms (MN). Here, the occurrence of RIBE caused by genotoxic signaling from irradiated human mesenchymal stromal cells (MSC) on human bone marrow CD34+ cells was investigated. For this purpose, healthy MSC were irradiated in order to generate conditioned medium containing potential genotoxic signaling factors. Afterwards, healthy CD34+ cells from the same donors were grown in conditioned medium and RIBE were analyzed. Increased DNA damage and chromosomal instability were detected in CD34+ cells grown in MSC conditioned medium when compared to CD34+ cells grown in control medium. Furthermore, reactive oxygen species and distinct proteome alterations, e.g., heat-shock protein GRP78, that might be secreted into the extracellular medium, were identified as potential RIBE mediators. In summary, our data provide evidence that irradiated MSC induce genetic instability in human CD34+ cells potentially resulting in the initiation of MN. Furthermore, the identification of key bystander signals, such as GRP78, may lay the framework for the development of next-generation anti-leukemic drugs.

Somatic mutations in genes coding for splicing factors, e.g., SF3B1, U2AF1, SRSF2, and others are found in approximately 50% of patients with myelodysplastic syndromes (MDS). These mutations have been predicted to frequently occur early in the mutational hierarchy of the disease, therefore, making them particularly attractive potential therapeutic targets. Recent studies in cell lines engineered to carry splicing factor mutations have revealed a strong association with elevated levels of DNA:RNA intermediates (R-loops) and a dependency on proper ATR function. However, data confirming this hypothesis in a representative cohort of primary MDS patient samples have so far been missing. Using CD34+ cells isolated from MDS patients with and without splicing factor mutations as well as healthy controls we show that splicing factor mutation- associated R-loops lead to elevated levels of replication stress and ATR pathway activation. Moreover, splicing factor mutated CD34+ cells are more susceptible to pharmacological inhibition of ATR resulting in elevated levels of DNA damage, cell cycle blockade, and cell death. This can be enhanced by combination treatment with the low-dose splicing modulatory compound Pladienolide B. We further confirm the direct association between R-loops and ATR sensitivity and the presence of a splicing factor mutation using lentiviral overexpression of wild-type and mutant SRSF2 P95H in cord blood CD34+ cells. Collectively, our results from n=53 MDS patients identify replication stress and associated ATR signaling to be critical pathophysiological mechanisms in primary MDS CD34+ cells carrying splicing factor mutations, and provide a preclinical rationale for targeting ATR signaling in these patients.

DNA damage and alterations in the DNA damage response (DDR) are critical sources of genetic instability that might be involved in BCR-ABL1 kinase-mediated blastic transformation of chronic myeloid leukemia (CML). Here, increased DNA damage is detected by γH2AX foci analysis in peripheral blood mononuclear cells (PBMCs) of de novo untreated chronic phase (CP)-CML patients (n = 5; 2.5 γH2AX foci per PBMC ± 0.5) and blast phase (BP)-CML patients (n = 3; 4.4 γH2AX foci per PBMC ± 0.7) as well as CP-CML patients with loss of major molecular response (MMR) (n = 5; 1.8 γH2AX foci per PBMC ± 0.4) when compared to DNA damage in PBMC of healthy donors (n = 8; 1.0 γH2AX foci per PBMC ± 0.1) and CP-CML patients in deep molecular response or MMR (n = 26; 1.0 γH2AX foci per PBMC ± 0.1). Progressive activation of erroneous non-homologous end joining (NHEJ) repair mechanisms during blastic transformation in CML is indicated by abundant co-localization of γH2AX/53BP1 foci, while a decline of the DDR is suggested by defective expression of (p-)ATM and (p-)CHK2. In summary, our data provide evidence for the accumulation of DNA damage in the course of CML and suggest ongoing DNA damage, erroneous NHEJ repair mechanisms, and alterations in the DDR as critical mediators of blastic transformation in CML.

At present, hemato-oncologic diagnostics is facing dynamic changes. This applies to the exploration and introduction of novel technologies such as next-generation sequencing or digital droplet PCR for myeloid and lymphatic malignancies in laboratory routine, or liquid biopsy for patients with lymphoid malignancies. Targeted therapies such as FLT3 or IDH1/IDH2 inhibitors for acute myeloid leukemia are entering clinical practice. Thus, the demand for hematologic precision diagnostics both at initial diagnosis and during the course of the disease are equally increasing, and a short turn-around time becomes crucial. NGS expands the armamentarium for minimal residual disease diagnostics, but novel questions arise relating to sensitivity, the appropriate time points of this analysis, or the thresholds triggering therapeutic interventions. In this review article, we summarize some of the most relevant current changes and subsequent challenges for diagnostics in various myeloid and lymphatic malignancies. Future directions of hemato-oncologic diagnostics in the next 5-10 years are highlighted.

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Relapse of acute myeloid leukemia (AML) remains a major determinant of outcome. A number of molecularly directed treatment options have recently emerged making comprehensive diagnostics an important pillar of clinical decision making at relapse. Acknowledging the high degree of individual genetic variability at AML relapse, next-generation sequencing (NGS) has opened the opportunity for assessing the unique clonal hierarchy of individual AML patients. Knowledge on the genetic makeup of AML is reflected in patient customized treatment strategies thereby providing improved outcomes. For example, the emergence of druggable mutations at relapse enable the use of novel targeted therapies, including FLT3 inhibitors or the recently approved IDH1/2 inhibitors ivosidenib and enasidenib, respectively. Consequently, some patients may undergo novel bridging approaches for reinduction before allogeneic stem cell transplantation, or the identification of an adverse prognostic marker may initiate early donor search. In this review, we summarize the current knowledge of NGS in identifying clonal stability, clonal evolution, and clonal devolution in the context of AML relapse. In light of recent improvements in AML treatment options, NGS-based molecular diagnostics emerges as the basis for molecularly directed treatment decisions in patients at relapse.

Life-long blood regeneration relies on a rare population of self-renewing hematopoietic stem cells (HSCs). These cells' nearly unlimited self-renewal potential and lifetime persistence in the body signifies the need for tight control of their genome integrity. Their quiescent state, tightly linked with low metabolic activity, is one of the main strategies employed by HSCs to preserve an intact genome. On the other hand, HSCs need to be able to quickly respond to increased blood demands and rapidly increase their cellular output in order to fight infection-associated inflammation or extensive blood loss. This increase in proliferation rate, however, comes at the price of exposing HSCs to DNA damage inevitably associated with the process of DNA replication. Any interference with normal replication fork progression leads to a specialized molecular response termed replication stress (RS). Importantly, increased levels of RS are a hallmark feature of aged HSCs, where an accumulating body of evidence points to causative relationships between RS and the aging-associated impairment of the blood system's functional capacity. In this review, we present an overview of RS in HSCs focusing on its causes and consequences for the blood system of mice and men.

Myelodysplastic syndromes (MDS) represent a wide range of malignant hematological stem cell disorders characterized by ineffective hematopoiesis with dysplasia, peripheral cytopenias, and a propens...

Considering the expanding therapeutic options for patients with acute myeloid leukemia (AML), minimal residual disease (MRD) diagnostics gain importance for treatment monitoring in this heterogeneo...

Introduction There is increasing evidence for an active role of the bone marrow (BM) microenvironment in the pathogenesis of Myelodysplastic Syndromes (MDS). Genetically engineered murine models have shown that isolated mutations in the BM niche can disrupt the non-mutated hematopoietic compartment and induce MDS-like phenotypes. However, it is still unclear whether primary MDS in humans may possibly be associated with acquired mutations non-hematopoietic BM stroma cells. Although chromosomal aberrations and mutations have been described in in ex vivo expanded MSC cultures from MDS and AML patients, little validation has been performed to address whether such molecular lesions were not clonal outgrowths resulting from the strenuous and massively expansive cell culture procedures. Materials and Methods We performed whole exome sequencing on paired ex vivo expanded MSCs and native BM samples of n=98 MDS and associated myeloid neoplasia cases treated at the Department of Hematology and Oncology of the Medical Faculty Mannheim, Heidelberg University, Germany (median age 73 years, range 44-86). As controls, we included a cohort of n=28 samples from healthy subjects (median age 75 years, range 36-84). MSCs were expanded adherently on plastic dishes by seeding 5x10e6 mononuclear cells in StemMACS MSC Expansion Medium XF (Miltenyi Biotec) for a median of 34 days, (95% confidence interval 22-50d). Whole exome sequencing was carried out using Nextera DNA Flex Tagmentation kit (Illumina) with IDT xGene Research probe v1 at a median coverage at 88x with BM MNC as germline control accounting for possible LOH in the BM sample. Validation experiments were performed by deep re-sequencing of single CFU-F colonies (n=4 patients), sequencing of serial cultures (n=7 patients) and re-sequencing of primary sorted native bone marrow MSCs from n=9 patients. Results In the exome sequencing analyses of ex vivo expanded MSCs we discovered multiple recurrent mutations in MSCs of MDS patients including but not limited to genes such as ZFX (n=8/98) and RANK (n=5/98). MSCs from MDS patients displayed an overall higher mutational burden and increased replicative stress as determined by gH2AX and RPA staining, which correlated with the mutational burden and shorter telomeres as compared to healthy controls. The analysis of mutational signatures revealed that MDS MSCs were distinct compared to healthy MSCs. Furthermore, we found that MDS MSCs displayed increased senescence assessed by flow bGAL staining and associated inflammatory gene expression determined by IL6 qPCR/ELISA for n=32 cases. To investigate whether acquired mutations in MSCs were driven by the ex vivo expansion we performed individualized amplicon based deep re-sequencing of serial culture passages and different BM aspirations for n=7 patients as well as single colony re-sequencing in n=4 patient cases. Furthermore, we re-sequenced primary sorted CD45-,CD235a-,CD31+/-,CD271+/- BM cells of n=9 cases. All of these validation experiments indicated that the discovered mutations were associated with expansion in culture and but not present in clonally relevant cell populations in the primary BM in vivo. Discussion Together with previously published data of the BM niche of myeloid neoplasms, our results add to the notion that MSCs in MDS are molecularly and functionally altered. Nevertheless, our current comprehensive sequencing analyses leave little doubt that if acquired mutations in the stroma of MDS patients play a role in MDS disease initiation at all, then at such a low clonal and possibly locally confined level, that they are not detectable with currently feasible sample acquisition and methodology. In our current study, we discovered no evidence for acquired mutations in BM derived MSCs in MDS. Disclosures Schmitt: Affimed GmbH: Research Funding. Flach: Gilead: Current Employment. Hofmann: BMS: Honoraria; Amgen: Honoraria; Novartis: Honoraria. Nowak: Pharmaxis: Current holder of individual stocks in a privately-held company, Research Funding; Celgene: Honoraria; AbbVie: Other: Investigator on funded clinical trial; Tolero Pharma, Pharmaxis, Apogenix: Research Funding; Affimed: Research Funding; Takeda: Honoraria.

With age, haematopoietic stem cells lose their ability to regenerate the blood system, and promote disease development. Autophagy is associated with health and longevity, and is critical for protecting haematopoietic stem cells from metabolic stress. Here we show that loss of autophagy in haematopoietic stem cells causes accumulation of mitochondria and an activated metabolic state, which drives accelerated myeloid differentiation mainly through epigenetic deregulations, and impairs haematopoietic stem-cell self-renewal activity and regenerative potential. Strikingly, most haematopoietic stem cells in aged mice share these altered metabolic and functional features. However, approximately one-third of aged haematopoietic stem cells exhibit high autophagy levels and maintain a low metabolic state with robust long-term regeneration potential similar to healthy young haematopoietic stem cells. Our results demonstrate that autophagy actively suppresses haematopoietic stem-cell metabolism by clearing active, healthy mitochondria to maintain quiescence and stemness, and becomes increasingly necessary with age to preserve the regenerative capacity of old haematopoietic stem cells.

Tightly regulated activity of the transcription factor MYC is essential for orderly cell proliferation. Upon deregulation, MYC elicits and promotes cancer progression. Proteasomal degradation is an essential element of MYC regulation, initiated by phosphorylation at Serine62 (Ser62) of the MB1 region. Here, we found that Ser62 phosphorylation peaks in mitosis, but that a fraction of nonphosphorylated MYC binds to the microtubules of the mitotic spindle. Consequently, the microtubule-destabilizing drug vincristine decreases wild-type MYC stability, whereas phosphorylation-deficient MYC is more stable, contributing to vincristine resistance and induction of polyploidy. PI3K inhibition attenuates postmitotic MYC formation and augments the cytotoxic effect of vincristine. Implications: The spindle's function as a docking site for MYC during mitosis may constitute a window of specific vulnerability to be exploited for cancer treatment.

Separase, a cysteine endopeptidase, is a key player in mitotic sister chromatid separation, replication fork dynamics, and DNA repair. Aberrant expression and/or altered separase proteolytic activity are associated with aneuploidy, tumorigenesis, and disease progression. Since genomic instability and clonal evolution are hallmarks of progressing chronic myeloid leukemia (CML), we have comparatively examined separase proteolytic activity in TKI-treated chronic phase CML. Separase proteolytic activity was analyzed on single cell level in 88 clinical samples and in 14 healthy controls by a flow cytometric assay. In parallel, BCR-ABL1 gene expression and replication fork velocity were measured by qRT-PCR and DNA fiber assays, respectively. The separase activity distribution (SAD) value indicating the occurrence of MNCs with elevated separase proteolytic activity within samples was found to positively correlate with BCR-ABL1 gene expression levels and loss of MMR (relapse) throughout routine BCR-ABL1 monitoring. Analyses of CD34+ cells and MNCs fractionized by flow cytometric cell sorting according to their separase activity levels (H- and L-fractions) revealed that CD34+ cells with elevated separase activity levels (H-fractions) displayed enhanced proliferation/viability when compared with cells with regular (L-fraction) separase activity (mean 3.3-fold, p = 0.0011). BCR-ABL1 gene expression positivity prevailed in MNC H-fractions over L-fractions (42% vs. 8%, respectively). Moreover, expanding CD34+ cells of H-fractions showed decreased replication fork velocity compared with cells of L-fractions (p

Reciprocal RUNX1 fusions are traditionally found in up to 10% of acute myeloid leukemia (AML) patients, usually associated with a translocation (8;21)(q22;q22) corresponding to the RUNX1-RUNX1T1 fusion gene. So far, alternative RUNX1 rearrangements have been reported only rarely in AML, and the few reports so far have focused on results based on cytogenetics, fluorescence in situ hybridization, and polymerase chain reaction. Acknowledging the inherent limitations of these diagnostic techniques, the true incidence of rare RUNX1 rearrangements may be underestimated. In this report, we present two cases of adult AML, in which we detected rare RUNX1 rearrangements not by conventional cytogenetics but rather by next-generation panel sequencing. These include t(16;21)(q24;q22)/RUNX1-CBFA2T3 and t(7;21)(p22;q22)/RUNX1-USP42, respectively. In both patients the AML was therapy-related and associated with additional structural and numerical alterations thereby conferring bad prognosis. This is in line with previous reports on rare RUNX1 fusions in AML and emphasizes the clinical importance of their detection. In summary, our report not only confirms the clinical utility of NGS for diagnostics of rare reciprocal rearrangements in AML in a real-life scenario but also sheds light on the variety and complexity within AML. It further emphasizes the need for collection of additional cases for deepening insights on their clinical meaning as well as their frequency.

Bone marrow cytomorphology and histopathology are the cornerstones for the initial diagnosis of myelodysplastic syndromes (MDS) and other related myeloid disorders. They provide a rapid first insight into diagnostic categories and thus help in clinical decision making. However, difficulties in the morphologic assessment of MDS exist due to inter- and intra-observer variability. In this study, we directly compared the results of cytomorphology and histopathology obtained in a real-world diagnostic scenario in 90 patients with myeloid malignancies aiming to evaluate their validity for diagnosing and classifying various myeloid malignancies. While both techniques placed 80% of our bone marrow samples into the same diagnostic category and thus showed a good correlation, our study also demonstrates the limitations in correlating marrow cytomorphology and histopathology, even following stringent and repetitive diagnostic assessments. This was particularly true for CMML, where not only additional diagnostic tools such as molecular genetics or clinical evaluation but also the analysis of the peripheral blood smears aided in finding the correct diagnosis. Overall, our data emphasize the need for a comprehensive diagnostic review in a patient-for-patient setting when a myeloid malignancy is suspected or confirmed. We propose that the combination of cytomorphologic and histopathologic assessment with clinical, laboratory, and genetic parameters is essential in achieving high diagnostic accuracy in an interdisciplinary setting.

Genotoxic bystander signals released from irradiated human mesenchymal stromal cells (MSC) may induce radiation-induced bystander effects (RIBEs) in human hematopoietic stem and progenitor cells (HSPC), potentially causing leukemic transformation. Although the source of bystander signals is evident, the identification and characterization of these signals is challenging. Here, RIBEs were analyzed in human CD34+ cells cultured in distinct molecular size fractions of medium, conditioned by 2 Gy irradiated human MSC. Specifically, γH2AX foci (as a marker of DNA double-strand breaks) and chromosomal instability were evaluated in CD34+ cells grown in approximate (I) &lt, 10 kDa, (II) 10–100 kDa and (III) &gt, 100 kDa fractions of MSC conditioned medium and un-/fractionated control medium, respectively. Hitherto, significantly increased numbers of γH2AX foci (p = 0.0286) and aberrant metaphases (p = 0.0022) were detected in CD34+ cells grown in the (II) 10–100 kDa fraction (0.67 ± 0.10 γH2AX foci per CD34+ cell ∨ 3.8 ± 0.3 aberrant metaphases per CD34+ cell sample, mean ± SEM) when compared to (I) &lt, 10 kDa (0.19 ± 0.01 ∨ 0.3 ± 0.2) or (III) &gt, 100 kDa fractions (0.23 ± 0.04 ∨ 0.4 ± 0.4) or un-/fractionated control medium (0.12 ± 0.01 ∨ 0.1 ± 0.1). Furthermore, RIBEs disappeared after heat inactivation of medium at 75 °C. Taken together, our data suggest that RIBEs are mainly mediated by the heat-sensitive (II) 10–100 kDa fraction of MSC conditioned medium. We postulate proteins as RIBE mediators and in-depth proteome analyses to identify key bystander signals, which define targets for the development of next-generation anti-leukemic drugs.

Accumulation of DNA damage and alteration of the DNA damage response (DDR) are critical features of genetic instability that is presumed to be implicated in the pathogenesis of monoclonal B-cell lymphocytosis (MBL) and chronic lymphocytic leukemia (CLL). Here, we show increased numbers of γH2AX foci, a marker of DNA double-strand breaks (DSB), in CD19+ cells of CLL patients as compared to CD19+ cells of MBL patients and healthy individuals. Furthermore, numerous γH2AX/53BP1 foci in CLL cells suggest activation of error-prone non-homologous end-joining repair mechanisms. Signatures of DDR proteins further indicate alterations of the DDR in CLL in contrast to a largely regular activation in MBL and healthy controls. In summary, our results provide evidence for the stepwise accumulation of DNA damage in the progression of MBL towards CLL and suggest increased DNA damage, error-prone DNA repair and altered DDR signaling to be critical mechanisms of clonal evolution in MBL and CLL.

Diagnostics of acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) have recently been experiencing extensive modifications regarding the incorporation of next-generation sequencing (NGS) strategies into established diagnostic algorithms, classification and risk stratification systems, and minimal residual disease (MRD) detection. Considering the increasing arsenal of targeted therapies (e.g. FLT3 or IDH1/IDH2 inhibitors) for AML, timely and comprehensive molecular mutation screening has arrived in daily practice. Next-generation flow strategies allow for immunophenotypic minimal residual disease (MRD) monitoring with very high sensitivity. At the same time, standard diagnostic tools such as cytomorphology or conventional cytogenetics remain cornerstones for the diagnostic workup of myeloid malignancies. Herein, we summarize the most recent advances and new trends for the diagnostics of AML and MDS, discuss the difficulties, which accompany the integration of these new methods and their results into daily routine, and aim to define the role hemato-oncologists may play in this new diagnostic era.

Owing to the introduction of next-generation sequencing (NGS) new challenges for diagnostic algorithms and the interpretation of the results for therapeutic decision making in hemato-oncology have arisen. Recurrent somatic mutations crossing the borders between different hematological entities and solid neoplasms have been detected. In analogy to mutant TP53, the same mutation type may occur in myeloid, B- or T-lymphatic malignancies or solid neoplasms. At the same time, a certain mutation can show different prognostic outcomes in different entities and co-existence of certain mutations may change the prognostic relevance. These insights may spark the investigation of targeted therapies with the same substances across different disease entities. This review article summarizes mutations that can emerge in different hematologic and solid malignancies and summarizes other obstacles in the era of modern molecular diagnostics, such as the phenomenon of "clonal hematopoiesis of indeterminate potential" being difficult to interpret in the individual patient.

Introduction: Somatic mutations in genes coding for splicing factors (e.g. SF3B1, U2AF1 and SRSF2) are found in about 50% of patients with Myelodysplastic Syndrome (MDS). These mutations have been shown to frequently occur early in the mutational hierarchy of the disease making them particularly attractive therapeutic targets. Recent research has revealed an association of splicing factor mutations (sfm) with elevated levels of DNA:RNA intermediates (R-loops), which induce replication stress and downstream activation of the ataxia telangiectasia and Rad3-related protein (ATR) pathway. The aim of this work was to investigate R-loops-associated ATR signaling as a novel therapeutic concept in primary CD34+ MDS patient cells carrying sfm, and to identify possible novel options for combination therapy. Methods: Using quantitative immunofluorescence microscopy we assessed levels of R-loops in primary CD34+ bone marrow cells isolated from MDS patients (n=23) with and without sfm. In addition, we evaluated the direct association of R-loops with induction of replication stress and activation of associated signaling by analyzing replication fork progression rates and phosphorylation of ATR target proteins. Furthermore, we determined the in vitro sensitivity of mutant (n=12) and non-mutant CD34+ (n=10) cells of MDS patients towards ATR inhibitors (VE-821 and AZD6738) alone and in combination with splicing modulator Pladienolide B and investigated the impact on DNA damage accumulation and apoptosis. We also performed these experiments in cord blood derived CD34+ cells overexpressing SRSF2P95H without other MDS-associated cellular alterations. Results: We found significantly elevated levels of R-loops in CD34+ cells from MDS patients carrying sfm compared to non-splicing factor mutated (non-sfm) MDS cells and healthy controls (mean MFI= 177 (sfm) vs. 78 (non-sfm) vs. 91 (healthy), p Conclusion: Overall, our results identify ATR as a promising novel therapeutic target in MDS with splicing factor mutations and provide a preclinical rationale for combination therapy with splicing modulator drugs. Disclosures Nolte: Novartis: Honoraria, Research Funding; Celgene: Honoraria, Research Funding.

Introduction: Next generation sequencing techniques have identified a large number of MDS associated acquired molecular lesions. However, translation of these possible molecular targets into new therapeutic strategies has been lagging behind. This is also due to a lack of functional experimental models of MDS, in which new hypotheses can be evaluated pre-clinically. Xenograft models in NSG mice have emerged as versatile preclinical platforms for investigation of functional pathomechanisms in MDS ([1] Medyouf et al., 2014, [2] Rouault-Pierre et al., 2017). The limiting factor of these models is the low engraftment of patient-derived CD34+ hematopoietic stem cells (HSCs). Efficient humanized 3D scaffolds in immune-compromised mouse models have been established, enabling to increase engraftment rates of normal and malignant hematopoiesis ([3] Reinisch et al., 2016, [4] Abarrategi et al., 2017). Therefore, we evaluated engraftment ability of IPSS low-risk, int-1 and high-risk-patient samples, in four different 3D scaffolds. Methods: Currently we transplanted samples from 10 MDS patients in parallel into NSG mice testing the following conditions: A) Intrafemoral co-injection of CD34+ HSCs and MSCs according to [1]. Subcutaneous implantation of 3D scaffolds. Gelfoam (B) and Bio-OSS (C) [4], Matrigel ossicles (D) [3] and primary human bone isolated after hip replacement, inserted with Gelfoam, preseeded in vitro with MSCs and mononuclear cells (MNCs) and injected in vivo with CD34+ HSCs 8 weeks after implantation (human bone ossicles) (E). Ossicles, bone marrow (BM), peripheral blood and spleens were analyzed 12 weeks after implantation of hematopoietic cells. Results: Gelfoam and human bone ossicles showed significantly higher hCD45+cell numbers compared to intrafemoral injection analyzed by flow cytometry. Engraftment in those two conditions was similarly robust. However, Gelfoam scaffolds showed higher percentual engraftment levels ranging up to 70% as compared to human bone ossicles ranging from 0.2% to 27%. Interestingly, we found systemic engraftment of hCD45+cells outside the injected bone fragment in the BM, peripheral blood and spleen solely in mice, which received human bone ossicles. In all other methods, hCD45+ cells could only be detected within the ossicles themselves. This result could possibly be explained due to transplantation of MNCs in this condition. That hypothesis was supported by another set of experiments using human bone ossicles (n=10), which showed that colonization of the scaffold was similar when transplanting either CD34+ cells + MSCs, MNCs+MSCs or MNCs only but systemic engraftment could only be seen in MNC transplanted mice. Conclusion: Our data show that hCD45+cells and MSCs from MDS BM were able to colonize humanized ossicle scaffolds. Gelfoam and human bone ossicles were the most promising novel methods to improve MDS xenograft models. For systemic engraftment, application of MNCs seems to be necessary. Disclosures Nolte: Novartis: Honoraria, Research Funding; Celgene: Honoraria, Research Funding.

Malignant hematopoietic cells of myelodysplastic syndromes (MDS)/chronic myelomonocytic leukemias (CMML) and acute myeloid leukemias (AML) may be particularly vulnerable to inhibition of poly(ADP ribose) polymerase 1/2 (PARP1/2) and apurinic/apyrimidinic endonuclease 1 (APE1). PARP1/2 and APE1 are critical enzymes involved in single-strand break repair and base excision repair, respectively. Here, we investigated the cytotoxic efficacy of talazoparib and APE1 inhibitor III, inhibitors of PARP1/2 and APE1, as single-agents, combined with decitabine and combined with each other in CD34+ MDS/CMML cells and in CD34+ or CD34- AML cells in comparison to healthy CD34+ donor cells. The surviving fraction of CD34+ MDS/CMML cells (n = 8; 4 MDS and 4 CMML), CD34+ or CD34- AML cells (n = 18) and healthy CD34+ donor cells (n = 8) was analyzed using the CellTiter-Glo luminescent cell viability assay (Promega, Southampton, UK). Cell proliferation of untreated MDS/CMML and AML cells was determined by trypan blue exclusion assay (Merck, Darmstadt, Germany). PARP1/APE1 mRNA expression was evaluated using validated primer sets for PARP1 (Hs_PARP1_1_SG QuantiTect Primer Assay, NM_001618) and APE1 (Hs_APEX1_1_SG QuantiTect Primer Assay, ENST00000216714) (Qiagen, Hilden, Germany). Immunofluorescence microscopy of γH2AX foci was performed using a JBW301-derived mouse monoclonal anti-γH2AX antibody (Merck). Talazoparib and APE1 inhibitor III demonstrated critical anti-leukemic efficacy as single-agents in about 19-25% of MDS/CMML/AML cell samples (Figure 1A and B). Low doses of talazoparib and APE1 inhibitor III further increased the cytotoxic efficacy of decitabine in about 78-86% of MDS/CMML/AML cell samples. Moreover, low doses of APE1 inhibitor III increased the cytotoxic efficacy of talazoparib in about 68% of MDS/CMML/AML cell samples. In summary, talazoparib and APE1 inhibitor III demonstrated substantial anti-leukemic efficacy as single-agents, in combination with decitabine and combined with each other. Hence, our findings support further investigation of these agents in sophisticated clinical trials. Figure 1 Cytotoxic efficacy of talazoparib and APE1 inhibitor III in healthy CD34+ donor cells, in CD34+ myelodysplastic syndrome (MDS)/chronic myelomonocytic leukemia (CMML) cells and in CD34+ or CD34- acute myeloid leukemia (AML) cells after 3 days of treatment. (A) The mean IC50 of talazoparib was significantly lower (*p = 0.016) in 1 MDS (MDS#2), 1 CMML (CMML#2) and 3 AML cell samples (AML#1, AML#2, AML#3) as compared to 8 healthy donor cell samples. (B) The mean IC50 of APE1 inhibitor III was substantially lower (p = 0.059) in 1 MDS (MDS#2) and 5 AML cell samples (AML#1, AML#2, AML#3, AML#6, AML#12) as compared to 8 healthy donor cell samples. Figure 1 Disclosures Fabarius: Novartis: Research Funding.

The accumulation of DNA damage and the alteration of the DNA damage response (DDR) are critical features of genetic instability that is presumed to be implicated in BCR/ABL1-mediated blastic transformation of chronic myeloid leukemia (CML). The aim of our study was to analyze underlying mechanisms of genetic instability with regard to DNA damage such as DNA double-strand breaks (DSB), DSB repair and DDR signaling during blastic transformation of CML. Immunofluorescence microscopy of γH2AX was performed for quantification of DSB in peripheral blood mononuclear cells (PBMC) of 8 healthy individuals, 24 chronic phase (CP)-CML patients under current/discontinued tyrosine kinase inhibitor (TKI) treatment (21 patients in deep molecular response (DMR), 3 patients in major molecular response (MMR)), 5 CP-CML patients under current/discontinued TKI treatment with loss of MMR, 3 de novo non-treated CP-CML patients and 2 blast phase (BP)-CML patients. In addition, immunofluorescence microscopy of γH2AX/53BP1 was used for semi-quantification of error-prone DSB repair. Furthermore, immunoblotting of p-ATM, p-ATR, p-CHK1, p-CHK2 and p-TP53 was performed in PBMC of CML patients in comparison to PBMC of healthy individuals. Our analysis revealed an increase in numbers of γH2AX foci in PBMC of CP-CML patients under current/discontinued TKI treatment with loss of MMR (1.8 γH2AX foci per PBMC ± 0.4), in PBMC of de novo non-treated CP-CML patients (2.3 γH2AX foci per PBMC ± 0.7) and in PBMC of BP-CML patients (4.9 γH2AX foci per PBMC ± 0.9) as compared to the number of γH2AX foci in PBMC of healthy individuals (1.0 γH2AX foci per PBMC ± 0.1) and in PBMC of CP-CML patients under current/discontinued TKI treatment in DMR/MMR (1.0 γH2AX foci per PBMC ± 0.1) (Figure 1A and B). Analysis of co-localizing γH2AX/53BP1 foci in PBMC suggested progressive activation of error-prone nonhomologous end-joining repair mechanisms during blastic transformation in CML. Signatures of p-ATM, p-ATR, p-CHK1, p-CHK2 and p-TP53 indicated alterations of the DDR. In summary, our data provide evidence for an accumulation of DNA damage in PBMC of CML patients towards BP-CML patients. We hypothesize that ongoing DSB generation, error-prone DSB repair and DDR alterations might be critical mechanisms of blastic transformation in CML. Figure 1 Analysis of γH2AX foci in freshly isolated peripheral blood mononuclear cells (PBMC) of healthy individuals and chronic myeloid leukemia (CML) patients. (A) Exemplary immunofluorescence microscopic images of γH2AX foci (green, Alexa 488) and cell nuclei (blue, DAPI) in PBMC of a healthy individual (HEALTHY#3), a chronic phase CML patient with a deep molecular response to tyrosine kinase inhibitor (CP-CML DMR#16), a de novo non-treated chronic phase CML patient (CP-CML#1) and a blast phase CML patient (BP-CML#2). (B) γH2AX foci levels in PBMC of healthy individuals and in PBMC of CML patients. Figure 1 Disclosures Saussele: Pfizer: Honoraria; Novartis: Honoraria, Research Funding; Incyte: Honoraria, Research Funding; BMS: Honoraria, Research Funding. Fabarius:Novartis: Research Funding.

Blood production is ensured by rare, self-renewing haematopoietic stem cells (HSCs). How HSCs accommodate the diverse cellular stresses associated with their life-long activity remains elusive. Here we identify autophagy as an essential mechanism protecting HSCs from metabolic stress. We show that mouse HSCs, in contrast to their short-lived myeloid progeny, robustly induce autophagy after ex vivo cytokine withdrawal and in vivo calorie restriction. We demonstrate that FOXO3A is critical to maintain a gene expression program that poises HSCs for rapid induction of autophagy upon starvation. Notably, we find that old HSCs retain an intact FOXO3A-driven pro-autophagy gene program, and that ongoing autophagy is needed to mitigate an energy crisis and allow their survival. Our results demonstrate that autophagy is essential for the life-long maintenance of the HSC compartment and for supporting an old, failing blood system. © 2013 Macmillan Publishers Limited. All rights reserved.