Welcome to the MDS 2023 Congress Calendar

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Myelodysplastic syndromes (MDS) and systemic inflammatory and autoimmune diseases (SIADs) have been linked in individual patients and in the literature series for years. Studies have found autoimmune disease (or its therapy) is a risk factor for the development of MDS, but MDS may also be an instigator of autoimmune disease. The associated inflammatory conditions seen include thyroid disease, neutrophilic dermatoses, polyarthritis, connective tissue diseases, vasculitis, and autoimmune cytopenias, to name a few. Epidemiology studies examining disease risk in MDS with and without comorbid autoimmune illness are inconsistent. MDS pathophysiology is tightly linked to excessive inflammatory activity in the bone marrow microenvironment, which may promote SIAD directly or by stimulation of the adaptive immune response. Alternatively, SIADs may promote clonal evolution and disordered marrow growth, nourishing the development of myeloid malignancy. Finally, immunosuppressant therapies used in autoimmune diseases have also preceded diagnoses of therapy-related myeloid neoplasms, including MDS. The recently discovered VEXAS syndrome, which is caused by a mutation affecting myeloid-restricted cells and manifests with both myelodysplasia and autoinflammation, may give insight into this biologic possibility. In this session, Dr. DeZern will review our current knowledge on the epidemiology, pathophysiology, and management of SIAD associated with MDS.

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Somatic UBA1 mutations have recently been recognized as the cause of an inflammatory-hematologic overlap disease called VEXAS (vacuoles, E1, X-linked autoinflammatory, somatic) syndrome. Patients with VEXAS syndrome are frequently diagnosed with myelodysplastic syndrome (MDS) and multiple myeloma and in addition have severe, systemic inflammation. UBA1 is the primary E1 enzyme required for initiating the majority of ubiquitylation in the cell, most disease-causing mutations occur at the start codon for the cytoplasmic isoform of the protein (p.Met41). These mutations lead to an isoform swap with loss of the normally active UBA1b (initiated from p.Met41) and emergence of a new catalytically impaired short isoform UBA1c specifically in mutated cells (initiated from p.Met67). Despite extensive investigation into the clinical manifestations of UBA1 mutations, very little is known about the mechanism of disease.

Here, we will outline the identification and molecular dissection of novel somatic mutations in UBA1 that lead to VEXAS syndrome. The majority of these mutations were identified through unbiased screening of exome sequencing data of patients with clinical manifestations similar to VEXAS syndrome but without a known pathogenic mutation. We systematically characterized these novel UBA1 mutations, and found that only p.Met41 mutations led to a loss of UBA1b levels and production of UBA1c, while all other variants did not alter isoform expression. Instead, these mutations reduce catalytic function of both cytoplasmic and nuclear isoforms through interfering with ATP binding, rendering the enzyme thermolabile, or specifically impairing the transfer of ubiquitin from UBA1 to the E2 enzyme. These results demonstrate that VEXAS disease causing mutations lead to a global loss of ubiquitylation through differing mechanisms. Finally, we will provide an update about the aberrant signaling leading to bone marrow failure and inflammation in VEXAS syndrome using patient cells, cell culture systems and animal models. This work will focus on single cell RNA sequencing studies in VEXAS syndrome and our preliminary data using mouse models of VEXAS syndrome. Together our work demonstrate the importance of proper levels of global ubiquitylation for bone marrow physiology.

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In this presentation, I will focus on the genetic characterization and clinical associations of clonel hematopoiesis (CH) in persons without known hematologic disease. Initial studies, often using genome-wide sequencing techniques, found somatic mutations indicative of CH in roughly 10-20% of persons aged 70y or older. More recent studies using more sensitive sequencing techniques, however, indicate that CH is much more common and may, in fact, be near-universal in older adults. For example, in a cohort of 200 patients without known hematologic disease who were undergoing total hip arthroplasty, we detected CH in 50% of subjects. I will review the associations of CH with hematologic and non-hematologic diseases found in these and other cohorts. Importantly, while the mutational landscape of CH in peripheral blood (PB) has been well characterized, detailed analyses addressing its spatial and cellular distribution in the bone marrow (BM) compartment are relatively sparse. Our cohort of indivuals undergoing hip replacement surgery offered us a chance to study CH driver mutations across different anatomical and cellular compartments. Initial data from this and other series suggest that CH may show intra-patient spatial heterogeneity, pointing to a potentially localized origing and early evolution of CH in the marrow niche.

While the absolute risk of progression from CH to overt myeloid neoplasia (most commonly MDS or AML) is low, our group has also shown that persistence of clonal hematopoiesis is very common in AML patients who achieve remission after induction chemotherapy. In the second part of my presentation, I will briefly summarize our recent data on CH and its clinical relevance in AML long-term surivors.

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Profound immune dysregulation is an increasingly recognized feature of myelodysplastic neoplasms (MDS), contributing to ineffective hematopoiesis and driving disease progression. Immune dysregulation in MDS is highly complex and composed of many interdependent factors, including clonal hematopoietic cells with somatic mutations providing faulty signals to the immune system and altered cells of the bone marrow microenvironment contributing to inflammation and immunosuppression. IST with antithymocyte globulin (ATG, either horse or rabbit), with or without addition of cyclosporine (CSA), has been evaluated for treatment of low-risk MDS in a number of phase II clinical trials with small numbers of patients and response rates ranging from 16% to 67%. Several novel agents are under investigation that target cell-intrinsic innate immune pathways, such as the TLR axis. Blocking NLRP3 inflammasome signaling is another appealing cell-intrinsic approach, given its importance in MDS pathogenesis. Immunotherapeutic approaches have also been tried in MDS (eg, checkpoint inhibitors), with disappointing overall response rates. However, targeting macrophage activity with an anti-CD47 antibody (magrolimab) and 5-azacitidine is promising. Immune modulatory approaches show therefore high promise in the treatment of MDS. Given the heterogeneity of the disease, both in terms of risk stratification as well as highly variable genetic traits and the type of immune dysregulation present, it will be of utmost importance to correctly identify which patients will most likely benefit from which approach.

Background And Aims

Chronic inflammation increases the risk of cancer. Despite growing evidence that chronic inflammation plays a role in myelodysplastic syndromes (MDS), innate immune and inflammatory signaling pathways underlying MDS pathogenesis remain poorly defined. We aim to characterize the role that chronic inflammation plays in MDS pathogenesis and the molecular mechanisms involved.

Methods

We conducted a series of in vitro, in vivo, and in silico experiments using Tet2-deficient mice and a human MDS cell line to study the biology of hematopoietic stem and progenitor cells (HSPCs) under chronic inflammation. Bioinformatic analyses of RNA sequencing results from our mouse model and a gene expression dataset from MDS patients were performed to characterize the molecular basis.

Results

We find that mice lacking Tet2 develop a hyper-inflammatory status, which is further upregulated by LPS-induced chronic inflammation. Chimeric mice transplanted with bone marrow cells isolated from LPS-treated Tet2-deficient mice exhibit early onset of MDS phenotypes and a significantly shorter life span. Chronic inflammation further promotes the self-renewal and myeloid differentiation of Tet2-deficient HSPCs in the short term but accelerates HSC exhaustion in the long run. Transcription profiling and subsequent bioinformatic analyses reveal upregulation of the Nlrc4 inflammasome in our mouse model and human CD34+ cells from MDS patients harboring TET2 mutations. The effects of Nlrc4 deletion and Nlrc4 inhibition on MDS development are under evaluation.

Conclusions

The Nlrc4 inflammasome signaling pathway serves as a mechanistic basis for the inflammatory component of MDS pathogenesis in Tet2-deficient HSPCs. Our findings have the potential to open up new avenues for MDS therapeutics.

Background And Aims

Background: The alteration of hematopoiesis in MDS patients is deeply associated with microenvironment alterations, in particular in MSCs. Notably, dysfunctions of MDS-MSCs persist following expansion ex vivo suggesting a hereditable epigenetic dysregulation which endures despite removal of disease-associated microenvironment factors.

Aims: Investigating the role of histone H2A variant MacroH2A1 (mH2A1) in promoting MDS-MSC alterations.

Methods

MSCs were collected from BM of MDS patients and matched healthy controls (HC).

Results

MDS patients had significant higher signature of mH2A1 in bone marrow slides and in MSCs. TLR4 also was upregulated and positively correlated to mH2A1 expression. To better investigate the relationship between mH2A1 and TLR4 in MDS- MSCs, we induced mH2A1 overexpression in HS-5 cells (mH2A1-OE) by mH2A1-CT-MYC plasmid. MH2A1-OE upregulated TLR4 and increased NFkB nuclear translocation. Proteomic analysis confirmed upregulation of inflammatory pathways. Moreover, several proteins associated to hypermethylation of DNA and histones. HPLC analysis confirmed higher SAM/SAH ratio in mH2A1-OE and 5-mC resulted also augmented. MH2A1-OE also acquire a more glycolytic metabolism characterized by decreased levels of NAD+/NADH and upregulation of LDHA. Interestingly, nuclear localization of LDHA was found associated to histone hypermethylation. Nuclear LDHA was also observed in MDS-MSC. Finally, coculturing healthy mH2A1-OE MSCs with CD34⁺ cells, we found a significative impairment of hematopoietic supporting capacity. Finally, we treated ex-vivo HC- and MDS-MSCs with azacytidine founding a significant reduction both of mH2A1 and TLR4.

Conclusions

Our findings establish that macroH2A1 is a key driver for the inflammatory, epigenetic, and metabolic regulation of MSC activity in MDS microenvironment.