SLF2 and SMC5 dysfunction drives HSC aging and predisposes to MDS, defining a new inherited bone marrow failure syndrome.

Rare inherited bone marrow failure syndromes with cancer predisposition associated with SRP72, SH2B3, MYSM1 and CBL variants: a literature review and case series

Introduction. Inherited bone marrow failure syndromes (IBMFS) comprise a heterogeneous group of hereditary disorders characterized by impaired hematopoiesis and an increased risk of myelodysplastic syndrome, acute myeloid leukemia, and other malignancies. Rare forms of IBMFS present a particular clinical challenge because they may manifest as isolated cytopenia, a myeloproliferative phenotype, or a syndromic disorder with early clonal evolution. Materials and methods. We analyzed five male patients with rare inherited bone marrow failure syndromes. All the patients had undergone comprehensive molecular genetic testing. Clinical manifestations, molecular genetic and cytogenetic findings, indications for allogeneic hematopoietic stem cell transplantation (HSCT), and treatment outcomes were evaluated. Results. Variants in SRP72 were identified in 2 patients, SH2B3 in 1 patient, MYSM1 in 1 patient, and combined CBL and STAG2 alterations also in 1 patient. The age at disease onset ranged from the first months of life to 9 years (median – 61 months), whereas the median age at diagnosis verification was 10 years, indicating a substantial diagnostic delay. The most unfavorable disease course was observed in the patient with MYSM1 deficiency who had developed monosomy 7, del(5q) and myelodysplastic syndrome with subsequent transformation to acute myeloid leukemia, and ultimately died of disease progression. HSCT was performed in two patients with SRP72 variants, with one patient still alive and the other one deceased. Conclusion. Our findings highlight the importance of early molecular genetic testing in children with persistent hematopoietic abnormalities, along with regular cytogenetic surveillance and timely referral of high-risk patients for HSCT.

SRSF2 mutations contribute to bone marrow immune microenvironment alterations

Somatic SRSF2 mutations are early lesions in myelodysplastic syndromes (MDS) and chronic myelomonocytic leukemia (CMML), yet how they contribute disease remain unclear. In this study, we generated two murine models that have not yet developed overt MDS/CMML-like phenotypes: (i) a cell-derived xenograft (CDX) by tail-vein injection of stable BA/F3- KRAS G12C - SRSF2 P95H cells and (ii) a Vav1-Cre conditional knock-in mouse heterozygous for Srsf2 P95H . Molecular assays, bulk RNA-seq, and single-cell RNA-seq (scRNA-seq) were used to profile the bone-marrow (BM) microenvironment. CDX mice carrying SRSF2 P95H displayed systemic immune dysregulation. Bulk RNA-seq of Vav1-Cre BM revealed attenuated T cell chemotaxis and elevated immunoglobulin production in Srsf2 P95H/WT animals. Extensive mis-splicing of spliceosomal, epigenetic, and cytoskeletal regulators ( Hnrnpa2b1, Rsrp1, H2az1, Erbin, Akap13 ) was also detected. scRNA-seq demonstrated a reduction in hematopoietic stem and progenitor cells (HSPCs) and an expansion of neutrophil precursors in Srsf2 P95H/WT mice, verifying by flow-cytometry assay. A loss of Natural killer (NK) cells and effector T cells, together with a shift of the B-cell lineage from early precursor states toward more mature and transcriptionally active populations were detected in Srsf2 P95H/WT group, accompanied by enrichment of antibody secretion–related programs. Sanger sequencing confirmed the presence of Srsf2 mutations in this B-cell subset and showed altered expression and alternative splicing of Hnrnpa2b1 , a well-studied target of SRSF2 with P95 mutation. Collectively, these findings suggest that the Srsf2 P95H/WT mutation contributes to the altered hematopoietic lineages composition and immune-related cellular states in BM, providing insights into its potential involvement in early-stage MDS and CMML progression.

Bone Marrow Failure Syndromes: Clinical and Genetic Characterization in TERT-associated Dyskeratosis Congenita.

KRAS G12D Blocks Erythroid Differentiation and Promotes Inflammatory Pathways at the Single Cell Level in Myeloid Malignancies 2251571

Myeloid neoplasms (MN) are characterized by myeloid blast expansion that blocks hematopoietic differentiation and causes cytopenia, a major cause of morbidity and mortality. KRASG12D mutations occur in up to 15% of MN, are enriched in therapy-resistant disease, and are linked to poor prognosis. Currently, no precision medicine strategies exist for KRASG12D-mutant MN. Progress has been limited by the lack of representative models and difficulty distinguishing KRAS-mutant from wildtype cells in patient samples. To address this, we used Genotyping of Transcriptomes (GoT), which co-captures single cell RNA-seq and mutational status within the same thousands of individual cells to elucidate specific KRASG12D-driven pathways in preleukemic Clonal Hematopoiesis (CH) and 3 Acute Myeloid Leukemia (AML) patient samples. We also developed a novel transplantable AdenoCreLox KRASG12D mouse model. In AML, mutant cells formed a distinct inflammatory, stem/progenitor-like population with elevated CD83 expression and quiescent features. In vitro, KRASG12D CD83+ cells displayed higher stemness and reduced differentiation compared to CD83− cells. An isolated KRASG12D CH sample revealed mutant cell overrepresentation in the myeloid lineages, specifically monocytes and erythrocytes. Treatment with a KRASG12D-specific inhibitor (MRTX1133) restored wildtype erythroid differentiation and downregulated inflammatory genes, including CD83. Lastly, a KRASG12D mouse model mimicking human disease with extramedullary granulocytic tumors was developed, where CD83 marked mutant cells. Resolution of these phenotypes was achieved with MRTX1133 treatment. Therefore, KRASG12D drives erythroid differentiation block, monocytic bias, and inflammation, which MRTX1133 reverses. We identify a novel quiescent CD83+ KRASG12D progenitor population in AML and demonstrate the therapeutic potential of MRTX1133 in vivo. Additionally, targeting CD83+ quiescent cells may prevent AML progression in KRASG12D patients. n/a Immune Mechanisms of Human Disease (HUM)

Tet2 deficiency drives age-related heterogeneous progression of myeloid neoplasms through epigenetic-immune microenvironment imbalance

Tet2 dysfunction drives myeloid neoplasm initiation and progression, yet the mechanisms underlying disease heterogeneity, age-dependent progression and immune microenvironment perturbation remain poorly understood. This study aimed to establish a hematopoietic specific Tet2 conditional knockout mouse model to elucidate these core mechanisms and recapitulate clinical features of Tet2 mutated myeloid neoplasms. We generated Mx1-Cre-mediated haematopoietic-specific Tet2 conditional knockout mice on a C57BL/6JGpt background using CRISPR-Cas9 and Cre-LoxP technologies. Haematopoietic phenotypes, pathological features and immune microenvironment dynamics were systematically characterised in 5- and 12-month-old mice, with wild-type littermates as controls. Statistical analyses were applied for intergroup comparisons of phenotypic and immunological indices. Tet2 deficiency induced myeloid neoplasms with distinct age-dependent progression. Five-month-old mice exhibited mild hematological abnormalities without overt pathology, whereas 12-month-old mice developed typical myeloid neoplasm phenotypes including pancytopenia, splenomegaly, myelodysplasia, with heterogeneous subtypes spanning myelodysplastic syndrome, myeloproliferative neoplasm and acute myeloid leukemia. These mice were also accompanied by severe immune dysregulation. Mechanistically, Tet2-deficient bone marrow established an immunosuppressive niche characterised by M2-like macrophage polarisation and a skewed CCR4 ligand profile with elevated CCL22 and diminished CCL17, which selectively recruited Foxp3⁺ regulatory T cells. Concurrently, serum cytokine profiling revealed broad immune activation spanning Th1-type, Th2-type and Th17-type responses. Male mice exhibited significantly accelerated disease progression compared with females. Tet2 deficiency drives myeloid neoplasm progression through the synergy of epigenetic dysregulation, age-related hematopoietic stem cell damage and immune microenvironment imbalance. This model recapitulates core clinical features of elderly Tet2-mutated myeloid neoplasms and provides a preclinical platform for mechanistic investigation and the development of epigenetic and immune-targeted precision therapies.

Premature senescence impairs hematopoietic stem cell function during sickle cell disease in mice and humans

Sickle cell disease (SCD) is a blood disorder affecting millions worldwide. Emerging evidence reveals that SCD pathophysiology increases the risk of myeloid malignancies and hematopoietic stem cell (HSC) dysfunction, likely due to chronic stress on bone marrow (BM). To investigate this further, we interrogated BM hematopoietic stem and progenitor cells (HSPCs) from mice and individuals with SCD and observed molecular signatures of chronic cellular stress including oxidative stress, DNA damage, and hallmarks of senescence. Consistent with these findings, SCD HSPCs displayed transcriptomic dysregulation of senescence-associated molecular programs and showed diminished mitogen response with prolonged cell cycle kinetics during time-lapse live cell imaging. SCD mice displayed a marked loss of immunophenotypic BM HSPCs by flow cytometry and functional blood repopulating HSPCs in transplantation studies, whereas human SCD BM HSPCs exhibited poor ex vivo hematopoietic colony forming ability, and these phenotypes were reversed following senescence-targeting therapy with either ABT-263 (Navitoclax) or the combination of dasatinib and quercetin (DQ). Thus, treatment with senescence-targeting therapy improves BM HSPC function in vivo in mice and ex vivo in cells from individuals with SCD and could represent a possible strategy to improve HSPC health, promote manufacture of high quality bespoke clinical products, and potentially enhance the safety of potentially curative gene therapies utilizing autologous HSPCs from individuals with SCD.