Aaron D. Viny

STAG2 is the most frequently mutated cohesin gene in myeloid neoplasms, yet the significance of multiple mutations within this X-linked tumor suppressor remains unknown. We analyzed a cohort of 1,967 adult patients with myeloid neoplasms and identified 233 cases (12%) harboring STAG2 mutations, including 38 cases (16%) with multiple STAG2 hits. Patients with multi-hit STAG2 mutations exhibited increased multilineage dysplasia compared with single-hit cases and experienced inferior overall survival, an effect driven primarily by patients with myelodysplastic syndromes (MDS). To investigate the molecular basis of recurrent STAG2 acquisition, we performed long-read sequencing in representative cases with phaseable STAG2 mutations. In the informative case examined, distinct truncating STAG2 mutations did not co-occur on the same DNA molecule, supporting independent acquisition rather than stepwise allelic inactivation. Cohort-level variant allele frequency patterns were consistent with recurrent evolutionary targeting of STAG2 across related clonal populations. Together, these findings support a model in which multi-hit STAG2 mutations arise through convergent evolution and define a biologically distinct, adverse-risk subset of MDS. Key points: Multi-hit STAG2 mutations identify a high-risk subset of MDS characterized by increased multilineage dysplasia and inferior survival. Long-read sequencing supports convergent evolutionary acquisition of STAG2 mutations rather than stepwise allelic inactivation.

Long-term survival in breast cancer is often limited by metastatic recurrence arising from disseminated cancer cells that persist in a dormant state. The mechanisms that enable these dormant cells to survive and subsequently reawaken remain incompletely understood. Here an unbiased genome-scale genetic screen identified Med4 as a cancer cell-intrinsic gatekeeper in metastatic reactivation. Correspondingly, MED4 haploinsufficiency was found to be prevalent in metastatic breast cancer and associated with poorer clinical outcomes. Syngeneic mouse metastasis models revealed that MED4 enforces metastatic dormancy. Mechanistically, and unexpectedly given the canonical role of the Mediator complex in transcriptional activation, MED4 suppresses enhancer priming (H3K4me1) and activation (H3K27ac). Loss of a single Med4 allele disrupts enhancer poise, leading to extracellular matrix remodelling and integrin-mediated mechanotransduction programmes that ultimately drive metastatic outgrowth. Together, these findings establish MED4 as a key regulator of breast cancer cell dormancy and nominate MED4 haploinsufficiency as a potential predictive biomarker for patients at high risk of metastatic relapse.

We hypothesized that a time‐limited frontline treatment strategy with abbreviated chemoimmunotherapy followed by targeted consolidation could achieve durable disease control with manageable toxicity in CLL. We evaluated the safety and efficacy of short‐course bendamustine/rituximab (BR) induction followed by venetoclax/rituximab (VR) consolidation. In a multicenter, single‐arm Phase 2 trial (NCT03609593), previously untreated CLL/SLL needing therapy received BR for three 28‐day cycles followed by venetoclax ramp‐up to 400 mg daily plus rituximab every 28 days for six cycles; venetoclax continued to 12 cycles (total treatment, 15 months). The primary endpoint was overall response rate (ORR); key secondary endpoints included uMRD, PFS/OS, and safety per CTCAE v4. Forty‐two patients were enrolled (median age 61.5 years; 64% unmutated IGHV; 29% complex karyotype; 10% TP53 aberrancy); 93% completed all planned therapy. At end of treatment, ITT ORR was 86% (CR/CRi 64%, PR 21%); among efficacy‐evaluable patients, ORR was 100% (CR/CRi 75%). End‐of‐therapy uMRD was achieved by 83% in bone marrow and 84% in blood among efficacy‐evaluable patients. Three‐year PFS and OS were 87.5% and 92.7%. TLS risk was downstaged after BR, and no TLS events occurred. Febrile neutropenia occurred in 12% of patients. Two on‐study deaths due to COVID‐19 occurred; no Richter transformation occurred. Time‐limited BR‐VR achieved high uMRD rates and durable remissions with a manageable safety profile. While the treatment landscape in CLL has largely shifted toward chemotherapy‐free regimens, these data demonstrate the biological proof‐of‐concept that limited induction chemotherapy can effectively mitigate TLS risk and facilitate safe outpatient ramp‐up of venetoclax.

The transcription factor GATA1 has pleiotropic hematopoietic functions, particularly in erythroid and megakaryocytic ontogeny. While mechanistic investigations have uncovered many facets of GATA1 biology, how GATA1 co-regulates divergent cell fates remains incompletely characterized. We previously described that loss of Stag2, a member of the cohesin complex and a recurrent mutational target in myelodysplastic syndrome (MDS) and myeloid leukemia of Down Syndrome, results in altered chromatin accessibility, transcription factor function, and cell differentiation. Hence, we hypothesized that chromatin accessibility determines GATA1 cistrome specificity and lineage fate decisions. To understand the connection between chromatin accessibility and GATA1, we comprehensively studied erythropoiesis in Stag2∆ mice. Defects in Stag2-deficient hematopoiesis included reduced numbers of erythroid progenitors (EryPs), impaired terminal erythroid differentiation, increased number of MkPs, and increased megakaryocytes. RNA- and ATAC-sequencing of EryPs revealed altered patterns of Gata1 target gene expression with altered accessibility in conjunction with loss of expression of erythroid targets and gain of megakaryocyte targets. Despite unchanged Gata1 expression, Gata1 occupancy was reprogrammed from erythroid to megakaryocyte targets with Fli1 motifs enriched at Stag2∆ Gata1 binding sites. Functionally, we observed that Stag2-deficient EryPs have diminished erythroid output and augmented megakaryocyte output in orthogonal differentiation assays, which was partially reversed with Fli1 knockdown. Human models and primary MDS patients recapitulated the essential phenotypic and molecular features of our in vivo murine MDS model. Collectively, this study establishes chromatin accessibility as a determinant of transcription factor binding specificity, revealing an accessibility-driven Gata1 retargeting mechanism underlying MDS dyserythropoiesis.

Background: Adolescents and young adults (AYAs) with acute lymphoblastic leukemia (ALL) represent a unique population. Treatment regimens can vary significantly depending on whether they receive care in a pediatric or in an adult setting. They also have distinctive care needs, social risk factors, and disease behavior compared to other age groups. Objective: These evidence-based guidelines of the American Society of Hematology (ASH) are intended to support patients, clinicians and other health care professionals in their decisions about the frontline management of ALL in AYAs. Methods: ASH formed a multidisciplinary guideline panel including hematologists, AYA psychosocial care specialists, pharmacists, methodologists, and patient representatives with efforts to minimize bias from conflicts of interest. An evidence review team at Brown University supported guideline development, including performing systematic evidence reviews up to November 2023. The panel prioritized clinical questions and outcomes according to importance for clinicians and patients. The panel used Grading of Recommendations Assessment, Development and Evaluation (GRADE), including GRADE Evidence-to-Decision frameworks, to assess evidence and make recommendations, which were subject to public comment. Results: The panel agreed on 15 recommendations and several good practice statements. Conclusions: Pediatric-inspired regimens containing asparaginase are recommended as frontline therapy compared to more traditional adult-inspired protocols, requiring significant supportive care and close follow up. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) isn't routinely recommended in first remission (CR1) but may be indicated for higher risk subsets or those with suboptimal responses to initial therapy. The use of targeted agents in frontline therapy is increasingly supported, though further research is needed to optimize this strategy.

The transcription factor GATA1 has pleiotropic hematopoietic functions, particularly in erythroid and megakaryocytic ontogeny. While mechanistic investigations have uncovered many facets of GATA1 biology, how GATA1 co-regulates divergent cell fates remains only partially characterized. We previously described that loss of Stag2, a member of the cohesin complex and a recurrent mutational target in myelodysplastic syndrome and Down Syndrome associated acute megakaryoblastic leukemia, results in altered chromatin accessibility, transcription factor function, and cell differentiation. Hence, we hypothesized that chromatin accessibility facilitates lineage specificity of GATA1, thereby permitting efficient cellular differentiation. To understand the connection between chromatin accessibility and GATA1, we performed comprehensive studies of erythropoiesis in Stag2 ^Δ mice. Defects in Stag2-deficient hematopoiesis included reduced numbers of erythroid progenitors (EryPs), impaired terminal erythroid maturation, increased number of MkPs, and increased megakaryocytes. RNA- and ATAC-sequencing of EryPs revealed altered patterns of Gata1 target gene expression with altered accessibility in conjunction with loss of expression of erythroid targets and gain of megakaryocyte targets. Gata1 occupancy was lost at erythroid targets, while occupancy increased at megakaryocyte targets. Functionally, we observed that Stag2-deficient EryPs have diminished erythroid output and augmented megakaryocyte output in orthogonal differentiation assays. Human models and primary MDS patients recapitulated the essential phenotypic and molecular features of our in vivo murine MDS model. Collectively, this study advances the understanding of the interplay between TF function and chromatin accessibility. Moreover, these data suggest a novel conceptual paradigm of dyserythropoiesis in MDS. Key Points: xxxxx

Transcription factors (TFs) influencing cell fate can be dysregulated in cancer. FLI1 is crucial for hematopoietic stem/progenitor cell (HSPC) function, with STAG2 regulating FLI1 target accessibility. STAG2 depletion enhances HSPC self-renewal, but its role in leukemic transformation is unclear. We uncovered that STAG2 loss maintains FLI1 target accessibility in murine HSPCs and enhances FLI1 binding in NPM1c leukemia. In our Stag2/Npm1c/+ murine model, myeloid-biased HSPCs with increased FLI1 accessibility are reservoirs for transformation, leading to a fully penetrant leukemia. STAG2 deleted NPM1c cell lines exhibit increased chromatin accessibility and chromatin-looping of key stem and leukemia genes including FLI1-target genes CD34 and MEN1. Similarly, enrichment for a CD34+ immunophenotype was observed in co-mutant leukemia patients. STAG2 deficient cells show increased chromatin-bound MENIN and increased sensitivity to MENIN inhibition. Our findings demonstrate that altered chromatin architecture can co-opt oncogenic TF signaling, such as FLI1, as a hallmark of leukemogenesis. Key Findings: Loss of STAG2 results in aberrant increased accessibility at FLI1 targets in mouse and human hematopoietic stem and progenitor cells Increased accessibility results in an increased fraction of chromatin-bound FLI1, which overlap with NPM1c targets in STAG2 NPM1c AML cells Stag2 Npm1c co-mutation leads to dysplastic murine AML phenotype arising from myeloid biased progenitors that exhibit increased Fli1 target accessibility In addition to higher chromatin-bound FLI1, co-mutant cells have higher chromatin-bound MENIN, including at the HOXA cluster, rendering cells highly sensitive to MENIN inhibition. Statement of Significance: Here, we identify enhanced FLI1 chromatin accessibility as a driver of stemness and leukemic transformation in STAG2 mutant leukemia. Through comprehensive in vivo and in vitro modeling, we demonstrate that altered chromatin architecture can co-opt oncogenic TF activity, like FLI1, to drive divergent leukemia development and therapeutic response.