Polyploidization resulted from massive DNA synthesis is crucial for megakaryocyte maturation, while the regulatory mechanisms of cell fitness upon this special cellular process remain poorly understood. Here, we reveal that glutamine synthetase (GLUL) facilitates thrombocytopoiesis by restricting ammonia accumulation during polyploidization. GLUL is found to be distinctly expressed in platelet-producing megakaryocytes and increasingly elevated with the progression of polyploidization, and GLUL deficiency impairs megakaryocyte maturation and platelet production. Mechanistically, GLUL detoxifies ammonia derived from adenosine deaminase acting on RNA 1 (ADAR1)-mediated double-stranded RNA (dsRNA) editing in megakaryocytes undergoing polyploidization. Ammonia accumulation is observed in megakaryocytes defective in GLUL, leading to lysosomal and mitochondrial damage and even cell death. Fulvotomentoside A (FtA) is identified as a potential GLUL agonist with the capacity to promote thrombocytopoiesis in mice after radiation and chemotherapy injury. Our findings uncover the biological significance of GLUL in megakaryocyte maturation and provide a new avenue for regulating thrombocytopoiesis.

FLT3-internal tandem duplication measurable residual disease testing for patients in remission from acute myeloid leukemia is now recommended by the recently updated clinical standard-of-care guidelines. This companion technical note provides important laboratory and clinical recommendations regarding such testing.

We present 5-year survival results in patients with R/R LBCL from TRANSCEND NHL 001 (TRANSCEND), including data from the separate long-term follow-up (LTFU) study. Overall, 345 patients were leukapheresed, 270 received liso-cel, and 257 were efficacy evaluable. Among efficacy-evaluable patients, median overall survival (OS) was 27.5 months (95% confidence interval [CI], 16.2‒47.3; leukapheresed set, 15.2 months [95% CI, 11.5‒23.4]) with estimated 5-year OS rate of 38% (95% CI, 32‒45; leukapheresed set, 33% [95% CI, 28‒39]). Median disease-specific survival (DSS; excludes deaths unrelated to disease progression) was 67.8 months (95% CI, 23.5‒not reached [NR]; leukapheresed set, 27.4 months [95% CI, 14.4‒69.7]) with estimated 5-year DSS rate of 52% (95% CI, 45‒59; leukapheresed set, 47% [95% CI, 41‒52]). Among efficacy-evaluable patients from TRANSCEND who were alive at end-of-study and enrolled in the LTFU (n=84), median OS and DSS were NR (95% CI, NR‒NR) and estimated 5-year OS and DSS rates were 78% (95% CI, 67‒86) and 92% (95% CI, 84‒97), respectively. Most deaths occurred ≤2 years after infusion; no new safety signals were observed with low rates of late severe infections and second primary malignancies. These data support the curative potential of liso-cel in patients with R/R LBCL. Clinicaltrials.gov: NCT02631044, NCT03435796.

Deletion of 17p is among the most adverse cytogenetic abnormalities in multiple myeloma (MM). By integrating RNA-seq data from patient MM cells with genetic dependency data from MM cell lines, we identified the protein kinase membrane-associated tyrosine/threonine 1 (PKMYT1) kinase, a member of the Wee family, as a potential therapeutic target in MM cells harboring del(17p). Genetic suppression or pharmacological inhibition of PKMYT1 activity with the selective inhibitor RP-6306 triggered accumulation of DNA damage, micronucleus formation and mitotic catastrophe, resulting in preferential cell death in del(17p) MM cells while largely sparing del(17p)-negative MM cells and healthy cells. RP-6306 also reduced tumor burden and extended survival in vivo in both xenograft and TP53-deficient syngeneic models. Collectively, our findings nominate PKMYT1 as an actionable target and support PKMYT1 inhibition as a biomarker-driven therapeutic strategy for patients with del(17p)/TP53-deficient MM.

Histidine-rich glycoprotein (HRG) is a 75-kDa plasma protein produced by the liver and circulating at about 2 µM, with an additional pool in platelets that is released upon activation. Previously, we demonstrated that HRG downregulates the contact system by binding polyanions and reducing their capacity to activate factor (F) XII. Although HRG localizes on the platelet surface, its role in platelet biology remains uncertain. Accordingly, we investigated whether HRG directly engages platelet receptors to regulate adhesion and aggregation. Using human and murine platelets, we show that HRG (a) binds to glycoprotein (GP)Ibα on resting and activated platelets and to GPIIb/IIIa on activated platelets, (b) competes with von Willebrand factor (VWF) for binding to GPIbα on resting platelets and with fibrinogen for binding to GPIIb/IIIa on activated platelets, and (c) attenuates platelet agglutination, aggregation, and platelet-mediated thrombus growth. Furthermore, in an endothelial-platelet flow system or a collagen-coated microperfusion chamber, HRG reduced VWF-mediated platelet string formation and attenuated platelet deposition under high-shear conditions. Plasma HRG levels in patients with sepsis or COVID-19 were about half those of healthy controls, and reducing HRG to these levels in vitro promoted a hyperreactive platelet phenotype. Therefore, HRG not only modulates coagulation but also platelet adhesion and aggregation by competing with VWF and fibrinogen for binding to GPIbα and GPIIb/IIIa.

Sickle cell disease (SCD) is characterized by chronic hemolysis, painful vaso-occlusive episodes (VOE) and end organ damage. High levels of fetal hemoglobin (HbF) attenuate the disease phenotype. We used a lentivirus vector (LVV) expressing an shRNA embedded in a microRNA (shmiR) targeting BCL11A in erythrocytes to induce HbF in a first-in-human pilot study in SCD. The purpose of the study was to assess hematopoietic stem/progenitor cells (HSPCs) collection, transduction parameters, safety, HbF induction and durability. Eleven eligible patients with SCD had HSC collection. Plerixafor-mobilized peripheral blood HSCs required for manufacturing were obtained in one mobilization cycle for 10/11 subjects and 11/11 patient products were successfully manufactured with a median time to release of product of 39 days. Ten patients were infused with autologous HSCs transduced with the shmiR vector. Engraftment occurred in all 10 patients. With a median follow-up of 58 months (range: 35-82) after infusion, no adverse events attributed to the gene vector have occurred. Transduction efficiency was 93.1%. One patient demonstrated low engraftment of transduced cells and had suboptimal HbF induction. In the remaining 9 patients, at 2 years post-treatment peripheral blood demonstrated 71% F cells with 11.9 pg HbF/F cells, both stable in 9 patients with ≥48 months follow-up. All patients who had VOEs prior to gene therapy demonstrated sustained mitigation of pain events. These data demonstrate excellent manufacturing efficiency and safety, with efficacy of targeting BCL11A using a shmiR LVV, and long-term durability of the shmiR vector, leading to a pivotal multi-site phase 2 trial currently underway (NCT05353647).

Patients with relapsed/refractory multiple myeloma (RRMM) have limited treatment options. Arlocabtagene autoleucel (arlo-cel, BMS-986393) is an autologous chimeric antigen receptor (CAR) T-cell therapy targeting G protein-coupled receptor class C group 5 member D (GPRC5D). This phase 1, dose-escalation/expansion study (NCT04674813) enrolled adult patients with RRMM and ≥3 prior antimyeloma treatment regimens, including an immunomodulatory drug (IMiD), a proteasome inhibitor, and an anti-CD38 antibody. At baseline, patients (N=84) had a median of 5 prior regimens and 49% had previously received BCMA-targeted therapy, of whom 38% received CAR T-cell therapy. Arlo-cel was administered as a one-time intravenous infusion of 25×106-450×106 CAR T cells. Primary endpoints were safety and maximum tolerated dose (MTD); secondary endpoints included overall response rate (ORR), progression-free survival (PFS), and overall survival (OS). Data cutoff was 23August2024. Cytokine release syndrome (CRS) occurred in 82% of patients, immune effector cell-associated neurotoxicity syndrome in 10%, and other select neurotoxicities in 12%; most were grade 1/2 and frequency appeared dose-dependent. One death occurred from CRS at highest dose level. On-target/off-tumor skin (30%), nail (19%), and oral (32%) adverse events were transient, grade 1/2; most resolved without intervention. MTD was not reached. With median follow-up of 16.1 months, ORR=87% (complete response rate=53%), median duration of response=18.0 months, and median PFS=18.3 months (95% CI, 11.8-21.9) (n=79). The 1-year OS rate was 90% (N=84). In conclusion, arlo-cel had a safety profile supportive of future study and demonstrated deep and durable responses, with promising PFS and OS in patients with heavily pretreated RRMM.

Polycythemia vera (PV) is a clonal hematopoietic stem cell (HSC) disorder resulting in overproduction of erythrocytes. While Interferon-a (IFN-a) has shown therapeutic efficacy in PV and other myeloproliferative neoplasms (MPN), its precise mechanism of action remains poorly understood. In this study, we identify natural killer (NK) cells as primary immune effectors responsive to IFN-a treatment in PV essential for disease control in vivo. Using a transgenic mouse model of PV, we demonstrate that IFN-a induces the expansion of CD27+ NK cells in the bone marrow. In patients with PV or ET undergoing IFN-a therapy, the frequency of CD56bright NK cells is increased and correlates with the molecular response. Depletion of NK cells abrogated the therapeutic effects of IFN-a. In vitro experiments demonstrate that NK cells preferentially killed Jak2VF mutant hematopoietic stem and progenitor cells (HSPCs) in a TNF-a dependent manner and independent of IFN-g or NKG2D. Notably, PV mice depleted of NK cells or lacking type-I interferon (IFN) receptor on NK cells showed accelerated disease progression in the absence of exogenous IFN-a. This suggests that direct sensing of basal levels of type-I IFNs by NK cells is essential for attenuating disease progression, emphasizing a critical role for NK cells in immune surveillance of MPN. These findings offer new insights into type-I IFN-mediated immune modulation in MPN and highlight the potential of NK cell activation to improve therapeutic outcomes.

Juvenile myelomonocytic leukemia (JMML) is an aggressive pediatric myelodysplastic syndrome or myeloproliferative disorder for which hematopoietic stem cell transplantation remains the only curative option; however, outcomes are particularly poor in patients harboring PTPN11 (encodes SHP2 phosphatase) mutations. Using a Shp2E76K/+ JMML mouse model, we identify a pathogenic IL-17A/PTGS2/NLRP3 signaling axis that drives bone marrow inflammation, suppresses antitumor immunity, and promotes leukemic progression. Shp2E76K/+ mice exhibited profound immune dysregulation, characterized by expansion of regulatory T cells (Tregs), increased T-cell exhaustion, and impaired cytotoxic function with reduced CD4⁺ and CD8⁺ T-cell frequencies. Mechanistically, mutant macrophages upregulated IL-17A, triggering NLRP3 inflammasome activation, PTGS2 induction, caspase-1 cleavage, and IL-1β maturation, thereby amplifying inflammatory signaling within the marrow niche. Therapeutically, IL-17A neutralization suppressed inflammasome activity, while combined inhibition of NLRP3 and PTGS2 restored cytotoxic T-cell function, reduced systemic and marrow inflammation, reversed myeloproliferation, and significantly prolonged survival in Shp2E76K/+ mice. Importantly, ex vivo treatment of primary JMML patient samples with dual NLRP3/PTGS2 inhibition combined with MEK blockade significantly reduced leukemic progenitor colony formation, supporting translational relevance. In patient-derived xenograft models of PTPN11-mutant JMML, dual NLRP3/PTGS2 inhibition combined with MEK blockade most effectively reduced leukemic burden, decreased human CD45⁺ engraftment, and depleted leukemic CD34⁺CD38⁺ progenitors and GMPs while restoring MEP populations, resulting in significantly improved overall survival. Together, these findings establish IL-17A/PTGS2/NLRP3 signaling as a central driver of immune suppression and myeloid expansion in PTPN11-mutant JMML and highlight combinatorial anti-inflammatory targeting as a promising therapeutic strategy for this high-risk disease.