The contribution of immune cells to thrombus architecture and mechanical properties in acute ischemic stroke (AIS) remains poorly understood. Using 3D imaging and multiplex staining, we mapped immune cells in human stroke thrombi and identified neutrophils as the dominant population. Analysis of 19 thrombi confirmed their positive correlation with collagen, increased stiffness, and poorer clinical outcomes. To preserve the spatial context, we developed a laser capture-based proteomic workflow and analyzed thrombus neutrophils from 34 patients with AIS stratified by 90-day outcomes, followed by validation in an independent cohort of 22 patients. Proteomic analysis revealed SERPINB3 as a neutrophil-enriched protein strongly correlated with poor prognosis. In murine models of FeCl₃-induced carotid artery thrombosis and middle cerebral artery occlusion, experiments using wild-type, neutrophil-depleted, and Serpinb3a knockout mice demonstrated that neutrophil-derived SERPINB3 promotes early thrombus formation, enhances collagen deposition, and contributes to progressive thrombus stiffening. Mechanistically, SERPINB3 secreted by neutrophils amplifies thrombus stiffness through upregulation of TGFβ1, neutrophil extracellular traps, and COL1A1. Targeted SERPINB3 knockdown delayed vascular occlusion, improved thrombolysis efficiency, and resulted in better neurological recovery. Collectively, these findings identify a neutrophil-driven mechanism underlying thrombus stiffening and establish SERPINB3 as both a prognostic biomarker and a promising therapeutic target in AIS. This project has been registered with the Chinese Clinical Trial Registration Platform (https://www.chictr.org.cn/index.html) and has successfully passed the review process (Registration Number: ChiCTR2300077911).

The TCF3::HLF fusion protein defines a highly aggressive and incurable subtype of B cell acute lymphoblastic leukemia (B-ALL). Using a newly established mouse model that faithfully recapitulates human TCF3::HLF B-ALL, including osteolytic bone lesions, we identified self-reinforcing IL-1β signaling networks as a central driver of disease progression. TCF3::HLF B-ALL cells displayed marked upregulation of inflammatory cytokines such as IL1B, IL6, and IFNG. Genetic deletion of IL1B or its receptor IL1R1 suppressed leukemic growth, reduced RANKL expression, and ameliorated bone destruction in vivo. Epigenetic profiling revealed a previously unrecognized intronic regulatory element within the IL1B locus bound directly by TCF3::HLF. Importantly, single-cell RNA-seq of patient samples demonstrated strong IL1B induction at relapse compared with diagnosis, underscoring its clinical relevance. Collectively, these findings establish the TCF3::HLF-IL-1β axis as a critical determinant of leukemic propagation and bone pathology, and highlight IL-1β blockade as a potential therapeutic strategy for this otherwise incurable leukemia.

Autologous second-generation CD7-directed CAR T-cells, expressing an anti-CD7 protein expression blocker to prevent self-killing fratricide, were infused in three pediatric/young adult patients with relapsed/refractory CD7+ acute myeloid leukemia resulting in measurable residual disease negativity. The safety profile was favorable.

CD4+CD25+Foxp3+ regulatory T cells (Tregs) are pivotal negative regulators of the adaptive immune system. Abnormalities in the number and/or function of Tregs contribute to the pathogenesis of primary immune thrombocytopenia (ITP). Strategies aimed at modulating Tregs offer potential therapeutic opportunities for ITP management. In this study, we demonstrated that inhibition of cyclin-dependent kinase 8 (CDK8) and CDK19 activity by the small-molecule inhibitor AS2863619 (AS) robustly promoted the conversion of CD4+CD25- effector T cells (Teffs) into CD4+CD25+Foxp3+ Tregs, endowing the converted Tregs with lineage stability and potent suppressive capacity. Mechanistically, AS rapidly augmented STAT5 phosphorylation and subsequent Foxp3 induction. STAT5 blockade completely abrogated this effect, confirming that the Treg-promoting activity of AS was critically dependent on STAT5 signaling. In parallel, AS suppressed STAT3 phosphorylation under IL-6-driven conditions, thereby attenuating Th17 polarization. These mechanistic findings were supported by global transcriptomic analysis, which revealed a profound transcriptional shift by broadly suppressing gene programs of Teff differentiation and function while simultaneously upregulating a robust signature characteristic of stable Tregs. Crucially, unbiased upstream analysis of these changes pinpointed STAT5, STAT3, and FOXP3 as the core transcription factors mediating the drug's effect. Functional metabolic analysis further revealed that AS mediated metabolic reprogramming in T cells by suppressing glycolysis, thereby providing the necessary metabolic adaptations for Treg conversion. In a murine model of active ITP, CDK8/CDK19 inhibition elevated Treg frequencies and ameliorated thrombocytopenia in a STAT5-dependent manner. Collectively, our study highlighted the therapeutic potential of CDK8/CDK19 inhibition in restoring immune homeostasis and managing ITP.

Chronic graft-versus-host disease (cGVHD) significantly contributes to late mortality after allogeneic stem cell transplantation, with bronchiolitis obliterans syndrome (BOS) being a particularly lethal and treatment-resistant complication despite available therapies. Bromodomain and Extra terminal (BET) proteins are epigenetic readers driving inflammatory transcriptional programs across multiple cell types. We hypothesized that BET inhibition would suppress inflammatory T and B cells while also decreasing macrophage polarization to a profibrotic phenotype, alleviating disease. In an established BOS cGVHD model, BET inhibition reduced germinal center formation and response through a reduction of the CXCL13:CXCR5 axis, inflammatory Tfh/GC B cells in the spleen along with a reduction in plasma cell infiltration within the lung. Mice with cGVHD had elevated pathogenic IgG1 and IgM, both in circulation and deposited on lung tissue, which was attenuated under BET inhibition. Single-cell RNA sequencing analysis revealed distinct cell states in the BOS lung vs. control. In cGVHD mice, GSEA analysis revealed upregulation of profibrotic Arginase1 and Tgfb1 expression in alveolar macrophages (AM) and interstitial macrophages (IM), which was significantly reduced with BET inhibition. Furthermore, BET inhibition targeted lung-infiltrating M2 macrophages, through selective depletion of CD206+FcgR+ IMs and AMs, ultimately resulting in reduced collagen deposition and improved lung function. Our findings reveal a previously unrecognized mechanistic axis of BET regulation during cGVHD fibrosis and highlight BET inhibition as a promising therapeutic strategy.

The phase 3 CRISTALLO trial (NCT04285567) compared first-line fixed-duration venetoclax-obinutuzumab (VenO) vs fludarabine, cyclophosphamide, and rituximab (FCR)/bendamustine-rituximab (BR) in patients with chronic lymphocytic leukemia, using undetectable minimal residual disease (uMRD) as the sole primary endpoint. Previously untreated patients with a cumulative illness rating scale score ≤6, creatinine clearance ≥70 mL/min, without del(17p)/TP53 mutations were randomized 1:1 to VenO or FCR/BR. The primary endpoint was uMRD (<10-4) in peripheral blood (PB) using next-generation sequencing at month 15. Key secondary endpoints included uMRD (<10-4) in PB and bone marrow (BM) at end of treatment (EOT), and progression-free survival (PFS). uMRD at deeper cutoffs were explored. At data cutoff (March 19, 2024), 80 patients received VenO and 86 received FCR/BR. Baseline characteristics were generally balanced across arms. The primary endpoint was met: 81.3% (VenO) and 54.7% (FCR/BR) achieved uMRD (<10-4) in PB at month 15 (P = .0004). uMRD (<10-4) in PB and BM at EOT was also higher with VenO vs FCR/BR. Short follow-up precluded evaluation of PFS at the first planned interim analysis; however, fewer patients progressed/died with VenO vs FCR/BR (7 vs 13). At month 15, 65.0% (VenO) and 25.6% (FCR/BR) achieved uMRD (<10-6) in PB. The overall safety profile was consistent with the known safety profile of each drug. No patient in the VenO arm was deemed high-risk for tumor lysis syndrome following obinutuzumab debulking; no clinical TLS occurred. These results confirm and extend the findings from the GAIA-CLL13 trial, validating increased depth of response with VenO vs chemoimmunotherapies.

T cell-based therapies have shown remarkable efficacy in multiple myeloma (MM), yet the disease remains largely incurable. Here, we investigated the constant domains of the immunoglobulin heavy chain (IgH) as novel targets for therapeutic T cell receptors (TCRs), after confirming high and homogeneous IGH expression in >95% of MM patients. MM cells secrete excessive monoclonal immunoglobulins (M-proteins) that drive complications but are inaccessible to CAR T-cell or antibody targeting. Peptides from IgA and IgG constant regions were eluted from HLA-A*02:01, and reactive TCRs were isolated from healthy donors using allo-HLA-A*02:01 presentation to circumvent self-tolerance. T cells engineered with two TCRs specific for IgA or IgG passed a stringent multi-tier safety screen and selectively eliminated MM cells from 20 HLA-A*02:01+ patients secreting the relevant IgH in vitro. In vivo, IgA-TCR T cells eradicated IgA+HLA-A*02:01+ MM cells in xenograft models and reduced circulating IgA in humanized mice. These findings establish immunoglobulin constant domains as viable TCR targets in MM, potentially making ~40% of patients of European descent eligible for TCR T cell therapy, and extension to additional HLA alleles could further broaden eligibility. The approach may also be applicable to lymphoma and antibody-mediated autoimmune diseases.

VEXAS syndrome is a severe adult-onset autoinflammatory disease caused by somatic mutations in the UBA1 gene, disrupting cytoplasmic ubiquitin-activating enzyme E1 function in hematopoietic progenitors. Its pathogenesis remains poorly understood, particularly the mechanisms by which UBA1 mutations disrupt myeloid cell function in the context of inflammatory stimuli. Here, we combine a genetically engineered THP-1 monocytic model with ex vivo analyses of blood and tissue samples from VEXAS patients to investigate the consequences of the canonical UBA1M41V mutation. We show that UBA1-mutated monocytes exhibit TNF-α-induced cell death, characterized by RIPK1 phosphorylation, and MLKL- and caspase-8-mediated cell death. Importantly, we extend these findings to patient-derived CD14⁺ sorted cells, confirming that these cells undergo aberrant apoptotic and necroptotic cell death. Mechanistically, activation of these cell death pathways appears to be promoted by defective NF-κB-dependent transcriptional responses and reduced cFLIP(L) expression following TNF-α stimulation. UBA1-mutated monocytes also display blunted cytokine responses to Toll-like receptor (TLR) agonists despite preserved TLR expression, linked to an impaired NF-κB response. UBA1M41V-derived macrophages exhibit a pro-inflammatory transcriptional profile with increased chemokine secretion that promotes monocyte recruitment. In addition, these UBA1-mutated macrophages display impaired efferocytosis due to lysosomal dysfunction. Together, these findings reveal a pathogenic axis in VEXAS syndrome linking UBA1 loss of function and defective ubiquitination to RIPK1-mediated inflammatory cell death, impaired antimicrobial signaling, and defective resolution mechanisms. Our study provides novel mechanistic insights into the myeloid dysfunction underlying inflammation and cytopenia in VEXAS and supports the therapeutic targeting of inflammatory cell death pathways.

Autologous stem cell transplantation (ASCT) with maintenance lenalidomide remains the mainstay of consolidation therapy for eligible multiple myeloma (MM) patients but preventing disease relapse remains a critical unmet need. Here we investigated whether immunosuppressive myeloid populations in bone marrow (BM) correlated with ASCT outcomes. We identified a subset of CD64+CD169+CD163+ macrophages that expressed CSF-1R, PD-L1, and CD155, and were expanded in patients who relapsed post-ASCT. Using a preclinical ASCT model with suboptimal endogenous anti-myeloma activity, we demonstrated that while neither CSF-1R inhibition nor lenalidomide monotherapy significantly improved outcomes, their combination synergistically attenuated disease progression and prolonged survival. Single-cell RNA sequencing revealed that lenalidomide expanded NK-like CD8+ T-cells but paradoxically also increased the frequency of Csf1r+ macrophages. Cell-cell communication analyses identified Csf1r+ macrophages as suppressors of these NK-like and effector-like exhausted (Tphex) CD8 T-cell populations through CD94/NKG2A and PD-L1/PD-1, respectively. CSF-1R blockade depleted these immunosuppressive macrophages, which correlated with decreased expression of inhibitory receptors and enhanced expression of activation markers in Tphex. Given the FDA approval of axatilimab for chronic GVHD, combining CSF-1R blockade with lenalidomide maintenance represents a readily testable strategy to improve progression-free survival after ASCT.

Thrombotic Thrombocytopenic Purpura (TTP) was first described just over a century ago and it is now 25 years since the identification of ADAMTS13 as the enzyme deficient in both antibody-mediated immune TTP and congenital TTP. The discovery of ADAMTS13 has been fundamental to the vast improvement seen in TTP outcomes. Understanding the interaction between ADAMTS13, platelets and vWF led to development of clinical ADAMTS13 assays and therefore quicker and accurate diagnosis, but also, critically, to novel therapies and monitoring of treatment. Landmark additions to immune TTP therapy have included anti-CD20 treatment with rituximab, in both the acute and elective setting and the use of the nanobody caplacizumab in acute TTP. In congenital TTP, the use of ADAMTS13 replacement is playing a role in reducing end-organ damage and morbidity, with recombinant ADAMTS13 now representing the gold standard for cTTP. The ability to measure response to treatment by monitoring ADAMTS13 activity has underpinned these treatment advances and allowed clinicians to tailor immunosuppressive treatment for iTTP and rADAMTS13 dosing in cTTP. Looking forward, there are many avenues for future development with potential expansion of recombinant ADAMTS13 to treat immune TTP, new, quicker assays to improve diagnosis, monitoring and immunomodulatory therapeutic advancement, all underpinned by ADAMTS13. Future endeavors for the role of ADAMTS13 in other thrombotic indications opens further exciting opportunities.

Bone marrow failure (BMF) syndromes are heterogenous diseases characterized by impaired hematopoiesis and risk of evolution to myelodysplastic syndrome (MDS) and leukemia. We report 6 unrelated individuals with variable BMF phenotypes and hypocellular MDS presenting at a median age of 10 years (4 weeks - 53 years). Genomic analysis revealed germline heterozygous variants in MDM4, including 4 null (frameshift, nonsense, and splice-site resulting in premature truncation confirmed by RNA sequencing) and 2 missense variants, of which one had previously been associated with a familial BMF syndrome. Mechanistically, MDM4 mutations are loss-of-function leading to enhanced p53 activation. We used CRISPR/Cas9 to delete MDM4 in healthy donor hematopoietic stem and progenitor cells (HSPCs). The resulting MDM4-haploinsufficient HSPCs exhibited increased p53 activity, impaired colony-forming capacity, and reduced engraftment potential in immunodeficient mice. Complementation studies revealed both p53-binding and RING-finger domains as necessary for MDM4-mediated hematopoietic regulation. To study variant effect in a confounder-free genetic background, we introduced patient-specific MDM4 variants into induced pluripotent stem cells (iPSCs). MDM4-mutant iPSCs yielded significantly reduced erythroid and myeloid cells and exhibited increased p53 activity, as evidenced by elevated p21 expression, confirming the role of MDM4 regulating hematopoiesis through p53. Transcriptome analysis of iPSC-derived hematopoietic cells revealed upregulation of p53 pathway. Importantly, one patient with MDS acquired loss-of-function TP53 mutations, suggesting maladaptive somatic rescue.Our findings establish MDM4 deficiency as a TP53 activating syndrome with features of BMF and variable hematopoietic manifestations. This study also highlights the critical role of the MDM4-p53 axis in maintaining hematopoietic homeostasis.

The H3K36me2 methyltransferase NSD2 is deleted in Wolf-Hirschhorn syndrome and aberrantly expressed in 10-15% of multiple myeloma (MM) due to a t(4;14) translocation. Although NSD2 is thought to be a primary driver in MM, the exact molecular mechanisms by which it regulates transcription remain unclear. We applied the dTAG system to acutely degrade NSD2 and used this, in combination with time-resolved SLAM-seq, to identify 307 transcriptional targets of NSD2. Reconstitution with either wild-type NSD2 or a catalytically inactive mutant (NSD2Y1179A) showed that NSD2's transcriptional effects are almost exclusively dependent on its SET domain activity. Mechanistically, H3K36me2 deposition by NSD2 antagonizes H3K27me3 levels, and treatment with two distinct PRC2 inhibitors demonstrated that approximately half of NSD2 target genes are regulated in an H3K27me3-dependent manner. CUT&Tag analysis showed that upon NSD2 depletion there was an increase in H3K27me3 that occurred at genome-wide intergenic regions, rather than at the promoters or gene bodies of NSD2 target genes. These data suggest that NSD2, via H3K36me2, antagonizes H3K27me3 deposition likely at distal regulatory elements including enhancers, creating a chromatin landscape favorable for target gene transcription. Importantly, NSD2 target genes were enriched for key oncogenic pathways, and 24 transcription factors implicated in neurodevelopment and acute leukemia, consistent with its role in Wolf-Hirschhorn syndrome and MM. Eight of these transcription factors are known oncogenic drivers in acute leukemia or MM, highlighting a novel molecular mechanism for NSD2's role in t(4;14) MM.

Relapsed or refractory (R/R) disease occurs in up to 40% of diffuse large B-cell lymphoma (DLBCL) patients following first-line immunochemotherapy. However the molecular mechanisms underlying drug persistence remain incompletely defined. Here, we performed single-cell RNA and B-cell receptor sequencing on paired diagnostic and R/R samples from eight patients who were either treatment-refractory or relapsed after remission, and validated our findings in three independent patient cohorts. We found that drug-persistent cells exhibited a transcriptional profile indicative of a less-differentiated state and adopted a memory B cell-like program with enhanced stem-like properties, which correlated with unfavorable clinical outcomes across multiple DLBCL cohorts. Functionally, drug-persistent cells showed significantly increased in vitro clonogenicity and in vivo tumor-initiating capacity. Mechanistically, the WNT signaling regulator CSNK1E was upregulated in these stem-like drug-persistent cells, in part through the activation of the APRIL-TNFRSF13B axis. Notably, CSNK1E inhibition impaired the growth and tumor-initiating capacity of drug-persistent cells and potentiated the efficacy of R-CHOP-based treatment both in vitro and in vivo. Together, our study reveals the stem-like transcriptional and functional properties of drug-persistent cells, and identifies CSNK1E as a critical mediator and therapeutic vulnerability to improve the efficacy of standard immunochemotherapy in DLBCL.

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative therapy for hematologic malignancies. The primary non-relapse complication after allo-HSCT is graft-versus-host disease (GVHD). The use of T regulatory (Treg) cells to prevent GVHD has emerged as a promising allogeneic T cell immunotherapy in the form of Orca-T. However, the precise differences in immune activation which may influence infection, GVHD, and relapse after Orca-T compared with unmanipulated peripheral blood stem cell (PBSC) grafts remain unexplored. Using peripheral blood specimens longitudinally collected between 3 weeks and one year after leukemia treatment, we report single-cell mRNA sequencing (scRNA-seq) and flow cytometric analysis of 51 HLA-matched patients receiving either Orca-T or unmanipulated PBSC grafts. Orca-T recipients exhibited increased frequencies of effector memory CD4+ T cells 3 weeks after transplant and this difference persisted through six months after treatment. scRNA-seq analysis 3 weeks post-transplant identified increased expression of FOXP3 and Helios amongst CD4+CD25- T conventional (Tcon) cells in Orca-T treated patients. Using flow cytometry, we then confirmed the increased frequency of this novel population of CD4+CD25-FOXP3+Helios+ Tcons 3 weeks post-treatment in patients receiving Orca-T. Further, we discovered that this T cell subset possessed a regulatory-like phenotype and correlated significantly with the frequencies of activated CD4+ and CD8+ T cell populations 3 months post-treatment, regardless of which therapy patients received. Overall, this study identifies a novel T cell subset which is enriched very early after cellular therapy for leukemia and may be predictive of long-term immune activation after Orca-T and PBSC-derived T cell infusion.

Quadruplet therapy with isatuximab, bortezomib, lenalidomide, and dexamethasone (Isa-VRd) followed by Isa-Rd in the randomized Phase 3 IMROZ study provided significant PFS benefit to transplant-ineligible, newly diagnosed multiple myeloma (NDMM) patients. In the primary analysis, more Isa-VRd/Isa-Rd-treated patients achieved MRD-negativity and MRD-negative complete response (CR) at any timepoint compared with VRd triplet therapy followed by Rd. Here, we report results from landmark analyses of MRD-negativity over time and its impact on clinical outcomes in IMROZ. Treatment with Isa-VRd/Isa-Rd led to deeper responses, with higher rates of MRD-negativity and MRD-negative CR at both the end of the initiation phase and during maintenance vs. VRd/Rd, up to 60 months of follow-up. Benefit with Isa-VRd/Rd was observed across key patient subgroups, including older (>70 years) and frail patients. The deeper responses achieved throughout treatment were associated with improved outcomes, with a significant prolongation in time-to-progression (TTP) in favor of Isa-VRd/Rd vs. VRd/Rd in patients who converted from MRD-positive to MRD-negative. TTP in patients who converted from MRD-negative at the end of initiation to MRD-positive also favored Isa-VRd. Evaluation of MRD status for individual patients at more than one timepoint may thus be useful to support decisions on treatment selection and treatment continuation/discontinuation. Our findings on the extent of MRD-negativity and MRD-negative CR benefit achieved in the initiation and maintenance phases by patients receiving Isa-VRd/Isa-Rd vs. VRd/Rd extend the IMROZ primary analyses and further support the Isa-VRd quadruplet regimen as a standard-of-care for front-line treatment of transplant-ineligible NDMM patients. Clinical Trial Information: ClinicalTrials.gov, NCT03319667.

Altered lipid metabolism enables growth of acute myeloid leukemia (AML) cells. While mitochondrial lipid oxidation is well characterized, the contribution of peroxisomal fatty acid oxidation (pFAO) is unclear. In this study, we demonstrate that AML cells upregulate the peroxisomal very-long-chain fatty acid (VLCFA) transporter ABCD1 and increase endogenous levels of pFAO relative to healthy hematopoietic cells. Genetic silencing or pharmacological inhibition of ABCD1, with eicosenol, impairs pFAO causing accumulation of VLCFAs and selective AML cell death in vitro and in vivo. Loss of ABCD1 disrupts peroxisomal fatty acid import and lipid homeostasis in AML, while normal progenitors remain viable by upregulating glycolysis. In murine models, ABCD1 inhibition with eicosenol reduces leukemia burden and prolongs survival without toxicity. These findings identify ABCD1 as a regulator of pFAO and a novel anti-AML therapeutic target.

Bispecific antibodies (bsAbs) such as glofitamab represent a promising therapeutic approach for relapsed/refractory B-cell non-Hodgkin's lymphoma (R/R B-NHL), but resistance mechanisms remain poorly understood. This study aimed to identify predictive markers of bsAbs resistance based on the response of 3D patient-derived lymphoma spheroids (PDLS) established from 39 R/R B-NHL samples. PDLS were treated with glofitamab for 3 days and B-cell depletion was quantified to assess the ex-vivo treatment response. Comprehensive immune profiling was performed on patient samples using multiparametric flow cytometry, single-cell RNA sequencing, CODEX spatial proteomics and functional assays. High responders to glofitamab possessed CD8+ T-cells with consistently higher cytotoxic and activation signatures across effector differentiation states, while low responders showed enrichment of exhausted CD8+ T-cell with enhanced expression of exhaustion markers (TIGIT, LAG3, PD1). Furthermore, low responders exhibited elevated functional CD4+ T-follicular helper (Tfh) cells in close proximity to malignant B-cell thus promoting their survival through IL21 and CXCL13 signaling pathways. Analysis of pretreatment RNA-seq data from 48 R/R B-NHL patients confirmed that high Tfh abundance is associated with poor glofitamab response. In PDLS, anti-TIGIT co-treatment enhanced glofitamab efficacy in low responders, and Tfh depletion experiments confirmed that reducing Tfh activity increased B-cell depletion. Together, these findings identify CD8+ T-cell exhaustion and functionally activated Tfh cells as key factors associated with glofitamab resistance in R/R B-NHL. This work supports their potential use as predictive biomarkers for selecting patients with higher probability of response and provides a foundation for future combination therapeutic strategies.

Selection of a hematopoietic progenitor cell donor for allogeneic hematopoietic cell transplantation (allo HCT) is essential for treatment planning; however, the parameters that define an "optimal" donor in the modern era are not well defined. Historically, donor-recipient human leukocyte antigen (HLA) mismatching correlated strongly with risk for graft versus host disease (GVHD) and reduced survival. For this reason, donor selection was typically hierarchical: HLA matched related and unrelated donors were evaluated first, followed by HLA mismatched donors (or deferral of HCT altogether) in patients lacking an HLA matched donor. The advent of post-transplant cyclophosphamide (PTCy)-based GVHD prevention has changed this paradigm. Survival outcomes following HLA-mismatched donor HCT with PTCy, including from related haploidentical or HLA-mismatched unrelated donors, are not different than HLA matched donor recipients in recent clinical trials and retrospective studies. These encouraging results present a new challenge: In the PTCy era, how should donors be prioritized among the many potential sources available? Herein we review HLA and non-HLA parameters that inform donor selection and discuss approaches to increase donor availability. Case vignettes focusing on concepts that may be adapted to heterogenous clinical scenarios are presented.

Clonal hematopoiesis of indeterminate potential (CHIP) is characterized by age-related somatic mutations in hematopoietic stem and progenitor cells (HSC/Ps) and is correlated with an increased risk of myeloid malignancies, elevated inflammatory pathways in circulating myeloid cells, higher all-cause mortality, chronic kidney disease, and cardiovascular disease. The pathophysiology of inflammatory bowel disease (IBD) is intrinsically linked to heightened inflammation. Nevertheless, the presence of CHIP in IBD and its role in the pathophysiology of IBD remains poorly elucidated. In the UK Biobank, CHIP was associated with an increased incidence of IBD. Females with CHIP had a 1.33-fold higher risk, which was further validated in All of Us data base (ßOR = 1.29). For Crohn's disease, DNMT3A mutations conferred a 1.81-fold increased incidence in females compared to non-DNMT3A-carriers, which rose to 2.09 for large clones (variant allele fraction ≥10%). In contrast, for ulcerative colitis, TET2 large clones were significantly associated, and only among individuals under 45. These associations were further identified using two-sample Mendelian randomization. In a mouse model of CHIP-IBD, HSC/Ps with Dnmt3a mutation demonstrated significantly worse pathophysiology compared to controls, due in part to heightened expression of Apurinic/apyrimidinic endonuclease 1 (APE1) in the bone marrow and colon. Treatment with the APE1/Ref-1 inhibitor APX3330 ameliorated CHIP-IBD driven by the Dnmt3a mutation.

Truncating and missense mutations of the CREBBP gene are highly prevalent in follicular lymphoma (FL) and diffuse large B cell lymphoma (DLBCL), the most common lymphoid malignancies. These mutations are acquired early during tumor evolution by a common precursor cell (CPC) and lead to either complete protein loss or single amino-acid substitutions in the acetyltransferase (KAT) domain. As a result, CREBBP is impaired in its ability to acetylate enhancer histones and non-histone proteins implicated in the germinal center (GC) reaction, the structure from which these tumors originate. However, whether truncating and KAT domain missense mutations are functionally equivalent in instructing the CPC remains unexplored. Using a conditional GC-specific knock-in mouse model for the highly frequent CREBBP-R1446H amino-acid change (CrebbpRH), here we show that, compared to complete Crebbp loss, missense mutants impose distinct quantitative and qualitative effects on the GC response. CrebbpRH controls unique transcriptional programs leading to the pre-neoplastic expansion of GCs with abnormal architecture, increased percentage of Tfh cells, and a skewed immune response toward memory B-cell differentiation. Expression of CrebbpRH, but not Crebbp loss, was by itself sufficient to initiate malignant transformation, indicating a stronger tumor-promoting activity. Of note, lymphoma cells with CREBBPRH and CREBBP loss showed distinct sensitivity to CREBBP/p300 small molecule inhibitors. Together with the differential distribution of missense and truncating mutations in FL and DLBCL, these findings have implications for the pathogenesis and therapeutic targeting of these cancers.