Citations

Abstract Background The disease severity index (DSI) for inflammatory bowel disease (IBD) combines measures of disease phenotype, inflammatory activity, and patient-reported outcomes. We aimed to validate the DSI and assess its utility in predicting a complicated IBD course. Methods A multicenter cohort of adults with IBD was recruited. Intraclass correlation coefficients (ICCs) and weighted Kappa assessed inter-rater reliability. Cronbach’s alpha measured internal consistency of DSI items. Spearman’s rank correlations compared the DSI with endoscopic indices, symptom indices, quality of life, and disability. A subgroup was followed for 24 months to assess for a complicated IBD course. Area under the receiver operating characteristics curve (AUROC) and multivariable logistic regression assessed the utility of the DSI in predicting disease progression. Results Three hundred and sixty-nine participants were included (Crohn’s disease [CD], n = 230; female, n = 194; mean age, 46 years [SD, 15]; median disease duration, 11 years [interquartile range, 5-21]), of which 171 (CD, n = 99; ulcerative colitis [UC], n = 72) were followed prospectively. The DSI showed inter-rater reliability for CD (ICC 0.93, n = 65) and UC (ICC 0.97, n = 33). The DSI items demonstrated inter-rater agreement (Kappa > 0.4) and internal consistency (CD, α > 0.59; UC, α > 0.75). The DSI was significantly associated with endoscopic activity (CDn=141, r = 0.65, P < .001; UCn=105, r = 0.80, P < .001), symptoms (CDn=159, r = 0.69, P < .001; UCn=132, r = 0.58, P < .001), quality of life (CDn=198, r = −0.59, P < .001; UCn=128, r = −0.68, P < .001), and disability (CDn=83, r = −0.67, P < .001; UCn=52, r = −0.74, P < .001). A DSI of 23 best predicted a complicated IBD course (AUROC = 0.82, P < .001) and was associated with this end point on multivariable analyses (aOR, 9.20; 95% confidence interval, 3.32-25.49). Conclusions The DSI reliably encapsulates factors contributing to disease severity and accurately prognosticates the longitudinal IBD course.

Objective This pilot study seeks to identify serum immune signatures across clinical stages of patients with chronic pancreatitis (CP). Methods We performed a cross-sectional analysis of prospectively collected serum samples from the PROspective Evaluation of Chronic Pancreatitis for EpidEmiologic and Translation StuDies-study. CP subjects were categorised into three clinical stages based on the presence/absence of metabolic complications: (1) CP with no diabetes and exocrine pancreatic dysfunction (EPD), (2) CP with either diabetes or EPD, and (3) CP with diabetes and EPD. Blinded samples were analysed using an 80-plex Luminex assay of cytokines/chemokines/adhesion molecules. Group and pairwise comparisons were performed to characterise immune signatures across CP subgroups. Results A total of 135 CP subjects (evenly distributed between clinical stages) and 50 controls were studied. Interleukin-6 (IL-6), interleukin-8 (IL-8), and soluble intercellular adhesion molecule 1 (sICAM-1) were significantly elevated in CP subjects compared to controls. The levels of IL-6 and IL-8 increased with advancing disease stages, with the highest levels observed in CP with diabetes and EPD (clinical stage 3). Furthermore, hepatocyte growth factor and macrophage-derived chemokine were significantly increased in clinical stage 3 compared to controls. Conclusion Our study reveals a progressive elevation in pro-inflammatory cytokines and chemokines with advancing clinical stages of CP. These findings indicate potential targets for the development of disease-modifying interventions.

AbstractIntroductionThe infusion of autograft Natural Killer Cells (NKC)/CD14+HLA‐DRDIM ratio is a predictor of survival in lymphoma patients undergoing autologous peripheral blood hematopoietic stem cell transplantation (APBHSCT). This study evaluated if the Day 100 NKC/CD14+HLA‐DRDIM ratio still functions as a prognostic immune‐biomarker.MethodsThis was a retrospective, single‐institution, cohort analysis including 107 patients in this study that had clinical assessment at Day 100 post‐APBHSCT from our prior phase III trial. We evaluated the prognostic ability of the Day 100 NKC/CD14+HLA‐DRDIM ratio to predict overall survival (OS) and progression‐free survival (PFS) using Cox regression model for outcome analysis and survival by Kaplan–Meier method.ResultsThe median follow‐up from day 100 was 94.7 months (range 4.83–158.1 months) for the entire cohort. Patients with a Day 100 NKC/CD14+HLA‐DRDIM ratio ≥1.67 experienced better OS and PFS versus those with a Day 100 NKC/CD14+HLA‐DRDIM ratio <1.67: median OS was not reached versus 49.7 months, the 5‐year OS rates were 91% (95% CI, 81%–96%) versus 40% (95% CI, 27%–55%), p < .0001, respectively; and median PFS was not reached versus 23.5 months, the 5‐year PFS rates were 66% (95% CI, 55%–81%) versus 21% (95% CI, 15%–40%), p < .0001, respectively. Day 100 NKC/CD14+HLA‐DRDIM ratio was an independent predictor for OS and PFS in the multivariate analysis.ConclusionsDay 100 NKC/CD14+HLA‐DRDIM ratio is a prognostic immune‐biomarker in lymphoma patients post‐ APBHSCT.

Introduction: In Cohorts 1+2 of the ZUMA-1 Phase 1/2 study of axi-cel in R/R LBCL, 11% and 31% of patients (pts) experienced Grade ≥3 cytokine release syndrome (CRS) or neurologic evenets), respectively. To minimize the toxicities seen with axi-cel, a safety management cohort, Cohort 6 (N=40), was added to evaluate whether prophylactic (ppx) corticosteroids (CS) could decrease grade ≥ 3 CRS or ICANS. The 2-year update of ZUMA-1 Cohort 6 showed no grade ≥3 CRS and 15% grade ≥3 ICANS without any difference in objective response rate (ORR) or complete response rate (CR) when compared to cohorts 1+2 (Oluwole Blood 2022). The FDA had previously approved an update to the prescribing information for axi-cel to include use of ppx CS across all approved indications in January 2022. However, ppx CS is not a mandatory standard treatment and we sought to establish the clinical outcomes in the real-world practice. Methods: To assess the clinical outcomes of pts receiving ppx CS, we conducted a multicenter retrospective analysis of pts with R/R LBCL who were treated with axi-cel since the FDA approval of ppx CS in January 2022. Baseline characteristics, toxicities, and efficacy were compared between the no ppx and ppx CS groups. CRS and ICANS were graded based on ASTCT 2019 guidelines. Event-free survival (EFS) was defined as time from axi-cel infusion to progression, re-treatment, or death. Overall survival (OS) was defined as time from axi-cel infusion to death due to any cause. Results: A total of 66 pts at 5 centers received axi-cel between Jan 31, 2022, and June 20, 2023. Thirty-five (52%) pts received ppx CS, with a median age of 63 years (26-85 years). By histology, 75% (n=50) of the pts had DLBCL, 13.6% (n=9) had high grade B-cell lymphoma (HGBL), 9.1% (n=6) had transformed follicular lymphoma (TFL) and 1.5% (n=1) primary mediastinal LBCL (PMBCL). 59% of the pts (n=37) had IPI &gt;2 and 66% (n=43) had stage III/IV disease. The baseline characteristics at the time of apheresis are shown in Table 1 and were comparable between the 2 groups, except for more HGBL, fewer prior lines of therapy and longer median time from apheresis to axi-cel infusion in the ppx CS group. Among the entire cohort, only 37% (n=25) met ZUMA-1 eligibility criteria at the time of lymphodepletion, and 67% (n=44) needed bridging therapy. Any grade CRS occurred in 88% (n=58) of the pts, with grade ≥2 CRS in 38% (n=25). Any grade ICANS occurred in 55% (n=37) of the pts, with grade ≥2 ICANS in 41% (n=27). Any grade ICANS was significantly lower in the ppx CS group than the no ppx group (45.7% vs 65.5%). The rates of any grade CRS, grade ≥2 CRS, grade ≥2 ICANS, the median time to CRS onset, ICANS onset, CRS duration, and ICANS duration were comparable between the 2 groups. Tocilizumab and steroids use was similar between two groups with a trend towards less ICU admission in patients in the ppx CS group. Overall, 14 (21%) pts developed infectious complications within 30 days of axi-cel infusion. The day 30 ORR was 84% and was comparable between the 2 groups (77% in the ppx group vs 93% in the no ppx group). The CR was 45.7% in ppx CS group compared to 65.5% in no ppx group. At a median follow up of 219 days (27-1178), 37 (56.1%) pts had progressed and 25 (37.9%) pts had died. The number of days to progress was significantly lower in the ppx CS arm. The median EFS and OS were not significant between the 2 groups. Conclusions: This multicenter retrospective study showed that the efficacy of treatment with axi-cel in R/R LBCL did not decrease with the use of ppx CS. No significant differences in efficacy or CAR-T-associated toxicities were noted in the 2 groups, potentially due to selective use with patients at presumed higher risk of severe CRS and ICANS. A larger dataset and longer follow-up is needed for risk-stratified analysis and the study is ongoing.

Background. Some patients who present with clinical features consistent with idiopathic hypereosinophilic syndrome (HES; absolute eosinophil count (AEC) ≥1.5 x 10 9/L with related end organ damage) are ultimately diagnosed with a myeloid neoplasm. Although FIP1L1::PDGFRA is the most common molecular abnormality in this setting, many other fusion genes, point mutations and cytogenetic abnormalities have been implicated in driving primary (neoplastic) eosinophilia. Given the poor prognosis of these disorders in the absence of treatment and the availability of targeted therapies for many of the driver mutations, it is becoming increasingly important to rapidly identify the underlying genetic alteration. In this regard, the expense and variable sensitivity of molecular diagnostic tests remains problematic. Although clinical features have been reported to distinguish between PDGFRA-associated myeloid neoplasms and D816V KIT-positive systemic mastocytosis with hypereosinophilia, little is known about the clinical phenotypes of other subsets of patients. This multicenter retrospective study aimed to assemble a large cohort of patients with HES secondary to a myeloid neoplasm to explore the utility of clinical and laboratory features in predicting the underlying molecular abnormality. Methods. Retrospective, de-identified data from 16 centers were collected via an online Research Electronic Data Capture repository. Patients and associated data were obtained from in-house research databases and/or electronic medical record searches at each site. Clinical and laboratory data were entered in accordance with local Institutional Review Boards. Inclusion criteria were peripheral blood hypereosinophilia (AEC &gt;1.5 x 10 9/L) on at least two occasions and one of the following: ≥1 confirmed genetic abnormality recurrently associated with primary myeloid neoplasms, other evidence of clonal eosinophilia, or increased blasts (≥2% in the blood or &gt;5% but &lt;20% in the marrow). Patients with acute myeloid leukemia were excluded. Results. A total of 277 patients followed between 1990 and 2022 were included in the analysis. Median length of follow up was 31 months (range &lt;1-356), and 217/277 (78%) were alive at last follow up. The most common genetic abnormality was FIP1L1::PDGFRA (n=131) followed by D816V KIT mutations (n=39) and alterations involving JAK2 (n=22) (Figure 1). Five patients had genetic abnormalities involving two distinct genes recurrently associated with eosinophilic myeloid neoplasms. The overall median age at diagnosis was 55 years (range 12-89) and 79% of the patients were male. When patients with abnormalities involving PDGFRA and PDGFRB were excluded from the analysis, the male predominance was significantly lower at 62% (p&lt;0.001, Fisher's exact test as compared to the data set as a whole). The overall pattern of organ system involvement was similar irrespective of the underlying genetic abnormality with a few notable exceptions. Cardiac involvement was most common in patients with FIP1L1:: PDGFRA, abnormalities involving JAK2 or without pathologic alterations identified (reported in 22%, 32% and 30%, respectively); whereas skin and gastrointestinal involvement, lymphadenopathy and splenomegaly were most frequent in patients with KIT D816V. Laboratory abnormalities also differed between groups. Whereas anemia was the most common blood abnormality (reported in &gt;50% of patients), erythrocytosis was noted primarily in patients with abnormalities involving JAK2. In contrast, circulating blasts were identified in 70% of patient with BCR::ABL1 and 29% of patients with chromosomal abnormalities or KIT D816V, but in &lt;15% of patients in any of the other groups. Whereas peak AEC alone did not discriminate between the different patient groups, the AEC/tryptase ratio was increased in patients with PDGFRA-associated myeloid neoplasms, molecular abnormalities involving JAK2, or chromosomal abnormalities as compared to those with KIT mutations (Figure 2). Conclusions. Despite the limitations of retrospective data analysis, the data from this large multicenter cohort of patients with HES due to a chronic myeloid neoplasm suggest that routine demographic, clinical and laboratory features vary depending on the underlying molecular abnormality. This approach could ultimately help guide empiric therapy when molecular studies are negative or unavailable.

Background: The use of CAR-T cell therapy has transformed treatment paradigms in B-cell malignancies. Ciltacabtagene autoleucel (cilta-cel) was approved for use in RRMM after four or more prior lines of therapy in 2022. While the pivotal studies exclusively treated patients in an inpatient setting, robust infrastructure planning at some centers across US has fostered outpatient administration of the commercially available product. Outpatient administration of CAR-T is more desirable due to superior financial sustainability, lower healthcare resource utilization, and greater patient autonomy during the treatment. Hence, we conducted a qualitative study to evaluate clinical and administrative perspectives and trends in outpatient administration of commercialized cilta-cel with an aim to understand best practices from certified CAR-T centers in the USA. Methods: A targeted literature review was conducted to better understand current practices around outpatient administration of CAR-T, and inform the development of primary research materials for designing subsequent interviews. Next, two 60-minute exploratory interviews were conducted with multi-stakeholder participants (n=5) from two certified cilta-cel centers, each with significant volume of outpatient administration of cilta-cel. Following the qualitative analysis of interviews, two 90-minute panels were conducted with multi-stakeholder participants (n=14) from six certified cilta-cel centers, including centers from exploratory interviews, focusing on clinical and administrative topics across the patient journey. Results: Each center in the study treated approximately 15-30 patients with cilta-cel in the outpatient setting. Using Likert scales, participants from all centers ranked space/capacity as the most important factor in decision-making process for outpatient cilta-cel administration, and ranked reimbursement incentives as a highly (67% of participants) or a moderately (33%) important factor. All participants agreed that having a dedicated outpatient infrastructure (dedicated space such as bed availability and internal processes including standard operating procedures (SOPs)), 24/7 support, outpatient bone marrow transplant (BMT) or cell therapy experience, and robust multidisciplinary teams were key to setting-up successful outpatient centers for cilta-cel therapy. The participants agreed that cilta-cel can be administered safely in an outpatient setting due to generally predictable, delayed onset of potential AEs, except in patients with significant comorbidities or organ dysfunction. Participants also considered caregiver support and lodging availability as factors of importance for outpatient administration. Institutionally established AE monitoring protocols are critical for safe use of cilta-cel in an outpatient setting. Over 50% of the centers interviewed have recently started to administer tocilizumab to treat mild grade 1 cytokine release syndrome (CRS) in an outpatient setting. Based on the findings across the phases of research, the patient journey for outpatient administration of cilta-cel was updated (Figure 1). While patients may be admitted for toxicity events, 100% of centers interviewed had 24-hour coverage and bed availability for these patients if needed. Conclusions: Overall, this study further supports the notion that centers can safely administer cilta-cel in an outpatient setting, if appropriate infrastructure is in place. Additional best practices for new outpatient sites include adequate infrastructure, SOPs, a well-trained and multidisciplinary team, and education of patients and caregivers (Table 1). Outpatient management and earlier intervention for low-grade AEs is currently evolving, with more real-world research required. Continued expert sharing of best practices can aid centers in implementing outpatient administration of CAR-T therapies. Funding: This analysis was supported by Janssen Research & Development, LLC and Legend Biotech USA, Inc

Despite notable advancements in treating chronic lymphocytic leukemia (CLL) with targeted therapies, a significant clinical challenge arises as a subset of CLL patients progress and develop Richter's transformation (RT), an aggressive form of lymphoma. While immune cell dysfunction and T cell defects are well-known characteristics of CLL, the alterations in immune cell subsets during CLL progression to RT remain largely unexplored. While CLL patients typically fail to respond to anti-PD1 pembrolizumab, a positive response has been observed in 20-40% of RT patients. Previously, our study involving three RT patients (1 responder and 2 progressors) revealed enriched regulatory T cells (Tregs) in the responders compared to progressors after pembrolizumab treatment (Iyer et al, ASH2020). Hence, we propose that dynamic changes in T cell subsets at baseline may be associated with response to pembrolizumab treatment. To this end, we performed single-cell RNA sequencing on sorted T cells (CD3 +) from PBMCs derived from 20 patients (responders (RES), n=5; stable disease (SD), n=5; progressive disease/progressors (PD), n=10). A total of 408,627 cells were captured, and an average of 1,393 genes were detected per cell per patient. Using a graph-based clustering approach (Seurat V4.3), we identified 19 clusters based on marker genes and transcriptional signatures and identified enriched pathways using Enrichr analysis. Our results showed that RES had an increased Th17 subset at baseline compared to PD (15% vs. 5%, p=0.01) and reduced Th2 T cells compared to SD (p=0.004) and PD (p=0.05). The Th17/Th2 ratio was higher in RES at baseline (Th17/Th2 R: 1.24, PD: 0.21, SD: 0.25, p0.05) and post-pembrolizumab (Th17/Th2 RES: 1.31, PD: 0.34, SD: 0.30, p0.05). Furthermore, RES had an increased fraction of proliferating CD4 T cells at baseline (4% RES vs. 0.4% SD and 0.4% PD, p=0.02) and post-treatment (1.9% RES vs. 0.8% PD and 0.34% SD, p=0.02). Although we observed an increasing trend in the fraction of Tregs in the RES at baseline [(7.6% RES vs.6.1% PD and 6.5% SD, p=0.4; ns) and post-treatment (10.3% RES vs. 8.3% PD and 5.8% SD, p= 0.2; ns] compared to PD and SD, the difference was not significant. Similarly, among CD8+ T cells, we observed an increasing trend in CD8+ effector T cell fraction in the responders at baseline (29.8% RES vs. 21% PD and 15.6% SD, p=0.9, ns) and post-treatment (30.1% RES vs. 21.2% PD and 19.9% SD, p=0.44, ns). However, the difference was not statistically significant. These findings highlight the dynamic changes in T cell subsets associated with pembrolizumab response. In terms of transcriptional changes in Tregs following pembrolizumab treatment among RES, PD, and SD, we observed dynamic changes on a few Treg marker genes, including TIGIT and TOX. TIGIT and TOX expression drastically decreased after treatment in RES (p &lt; 0.0001), while expression did not change in PD and SD. There were no significant changes in the expression of FOXP3 or CD27 in RES, PD, and SD before and after the treatment. In CD8 effector T cells, GZMK, GZMA (granzymes), and PRF1 (perforin) are marker genes. We observed higher expression of GZMK and GZMA in RES (p &lt;0.0001) at the baseline compared to SD and PD. In the proliferating CD4 T cells, we observed increased expression of IDH2 (Isocitrate dehydrogenase 2-key enzyme of TCA cycle) in RES at the baseline, as compared to PD and SD, indicating increased TCA cycle activity in the proliferating T cells. Pathway analysis of T cell clusters using the Enrichr database showed TNFA-IFNG-MYC targets are enriched in CD8 + cells, IL2-STAT5 signaling is upregulated in Th17, TREGs, and E2F cell cycle associated pathways enriched in CD4 + proliferation cluster. In conclusion, our study unveils significant baseline differences in CD4 subsets between RES and PD/SD subjects and dynamic changes in T cell subsets and transcriptional signatures. These findings offer potential predictors of pembrolizumab response in RT, such as increased Th17/Th2 ratio, enriched proliferating CD4 + T cells, and elevated TIGIT, TOX gene expression in Tregs, GZMK, and GZMA in CD8 effector cells. This deeper understanding of the immunological landscape in RT patients sheds light on the interplay between T cell subsets and treatment response in RT, paving the way for personalized therapeutic strategies. Further validation and exploration can lead to improved outcomes and tailored interventions for RT.

Introduction: Molecular classifications have been developed to characterize the heterogeneity of diffuse large B cell lymphoma (DLBCL), with activation of BCL6 and Notch signaling pathways acting as driving pathogenic features in C1/BN2 subtype tumors. Among C1/BN2 defining variants are truncating/inactivating SPEN mutations. SPEN regulates the Notch signaling pathway by initiating formation of a repressive complex that facilitates transcriptional repression of Notch target genes. Our group has identified SPEN mutations enriched in DLBCL cases failing to achieve event-free status at 24 months (EFS24). This contrasted with generally favorable outcomes in C1/BN2 tumors, suggesting a potential high-risk molecular feature with unexplored significance. Presenting an opportunity to expand underlying mechanisms and risk stratification in C1/BN2 tumors, we aimed to use a functional genomic approach, combined with clinical data, to characterize the alternative biology stemming from SPEN truncating mutations. Methods: FFPE tumor biopsies from newly diagnosed DLBCL cases (N=444) enrolled in the Mayo Clinic/Iowa Lymphoma Molecular Epidemiology Resource (MER) program were analyzed by WES (n=404) and RNA-seq (n=321). Biologic and clinical variables were annotated for all cases. CRISPR/Cas9 introduced truncating mutations to the endogenous SPEN locus in OCI-LY3 & SU-DHL-2 ABC-type human cell lines to establish models of SPEN depletion. Functional in vitro analysis utilized standard methods for RNA-seq, cell proliferation, western blot, and flow cytometry. Results: WES identified 29/404 ndDLBCL (7.2%) harboring SPEN mutations; n=17 missense and n=12 nonsense or frameshift insertions/deletions (truncating variants - [trunc]), the later considered as the focal point of our study. Against all cases, SPEN trunc cases displayed enrichment for high-risk factors including non-GCB COO (p=0.06, OR=3.7, 95% CI [0.9, 22.2]) and primary refractory disease (PTR; p=0.02, OR=5.0, 95% CI [1.05, 19.9]), and demonstrated inferior OS (p=0.06, HR=2.2), where a majority of clinical progression events occurred within 12 months of diagnosis. Leveraging RNA-seq, we observed 11 of 11 SPEN trunc cases exhibiting a double-hit negative gene expression signature, 9/11 cases with inflammatory or depleted microenvironment (LME), and 8/11 with a signature associating with intermediate/high risk of EFS24 failure. Applying the LymphGen algorithm, 5/12 SPEN trunc cases received the BN2 classification, observing co-occurring mutations with CD70 (p&lt;0.01, OR=9.68), BRCA2 (p=0.03, OR=5.84), TET2 (p=0.02, OR=4.91), IRF4 (p=0.02, OR=7.27), and PTPRD (p&lt;0.01, OR=8.31) genes, and were mutually exclusive with ARID1A, BCL2, EZH2, FAS, HLA-B, IRF8, and TMEM30A mutations ( Figure 1A). Isolating SPEN trunc against BN2 cases without SPEN variants (n=14), despite similar clustering of non-GCB COO (p=0.7), PTR was exclusively observed in SPEN trunc cases, accompanied again by inferior OS (p=0.07, HR=4.2; Figure 1B). In the OCI-LY3 SPEN depletion model, GSEA analysis from RNA-seq revealed activation of E2F (NES=2.7; p=9.4E-20) and MYC target genes (NES=2.3; p=4.1E-6), while both OCI-LY3 and SU-DHL-2 models featured depletion of antigen presentation genes (NES= -1.8, p=5.7E-4; NES= -2.2, p=3.8E-7, respectively). A decrease of MHC class II proteins (HLA-DR, HLA-DP) was confirmed by flow cytometry in both models (p&lt;0.01). Hypothesizing loss of SPEN enhances reliance on the BCL6-HDAC3 axis featured in BN2 tumors, we treated both SPEN depletion models with a class-I HDAC inhibitor highly selective for HDAC3, BRD-3308, and indeed observed a 1.4 and 2.4-fold increase in sensitivity compared to WT cells (p=0.07, p&lt;0.01, respectively). Significance: We find SPEN trunc mutations in poor acting DLBCL cases with clinical and biologic characteristics that diverge from C1/BN2 biology. The enhanced rate of clinical progression highlights urgency to better characterize these tumors. Our data suggests loss of SPEN regulatory mechanisms may act cooperatively with C1/BN2 biology to facilitate tumor immune evasion and drive progression through Notch-mediated pathways. Importantly, in vitro evidence shows SPEN deficient lymphoma cells are susceptible to targeted therapeutics against dependent pathways, providing rationale for advancing individualized care strategies for affected patients.

MB and VA equal contributors AB and STO co-corresponding authors This study was initiated following evaluation of a 32 year-old woman who presented with a history of thrombocytopenia identified in childhood who subsequently developed features of myelofibrosis (MF). A bone marrow biopsy demonstrated hypercellularity in conjunction with megakaryocyte hyperplasia and marked reticulin fibrosis. Molecular testing for JAK2, CALR, and MPL mutations was negative. Given the unusual association between congenital thrombocytopenia and MF in this patient, exome sequencing was performed, revealing a heterozygous R304W mutation in the coiled coil (CC) domain of STIM1. Activating mutations in the CC and EF hand domains of STIM1 have been associated with Stormorken syndrome, a rare congenital platelet disorder associated with abnormal store operated calcium entry (SOCE). We subsequently identified a second patient with MF associated with a STIM1 activating mutation. This individual was found to have severe thrombocytopenia at birth, and exome sequencing revealed a heterozygous S88G mutation in the EF hand of STIM1. A bone marrow biopsy obtained at 6 months of age revealed atypical megakaryocytes and grade 1-2 MF. A repeat biopsy at age 2 showed persistence of stable MF. The unusual finding of MF in these two patients suggested the possibility of altered calcium signaling as a shared mechanism driving congenital platelet disorders such as Stormorken syndrome and myeloproliferative neoplasms (MPNs) including MF. In support of this notion, we identified elevated STIM1 expression in MF vs normal megakaryocyte progenitors, as well as in platelets from patients with essential thrombocythemia (ET) vs healthy controls. Additionally, we found that STIM1 expression was significantly elevated in CD34+ hematopoietic stem/progenitor cells (HSPCs) from both ET and MF patients vs healthy controls. Notably, STIM1 expression was increased in both JAK2 and CALR-mutant MF patients. Collectively, these findings provide evidence of aberrant STIM1 expression in MPN patient cells. To determine the functional role of STIM1 in MPN disease development, colony assays and patient-derived xenograft (PDX) experiments were performed with MF patient CD34+ cells subjected to CRISPR ablation of STIM1. Strikingly discordant results were observed with JAK2 vs CALR-mutant patient samples. Abrogation of STIM1 in CALR-mutant CD34+ cells led to decreased colony formation, and NSGS mice engrafted in parallel with STIM1-targeted cells exhibited decreased human CD45+ cell engraftment in conjunction with prolonged survival. These findings suggest an important role for STIM1 in CALR-mutant MPN disease phenotypes. In contrast, targeting of STIM1 in JAK2-mutant CD34+ cells led to increased colony formation and exacerbated disease phenotypes in vivo as manifested by enhanced human CD45+ cell engraftment, worsened splenomegaly, and early lethality. Similar results were obtained in experiments utilizing pharmacologic inhibitors of SOCE activity. Taken together, these findings indicate that the consequences of aberrant STIM1 activity may be context-dependent relating to specific MPN driver mutations. To expand these observations, we identified a separate cohort of 9 family members in Italy with Stormorken syndrome and confirmed STIM1 EF hand mutations. In ex vivo megakaryocytic differentiation assays, cells from affected individuals exhibited a defect in proplatelet formation. These observations were corroborated by initial analyses of a newly generated Stim1 R304W conditional knock-in mouse which recapitulated the characteristic thrombocytopenia found in patients with Stormorken syndrome. In summary, this study represents the first demonstration of MF development in patients with Stormorken syndrome, thereby uncovering a previously unrecognized hallmark of altered calcium signaling via aberrant STIM1 activation underlying Stormorken syndrome and MPNs. Our findings suggest distinct mechanisms relating to the interaction between JAK2 vs CALR mutation and altered STIM1 activity. Further studies of these relationships may have important ramifications for potential therapeutic approaches targeting these pathways.

Introduction: Anemia is a cardinal feature of myelofibrosis (MF), along with splenomegaly and constitutional symptoms. Red blood cell (RBC) transfusions, often used to manage anemia in patients (pts) with MF, are a negative prognostic factor for overall survival and are associated with diminished quality of life and increased healthcare-related economic burden. Momelotinib (MMB), a Janus kinase (JAK) 1/JAK2/activin A receptor type 1 inhibitor, has demonstrated clinically meaningful and durable improvements in anemia, splenomegaly, and symptoms. Prespecified anemia endpoints in MMB phase 3 studies prioritized achievement of a strict transfusion independence response, defined as no transfusions for ≥12 wk immediately before the end of wk 24, with all hemoglobin levels ≥8 g/dL. Longitudinal analysis of transfusion intensity (units per 28 days) in a phase 2 trial of MMB in pts with transfusion-dependent MF demonstrated a reduction in transfusion burden in most (85%) pts (Harrison C, et al. EHA 2023). Here, we further characterize the impact of MMB and comparators on transfusion burden in pts with JAK inhibitor-naive and -experienced MF from the phase 3 SIMPLIFY-1 and MOMENTUM trials. Methods: This analysis evaluated time-dependent transfusion burden in pts enrolled in the phase 3 SIMPLIFY-1 (NCT01969838) and MOMENTUM (NCT04173494) trials. SIMPLIFY-1 included pts with JAK inhibitor-naive MF randomized (1:1) to receive MMB or ruxolitinib (RUX). In MOMENTUM, pts with symptomatic (Myelofibrosis Symptom Assessment Form Total Symptom Score ≥10), anemic (hemoglobin &lt;10 g/dL), JAK inhibitor-experienced MF were randomized (2:1) to receive MMB or danazol (DAN). All RBC units transfused were collected during the 24-wk randomized treatment period of each study and during the 84 days before receipt of randomized treatment on study for baseline assessment. Time-dependent transfusion burden was quantified by number of RBC units administered, in a tabular display of baseline- and treatment-period intensity. Pts were grouped jointly based on the baseline- and treatment-period intensity of RBC units per 28 days into ordinal bins: exactly zero units, &gt;0 to 1 unit, &gt;1 to 2 units, &gt;2 to 3 units, &gt;3 to 4 units, and &gt;4 units. Results: In SIMPLIFY-1 (JAK inhibitor-naive pts), 150 of 213 evaluable pts (70%) in the MMB arm and 163 of 216 evaluable pts (76%) in the RUX arm required zero units of RBC transfusion per 28 days at baseline. Of pts who required zero units of transfusion at baseline, a higher proportion in the MMB arm (142 of 150 [95%]) maintained a requirement of zero RBC transfusions during randomized treatment of 24 wks vs the RUX arm (93 of 163 [57%]). Overall, the mean RBC transfusion burden per 28 days declined 0.10 units (SD, 0.701) from baseline to randomized treatment in the MMB arm and increased 0.39 units (SD, 1.016) in the RUX arm. Using ordinal bins, 87% of pts in the MMB arm maintained (144 [67.6%]) or improved (41 [19.2%]) RBC transfusion intensity during randomized treatment compared with baseline vs 54% in the RUX arm (maintained, 94 [43.5%]; improved, 23 [10.6%]) (Figure). In MOMENTUM (JAK inhibitor-experienced pts), most pts had some transfusion requirement at baseline, with 26 of 130 (20%) in the MMB arm and 11 of 65 (17%) in the DAN arm requiring zero units of RBC transfusion per 28 days. During randomized treatment, a higher proportion of pts in the MMB arm (46 of 130 [35%]) required zero units of RBC transfusion vs the DAN arm (11 of 65 [17%]), including a higher proportion of those who had zero RBC transfusion requirement at baseline who maintained zero RBC transfusion requirement during randomized treatment (MMB, 92%; DAN, 64%). The mean RBC transfusion burden per 28 days declined 0.86 units (SD, 1.748) from baseline to randomized treatment in the MMB arm and declined 0.28 units (SD, 1.584) in the DAN arm. Using ordinal bins, 85% of pts in the MMB arm maintained (25 [19.2%]) or improved (85 [65.4%]) RBC transfusion intensity compared with baseline vs 63% in the DAN arm (maintained, 7 [10.8%]; improved, 34 [52.3%]). Conclusions: These data demonstrate that MMB was associated with better maintenance of RBC transfusion intensity and zero RBC transfusion status vs RUX in pts with MF who were JAK inhibitor naive and showed greater reduction in RBC transfusion burden from baseline vs DAN in pts with MF who were JAK inhibitor experienced. Across both trials, ≥85% of pts treated with MMB maintained or improved transfusion intensity.