Chen, Dong

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.

BACKGROUND: Recent World Health Organization (WHO) classifications (5 th edition), International Consensus Classification (ICC) recognized TP53-mutated ( TP53mut) myeloid neoplasms (MNs) as a distinct subcategory, acknowledging their uniformly poor outcomes. However, there are critical differences between the two guidelines in how TP53 allelic status is assigned. Both WHO-5 and ICC acknowledged the poor outcome of multi-hit TP53mut but excluded single-hit TP53mut. These changes are driven by a pivotal study demonstrating favourable outcome of single-hit TP53mut, however this study predominantly included de novo myelodysplastic syndromes (MDS) cases (Bernard et al. Nat Med 2020). In contrast, we previously reported poor outcome of TP53mut therapy-related myeloid neoplasm (t-MN) irrespective of the allelic status of TP53 (Hiwase et al Blood 2022andShah et al BCJ 2023). Finally, the ICC removed the subcategory of “therapy-related,” substituting it with diagnostic qualifiers instead. The WHO has grouped t-MN with secondary MN and renamed it as “myeloid neoplasm post cytotoxic therapy,” with the assertion that only multi-hit T P53mut MDS occurring post-cytotoxic therapy have poor outcome compared with single-hit. METHODS: We analyzed one of the largest international cohorts of TP53mut MN (n=544) with full characterization of TP53mut allele status utilizing uniform ICC criteria and similar large numbers of de novo and t-MN cases managed at Mayo Clinic Enterprise (USA) and South Australian MDS Registry, Adelaide (Australia) with clinical, integrated genomic profiling, and long-term follow-up. RESULTS: In our cohort of TP53mut MN (n=544), 475 (87.3%) MN had TP53mut variant allele frequency (VAF) of ≥10% and thus satisfied ICC criteria for TP53mut MN. Majority of TP53mut t-MN presented with MDS (bone marrow (BM) blasts 0-9%) compared de novo MN (62% vs. 48%; P=0.0012). While acute myeloid leukemia (AML) (BM blasts ≥20%) were more prevalent in TP53mutde novo MN compared to t-MN (38% vs. 24%; P= 0.001) and there was no difference in frequency of MDS/AML (BM blasts 10-19%) between the two cohorts (14% vs. 14%; P=0.8) ( Figure 1A). Majority of TP53mut were observed in the DNA-binding domain in t-MN and de novo MN (95% vs. 96.2%; P=0.48). However, mutations in Tetramer Domain were more frequent in t-MN (4.3% vs. 0.3%; P=0.002), whereas those in the TAD2 domain were more frequent in de novo TP53mut MN (2.4 vs. 0%; P =0.006). Integrating the mutation, conventional G-banding cytogenetic, copy number variation (CNV), FISH, and SNP array analysis, TP53mut MDS (BM blast 0-9%; n=260) were classified as multi-hit (n=179, 68.9%) or multi-equivalent (n=35, 13.5%) and single-hit (n=46, 17.7%) (Arber et al. Blood 2022). Striking enrichment of multi-hit/multi-hit equivalent was observed in TP53mut t-MDS compared to de novo MDS (91% vs. 72%; P<0.0001). While single-hit TP53mut were prevalent in de novo MDS compared to t-MDS (28% vs. 9%; P<0.0001). Importantly, median overall survival (OS) of single-hit was significantly longer than multi-hit de novo MDS (25.4 vs. 7.2 months; P=0.0002). In contrast to this we did not observe OS difference between single-hit and multi-hit TP53mut t-MDS (11.6 vs. 10.9 months; P =0.73) ( Figure 1B). CONCLUSION: Our study based on a large international cohort of T53mut MN provides compelling evidence that in contrast to de novo MDS, single hit TP53mut t-MDS is associated with poor outcome. Our data supports the consideration of single hit t-MDS as a multi-hit equivalent.

Background: Severe platelet (plt) dense granule (DG) deficiency is a hallmark of Hermansky-Pudlak syndrome (HPS), a rare, heterogeneous group of genetic disorders characterized by oculocutaneous albinism, bleeding diathesis, and lysosomal storage defects. A subset of HPS patients (pt) who has HPS1, HPS2, and HPS4 may also experience pulmonary fibrosis, granulomatous colitis, and/or immunodeficiency (syndromic HPS). Platelet transmission electron microscopy (PTEM) has been considered a valuable tool to screen such patients, and molecular testing aids in confirming te diagnosis, subclassifying the HPS and providing information on prognosis in pt. To elucidate the effectiveness of PTEM and next-generation sequencing (NGS) to identify and subclassify HPS pt, we conducted a comprehensive study on a cohort of pt with severe plt DG deficiency. Methods: After IRB approval, consecutive samples submitted to our reference laboratory for PTEM testing were analyzed. Whole mount (WM) PTEM tests were performed on all pt. Targeted NGS of the ISTH tier 1 genes (including 11 HPS-related genes) was performed on a cohort of patients who had < 0.3 mean DG/plt (200 plt counted) by PTEM. Data collected included demographics, PTEM findings, and genetic variants classified based on the 2015 ACMG criteria. Results: A total of 38 pt met our study criteria, the median age at PTEM testing was 39 years (range, 5 months to 76 years), and 22 (58%) were female. Ethnic backgrounds included Caucasian, Albanian, Puerto Rican, and other (unavailable). The mean DG/plt was 0 (0-0.2). A variant in an HPS-related gene was found in 26/38 patients (68%). The spectrum of variants in HPS-related genes is shown in Table 1, encompassing single-nucleotide substitutions, insertions, deletions, and frameshift mutations involving HPS1, HPS3, HPS5, HPS6, and HPS7 ( DTNBP1) genes. In addition to the previously reported pathogenic variants, several novel/previously unreported variants were discovered (Table 1). Interestingly, some patients presented with multiple variants, suggesting potential compound heterozygosity. No variants were found for the remaining 12 patients (32%). Conclusion: Our NGS-based genetic study of 38 patients with severe DG deficiency provides valuable insights into the complexity of this rare disorder. The high yield of finding variants in HPS-related genes verified that WM-PTEM is a useful screening tool for identifying HPS patients. The identification of known variants in HPS-associated genes confirms the importance of genetic testing not only in the diagnosis of HPS but also provides information on prognosis in syndromic HPS. Pathogenicity of novel variants remains to be elucidated. Moreover, the observed 32% of patients who had negative NGS results suggest the existence of as yet undiscovered genetic mechanisms for the severe platelet DG deficiency.

We identified a patient with a recently described syndrome, monoclonal gammopathy of thrombotic significance (MGTS; Blood. 2023 Apr 6;141(14):1772-1776), and three additional patients with high 4Ts scores who were consistently negative in the PF4-polyanion HIT ELISA (Lifecodes PF4 IgG, Immucor). The MGTS patient, with a monoclonal IgG kappa, had recurrent thrombosis, and transient mild thrombocytopenia (nadir in the low 100s) over a period of years, and was noted to have a HIT ELISA optical density (OD) of 0.117. The three HIT patients experienced thrombocytopenia and thrombosis with ELISA ODs of 0.37, 0.18 and 0.20. All patients were positive in platelet-activation (functional) testing demonstrating PF4 dependence and inhibited with both high concentrations of heparin (100U/mL) and the FcγRIIa blocking monoclonal antibody (mAb) IV.3, consistent with the presence of anti-PF4 antibodies in the patient samples ( data not shown). Because the serologic profile of these patients suggested a novel HIT subtype characterized by negative HIT ELISA results, we undertook a functional platelet assay screen of 500 consecutive HIT ELISA-negative patients tested in our diagnostic laboratory. Research studies were approved by the Institutional Review Board of Mayo Clinic. Of the 500 patients tested, 20 (4.0%) stimulated platelet activation in the PF4-dependent P-selectin Expression Assay (PEA ≥19%; data not shown). To exclude non-specific activation that can be induced by HLA antibodies, additional testing was performed to evaluate whether platelet activation was PF4-dependent using buffer or PF4-treated platelets. Three patients demonstrated PF4-dependent activation that was inhibited by high heparin concentrations and mAb IV.3, as would be expected for HIT antibodies (ELISA-negative HIT, EN-HIT1-3; Figure 1). On retrospective review, all three patients thus identified had clinical histories and courses consistent with high clinical probability for HIT. To develop tools to study this new class of antibodies, monoclonal HIT antibodies were generated in mice after PF4/heparin immunizations and screened using a novel approach that included simultaneous testing of hybridoma supernatants in the PEA and PF4-polyanion ELISA. This strategy was designed to enabled us to identify mAbs that activated platelets (in the PEA), but that did not bind antigenic targets in the HIT ELISA. A novel mAb 431.4 that was developed using this approach, and the well-characterized HIT-like mAb KKO were evaluated for their abilities to both bind PF4-polyanion targets in ELISA, and to activate PF4-treated platelets in the PEA (Figure 2). In significant contrast to KKO, mAb 431.4 did not bind PF4/polyanion complexes, however, like KKO, strongly activated platelets in a PF4-dependent manner. Activation induced by both KKO and mAb 431.4 was inhibited by high heparin concentrations, as would be expected for HIT antibodies. In vivo murine studies using this novel mAb are pending at this time. In summary, the non-canonical diagnostic profile of HIT ELISA-negative but platelet activation-positive antibodies were found at a relatively high incidence in HIT-suspected patients (0.6%; 3 of 500 ELISA-negative patients). These findings have important diagnostic/management implications and suggest a re-evaluation of ASH's HIT management guidelines as noted in recommendations 2.7 and 2.8 of that document (“In patients with an intermediate (Recommendation 2.7) or high (Recommendation 2.8)-probability 4Ts score and a negative immunoassay, the ASH guideline panel recommends discontinuation of the non-heparin anticoagulant and resumption of heparin, if indicated ”; Blood Adv (2018) 2 (22): 3360-3392). Figure 1. A subset of ELISA-negative HIT-suspected patients harbor anti-PF4 platelet-activating antibodies. Three ELISA-negative (EN) HIT patient samples from a screen of 500 samples demonstrate PF4-dependent platelet activation and inhibition with high heparin concentration and mAb IV.3 incubation. PBS, phosphate buffered saline; IC, isotype control; HDH- high dose heparin (100U/mL). Figure 2. Murine mAb 431.4 serologically mimics pathogenic ELISA-negative HIT/MGTS antibodies. ELISA and PEA testing was performed using the “HIT-like” mAb KKO, novel mAb 431.4, or an isotype control (IC) antibody. PVS-polyvinyl sulfonate (polyanion used in the Immucor IgG ELISA assay).

BACKGROUND: Recently proposed World Health Organization (WHO, 5 th edition) and International Consensus Classification (ICC) recognized myeloid neoplasms (MN) harboring TP53-mutated ( TP53mut) as a separate entity. However, there are critical differences between the two classifications regarding allelic-status, variance allele frequency (VAF) cut-off and blast categories, that may lead to under- or overestimation of the risk. METHODS: We analyzed MN harboring TP53mut (VAF ≥2%, n=536) managed at Mayo Clinic (USA) and South Australia Health Network (Australia). ICC (Arber et al, Blood 2022) and WHO (Bluebook, Beta v2) definitions were used to stratify MN harboring TP53mut. RESULTS: Of 536 cases, 379 (71%) had myelodysplastic syndromes (MDS) (<20% blasts) and 157 (29%) had acute myeloid leukemia (AML). Using WHO, 160 (42%) of 379 were classified as MDS-bi TP53 as they harbored 2 TP53mut (n=115; 30%) or 1 TP53mut plus confirmed loss of heterozygosity (LOH) or copy neutral LOH (cnLOH) of TP53 locus (n=45; 12%). Sixty-two (16%) TP53mut MDS with VAF >49% were classified as presumptive MDS-bi TP53. Of the 157 cases with 1 TP53mut VAF ≤49%, 17 confirmed to have an intact wild-type TP53 copy and were classified as monoallelic. While 140 (89%) cases did not have copy number variation (CNV) analysis. We next evaluated the number of TP53mut cases classified differently by WHO and ICC. As WHO does not recognize TP53mut AML as a separate entity, 157 (29%) TP53mut AML were not classifiable. 46% (174/379) of the TP53mut MDS including 48 (30%), 12 (19%) and 79 (65%) of bi TP53, presumptive bi TP53 and monoallelic TP53mut MDS according to WHO were classified differently by ICC ( Figure 1A). Discordance between the two classifications were predominantly driven by: (i) The difference in VAF cut-off. Sixty patients (11%) with TP53mut VAF <10% were excluded from the ICC classification of TP53mut MN as it mandates TP53mut VAF cut-off ≥10%. 11 (18%) and 41 (68%) of these had bi TP53, monoallelic TP53mut MDS by WHO criteria while 8 (13%) had AML. Importantly, within the VAF <10% cohort, median overall survival (OS) of 2 TP53mut or 1 TP53mut with 17p13.1 (hereafter 17p) deletion or complex karyotype (CK, n=30) was significantly poor compared to 1 TP53mut VAF <10% (11.6 vs 32.4 months; P =0.002, Figure 1B), suggesting that ICC may underestimate the poor prognosis of multi-hit or multi-hit equivalent TP53mut MN with VAF <10%. (ii) The difference in bone marrow blast cut-off. The underlying assumption by WHO is that prognosis of bi TP53mut MDS is poor irrespective of blast percentage category (0-9% vs 10-19%). In contrast, ICC considers that TP53mut MDS/AML (blasts 10-19%) is associated with poor prognosis irrespective of TP53 allelic status. Median OS of TP53mut MDS with 10-19% blasts was significantly poor compared to blast 0-9% (6.4 vs 11.6 months, P <0.0001). Second, median OS of bi TP53mut was significantly poor than monoallelic TP53mut in MDS- blast 0-9% (10.1 vs 15.9 months; P =0.0001) but not in blasts 10-19% (6.8 vs 6.2 months; P =0.19). Hence, exclusion of monoallelic TP53mut MDS with blast 10-19% as TP53mut MN from the WHO classification may underestimate the poor prognosis. (iii) The difference in the definition of biallelic and multi-hit TP53 loss. 35 cases with 1 TP53mut VAF ≤49%, had 17p deletion but did not have CNV analysis to confirm the loss of TP53 locus and could not be classified further using WHO. ICC classified 18 (50%) of these cases as multi-hit. Median OS of 1 TP53mut VAF ≤49%, and 17p deletion on karyotype was significantly poor than 1 TP53mut (VAF ≤49%without 17p deletion on karyotype (6.4 vs 14.6 months, P =0.001). (iv) The difference in the definition of multi-hit equivalent. 32% (33/104) WHO defined monoallelic cases without available CNV data, were classified as multi-hit-equivalent by ICC as they harbored CK. However, WHO does not consider CK as presumptive evidence of bi TP53. Median OS of 1 TP53mut VAF ≤49% with CK was significantly poor compared to 1 TP53mut without CK (8.2 vs 26.9 months, P =0.0008). CONCLUSION: Our study provides evidence that poor prognosis of ‘multi-hit’ TP53 with VAF <10% is underestimated by ICC. On the other hand, poor prognosis of monoallelic TP53 MDS with 10-19% blasts as well as 1 TP53mut VAF ≤49% in the presence of CK is underestimated by WHO. These data suggest that both classifications can be further refined.

Abstract Objectives To determine the impact of residual platelets on dilute Russell’s viper venom time (DRVVT) assay in frozen-thawed plasma submitted for lupus anticoagulant (LAC) testing. Methods We measured platelet counts in frozen-thawed samples submitted for LAC testing and evaluated the association between platelet count and the DRVVT screening time and ratios. We also spiked platelets into a LAC-positive sample to observe the effect on the DRVVT. Results Progressive increase in platelet count resulted in a statistically significant shortening of the DRVVT assay results on plasma after 1 freeze-thaw cycle. A similar effect was noted on the LAC-positive sample. Conclusions Residual platelets in plasma samples result in shortening of DRVVT assay after 1 freeze-thaw cycle. This may result in a false-negative LAC test result.

AbstractThe World Health Organization (WHO) classification system categorizes advanced systemic mastocytosis (SM‐Adv) into aggressive SM (ASM), mast cell leukemia (MCL), and SM with associated hematological neoplasm (SM‐AHN). By contrast, the International Consensus Classification (ICC) requires “immature” MC cytomorphology for the diagnosis of MCL and limits SM‐AHN to myeloid neoplasms (SM‐AMN). The current study includes 329 patients with SM‐Adv (median age 65 years, range 18–88; males 58%): WHO subcategories SM‐AHN (N = 212; 64%), ASM (N = 99; 30%), and MCL (N = 18; 6%); ICC subcategories SM‐AMN (N = 190; 64%), ASM (N = 99; 33%), and MCL (N = 9; 3%); WHO‐defined MCL with “mature” MC cytomorphology and SM‐AHN associated with lymphoid neoplasms were operationally labeled as “MCL‐mature” (N = 9) and SM‐ALN (N = 22), respectively, and distinguished from ICC‐defined MCL and SM‐AMN. Multivariable analysis that included the Mayo alliance risk factors for survival in SM (age >60 years, anemia, thrombocytopenia, increased alkaline phosphatase) revealed more accurate survival prediction with the ICC versus WHO classification order: (i) survival was significantly worse with MCL‐immature versus MCL‐mature (hazard ratio [HR] 15; p < .01), (ii) prognostic distinction between MCL and SM‐AHN/AMN was confirmed in the context of ICC (HR 9.3; p < .01) but not WHO classification order (p = .99), (iii) survival was similar between MCL‐mature and SM‐AMN (p = .18), and (iv) SM‐AMN (HR 1.7; p < .01) but not SM‐ALN (p = .37) was prognostically distinct from ASM. The current study provides evidence for the independent prognostic contribution of both the ICC system for SM‐Adv and the Mayo alliance risk factors for survival in SM.