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Autoimmune thrombotic thrombocytopenic purpura (aTTP) is caused by autoantibodies to the von Willebrand Factor cleaving enzyme, ADAMTS13. Despite recent advances in the treatment of acute aTTP, relapse rates remain high. Guidance for the treatment of patients in clinical remission but with persistent severe ADAMTS13 deficiency who fail to respond to rituximab remains unclear. We report a case of a 29-year-old man diagnosed with aTTP at the age of 11. Over a period of 18 years, he had five clinical relapses with persistent severe ADAMTS13 deficiency (

Leukemic relapse remains a major barrier to successful allogeneic hematopoietic stem cell transplantation (allo-HSCT) for aggressive hematologic malignancies. The basis for relapse of advanced lymphoid malignancies remains incompletely understood and may involve escape from the graft-versus-leukemia (GvL) effect. We hypothesized that for patients with chronic lymphocytic leukemia (CLL) treated with allo-HSCT, leukemic cell-intrinsic features influence transplant outcomes by directing the evolutionary trajectories of CLL cells. Integrated genetic, transcriptomic, and epigenetic analyses of CLL cells from 10 patients revealed that the clinical kinetics of post-HSCT relapse are shaped by distinct molecular dynamics. Early relapses after allo-HSCT exhibited notable genetic stability; single CLL cell transcriptional analysis demonstrated a cellular heterogeneity that was static over time. In contrast, CLL cells relapsing late after allo-HSCT displayed notable genetic evolution and evidence of neoantigen depletion, consistent with marked single-cell transcriptional shifts that were unique to each patient. We observed a greater rate of epigenetic change for late relapses not seen in early relapses or relapses after chemotherapy alone, suggesting that the selection pressures of the GvL bottleneck are unlike those imposed by chemotherapy. No selective advantage for human leukocyte antigen (HLA) loss was observed, even when present in pretransplant subpopulations. Gain of stem cell modules was a common signature associated with leukemia relapse regardless of posttransplant relapse kinetics. These data elucidate the biological pathways that underlie GvL resistance and posttransplant relapse.

Resistance to the graft-versus-leukemia (GvL) effect remains the major barrier to successful allogeneic hematopoietic stem cell transplantation (allo-HSCT) for aggressive hematologic malignancies. The basis of GvL resistance for advanced lymphoid malignancies remains incompletely understood. We hypothesized that for patients with chronic lymphocytic leukemia (CLL) treated with allo-HSCT, leukemic cell-intrinsic features shape GvL outcomes by directing the evolutionary trajectories of CLL cells. Integrated genetic, transcriptomic and epigenetic analyses of CLL cells from 10 patients revealed that the clinical kinetics of post- HSCT relapse are shaped by distinct molecular dynamics and suggest that the selection pressures of the GvL bottleneck are unlike those imposed by chemotherapy. No selective advantage for HLA loss was observed, even when present in pre-transplant subpopulations. Regardless of post-transplant relapse kinetics, gain of stem cell modules was a common signature associated with leukemia relapse. These data elucidate the biological pathways that underlie GvL resistance and post-transplant relapse.One Sentence SummaryWe find that the clinical kinetics of chronic lymphocytic leukemia relapse after stem cell transplant are underwritten by distinct genetic and epigenetic evolutionary trajectories and suggest that the selection pressures of the post-transplant, immunologic bottleneck are unlike those imposed by chemotherapy.

Introduction: Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a life-threatening disease with a mortality 10-20% despite emergent therapeutic plasma exchange (TPE). The distinguishing aspect of iTTP from other thrombotic microangiopathies is a severe deficiency of ADAMTS13 ( Methods: Parkland Health and Hospital System records were reviewed ADAMTS13 activity tests (n = 361) from January 2019 to March 2021, excluding patients with known iTTP and/or outpatient tests; resulting in a final cohort of 42 patients with inpatient ADAMTS13 activity tests for suspected iTTP. Suspicion for iTTP-time zero for our time to TPE analysis-was determined by the time that the ADAMTS13 order was placed. Hematology consultation time was based on when the order was placed by the provider. The initiation of TPE, as documented by the apheresis team, was the end-time for the time to TPE calculation. Thus, time to TPE was the time elapsed between the electronic ADAMTS13 order being placed and TPE being initiated. Results: The median patient age was 43 years with 36% Black patients and 50% Hispanic. Hematology service consultation occurred in 95% of cases, although only 79% of hematology consultations occurred before ADAMTS13 activity orders were placed (Table 1). The most common services to order an ADAMTS13 activity prior to hematology consultation were obstetrics and gynecology (2/2, 100%), neurology (1/1, 100%), and medical intensive care (5/14, 36%) with 88% of these tests being placed for patients with a PLASMIC score ≤ 4. None of these patients were diagnosed with iTTP. Using a PLASMIC score ≥6 as a diagnostic test for iTTP, the sensitivity was 50%, specificity 84%, positive predictive value 20%, and negative predictive value was 94%. A subgroup analysis of patients empirically treated for iTTP (n = 7) demonstrated a wide variation in the time from ADAMTS13 activity orders being placed to initiation of TPE, ranging from 4 hours 44 minutes to 3 days 14 hours (Table 2). Only one patient (without a pre-existing central line) received empiric TPE in under 6 hours (5 hours and 20 minutes). One patient had an ADAMTS13 activity that resulted with a critical ADAMTS13 deficiency and was initiated on TPE; this level was re-analyzed, found to be spurious, and the TPE was ceased immediately. No patients received empiric plasma transfusion. Discussion: At our county, public hospital, 95% of cases with suspected iTTP involved hematology consultation during their evaluation, but the most common situations where hematology was not involved at all or was involved late were due to non-internal medicine services, identifying areas for focused educational interventions. The PLASMIC score demonstrated insufficient sensitivity (50%) to confidently exclude iTTP, suggesting that it is an inadequate risk stratification tool for our specific patient population. This may be due to differences between our patient population (with a median age of 43 and 12% white patients) and the derivation cohort for the PLASMIC score (with a median age of 51 and 77% white patients; Bendapudi 2017). The finding that only one patient without a pre-existing central line received TPE in ≤6 hours suggests that there is room for quality improvement interventions to hasten time to treatment. This initial study has led to the development of systemic, hospital-wide electronic medical record order set changes combined with educational interventions which will be evaluated prospectively for its impact on iTTP diagnosis and treatment. Broadly, this study re-demonstrates that the evaluation, diagnosis, coordination, and treatment of iTTP is often logistically challenging. Promoting earlier hematology consultation and optimizing EMR interventions is likely to facilitate appropriate ADAMTS13 testing, expedite results, and help coordinate the initiation of TPE in patients with suspected iTTP. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

The factors mediating GvL resistance following allogeneic stem cell transplant (SCT) in lymphoid malignancies remain incompletely characterized. Because cell-intrinsic features shape chemotherapeutic relapse, we hypothesized that they also shape GvL outcomes by influencing evolutionary trajectories of CLL relapse after reduced intensity conditioning SCT (RIC). We identified 9 heavily pre-treated patients (pts) (range: 1-5 therapies, median: 3) with various times to CLL relapse after RIC (range: 83-1825 days), of which 8 had at least partial responses before relapse. To define evolutionary trajectories, we generated paired whole-exome and RNA sequencing data from purified CLL cells pre/post-RIC, using MuTect2 and ABSOLUTE algorithms to identify somatic alterations (SAs) and corresponding cancer cell fractions (CCFs). 5 pts had clonal SAs in TP53 and/or SF3B1 pre-SCT, and no single SA was specific to post-RIC. Furthermore, we found no SAs nor altered expression of HLA class I/II or b2M in either baseline or post-RIC samples. However, we found 6 relapse pairs to exhibit complex branched evolution involving CCF shifts of at least 0.2 in subclonal and clonal SAs whereas 3 pairs showed genomic stability. Clonal evolution was associated with longer time to relapse (Wilcoxon, p=0.02; median 798 versus 304 days) as well as complete response (p=0.05), suggesting that GvL immune escape may be facilitated by clonal evolution. To determine the phenotypic consequences of clonal evolution, we examined single cell transcriptomes using scRNAseq from paired pre/post-RIC CLL cells from 2 pts with early (304, 442 days; "ERs") and 2 pts with late (1801, 1825 days; "LRs") relapses after RIC. Using the inDrop platform, we profiled a median of 3560 CLL cells/pt (range: 2254-5278). Clustering using Seurat revealed marked transcriptional stability after RIC in ERs whereas dramatic shifts in gene expression programs were observed in LRs. Single cell trajectory analysis using Monocle identified ordered biological processes through which LRs, but not ERs, progressed. Branched expression analysis revealed multiple patient specific pathways defining LRs, including within chromatin regulators (EBF1, BANK1), oncogenic pathways (AFF3, DENND4A) and ribosomal biosynthesis (EEF1G, NACA). Thus, genetic evolution in LRs results in distinct phenotypic consequences. To directly link SAs with transcriptional outcomes, we interrogated scRNAseq data for known SAs identified by WES. In one LR, loss of a CLL cancer driver (RPS15mut) was observed in two of three post-RIC transcriptional clusters, either through deletion of chr.19p (where RPS15 resides) or reversion to the wildtype allele (implying loss of heterozygosity). In addition, genomic and transcriptional loss of HLA genes were detectable in pre-RIC clusters that failed to expand at relapse in both LRs, suggesting that pre-existing HLA loss does not provide a selective advantage for CLL relapse after RIC, consistent with our bulk analyses. These data highlight how scRNAseq can delineate genetic selection pressures within subpopulations of a single patient. To investigate whether epigenetic dysregulation underlies these genetic changes, we measured locally disordered methylation (LDM), a known epigenetic mechanism of CLL genetic variability. Genome-wide methylome profiles revealed increases in LDM in LRs compared to ERs for various genomic regions (Kruskal-Wallis (KW), p Altogether, these data highlight important features of GvL resistance in CLL: 1) GvL selective pressure, shown by LRs, can shape evolutionary trajectories through genotypic alterations that directly exert phenotypic consequences; 2) alterations in HLA genes have less influence in CLL than in myeloid malignancies; and 3) GvL immune editing may select for epigenetic variability that facilitates evasion through stem-like states. Disclosures Brown: Octapharma: Consultancy; Novartis: Consultancy; Loxo: Consultancy, Research Funding; Kite: Consultancy, Research Funding; Janssen: Honoraria; Invectys: Other: other; Gilead: Consultancy, Research Funding; Genentech/Roche: Consultancy; Dynamo Therapeutics: Consultancy; Catapult Therapeutics: Consultancy; BeiGene: Consultancy; AstraZeneca: Consultancy; Acerta Pharma: Consultancy; Morphosys: Other: Data safety monitoring boards ; Sun Pharmaceuticals, Inc: Research Funding; Sun: Research Funding; Verastem: Consultancy, Research Funding; TG Therapeutics: Consultancy; Teva: Honoraria; Sunesis: Consultancy; Pharmacyclics: Consultancy; Pfizer: Consultancy. Getz:MuTect, ABSOLTUE, MutSig and POLYSOLVER: Patents & Royalties: MuTect, ABSOLTUE, MutSig and POLYSOLVER; IBM: Research Funding; Pharmacyclics: Research Funding. Ho:Jazz Pharmaceuticals: Consultancy; Jazz Pharmaceuticals: Research Funding; Omeros Corporation: Membership on an entity's Board of Directors or advisory committees. Neuberg:Celgene: Research Funding; Pharmacyclics: Research Funding; Madrigal Pharmaceuticals: Equity Ownership. Soiffer:Gilead, Mana therapeutic, Cugene, Jazz: Consultancy; Jazz: Consultancy; Kiadis: Other: supervisory board; Mana therapeutic: Consultancy; Cugene: Consultancy; Juno, kiadis: Membership on an entity's Board of Directors or advisory committees, Other: DSMB. Ritz:TScan Therapeutics: Consultancy; Equillium: Research Funding; Merck: Research Funding; Kite Pharma: Research Funding; Aleta Biotherapeutics: Consultancy; Celgene: Consultancy; Avrobio: Consultancy; LifeVault Bio: Consultancy; Draper Labs: Consultancy; Talaris Therapeutics: Consultancy. Wu:Neon Therapeutics: Other: Member, Advisory Board; Pharmacyclics: Research Funding.

We report a clinical trial testing vaccination of autologous myeloblasts admixed with granulocyte-macrophage colony-stimulating factor secreting K562 cells after allogeneic hematopoietic stem cell transplantation (HSCT). Patients with myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML) with ≥5% marrow blasts underwent myeloblast collection before HSCT. At approximately day +30, 6 vaccines composed of irradiated autologous myeloblasts mixed with GM-K562 were administered. Tacrolimus-based graft-versus-host disease (GVHD) prophylaxis was not tapered until vaccine completion (∼day 100). Thirty-three patients with AML (25) and MDS (8) enrolled, 16 (48%) had ≥5% marrow blasts at transplantation. The most common vaccine toxicity was injection site reactions. One patient developed severe eosinophilia and died of eosinophilic myocarditis. With a median follow-up of 67 months, cumulative incidence of grade 2-4 acute and chronic GVHD were 24% and 33%, respectively. Relapse and nonrelapse mortality were 48% and 9%, respectively. Progression-free survival (PFS) and overall survival (OS) at 5 years were 39% and 39%. Vaccinated patients who were transplanted with active disease (≥5% marrow blasts) had similar OS and PFS at 5 years compared with vaccinated patients transplanted with