Enhancer deregulation inTET2-mutant clonal hematopoiesis is associated with increased COVID-19 severity and mortality

Background: COVID-19 causes significant morbidity and mortality, albeit with considerable heterogeneity among affected individuals. It remains unclear which host factors determine disease severity and survival. Given the propensity of clonal hematopoiesis (CH) to promote inflammation in healthy individuals, we investigated its effect on COVID-19 outcomes. Method(s): We performed a multi-omics interrogation of the genome, epigenome, transcriptome, and proteome of peripheral blood mononuclear cells from COVID-19 patients (n=227). We obtained clinical data, laboratory studies, and survival outcomes. We determined CH status and TET2-related DNA methylation. We performed single-cell proteogenomics to understand clonal composition in relation to cell phenotype. We interrogated single-cell gene expression in isolation and in conjunction with DNA accessibility. We integrated these multi-omics data to understand the effect of CH on clonal composition, gene expression, methylation of cis-regulatory elements, and lineage commitment in COVID-19 patients. We performed shRNA knockdowns to validate the effect of one candidate transcription factor in myeloid cell lines. Result(s): The presence of CH was strongly associated with COVID-19 severity and all-cause mortality, independent of age (HR 3.48, 95% CI 1.45-8.36, p=0.005). Differential methylation of promoters and enhancers was prevalent in TET2-mutant, but not DNMT3A-mutant CH. TET2- mutant CH was associated with enhanced classical/intermediate monocytosis and single-cell proteogenomics confirmed an enrichment of TET2 mutations in these cell types. We identified celltype specific gene expression changes associated with TET2 mutations in 102,072 single cells (n=34). Single-cell RNA-seq confirmed the skewing of hematopoiesis towards classical and intermediate monocytes and demonstrated the downregulation of EGR1 (a transcription factor important for monocyte differentiation) along with up-regulation of the lncRNA MALAT1 in monocytes. Combined scRNA-/scATAC-seq in 43,160 single cells (n=18) confirmed the skewing of hematopoiesis and up-regulation of MALAT1 in monocytes along with decreased accessibility of EGR1 motifs in known cis-regulatory elements. Using myeloid cell lines for functional validation, shRNA knockdowns of EGR1 confirmed the up-regulation of MALAT1 (in comparison to wildtype controls). Conclusion(s): CH is an independent prognostic factor in COVID-19 and skews hematopoiesis towards monocytosis. TET2-mutant CH is characterized by differential methylation and accessibility of enhancers binding myeloid transcriptions factors including EGR1. The ensuing loss of EGR1 expression in monocytes causes MALAT1 overexpression, a factor known to promote monocyte differentiation and inflammation. These data provide a mechanistic insight to the adverse prognostic impact of CH in COVID-19.

Review of clonal hematopoiesis, subtypes and its role in neoplasia and different morbidities.

Clonal hematopoiesis (CH) is the development of a certain cell lineage which is the cornerstone of hematologic malignancy especially myeloid neoplasms, however, can also be found in old age (6th-7th decade). CH is caused by many different somatic mutations most commonly in DNMT3A, TET2, ASXL1, SF3B1 and TP53. It is detected by different sequencing methods, the most commonly used ones are next generation sequencing (NGS) which can be whole exome, whole genome sequencing or a panel for certain genes. CH is divided into multiple categories depending on the clinical picture associated with it into: clonal monocytosis of undetermined significance (CMUS), clonal hematopoiesis of indeterminate significance (CHIP), clonal cytopenia and monocytosis of undetermined significance (CCMUS) and clonal cytopenia of undetermined significance (CCUS). In order to diagose CH, first other hematologic malignancies must be ruled out CH is also associated with many different entities including lung cancer and some studies have shown that COVID-19 infections are affected by CH. Certain traits and infections are associated with CH including smoking, obesity, and cardiovascular disease. A minority of patients with CH progress to a malignant process (between 0.5 %-2 %) which do not require treatment, however, any patient with CH should be kept under surveillance in order to detect any malignancy early and be treated accordingly. SIMPLE SUMMARY: Clonal hematopoiesis (CH) is considered to be the predisposing factor for development of different hematologic neoplasms. With the help of NGS, patients with CH can be monitored more closely. Several studies have shown that these patients might develop hematologic neoplasms in their lifetime. It has been subdivided into multiple groups according to the clinical picture and/or blood counts.

Shedding Light on the Pathogenesis of Splanchnic Vein Thrombosis.

Splanchnic vein thrombosis is a rare but potentially life-threatening manifestation of venous thromboembolism, with challenging implications both at the pathological and therapeutic level. It is frequently associated with liver cirrhosis, but it could also be provoked by myeloproliferative disorders, cancer of various gastroenterological origin, abdominal infections and thrombophilia. A portion of splanchnic vein thrombosis is still classified as idiopathic. Here, we review the mechanisms of splanchnic vein thrombosis, including new insights on the role of clonal hematopoiesis in idiopathic SVT pathogenesis, with important implications from the therapeutic standpoint.

Emergency Hematopoiesis in the Pathobiology of COVID-19: The Dark Side of an Early Innate Protective Mechanism.

The recognition of pathogens to which we are constantly exposed induces the immediate replenishment of innate immune cells from the most primitive stages of their development through emergency hematopoiesis, a central mechanism contributing to early infection control. However, as with other protective mechanisms, its functional success is at risk when the excess of inducing signals accelerates immunological catastrophes. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection exhibits a clinical spectrum that ranges from completely asymptomatic states to fatal outcomes, with the amplification of inflammatory components being the critical point that determine the progress, complication, and severity of the disease. This review focuses on the most relevant findings that entail emergency hematopoiesis to SARS-CoV-2 infection response and revolutionize our understanding of the mechanisms governing the clinical prognosis of COVID-19. Of special interest are the metabolic or hyperinflammatory conditions in aging that exacerbate the phenomenon and favor the uncontrolled emergency myelopoiesis leading to the evolution of severe disease.

Impact of Tet2-Mutant Clonal Hematopoiesis on Solid Tumor Immunology and Response to Checkpoint Blockade

Background Clonal hematopoiesis (CH) is an age-related phenomenon characterized by the overrepresentation of blood cells arising from a single, mutant clone and is detectable in 10-20% of individuals over 70.1 CH has now been implicated in a variety of non-hematological disorders, such as cardiovascular diseases and Covid-19 infections, by exacerbating the innate inflammatory response.2-4 However, the impact of CH in solid tumors and response to immune checkpoint blockade (ICB) is unknown. Methods To assess the prevalence and role of CH in patients with solid tumors, we analyzed publicly available data from the MSKCC-IMPACT study.5, 6 To mechanistically study CH in solid tumors, we established an orthotopic model of pancreatic adenocarcinoma (PDAC) in mice with Tet2+/- CH. CH and WT mice were treated with either ICB (aCTLA-4 + aPD-1) or vehicle control. Single-cell (sc-) RNAseq was performed on tumor infiltrating lymphocytes (n=3/group) while remaining mice were observed for disease progression and overall survival (n=10/group). Results Analyzing CH frequencies in a cohort of patients with solid tumors, we observed that the prevalence of CH was approximately 5 times higher in patients with cancer when compared to healthy age-matched controls. Further, patients with detectable CH clones had significantly worse overall survival (figure 1A). In vivo, sc-RNAseq data revealed that myeloid cells present within the pancreatic tumors of mice with Tet2+/- CH were significantly enriched for both type I and type II interferon (IFN) signaling (figure 1B). Further, these IFN+ myeloid cells were ablated after ICB therapy in Tet2+/+ WT mice but persisted in mice with Tet2+/- CH (figure 1C). PDAC tumors from mice with Tet2+/- CH had approximately half the total number of infiltrating CD8 T cells at baseline when compared to those from Tet2+/+ WT mice. Upon ICB treatment, CD8 effector cells only expanded in the tumors from Tet2+/+ WT mice. Functionally, this translated to more rapidly progressing tumors, resistance to ICB, and reduced overall survival in mice with Tet2+/- CH (figure 1D). Conclusions CH is present in upwards of 30% of patients with solid tumors and is associated with significantly worsened prognosis. Modeling PDAC in the presence of Tet2+/- CH in vivo revealed distinct alterations in the tumor microenvironment that ultimately influenced tumor progression and response to ICB. This proposed research bridges the fields of solid tumor immunology and clonal hematopoiesis to address novel mechanisms of immunotherapy resistance that will span cancer type and, ultimately, improve patient care.

Allogeneic hematopoietic stem cell transplantation: lessons learned by a molecular immunologist/transplant patient.

Much has been learned about the genes and pathways that contribute to a diverse array of hematopoietic malignancies and other hematopoietic diseases. However, for many of these diseases, an allogeneic hematopoietic stem cell (HSC) transplant remains the preferred treatment option. This opinion article provides the perspective of a molecular immunologist who became a transplant patient after many years studying basic mechanisms of blood cell development. Among many lessons learned were the magnitude of racial and ethnic disparities in donor registries, the substantial improvement in outcomes over time that were due to the collective impact of numerous advances, the benefits and limitations of genetic and clinical data, and the remarkably intricate balance between promoting graft-versus-disease activity of donor cells while suppressing graft-versus-host disease (GVHD).

Immune Mechanisms of Plaque Instability.

Inflammation crucially drives atherosclerosis from disease initiation to the emergence of clinical complications. Targeting pivotal inflammatory pathways without compromising the host defense could compliment therapy with lipid-lowering agents, anti-hypertensive treatment, and lifestyle interventions to address the substantial residual cardiovascular risk that remains beyond classical risk factor control. Detailed understanding of the intricate immune mechanisms that propel plaque instability and disruption is indispensable for the development of novel therapeutic concepts. In this review, we provide an overview on the role of key immune cells in plaque inception and progression, and discuss recently identified maladaptive immune phenomena that contribute to plaque destabilization, including epigenetically programmed trained immunity in myeloid cells, pathogenic conversion of autoreactive regulatory T-cells and expansion of altered leukocytes due to clonal hematopoiesis. From a more global perspective, the article discusses how systemic crises such as acute mental stress or infection abruptly raise plaque vulnerability and summarizes recent advances in understanding the increased cardiovascular risk associated with COVID-19 disease. Stepping outside the box, we highlight the role of gut dysbiosis in atherosclerosis progression and plaque vulnerability. The emerging differential role of the immune system in plaque rupture and plaque erosion as well as the limitations of animal models in studying plaque disruption are reviewed.

Liquid biopsy for diagnosis in patients with suspected pancreatic and biliary tract cancers: PREVAIL ctDNA pilot trial

Background: Most patients with pancreatic cancer (PC) and biliary tract cancer (BTC) present with advanced disease. In confirmed cases, circulating tumour DNA (ctDNA) may be detected through liquid biopsy in 80-90%. Obtaining a diagnostic biopsy can be technically challenging, require complex invasive procedures and may not be feasible due to comorbidity. Reduction in capacity of aerosol generating diagnostic procedures in many healthcare systems due to COVID19 has highlighted the unmet need for simple, noninvasive diagnostic tools. We piloted the use of ctDNA to support the diagnostic pathway in patients with suspected cancer across 6 tumour types, here we present its use in PC/BTC. Methods: This single centre prospective cohort pilot trial was conducted at the Royal Marsden from June 2020 to August 2021. 16 patients were planned each in the PC and BTC cohorts. Eligibility included radiologically suspicious PC/BTC without histological diagnosis, patients with prior non-diagnostic biopsy and inaccessible tumours. Liquid biopsy for ctDNA was collected for plasma based next generation sequencing, using a custom 59 gene panel of common variants in PC/BTC tumours, including analysis for somatic, copy number and structural variants. Clonal haematopoiesis of indeterminate potential (CHIP) and germline variants were identified and subtracted. A molecular tumour board (MTB) reviewed results for interpretation and clinical context. Primary outcome was the proportion of patients with a ctDNA result consistent with a diagnosis of malignancy following MTB discussion. Results: 32 patients with suspected PC (n= 16) and BTC (n=16) were recruited. Baseline characteristics are shown in table. ctDNA was detected in 69% off, 23 patients had a subsequent biopsy. The sensitivity and specificity of ctDNA as a diagnostic tool was 80% (90% CI 49.3-96.3) and 100% (90% CI 36.8-100) for PC respectively, and 100% (90% CI 60.7-100) and 75% (90% CI 24.9- 98.7) for BTC respectively. There were 2 false negatives in the PC cohort subsequently diagnosed with PC, and 1 false positive in the BTC cohort subsequently diagnosed with oesophageal cancer. Conclusions: ctDNA can be used to support a diagnosis of cancer in patients with radiologically suspected PC/BTC. A blood first, tissue second strategy in the diagnosis of PC/BTC could improve diagnostic efficiency, speed, and add resilience to the current diagnostic pathway.

Clonal hematopoiesis in patients with COVID-19 is stable and not linked to an aggravated clinical course

Introduction: Individuals with clonal hematopoiesis (CH) have a higher risk of malignant and cardiovascular diseases. The latter has been linked to a higher inflammatory tonus in clonal myeloid and T cells driving pro-inflammatory circuits. As 'hyperinflammation' is one hallmark associated with fatal outcome of COVID-19, our study aimed to characterize the prevalence and clinical impact of CH in COVID-19. Methods: 160 individuals, which were either hospitalized or came for follow-up evaluation with COVID-19 were analyzed for somatic mutations indicative of CH (≥2% variant allele frequency). Trial protocols were approved by the institutional review board at Innsbruck Medical University (EK-Nb: 1091/2020 and 1103/2020). Detection of CH variants was performed by next generation sequencing on MiSeq devices using the TrueSight Myeloid sequencing panel from Illumina. For data analysis, the SeqNext software of JSI Medical Systems was utilized. Only coding variants not frequent in the general population with a variant allele frequency (VAF) between 2% and 45% were included in the dataset. Results: CH was detected in 31 of 160 (19.4%) evaluable individuals, with an age and gene distribution comparable to published data. To characterize the interplay between CH, inflammation and COVID-19 course, we divided our patient cohort into 'Severe COVID-19' and 'Non-severe COVID-19' based on the following criteria: Patients, requiring ≥2 liters/ minute of supplemental oxygen support at any given time point were classified as 'Severe COVID-19'. Of the study cohort, 99 patients (61.9%) had non-severe COVID-19 while 61 (38.1%) had severe COVID-19 according to our criteria. Of the latter, 37 patients (23.1%) had to be admitted to an intensive care unit due to respiratory insufficiency. However, the presence of CH and COVID-19 disease severity revealed no association between CH and 'severe COVID-19' (p-value: 0.678). Moreover, as COVID-19 does not spare individuals with active hematologic diseases, it is important to understand the dynamics of the clonal composition during active viral disease and upon its resolution. Analysis of 15 variants of eight individuals at different timepoints (up to six months follow-up) revealed that the clonal size is stable during the course of SARS-CoV2 infection. Conclusion: In summary, we demonstrate that CH is not indicative for an aggravated course of COVID-19 and that the clone size is not significantly modulated during the course of COVID-19.

Half: A Prospective Multi-Centre Phase II Clinical Trial Evaluating the Efficacy and Safety of Tyrosine Kinase Inhibitors' Discontinuation after Two-Step Dose Reduction in Patients with Chronic Myeloid Leukemia in Deep Molecular Remission

Background. Treatment-free remission (TFR) has become a new treatment goal for chronic myeloid leukemia (CML) patients. However, usually abrupt tyrosine kinase inhibitors (TKIs) therapy discontinuation has been successful only in about half of eligible patients and it can cause burdening TKI withdrawal syndrome (TWS) in about 30% of them. Moreover, any robust clinical or biological factor predictive for successful TFR has not been identified yet. On top of that, sustainable deep molecular response (DMR) as the main prerequisite for TKI discontinuation attempt is achieved only in 20-40% of patients. The majority of CML patients, therefore, need to be treated with the effective and well-tolerated drug for a long time or even life-long. Study design and methods. With the recognition of all these aspects, we designed a nationwide prospective investigator-initiated phase II clinical trial HALF (ClinicalTrials.gov NCT04147533) in order to evaluate efficacy and safety of TKI discontinuation after previous two-step dose reduction in patients with CML in DMR (Fig. 1). Step-wise TKI dose reduction, i.e. half of the standard during the first 6 months after study entry, and the same dose given alternatively (every other day) during the next 6 months, was derived from pharmacokinetics and experimental data as well as from clinical trials' results. We assume that the step-wise and eventually meaningful TKI dose reduction enables a higher rate of patients achieving successful TFR with less pronounce TWS, or even would represent a more reasonable and safer alternative to the complete and sudden TKI interruption. This unique nationwide academic project has been facilitated by hematological patients care centralization in the Czech Republic. A primary study objective is to evaluate the proportion of patients in major molecular response (MMR) at 6 and 12 months and in TFR at 18, 24, and 36 months after the study enrollment, respectively, and molecular recurrence-free survival at all mentioned time points as well. Main secondary and exploratory objectives are: to evaluate the proportion of patients loosing MMR and in whom MMR and MR4.0 would be re-achieved after TKI re-introduction, time to MMR and MR4.0 re-achievement, FFS, PFS, OS, TWS, and QoL assessment, predictive factors for successful TFR identification, quantification of BCR-ABL1 using digital droplet PCR at both the DNA and mRNA levels, immunological profiling, BCR-ABL1 kinetics mathematical modeling, assessment of TKI pharmacokinetics, clonal hematopoiesis and pharmaco-economics. Results. The study was launched in December 2019;however, due to the COVID-19 outbreak, patients' recruitment started on June 16, 2020. Here, characteristics of the first 74 patients included in the study until April 2021 are presented. There were 37 males and 37 females, with median age at the time of diagnosis of 53 years (range, 23-74) and at the time of the study entry of 67 years (range, 35-86). A median time of CML disease, TKI treatment, and DMR duration before the study initiation was as follows: 9.9 years (range, 4.4-22.5), 9.8 years (range, 4.2-20.2), and 7.3 years (range, 3.2-18.3), respectively. The ELTS score was low, intermediate, high and unknown in 62.2%, 21.6%, 13.5%, and 2.7% of patients, respectively. At the time of study entry, 58 patients (79.5%) were treated with imatinib, 10 (13.7%) with nilotinib, and 5 (6.8%) with dasatinib, respectively, whereas in 63 patients (86.3%) it was in the first line of therapy. With almost half of patients (48.6%), the TKI dose was already reduced at the time of study entry. With 10 (13.5%) patients, interferon-α treatment preceded TKI administration. At the time of this preparation, on July 26, 2021, altogether 102 patients (from planned 150) have been enrolled in the study;48 of them (47.1%) have already moved to the second de-escalation phase and 9 (8.8%) patients to the TFR phase. There were 2 cases of confirmed MMR loss (both in month 8 after the study entry) and no patient experienced symptoms resembling TWS. Conclusions. Despite the COVID-19 pandemic, the HALF study was successfully launched and initiated in the majority of centers, with 102 already included patients and continuing intensive enrolment. Based on our very preliminary results, the step-wise dose reduction seems to be an effective and safe approach. More included patients, longer follow-up and further analyses are needed in order to reach all set up objectives. [Formula presented] Disclosures: Žácková: Angelini: Consultancy, Speakers Bureau;Novartis: Speakers Bureau. Faber: Angelini: Consultancy, Other: conference fees, Research Funding, Speakers Bureau;Bristol-Myers Squibb: Consultancy, Other: conference fees, Research Funding, Speakers Bureau;Novartis: Consultancy, Other: conference fees, Research Funding, Speakers Bureau;Pfizer: Other: conference fees;TERUMO: Other: conference fees. Bělohlávková: Novartis: Consultancy;BMS/Celgene: Consultancy. Horňák: Angelini: Honoraria. Svobodník: Roche: Speakers Bureau;Janssen-Cilag: Speakers Bureau. Machová Poláková: Incyte: Consultancy;Angelini: Consultancy;Novartis: Research Funding. Mayer: Principia: Research Funding.

Clonal Hematopoiesis of Indeterminate Potential Is Associated with Increased Age-Independent Morbidity and Mortality in Patients with COVID-19- the Beyond DNA COVID-19 Project

Background: SARS-Cov-2 infections are associated with increased mortality and morbidity, largely due to inflammatory cascades and cytokine release syndrome (CRS). Clonal hematopoiesis of indeterminate potential (CHIP) is defined by the presence and subsequent expansion of somatic, leukemia-associated driver mutations in apparently healthy individuals with normal blood counts. CHIP has been associated with increased inflammation, with cytokines such as IL1-b, IL6 and TNF-a being elevated at baseline in affected individuals. We hypothesized that the presence of CHIP in patients with COVID-19 would result in excessive inflammation-related mortality and morbidity. Methods: We used the Mayo Clinic COVID-19 database to identify patients with COVID-19 on whom peripheral blood mononuclear cells (PBMC) were available for research use (IRB approved). We carried out target-capture next generation sequencing for 220 CH related genes, by previously described methods (1000 x coverage, variant allele fraction/VAF detection limit >0.5%;Kusne Y et al AJH 2021). CHIP was defined by the presence of a CH mutation with a VAF>1% in an individual with normal baseline blood counts. Demographics, blood counts, and inflammatory markers (CRP and cytokine levels- ELISA assay) at COVID-19 diagnosis and during follow-up (as clinically indicated) were collected. COVID-19 disease severity was classified based on the presence and severity of CRS, graded using the Penn Grading Scale (Porter et. al., 2018), and the WHO ordinal scale (WHO Blueprint, 2020). We used Fisher's exact test and the Wilcoxon rank sum test to compare categorical and continuous variables. Survival analysis was performed using the Kaplan-Meier method. We accounted for differences in age and sex using multivariable-adjusted proportional hazards regression models. Results: Seventy-two CHIP mutations were detected in 56 (25%) of the 227 patients with COVID-19 that had PBMC available;median age 69 years (range;42-99 years), 61% male. Fifteen (26%) patients had 2 CHIP mutations, while 1 patient had 3 CHIP mutations. Common mutations encountered included DNMT3A (32%), TET2 (19%), SF3B1 (8%), ASXL1 (6%), MPL (5%), and TP53 (5%;Figure 1A). COVID-19 patients with CHIP were older in age (median 69 vs 57 years;p<0.0001) and had higher baseline MCP-1 (p=0.04) levels. However, there were no differences in sex, comorbidities, blood counts, IL1-b, IL6 and TNF-a levels between the two groups. The median follow-up for the entire cohort was 9 months. The relative change from baseline in blood counts and inflammatory markers (CRP and cytokines) during follow-up was similar in CHIP and non-CHIP patients, with the exception that COVID-19-onset neutropenia was more common in CHIP patients (8% vs 1%;p=0.017) compared to those without CHIP. At last follow up neutropenia had resolved in all patients. Both groups had comparable number of patients with CRS (61% CHIP vs 53% non-CHIP patients, p=0.354, Figure 1B), however, CHIP patients had more severe CRS (median Penn Grade 3 versus 2 in non-CHIP, p=0.018, Figure 1C). Based on the WHO ordinal scale, CHIP patients were more likely to experience hospitalization with severe disease and death (61% versus 45% in non-CHIP, p = 0.049). Moreover, COVID-19 CHIP patients experienced worse overall survival in comparison to patients without CHIP (median 13.1 months vs not reached, p<0.001, Figure 1D). This association remained consistent after adjusting for age and sex at the time of COVID-19 diagnosis (HR 3.15, 95% 1.32 - 7.55, p = 0.010). At last follow-up, 22 deaths were documented: 13 (23%) in patients with CHIP and 9 (5%) in the non-CHIP group (p=0.02), with the primary cause for mortality being hypoxic respiratory failure (62% in CHIP vs 44% non-CHIP, p=0.04). Conclusions: In this study, we observe an age-independent impact of CHIP on COVID-19 associated inflammatory morbidity (CRS) and mortality (hypoxemic respiratory failure). We are currently carrying out detailed single cell (ssDNA, RNA and ATAC-seq) and proteomic studies (O-link PEA assays) to better elucidate this pathophysiology. [Formula presented] Disclosures: Patnaik: Kura Oncology: Research Funding;StemLine: Research Funding.

Evaluation of the Relationship between Clonal Hematopoiesis and Severe COVID-19 Disease in Rhesus Macaques

Clinical manifestations of infection with the novel SARS-CoV-2 in humans are widely varied, ranging from asymptomatic to COVID-19 respiratory failure and multiorgan damage. Profound inflammation is the hallmark of severe COVID-19 disease, and commonly does not occur until the second week of infection. Although risk factors for this late hyperinflammatory disease have been identified, most notably age and pre-existing co-morbidities, even within high-risk groups the specific factors leading to severe COVID-19 illness remain elusive. Acquired somatic mutations in hematopoietic stem and progenitor cells (HSPCs), termed clonal hematopoiesis (CH), are associated with advanced age, and loss of function (LOF) mutations in certain genes, most commonly DNMT3A and TET2, have been linked to a marked hyperinflammatory phenotype as well as clonal expansion of mutant HSPCs. Given the similar age range of frequent CH and severe COVID-19 disease, the presence of CH could impact the risk of severe COVID-19. Several human cohort studies have suggested this relationship may exist, but results to date are conflicting. Rhesus macaques (RM) have been established as a model for SARS-CoV infection and are being utilized to test therapies and vaccine development, but up to now, macaques have not been reported to develop late hyperinflammatory COVID-19 disease. We have created a robust RM model of CH by introducing LOF TET2 mutations into young adult HSPC via CRISPR/Cas9 followed by autologous transplantation, recapitulating the clonal expansion and hyperinflammatory phenotype. Thus, we hypothesized that macaques with CH could develop severe late COVID-19 disease and be utilized as a model to study disease pathophysiology or test therapeutic approaches. Macaques with either engineered (n=2) or natural CH (n=1) along with age-matched transplanted controls (n=3) were inoculated with SARS-CoV-2 and monitored clinically and via laboratory studies until 12 days post-inoculation (dpi). Macaques normally clear infection and symptoms within 3-5 days of infection. No significant differences in clinical symptoms and blood counts were noted, however, an aged animal with natural DNMT3A CH died on 10 dpi. IL-6 levels were somewhat higher in sera of the CH animals until 12 dpi, and in BAL, mean concentrations of MCP-1, IL-6, IL-8 and MIP-1b were consistently higher in CH macaques compared to controls. Interestingly, we found the median copy number of subgenomic SARS-CoV-2 RNA was higher at every timepoint in the CH group as compared with the control group, in both upper and lower respiratory samples. Lung sections from euthanasia at 10 or 12 dpi showed evidence of mild inflammation in all animals. However, in the immunohistochemical analysis, the viral antigen was detected in the lung tissues of all three animals in the CH group even at the time of autopsy, whereas only one animal of three controls had detectable viral antigen. Although the striking inflammation and serious disease have not been observed, data so far provide evidence of potential pathophysiological differences with or without CH upon SARS-CoV-2 infection. We continue to expand sample size and conduct further analyses to draw a solid conclusion, but we believe this model may be of benefit to understand the relationship between COVID-19 disease and CH. Disclosures: No relevant conflicts of interest to declare.

COVID Vaccine Antibody Responses in Patients with Hematologic Malignancies in a Myeloid Enriched Cohort: A Better Antibody Response in Patients with Myeloid Malignancies Than B-Cell Malignancies

Background: The risk of severe COVID-19 is increased in patients (pts) with hematologic malignancies, with a reported risk of death of 34% (Vijenthira et al, 2020). The ASH-ASTCT COVID-19 vaccine guidelines indicate that certain immunocompromised patient populations could have an attenuated response to the SARS-CoV-2 vaccine. However, most SARS-CoV-2 vaccine trials required pts to be off immune suppression to be eligible and therefore excluded most pts with hematologic malignancies. Little is known about the efficacy of SARS-CoV-2 vaccines in pts with hematologic malignancies. In this study, we aimed to evaluate the serological response of Pfizer and Moderna vaccination after two doses given in pts with hematologic malignancies with a focus on pts with myeloid malignancies. Methods: Patients with a history of hematologic malignancies treated at the University of Texas Southwestern Medical Center and received two doses of vaccination with quantitative measurement of SARS-CoV-2 IgG Spike antibody to assess vaccination response were included in this study. Baseline patient and disease characteristics including disease status and therapy given at the time of vaccination were collected. Time to vaccine response was defined as having a positive quantifiable spike IgG antibody titer per the lab reference range. The development of COVID-19 infection as well as antibody titer levels were collected. Categorical variables were compared using Chi-square and Fisher's exact tests and student t-test and ANOVA test were used to compare continuous variables. Results: A total of 61 pts with hematologic malignancies had spike IgG antibody testing after receiving 2 doses of the vaccine were included in this study. The median age at the time of vaccination was 72 (22-85) and 46% of pts were female. Eighty five percent of pts were Caucasian. The majority of pts (67.3%) had a myeloid malignancy (MDS/CMML 29.5%, AML 14.8%, myelofibrosis 16.4%, CML 6.6%), followed by chronic lymphocytic leukemia (16.4%), and others (6.6%). The median time from hematologic malignancy diagnosis to the first vaccine dose was 51 months (0.4-337 months). At the time of vaccine administration, 46 (75%) of pts were on active therapy and 39 (64%) of pts had active disease. Median time from the second vaccine dose to IgG spike antibody testing was 64 days (26-268 days). Most pts (75%) mounted a serological response with quantifiable COVID-IgG spike antibodies, 85% and 56% in myeloid and lymphoid malignancy, respectively. All pts with MDS/CMML/CCUS and CML mounted an immune response (100%), followed by acute myeloid leukemia (n: 7/9, 78%) and myelofibrosis (n: 6/10, 60%). Eight (13%) of pts were receiving hypomethylating agent therapy at the time of vaccination and all (100%) had a positive IgG response. Only one patient developed COVID-19 infection post vaccination with a documented IgG response and 2 pts had COVID-19 infection prior to the first dose of vaccination, both of these pts had IgG titers >10,000. Sixty percent of pts (9/15) with negative IgG response received treatment with either CD20 monoclonal antibodies or BTK inhibitors within 12 months of the first vaccine dose. Two out of three pts (67%) receiving Ruxolitinib had negative serology. Seven pts were on treatment with hydroxyurea, interestingly, all but the 2 pts with polycythemia vera had a negative antibody titer while on treatment with hydroxyurea. There was a strong positive correlation between vaccine titer and absolute lymphocyte count (r 2=0.27, p<0.001) (Figure). Conclusions: In this retrospective study, we demonstrate a higher rate of COVID-19 vaccine efficacy in pts with myeloid malignancy with varying responses per treatment and disease subtype compared to pts with B-cell malignancy with variable anti-CD20 or BTK inhibitor therapy. Pts with myelodysplastic syndromes, overlap syndromes of clonal cytopenia of undetermined significance all developed spike antibodies irrespective of hypomethylating therapy or Hydrea as did pts with chronic myeloid leukemia. However, pts with polycythemia vera nd those on treatment with Ruxolitinib had an attenuated response to the vaccine. Albeit this single center study, pts with myelodysplastic syndromes should be offered COVID vaccines irrespective of their blood counts or ongoing treatment. Our findings should be validated in a larger group of patients. [Formula presented] Disclosures: Patel: Agios: Membership on an entity's Board of Directors or advisory committees;Celgene-BMS: Membership on an entity's Board of Directors or advisory committees;PVI: Honoraria. Anderson: Celgene, BMS, Janssen, GSK, Karyopharm, Oncopeptides, Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Awan: Cardinal Health: Consultancy;BMS: Consultancy;Dava Oncology: Consultancy;Karyopharm: Consultancy;Merck: Consultancy;Johnson and Johnson: Consultancy;Incyte: Consultancy;Beigene: Consultancy;Verastem: Consultancy;MEI Pharma: Consultancy;Celgene: Consultancy;Kite pharma: Consultancy;Gilead sciences: Consultancy;Pharmacyclics: Consultancy;Janssen: Consultancy;Abbvie: Consultancy;ADCT therapeutics: Consultancy;Astrazeneca: Consultancy;Genentech: Consultancy. Madanat: Blue Print Pharmaceutical: Honoraria;Onc Live: Honoraria;Stem line pharmaceutical: Honoraria;Geron Pharmaceutical: Consultancy.

Clinico-Biological Features and Clonal Hematopoiesis in Patients with Severe COVID-19.

Advanced age or preexisting comorbidities have been characterized as risk factors for severe coronavirus disease 2019 (COVID-19) cases requiring hospitalization and intensive care. In recent years, clonal hematopoiesis (CH) of indeterminate potential (CHIP) has emerged as a risk factor for chronic inflammatory background and subsequent aging-associated diseases. The purpose of this study was to identify biological factors (particularly leukocyte subtypes and inflammatory markers) associated with a risk of clinical deterioration (i.e., orotracheal intubation (OTI)) and to determine whether CH was likely to influence clinical and biological behavior in patients with severe COVID-19 requiring hospitalization. Here, we describe clinical and biological features, including the screening of CHIP mutants in a well-annotated cohort of 122 hospitalized patients with a laboratory-confirmed diagnosis of COVID-19 (55% requiring OTI). We showed that elevated white blood cell counts, especially neutrophils and high C-reactive protein (CRP) levels at admission, were associated with an increased requirement of OTI. We noticed a high prevalence of CH (25%, 38%, 56%, and 82% of patients aged <60 years, 60-70 years, 70-80 years, and >80 years) compared to a retrospective cohort of patients free of hematological malignancy explored with the same pipelines (10%, 21%, 37%, and 44%). However, the existence of CH did not significantly impact clinical outcome, including OTI or death, and did not correlate with other laboratory findings.