PPM1D Mutations Research Articles

TMOD-21. MOUSE MODEL TO CONDITIONALLY EXPRESS A DIFFUSE MIDLINE GLIOMA DERIVED MUTATION IN THE ONCOGENIC PHOSPHATASE PPM1D

Abstract Diffuse Midline Gliomas (DMGs) are incurable brain tumors of children and adults, and there is an urgent need for new therapeutic approaches. Their location within critical areas of the brain precludes complete surgical removal. While current treatment mainly relies on radiation therapy, its efficacy remains palliative. DMGs commonly harbor truncating mutations in the Mn2+/Mg2+-dependent protein phosphatase 1D (PPM1D), leading to a gain-of-function in PPM1D by enhancing protein stability and activity. Thus, investigating PPM1D protein expression and its regulatory mechanisms is crucial for understanding its oncogenic role and identifying therapeutic targets. To address this, we developed a Ppm1d-loxP-exon6-loxP-exon6-E518X-tag mouse allele (Ppm1d-FL). This allele allows conditional expression of DMG-derived truncating mutations from the endogenous Ppm1d locus when the loxP sites are recombined in the presence of Cre recombinase. Tosimulate primary gliomas, we utilized the RCAS/tv-a retrovirus system and Cre/loxP recombination platforms. Mouse pups were injected with RCAS retroviruses bearing oncogenic platelet-derived growth factor B, Cre recombinase, and luciferase reporter genes into the brainstem. We confirmed that Cre leads to expected recombination of Ppm1d-FL, leading to expression of DMG-derived truncated Ppm1d-E518X-Tag mRNA. We examined tumor-free survival data, which indicates accelerated tumor formation with Ppm1d-FL compared to littermate controls with wildtype Ppm1d. The tumors demonstrated expression of molecular biomarkers commonly found in DMGs. Single-cell RNA sequencing has identified pathways activated or inactivated upon Ppm1d mutation. These data shed light on the complex interplay between PPM1D mutations and glioma pathogenesis and may guide the design of therapies that target PPM1D molecular pathways.

Ultrarare Variants in DNA Damage Repair Genes in Pediatric Acute-Onset Neuropsychiatric Syndrome or Acute Behavioral Regression in Neurodevelopmental Disorders

Introduction: Acute onset of severe psychiatric symptoms or regression may occur in children with premorbid neurodevelopmental disorders, although typically developing children can also be affected. Infections or other stressors are likely triggers. The underlying causes are unclear, but a current hypothesis suggests the convergence of genes that influence neuronal and immunological function. We previously identified 11 genes in pediatric acute-onset neuropsychiatric syndrome (PANS), in which two classes of genes related to either synaptic function or the immune system were found. Among the latter, three affect the DNA damage response (DDR): PPM1D, CHK2, and RAG1. We now report an additional 17 cases with mutations in PPM1D and other DDR genes in patients with acute onset of psychiatric symptoms and/or regression that their clinicians classified as PANS or another inflammatory brain condition. Methods: We analyzed genetic findings obtained from parents and carried out whole-exome sequencing on a total of 17 cases, which included 3 sibling pairs and a family with 4 affected children. Results: The DDR genes include clusters affecting p53 DNA repair (PPM1D, ATM, ATR, 53BP1, and RMRP), and the Fanconi Anemia Complex (FANCE, SLX4/FANCP, FANCA, FANCI, and FANCC). We hypothesize that defects in DNA repair genes, in the context of infection or other stressors, could contribute to decompensated states through an increase in genomic instability with a concomitant accumulation of cytosolic DNA in immune cells triggering DNA sensors, such as cGAS-STING and AIM2 inflammasomes, as well as central deficits on neuroplasticity. In addition, increased senescence and defective apoptosis affecting immunological responses could be playing a role. Conclusion: These compelling preliminary findings motivate further genetic and functional characterization as the downstream impact of DDR deficits may point to novel treatment strategies.

Clonal Hematopoiesis and Therapy-Related Myeloid Neoplasms After Autologous Transplant for Hodgkin Lymphoma.

Therapy-related myeloid neoplasm (t-MN) is a life-threatening complication of autologous peripheral blood stem cell transplantation (aPBSCT) for Hodgkin lymphoma (HL). Although previous studies have reported an association between clonal hematopoiesis (CH) in the infused PBSC product and subsequent post-aPBSCT risk of t-MN in patients with non-HL, information about patients with HL treated with aPBSCT is not available. We constructed a retrospective cohort of 321 patients with HL transplanted at a median age of 34 years (range, 18-71). Targeted DNA sequencing of PBSC products performed for CH-associated or myeloid malignancy-associated genes identified pathogenic mutations in these patients. CH was identified in the PBSC product of 46 patients (14.3%) with most prominent representation of DNMT3A (n = 25), PPM1D (n = 7), TET2 (n = 7), and TP53 (n = 5) mutations. Presence of CH in the PBSC product was an independent predictor of t-MN (adjusted hazard ratio [aHR], 4.50 [95% CI, 1.54 to 13.19]). Notably all patients with TP53 mutations in the PBSC product developed t-MN, whereas none of the patients with DNMT3A mutations alone (without co-occurring TP53 or PPM1D mutations) did. Presence of TP53 and/or PPM1D mutations was associated with a 7.29-fold higher hazard of t-MN when compared with individuals carrying no CH mutations (95% CI, 1.72 to 30.94). The presence of TP53 and/or PPM1D mutations was also associated with a 4.17-fold higher hazard of nonrelapse mortality (95% CI, 1.25 to 13.87). There was no association between CH and relapse-related mortality. The presence of TP53 and/or PPM1D mutations in the PBSC product increases the risk of post-aPBSCT t-MN and nonrelapse mortality among patients with HL and may support alternative therapeutic strategies.

HGG-03. TRUNCATING MUTATIONS IN PPM1D COOPERATE WITH PI3K ALTERATIONS TO DRIVE PEDIATRIC DIFFUSE MIDLINE GLIOMAS

Abstract Mutations in PPM1D – coding for the phosphatase WIP1 - are present in 8 -12% of all Diffuse Midline Glioma (DMG), H3 K27-altered – a universally fatal subtype of pediatric high-grade tumors. PPM1D mutations are mutually exclusive with TP53 mutations and mainly lead to a truncation of its C-terminal regulatory domain. Truncated PPM1D (PPM1Dtr) has increased protein stability and impairs the p53-dependent DNA Damage Response (DDR) by dephosphorylating its numerous targets (e.g p53, H2A.X, CHK1) which contributes to its oncogenicity. However, because wildtype p53 is present in PPM1Dtr tumors, its activation is suppressed but not completely ablated suggesting that PPM1D mutant tumors may evolve differently from p53 mutant ones. Our analysis of whole genome sequencing datasets indeed found that PPM1D mutations uniquely co-occur with alterations in the PI3K/mTOR pathway suggesting potential cooperativity in enhancing tumorigenesis. Using mouse neural stem cells (mNSCs) as an isogenic model system, we have engineered specific combinations of oncogenic alterations to study their impact on cell proliferation, PI3K/mTOR pathway activation and response to DNA damage and replication stress. We find that PPM1Dtr cooperates with PIK3CA alterations to increase proliferation and signaling through the PI3K/mTOR pathway. Notably, in an in utero electroporation model, mutant PIK3CA accelerates the development of high-grade tumors that infiltrate deep into the brainstem. Our study also indicates a vulnerability to inhibition of the PI3K/mTOR pathway in PPM1Dtr-PI3K co-altered tumors. Future work will aim at 1) exploring the mechanism of cooperation and impact on replicative stress response and 2) developing and testing a rational therapeutic strategy for PPM1D-mutant tumors.

211 Biallelic null mutations in PPM1D cause a novel combined immunodeficiency with severe neurodevelopmental defects

211 Biallelic null mutations in PPM1D cause a novel combined immunodeficiency with severe neurodevelopmental defects

Abstract 1075: Buccal mucosal remodeling predicts esophageal cancer risk

Abstract Lifestyle habits, including alcohol consumption, tobacco smoking, and germline variants of ALDH2 and ADH1B, increase the risk of developing esophageal squamous cell carcinoma (ESCC). However, current prediction methods that rely on self-reported lifestyle information lack accuracy. We previously demonstrated that driver-mutated clones remodel the esophageal epithelium with age and that this remodeling is accelerated in heavy drinkers and smokers. Nonetheless, predicting cancer from clonal expansion in normal tissues remains challenging, due to limited sample availability beyond the blood. The squamous epithelium continuously covers the esophagus, throat, and oral cavity. Therefore, we evaluated buccal mucosal remodeling by mutant clones and its potential as a predictive biomarker of ESCC. A total of 387 buccal mucosa samples were collected from 110 subjects, including 62 with ESCC and 48 without, using swabs of three different sizes, followed by error-corrected sequencing targeting 26 driver genes that showed positive selection in samples from ESCC and physiologically normal esophageal tissues, as well as ALDH2 and ADH1B. Somatic mutations were detected in all samples (median, 27 (1-134)). In total, 13,235 mutations, including 12,085 nonsynonymous and 1,150 synonymous mutations, with VAFs ranging from 0.0016-0.12 (median, 0.0025), were detected. Ten of the 26 genes, TP53, CHEK2, NOTCH1, CDKN2A, NOTCH2, FAT1, AJUBA, PPM1D, ARID1A, and ZNF750 showed positive selection (dN/dS >1, q<0.1). Correlation analysis demonstrated that driver mutations in TP53, FAT1, and PPM1D were positively correlated with not only germline risk variants of ALDH2 but also alcohol consumption. The impact of alcohol consumption on the number and sum of VAFs of mutations in each of the three genes was analyzed and stratified by the presence or absence of the germline risk variant of ALDH2, and positive correlations were observed only among subjects with risk variants. Compared to subjects without ESCC, patients with early-stage or advanced ESCC displayed significantly higher numbers and sums of VAFs of driver mutations (p<0.05). These results indicated that buccal mucosal remodeling driven by positively selected mutations is associated with lifestyle and germline risk factors for ESCC, thus motivating the establishment of a predictive model for ESCC using genetic swab data. The prediction model for ESCC using sequencing data outperformed a model using self-reported lifestyle and alcohol flushing reaction and a model using lifestyle and germline risk variants (AUC of 0.94, 0.72, and 0.88, respectively). In conclusion, this is the first study to use clonal expansion in normal tissues to predict the presence of solid organ cancer, and our study successfully established a prediction model for ESCC based on buccal mucosal remodeling and germline variants. Citation Format: Akira Yokoyama, Tomonori Hirano, Koichi Watanabe, Masashi Tamaoki, Kenshiro Hirohashi, Yoshihiro Ishida, Yoshikage Inoue, Yasuhide Takeuch, Yo Kishimoto, Soo Ki Kim, Chikatoshi Katada, Yasuhito Nanya, Hiroshi Seno, Seishi Ogawa, Manabu Muto, Nobuyuki Kakiuchi. Buccal mucosal remodeling predicts esophageal cancer risk [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1075.

Abstract 2801: Identifying gut microbial determinants of clonal hematopoiesis of indeterminate potential (CHIP) in immunotherapy treated melanoma patients

Abstract INTRO: Clonal hematopoiesis (CH) of indeterminate potential (CHIP) is associated with poor outcomes in those with non-hematologic cancers. CH mutated macrophages and neutrophils have increased capacity to home to peripheral tissues, driving local inflammation; they are also implicated in immunotherapy related toxicity. The relationship between CH and the microbiome in those treated with immunotherapy is not well understood. RESULTS: 35 patients with stage IV melanoma treated with upfront immunotherapy; treatment and cohort characteristics are below (Table 1). We performed error corrected duplex sequencing on peripheral blood mononuclear cells using a panel previously validated for CH mutations. With a cutoff of 0.5% variant allele frequency (VAF), among 10 CHIP positive patients, we found mutations in TET2 (8/10), DNMT3A (7/10), PPM1D (2/10), and JAK2 (1/10). There was no difference in either survival or response based on CHIP status (Log-Rank Chi-Square p=0.44); however, CHIP positivity was associated with greater microbiome richness as measured by alpha diversity (p=0.0012 Shannon diversity) and distinct structural/compositional diversity vs CHIP negative patients as measured by beta diversity (p=0.032, R Squared= 0.045). We inferred KEGG pathway activity from whole genome sequencing and identified that CHIP positive patients were enriched for exopolysaccharide biosynthesis while CHIP negative patients had higher expression of nucleotide sugars biosynthesis and amino acid metabolism pathways. DISCUSSION: In patients treated with immunotherapy for melanoma, microbiome diversity signatures correlate with presence of CHIP. The analysis suggests that there are distinct taxonomic and functional features defining CHIP positivity. The effect of these cells in the tumor microenvironment and their role in immunotherapy response requires further exploration. Citation Format: Eleanor A. Fallon, Samuel Urrutia, Reed Ayabe, Manoj Chelvanambi, Ashish Damania, Sarah Johnson, Tomoyuki Tanaka, Zongrui Li, Yongwoo David Seo, Samuel Cass, Matthew C. Wong, Nadim Ajami, Jennifer Wargo, Koichi Takahashi. Identifying gut microbial determinants of clonal hematopoiesis of indeterminate potential (CHIP) in immunotherapy treated melanoma patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2801.

Low-Frequency PPM1D Gene Mutations Affect Treatment Response to CD19-Targeted CAR T-Cell Therapy in Large B-Cell Lymphoma.

Chimeric antigen receptor T (CAR T)-cell therapy has become a standard treatment option for patients with relapsed or refractory diffuse large B-cell lymphoma (r/r DLBCL). Mutations in the PPM1D gene, a frequent driver alteration in clonal hematopoiesis (CH), lead to a gain of function of PPM1D/Wip1 phosphatase, impairing p53-dependent G1 checkpoint and promoting cell proliferation. The presence of PPM1D mutations has been correlated with reduced response to standard chemotherapy in lymphoma patients. In this study, we analyzed the impact of low-frequency PPM1D mutations on the safety and efficacy of CD19-targeted CAR T-cell therapy in a cohort of 85 r/r DLBCL patients. In this cohort, the prevalence of PPM1D gene mutations was 20% with a mean variant allele frequency (VAF) of 0.052 and a median VAF of 0.036. CAR T-induced cytokine release syndrome (CRS) and immune effector cell-associated neuro-toxicities (ICANS) occurred at similar frequencies in patients with and without PPM1D mutations. Clinical outcomes were globally worse in the PPM1D mutated (PPM1Dmut) vs. PPM1D wild type (PPM1Dwt) subset. While the prevalent treatment outcome within the PPM1Dwt subgroup was complete remission (56%), the majority of patients within the PPM1Dmut subgroup had only partial remission (60%). Median progression-free survival (PFS) was 3 vs. 12 months (p = 0.07) and median overall survival (OS) was 5 vs. 37 months (p = 0.004) for the PPM1Dmut and PPM1Dwt cohort, respectively. Our data suggest that the occurrence of PPM1D mutations in the context of CH may predict worse outcomes after CD19-targeted CAR T-cell therapy in patients with r/r DLBCL.

Mutational Profile and Dynamics of PPM1D-Mutant Clones in the Spectrum of Myeloid Disorders

Introduction Mutations in PPM1D a regulator of DNA damage response, are enriched in patients with clonal hematopoiesis (CH) exposed to cytotoxic treatment or with therapy-related myeloid neoplasm. However, their role in leukemic transformation is unclear. Here, we describe a large cohort of patients with PPM1D mutations from CH to acute myeloid leukemia (AML) to understand the molecular landscape of mutant PPM1D related disease and the longitudinal dynamics of CH under treatment. Methods We included, in a non-sequential cohort, 96 PPM1D mutated patients treated at Gustave Roussy with CH, clonal cytopenia of unknown significance (CCUS), myelodysplastic syndrome (MDS), myeloproliferative neoplasm (MPN) or AML. A 77 gene panel NGS analysis was performed. An additional 16 PPM1D mutated AML patients from ALFA trials (1200, 0701,0702) were included. 10 patients with ovarian cancer from this cohort had sequential blood samples (OvBIOMark trial) available prior to hematologic evaluation, from the diagnosis or first relapse of their cancer through the course of therapy. Those samples were analyzed with a UMI based 18 gene panel (HaloplexHS, Agilent). Overall survival (OS) analyses were performed with the Kaplan-Meier method from the time of diagnosis until death from any cause. Results Among the 112 patients with PPM1D mutations, 23 (21%) had CH, 36 (32%) CCUS, 19 (17%) MDS, 25 (22%) AML (including 4 relapses), and 9 (8%) MPN. Median age was 65 [range, 21-88] years with 67% of females. Only 18% of the patients had no previous cancer history. Most frequent primary cancers were gynecological cancer (27%), lymphoid malignancies (22%), and breast cancer (17%). Median time between primary cancer diagnosis and hematologic assessment was 5.3 [range, 1.2-8.5] years. Eighty six percent of patients had one PPM1D mutation, 9% had 2, and 5% had 3 or more (restricted to CH and CCUS). Median variant allele frequency (VAF) was 3% [0.2-38], 3% [1-31], 2.4% [1-41], 23% [1-50], and 4% [1-42] in CH, CCUS, MDS, AML and MPN, respectively. Among CH/CCUS patients, PPM1D was the sole detected somatic mutation in 39% (23/59), compared to 9% (5/53) in MDS/AML/MPN patients (odds ratio=6, p=0.0004); 3/5 of the latter had complex karyotype. The most frequently co-mutated genes were DNMT3A (29%) and TP53 (25%), uniformly across all conditions ( Fig 1A). MDS-related gene mutations, RUNX1 (7%), ASXL1 (4%), SF3B1 (4%), SRSF2 (4%), U2AF1 (4%), were specific to AML/MDS/MPN. Among 28 patients with both PPM1D and TP53 mutations, PPM1D mutations were dominant or co-dominant in 64% (18/28), and secondary in 36% (10/28). IPSS-M risk of evaluable MDS was high/very high in 54% (7/13) of patients. ELN 2022 classification of AML was adverse in 68% (17/25) of patients. AML treatment options included best supportive care for 8% of patients (2), 5-Azacytidine for 32% (8), intensive chemotherapy for 60% (15). With a median follow up of 2.4 years, the median OS was 4.6 (CI95%; 4.1-NA), 1.31 (CI95%; 0.53-NA), 1.27 (0.43-NA), 0.66 (CI95%; 0.42-1.26) and 20.4 (CI95%; 20.4-NA) years for CH, CCUS, MDS, AML and MPN, respectively. TP53 mutation status did not stratify OS. Four ovarian cancer patients with CH/CCUS transformed to MDS/AML with a median of 5.3 [1-12] years. At transformation, 3/4 had a stable PPM1D mutation, 1/4 an increase in PPM1D VAF (2 to 28%), and 3/4 had TP53 mutations before and at transformation. We analyzed 67 timepoints from 10 ovarian cancer patients during therapy (median 7 per patient). 10/10 received alkylating agents and 5/10 PARPi. The median number of mutations per patient was 4 and 6 at baseline and last follow-up, respectively. PPM1D-mutated clone size increased from 0.4% [0.1-3] at baseline to 7% [2-30] at last follow-up. Beyond clonal expansion, PPM1D VAF dynamics showed non-linear changes related to alkylating agents exposure: 2/10 patients had a continuous expansion, 2/10 had expansion then contraction (GR-1/3, Fig 1B), and 6/10 had expansion then stabilization (GR-2, Fig 1B). Conclusion We described a large cohort of PPM1D mutated patients from CH to AML. Their prognosis was poor independently of TP53 mutation at AML/MDS stage. PPM1D mutations were frequently part of the dominant clone. To confirm the clonal architecture, single cell sequencing analysis in 8 AML/MDS patients are ongoing. Trajectory of PPM1D mutations in ovarian cancer patients revealed a non-linear alkylating agent dependency which warrants further investigation.

Prevalence, Dynamics and Clinical Significance of Clonal Hematopoiesis of Indeterminate Potential (CHIP) in Newly Diagnosed Cancer Patients

INTRODUCTION Prevalence of CHIP in cancer patients (pts) is estimated at about 25%, its presence being associated with inferior outcomes and with increased risk of development of therapy-related myeloid neoplasms (TRMN). Despite the increased body of knowledge on cancer and CHIP, processes driving the selection of clones and their latter malignant transformation have not been fully elucidated. We hypothesized that CHIP in cancer pts might not only lead to TRMN but also affect the prognosis of the primary neoplasm and its treatment-related toxicity. Our study aims to describe the prevalence and dynamics of CHIP in treatment-naïve pts with cancer and to analyze its impact on clinical outcomes. METHODS This study included 103 pts with a first cancer diagnosis at age ≥ 60 years and eligible for anticancer treatment without prior exposure to cytostatic agents. Peripheral blood (PB) samples were collected at diagnosis and 6 months after treatment. A customized NGS panel covering common CHIP genes ( DNMT3A, TET2, ASXL1, JAK2, PPM1D, TP53, SF3B1, GNB1, SRSF2, CHEK2, CBL, GNAS, and NRAS) was used to identify CHIP-positive (VAF≥ 1%) and CHIP-negative cases. Clonal dynamics were assessed through NGS at 6 months after treatment, categorized as ‘growing’ when their VAF increased by more than 25% compared to the baseline, ‘shrinking’ when VAF decreased by more than 25% compared to the baseline and ‘stable’ if it remains unaltered. RESULTS Baseline characteristics are shown in table 1.The prevalence of CHIP in our cohort was 35%, with an average of 1.5 somatic variants per patient and 54 identified variants, and a median VAF of 4.7% (IQR 2.5-11.0%). Notably, mutations in DNMT3A (33%), TET2 (28%), and PPM1D (13%) were the most prevailing gene aberrations, accounting for nearly 75% of all variants, while other common CHIP genes such as ASXL1 (9%) or JAK2 (0%) were less frequent. TP53 variants represented 9% of all mutations, whereas SF3B1, GNB1, SRSF2, and CBL each accounted for 2%. Breast cancer pts displayed a significantly higher prevalence of CHIP compared to other primary neoplasms (66% vs. 36%, p=0.01) whereas no patient with bladder neoplasm presented CHIP at diagnosis (p=0.04). These observations were not warranted only by differences in the age or smoking habit of these subgroup of neoplasms. The mutational spectrum of CHIP across different cancer categories was comparable. Among 20 paired samples sequenced (baseline and post-genotoxic exposure), 41% of all variants exhibited a growing pattern, 31% a shrinking pattern, and 28% remained static (Figure 1). Platinum-based therapy exposition promoted clonal expansion in DNMT3A mutations (p=0.03), while this effect was not observed in PPM1D or other genes, likely due to the low sample size. Age, tobacco use, and type of primary neoplasm did not appear to influence clonal fitness. There were no significant differences in the incidence of infectious complications or chemotherapy-induced hematologic toxicity between CHIP-positive and CHIP-negative cohorts. With the current follow-up time (16.8 months), the overall response (ORR) and complete response rates (CR) appeared comparable (ORR: 94% in CHIP-positive vs. 85% in CHIP-negative; CR: 79% vs. 70%, respectively). A patient with diffuse large B-cell lymphoma and CHIP ( ASXL1, PPM1D, and TP53 variants) developed a TRMN (MDS-MD) 7 months after completing R-CHOP treatment. CONCLUSION The prevalence of CHIP in our cancer pts cohort is 35%, with breast cancer cases displaying a CHIP occurrence around 62% not previously reported. Our study highlights an enrichment of mutations in PPM1D in treatment-naïve cancer pts, surpassing the frequency of ASXL1 in contrast to prior literature. Genotoxic therapy promotes clonal expansion in 41% of variants in our cohort; although factors influencing CHIP fitness remain poorly understood, DNMT3A showed heightened susceptibility to platinum therapy. Finally, and in contrast contrast with our initial hypothesis, we found no evidence of impaired outcomes in the CHIP population. These results emphasize the need for further longitudinal follow-up. Acknowledgements: This work was supported by two grants from the Instituto de Salud Carlos III (PI20/00881 and PI 20/00531)(Co-funded by European Regional Development Fund. ERDF, a way to build Europe). 2021 SGR 00560 (GRC) Generalitat de Catalunya; economical support from CERCA Programme.

Can Emergency Hematopoiesis Due to Sepsis Lead to Clonal Hematopoiesis? Implications for Understanding the Pathogenesis of Clonal Evolution

O.O & T.K are co-first authors. Clonal (myelo) hematopoiesis of indeterminate potential (CHIP) arises from somatic mutations in myeloid genes, providing a proliferative and survival advantage to the affected “CHIP-initiating” early hematopoietic precursor cells. Understanding the conditions that lead to the emergence of detectable clones (early seeding of myeloid neoplasia-MN) is of great interest due to its clinical implications. Among CH facilitating states, aging has been extensively studied, but a clear distinction between the impact of chronological versus biological aging remains challenging. Additionally, other factors contributing to CHIP development may include chemotherapy, genetic predisposition, bone marrow failure states, or immunodeficiency. However, not all CHIP-promoting factors have been identified because they are subtle, pathophysiologically complex, and thus remain cryptic. We hypothesized that episodes of emergency hematopoiesis (EH), such as those caused by acute infections, could potentially result in acquisition of CHIP with repeated episodes of EH resulting in clonal expansion. If this hypothesis is confirmed, one could envision that both instances of significant hematopoietic expansion (high leukocytosis) and repeated cycles of EH could be at play in conjunction with chronological factors. For instance, the older an individual is, the greater is the number of EH episodes possible. To examine our theory, we prospectively collected blood samples from patients admitted at the intensive care unit (ICU) of Cleveland Clinic and Yale University. Inclusion criteria required a white blood cell (WBC) count ≥ 15K/uL. Patients with known or prior malignancies and those exposed to chemotherapy were excluded. For relevant comparisons, we assessed CH incidence in our cohort against a group of patients with solid tumors screened for CH (n=107) but without acute infections, along with historical CHIP cohorts. CH screening employed a targeted NGS myeloid gene panel with a reported VAF cut-off of 2%. A total of 78 individuals admitted to the ICU with possible infections and leukocytosis were enrolled in this study. The median age was 70 years (IQR: 61-77), with a M:F ratio of 1.7 (Table 1). Time from leukocytosis onset to sampling was 3 days (IQR: 1-5), the median WBC at ICU admission was 18 K/uL (IQR: 16-21), and the median absolute neutrophil count (ANC) was 16 K/uL (IQR: 12-20). Overall, 94 variants were identified including 16 (median VAF 50.1) variants of potentially germline origin, and 4 variants of unknown significance. We observed 74 CHIP-associated mutations in 37 (47%) patients at a median VAF of 14% (4-47%). The landscape of CHIP mutations included alterations in DNMT3A (20%), TET2 (12%), ASXL1 (12%), SMC1A, TP53, and PPM1D genes (6% each). Although higher rates of CHIP were expected in the cancer cohort, no difference was found between the two groups (40% vs. 47% in the ICU, p=0.3). DNMT3A, ASXL1 and PPM1D mutations were more frequently encountered in the cancer cohort (Table 1). The prevalence of CHIP in the ICU cohort was higher in older age groups: 30-39 (29%), 50-69 (49%), and ≥70 (51%), compared to the expected frequency in comparable age ranges (and median range) in a historical healthy population, which was 1%, 4%, and 10%, respectively (<0.00001; Fig.1). Notably, CHIP was more prevalent among smokers (57%; p=0.003). No significant differences were found when comparing CHIP + and CHIP - patients of the ICU cohort with regards to WBC (median 18K/uL both). Similarly, CHIP prevalence did not change according to the degree of leukocytosis in an analysis where patients were ranked by WBC (≥18K/uL at 44% vs. <18K/uL at 46%). When looking at the impact of CHIP on critical care outcomes, a logistic regression model accounting for age, gender, and mutation type revealed that the presence of DNMT3A mutations was associated with a higher risk of diagnosis of overt septic shock (log OR= 2.4, 95% CI 0.19-5.4, p<0.05). In summary, our prospective observational study has shown that sepsis is associated with preferential mutant clone expansion, primarily due to EH rather than the extent of leukocytosis and may be contributing to the acquisition of new clones. Whether such episodes result in permanent acquisition of new CHIP mutations with potential for MN progression will be the subject of longitudinal analysis of these samples, and findings will be presented at the ASH meeting.

KPT-8602 Induced Hematopoietic Differentiation in U2AF1 S34F Mutant Cells and Myelodysplastic Syndromes Bone Marrow Stem and Progenitor Cells

Myelodysplastic syndromes (MDS) are a group of clonal bone marrow (BM) neoplasms characterized by ineffective hematopoiesis, cytopenia's, and a high risk of progression to acute myeloid leukemia. Current standard therapies include erythropoiesis stimulating agents for lower risk disease and DNMTi for higher risk MDS; however, less than half of patients respond and even the best responses are transient and non-curative. The majority of MDS patients harbor at least one of ~40 commonly found somatic gene mutations, most of which occur in splicing factor genes such as U2AF1, which also have non-canonical roles in nuclear export. KPT-8602 (Eltanexor) is a novel selective inhibitor of nuclear export (SINE) that acts by disrupting nuclear export of cargo relevant in MDS. We hypothesized that U2AF1 S34 F mutant cells would be selectively sensitive to treatment with KPT-8602. We created immortalized murine hematopoietic progenitor cells by retroviral transduction of stimulated bone marrow (BM) cells isolated from U2AF1 WT or U2AF1 S34F mice with a HOXB8_ER vector. Estrogen drives the hematopoietic transcription factor immortalizing the cells in a progenitor state, however, upon estrogen withdrawal the cells will differentiate and eventually die. This differentiation can be driven by treatment with specific growth factors such as erythropoietin (EPO) for erythroid differentiation or granulocyte macrophage colony stimulating factor (GM-CSF) for myeloid differentiation. KPT-8602 exposure induced differentiation and increased hematopoiesis in murine cell models and primary MDS samples. U2AF1 WT and U2AF1 S34F cells were plated in medium lacking estrogen and treated with GM-CSF (10nM) or EPO (1nM) with or without KPT-8602 (10nM) for 72h, then stained with Ly6C, CD11b, Ter119, and CD71 for flow cytometry analysis. In addition, we performed colony forming capacity assays in both the murine cells and primary MDS BM stem and progenitor cells and age-comparable healthy donors, with 14 day KPT-8602 exposure. Treatment with GM-CSF significantly increased the expression of Ly6C in both U2AF1 WT and U2AF1 S34F cells (WT fold change untreated vs GMCSF =1.9, p=0.03; S34F fold change untreated vs GMCSF =2.3, p<0.01). However, addition of KPT-8602 caused significantly more Ly6C expression than GM-CSF alone in the mutant cells (WT fold change GMCSF vs combination =3.1, p=0.06; S34F fold change GMCSF vs combination =4.0, p<0.01). There were no significant changes in CD11b expression with KPT-8602 treatment. We did not find a statistically significant increase in erythroid markers assessed by Ter-119 and CD71 after EPO treatment, however, KPT-8602 treatment alone showed a trend of increased expression of Ter-119 and CD71 in the mutant cells that fell just below statistical significance (Ter119 p=0.08 for WT, p=0.09 for S34F; CD71 p=0.21 for WT, p=0.06 for S34F). Additionally, we looked at selective toxicity of U2AF1 S34Fby WST-1 reagent and found no differences in toxicity between the WT or mutant cells with KPT-8602. However, U2AF1 WT and U2AF1 S34F progenitor cells showed an increase in colony forming capacity (n=1 with technical duplicates) when plated in the presence of KPT-8602 showing an average fold change in colony growth of 1.4 for U2AF1 WT and 1.3 for U2AF1 S34F underscoring the ability of KPT-8602 to induce differentiation. To confirm these results were not cell line artifacts, we next treated primary BM stem and progenitor cells from MDS patients (n=2) and healthy donors (n=4). MDS patient 1 (age 73y) was diagnosed with MDS-MLD-EB1 and harbored mutations in TP53, ASXL1, BCOR, TET2 and PPM1D. MDS patient 2 (age 79y) was diagnosed with MDS/MPN and harbored an SF3B1 mutation. Healthy donors (n=4) were all male and had a median age of 65y. Treatment with KPT-8602 (10nM) significantly increased burst and colony forming unit-erythroid (BFU-E/CFU-E) in MDS primary cells (p=0.02) with no significant increase in the healthy donors (p=0.57) (BFU-E/CFU-E fold increase was 1.1 for healthy donors and 3.5 for MDS). Collectively, these findings suggest that KPT-8602 promotes myeloid and erythroid differentiation and further validates the use of KPT-8602 as a therapeutic strategy for MDS. Future studies will fully elucidate the specific mechanisms by which KPT-8602 acts in the context of splicing factor mutations, and other commonly found MDS mutation types.

Clonal Hematopoiesis Is Associated with Severe COVID-19 Enhancing Inflammatory Responses in Myeloid Cells

Background Clonal hematopoiesis (CH) is prevalent among aged populations and highlighted because its association with not only hematological malignancies but various benign diseases (e.g. cardiovascular diseases). Of particular interest among these diseases is COVID-19. To date, the association between severe COVID-19 and CH-related gene mutations or mosaic chromosomal alterations (mCAs) was examined using biobank samples taken long before the pandemic and the association has not been tested in a sufficiently large cohort of patients on the basis of CH evaluated at the time of COVID-19 diagnosis. Moreover, no study examined the joint effect of gene mutations and mCAs. The mechanism of the association between severe COVID-19 and CH has not been addressed either. Methods To address these issues we enrolled a total of 4,541 patients with COVID-19, of whom 54% had a severe infection. We performed targeted-capture sequencing of 42 CH-related genes and SNP-array analysis to detect CH-related mutations and mCAs. We also performed RNA-seq (n=987) of whole blood samples and plasma proteomic analysis (n=1,200) using the Olink technology to investigate the effect of biological consequence of CH, which was applied to understand the underlying mechanism of sever COVID-19. Results We identified gene mutations and mCAs in 16.3% and 6.2% of COVID-19 patients, respectively. They coexisted in 2.4% patients. As reported in CH in normal individuals, most frequent alterations included mutations in DNMT3A (7.6%), TET2 (4.1%), ASXL1 (1.4%), PPM1D (1.7%), and mCAs such as 14qUPD, and del(20q). To evaluate the risk of severe COVID-19 conferred by CH, we compared the age-stratified frequencies of CH between severe and non-severe COVID-19 patients (Figure, a). Focusing on CH in ≧10% clonal fractions, CH was significantly enriched in severe COVID-19 in elderly patients, we detected a significant enrichment of cases with both gene mutations and mCAs and isolated gene mutations, but not that of isolated mCAs, in severe cases. Multivariable logistic regression analysis with adjustment for age and sex revealed the significant association of CH defined either CH-mutations or mCA with severe COVID-19 with an odds ratio (OR) of 1.34 [95%CI=1.03-1.84] in patients aged ≥65 years. Particularly, CH defined by combined gene mutations and mCAs conferred a remarkable increase in the risk of severe COVID-19 [OR=12.1, 95%CI=1.61-90.6], suggesting the presence of their synergistic impact on severe COVID-19. To elucidate the underlying mechanism of the observed association between severe COVID-19 and CH, we next evaluated the transcriptomic/proteomic features of severe COVID-19 and CH (Figure, b). In severe COVID-19, multiple inflammatory pathways including IFN-α/γ, TNF-α, and IL-6 responses were consistently up-regulated in both transcriptomic and proteomic analysis. Similar to these features of severe COVID-19, CH was also associated with inflammatory response and IFN-α/γ responses in RNA expression while the impact of CH on protein expression was not prominent. To further clarify the transcriptomic features of severe COVID-19 and CH, we performed deconvolution analysis of gene expression to estimate the fraction of each cell component and cell-type-specific expression profiles. Severe COVID-19 was characterized by elevated fractions of neutrophils, activated dendritic cells (DCs), and decreased fractions of several types of lymphocytes, while only a marginal increase of activated DCs was observed in CH. Cell-type-specific pathway analysis revealed up-regulations of inflammatory responses and IL-6/TNF-a signaling in neutrophils/monocytes were associated with both severe COVID-19 and CH independently, suggesting that CH might be involved in the development of severe COVID-19 through the augmentation of inflammatory responses in these myeloid cells, which are further augmented by increased neutrophils induced by COVID-19 independent of CH. Conclusion CH was significantly associated with an increased risk of severe COVID-19, particularly when the patients had both gene mutations and mCAs, where the augmented inflammatory responses by myeloid cells can be a mechanism of severe COVID-19 risk conferred by CH. Our findings highlight the link between the mechanism of severe COVID-19 and the biological effects of CH.

1-Year Data Analysis from a Cancer Center Molecular Tumor Board Dedicated to Clonal Hematopoiesis

Background Nearly 25% of cancer patients harbor clonal hematopoiesis of indeterminate potential (CHIP). Detection of clonal hematopoiesis (CH) in routine clinical practice is increasing due to incidental findings during sequencing analysis of circulating cell-free DNA (cfDNA) or exploration of unexplained cytopenia. To improve clinical management of these patients in our institution, we set up a multidisciplinary molecular tumor board (MTB) dedicated to patient cases with CH, CHIP, and clonal cytopenia of undetermined significance (CCUS) in 2022. Methods Between June 2022 and June 2023, our MTB reviewed a total of 345 cases, of which 212 referred by the solid tumor MTB and 133 referred by hematologists. The former 212 cases with CH were identified through cfDNA sequencing (FoundationOne Liquid CDx) within the Gustave Roussy Cancer Profiling study (NCT04932525), which includes some genes recurrently mutated in hematologic malignancies ( ASXL1, DNMT3A, IDH1, IDH2, JAK2, MPL, MYD88, SF3B1, TET2, U2AF1). A variant allele frequency (VAF) of at least 10% for the CH mutation was required to refer cases to the MTB, except for JAK2, MPL, and MYD88 mutations. The latter 133 cases were screened for CH mutations on peripheral blood leukocytes using a next-generation sequencing (NGS) assay targeting 174 genes recurrently mutated in hematologic malignancies. In addition to molecular data, standard clinical and biological parameters were recorded for each individual case. Results Patients referred by the solid tumor MTB In this cohort of 212 patients, median age was 72 years old (range, 48-91), sex ratio (M/F) was 1.4, median prior anticancer treatment lines was 2 (0-9), and time between MTB and cancer diagnosis was 2.3 years (0.2-34). The most frequent tumor types were lung (23%), colorectal (20%), prostate (19%), gynecological (12%) and breast (9%) cancers. The most frequently mutated genes were DNMT3A (59%), TET2 (30%), ASXL1 (24.5%), JAK2 (23%), SF3B1 (7.5%), and MYD88 (6%), with a median VAF of 4.2%, 3.0%, 8.5%, 1.0%, 5.0%, and 0.20%, respectively. Fifty percent of patients harbored more than 1 mutation. Six patients had a known history of myeloproliferative neoplasm (MPN). The proportion of cases with CH, CHIP, and CCUS was 15%, 59%, and 17%, respectively. The CH risk score of myeloid malignancy (CHRS, Weeks et al.) could be calculated in 126 cases but may underestimate risk due to the limited gene list considered, and revealed 69 (55%) low-risk, 52 (41%) intermediate-risk, and 5 (4%) high-risk patients. Our MTB recommended hematologic consultation for additional investigations in 58 patients, of which 22 were actually referred (main reason for not referring patients was advanced cancer disease). Four patients were diagnosed with hematologic malignancy (1 MPN, 1 chronic myeloid leukemia, 2 myelodysplastic syndromes [MDS]). Patients referred by a hematologist In this cohort of 133 patients, median age was 69 years old (53-89), and sex ratio (M/F) was 0.6. Eighty-six percent of patients had a cancer history, median prior anticancer treatment lines was 2 (0-7), time between MTB and cancer diagnosis was 3.5 years (0.2-34). The most frequent tumor types were lymphoid disorders (39%), breast cancer (15%), and gynecological cancer (15%). The proportion of CH, CHIP, and CCUS was 11%, 33%, and 41%, respectively. The most frequently mutated genes were DNMT3A (48,5%), PPM1D (24%), TET2 (22%), TP53 (17%), ASXL1 (6%), JAK2 (4.5%) and CHEK2 (4.5%), with a VAF of 2.5%, 2,3%, 4.0%, 2.0%, 8.0%, 1.0%, and 2.5%, respectively. Sixty percent of patients harbored more than 1 mutation. The CHRS could be calculated in 98 cases and revealed 34% low-risk, 50% intermediate-risk, and 16% high-risk CH patients. No need for a specific follow-up was recommended by the MTB in 33 patients. Among the 85 patients with hematologic follow-up, 3 (for which the CHRS was intermediate in 2 cases and high in 1 at the time of MTB evaluation) rapidly progressed to a myeloid malignancy ( Figure 1) (2 MDS and 1 MDS/MPN). Conclusions Our study highlights the utility of a MTB dedicated to CH, CHIP and CCUS for the identification of high-risk patients, early detection of hematologic malignancies, and appropriate therapeutic management. Long-term follow-up is needed to validate the CHRS but the design of a specific score for patients with cancer may be helpful due to the specific features of this population (high prevalence of PPM1D mutations, post-treatment cytopenia).

Clonal Hematopoiesis in Whole-Blood and Cell-Free DNA of Ovarian Cancer Patients Undergoing PARP-Inhibitor Treatment: An Exploratory Analysis of the ENGOT-ov48/Eudario Trial

Clonal hematopoiesis (CH), characterized by the expansion of somatically mutated hematopoietic stem cells, is an age-related phenomenon associated with the development of hematologic malignancies, increased cardiovascular risk, and other age-related proinflammatory conditions. In patients with solid tumors, cytotoxic therapies differentially select for clones with mutations in the DNA damage response (DDR) pathway, i.e. TP53 and PPM1D, leading to an elevated risk for therapy-related myeloid malignancies (t-MNs). Poly(ADP-ribose) polymerase inhibitors (PARPi) are frequently used to treat ovarian cancer with particularly high efficacy reported in tumors exhibiting homologous recombination (HR) deficiency caused by mutations in BRCA1/2 or other HR pathway genes. However, recent data indicate that PARPi treatment is also associated with an elevated risk for t-MNs. Here, we performed an in-depth analysis of CH in whole-blood (WB) and plasma of patients with relapsed high-grade ovarian cancer (HGOC) receiving platinum-based chemotherapy and PARPi treatment, elucidating the mutational landscape of CH, gene-specific dynamics, as well as the potential interference of CH with putative tumor-derived mutations in cell-free DNA (cfDNA). Serial specimen of 103 patients with relapsed, platinum-sensitive HGOC participating in the European Trial on Enhanced DNA Repair Inhibition in Ovarian Cancer (EUDARIO) study (ENGOT-ov48/NCT03783949) were analyzed using error-corrected targeted sequencing with a custom panel covering 45 myeloid and 27 HR-related genes. Study treatment consisted of six cycles of carboplatin-based chemotherapy followed by maintenance therapy with Niraparib ± the HSP90 inhibitor Ganetespib. A total of 128 somatic mutations with variant allele frequencies (VAFs) ≥ 1% were identified in 58 patients (56%) with a high fraction of DDR mutations (51 PPM1D mutations in 27 patients, 7 TP53 mutations in 7 patients). Age (median 62 years) and the number of previous therapy lines (median 1, range 1-5 lines) were significantly associated with the presence of CH. Specifically, prior exposure to PARPi treatment was strongly associated with both the presence of CH and the number of CH mutations. CH-positive patients had significantly shorter progression-free survival (median 7.9 months vs 10.6 months, p = 0.021 in log-rank test), and a trend for shorter overall survival (median 21.1 months vs 27.7 months, p = 0.16) in univariate survival analysis. With respect to adverse events, CH-positive patients more frequently had infections during study treatment (49% vs 26%, p = 0.025). All but 5 CH mutations with VAF ≥ 1% were also detectable in cfDNA with significant correlation of VAFs (R = 0.84, p < 0.0001). Mutations occurring solely in cfDNA (putatively tumor-derived) had a high fraction of TP53 and HR-related mutations, while DNMT3A and PPM1D, were rarely mutated (Figure 1). However, 23/87 (26%) of TP53 mutations and 31/98 (32%) of mutations in HR-related genes detected in cfDNA were of hematopoietic origin, underlining the importance of parallel sequencing of WB in liquid biopsies to avoid false positive results. The dynamics of CH clones under carboplatin and PARPi treatment were assessed in paired WB samples at initiation/end of treatment, which were available for 62 patients. 96 clones that initially had a VAF < 1% emerged during the treatment, including 56 PPM1D- and 10 TP53-mutated clones. Gene-wise comparison revealed a significantly higher median clonal fitness in PPM1D- and TP53-mutated clones compared to TET2- or DNMT3A-mutated clones (Figure 2). PPM1D-mutated clones exhibited lower fitness during PARPi treatment compared to carboplatin treatment (p = 0.0015 in Wilcoxon rank sum test), which was not the case for TP53-mutated clones. Finally, 8 samples with multiple mutations were subjected to single-cell genotyping on the Mission Bio Tapestri platform to investigate their clonal architecture. Preliminary data indicate clonal exclusiveness of co-occurring DDR mutations. In summary, our data reveals a high prevalence of CH in patients with relapsed HGOC and provides novel insights into the clonal architecture and dynamics of CH under carboplatin and PARPi treatment with a differential selection of DDR-driven clones. Moreover, we report a relevant interference of CH-derived mutations with tumor-derived mutations in cfDNA.

Genomic Landscape of Ccus Compared to MDS Indicates a Potential Applicability of the IPSS-M

Background: The 5 th edition of the WHO classification newly included myeloid precursor lesions introducing CCUS as an entity. CCUS is defined as clonal hematopoiesis (CH) in the presence of unexplained, persistent cytopenia requiring detection of either somatic mutation in certain CH associated genes or clonal chromosomal abnormalities. Aim: Characterize a large CCUS cohort with respect to cytogenetics and molecular genetics and compare the findings to an MDS cohort to evaluate differences in the genomic landscape. Methods: The CCUS cohort comprised 222 cases (median age: 76 y; female: 33%), the MDS cohort 698 cases (median age: 73 y; female: 43%). The diagnoses were established following WHO 2022. All samples were analyzed by cytomorphology, cytogenetics, targeted NGS panel (median coverage 1500x) and whole genome (median coverage 100x) sequencing. Mutation (MUT) status of 59 genes associated with myeloid malignancies were analyzed in detail (54 CH associated; 5 relevant for IPSS-M). Results: Significant differences in age, gender, BM blasts, blood parameters and number and types of cytopenias were detected. CCUS patients (pts) were older, had more WBC, less PLT, harbored a higher HB, less BM blasts and were even more predominantly male compared to MDS pts (all p<0.05). Within the CCUS cohort 29 pts (13%) showed cytogenetic abnormalities (CA) only (thereof 69% loss of chromosome Y (Y-loss)), while the remaining 193 pts (87%) showed at least one MUT (VAF ≥2%) in any of the 54 CH associated genes (thereof 84% MUT only; 16% MUT+CA). Regarding cytogenetics 162 CCUS pts (73%) harbored normal karyotypes while CA were detected in 27% (MDS: 43%; p<0.001) with Y-loss being most frequent (39/60; 65%). Y-loss was more frequently found in CCUS than in MDS (17% vs. 5%; p<0.001), while complex karyotypes and del(5q) were more frequent in MDS (11% and 16% vs. 1% and 0%; both p<0.001). Based on WGS data additional pts with Y-loss (n=7; confirmed by FISH) and recurrent CN-LOH (4q: n=4; 7q: n=5) were observed. With respect to somatic MUTs, 356 MUTs were found within the entire CCUS cohort (in 28 CH genes, 3 non-CH genes). Overall, CCUS pts showed less MUTs (median: 1 [0-6]) compared to MDS (median: 2 [0-12]; p<0.001). CCUS pts most frequently harbored MUTs in DNMT3A (32%), TET2 (28%) and ASXL1 (14%) followed by MUTs in splicing genes and TP53 (Fig. 1A). MUTs in DNMT3A and PPM1D were more frequent in CCUS than MDS while MUTs in ASXL1, TP53, SF3B1, STAG2, RUNX1, NRAS, CUX1 were less frequent in CCUS (each p<0.05). Notably, biallelic TP53 MUTs were less frequent in CCUS compared to MDS ( TP53bi of mutated: 14% vs. 55% p=0.008). Within the 15 most frequently mutated genes in CCUS, MUTs in 6 genes ( DNMT3A, SF3B1, TP53, CBL, STAG2, PPM1D) showed a median VAF <10%. Nine of the top 15 genes showed significantly lower median VAFs than in MDS ( DNMT3A, TET2, ASXL1, SRSF2, U2AF1, SF3B1, TP53, PPM1D, IDH2; each p<0.05). Thus, the frequency and VAF of ASXL1, TP53, SF3B1 MUTs were significantly lower in CCUS than in MDS, while DNMT3A and PPM1D MUTs were significantly more often detected in CCUS but at a lower VAF than in MDS. Combining cytogenetics and mutational analysis we calculated the IPSS-M, a patient-specific risk score for MDS resulting in six risk categories, and detected a clear skewing towards low risk categories in CCUS (Fig. 1B). The frequency of categories very low (VL) and low (L) were significantly higher in CCUS than in MDS (30% vs. 15%; 50% vs. 40%; both p<0.013), while high and very high categories were more rare (1% vs. 13%; 1% vs. 14%; both p<0.001). Although CCUS follow-up data were short (median: 1.5 y), no differences in overall survival were observed between CCUS VL+L and MDS VL+L, while within CCUS survival differed between VL+L and the remaining cases ( p=0.05). Conclusions: Our data confirm the comparable mutational spectrum between CCUS and MDS but clearly show major differences in the frequency and VAF of distinct gene mutations. These biological differences hint towards different subgroups within CCUS with cases closer to MDS than others. A combined risk score for MDS and CCUS would reflect this continuous spectrum and has the potential to derive an objective risk assessment irrespective of observer-dependent grading of dysplasia. Our study indicates plausible short term results for CCUS patients stratified according to the IPSS-M. However, the definite applicability of the IPSS-M needs to be confirmed in larger CCUS studies with longer follow-up.

PPM1D modulates hematopoietic cell fitness and response to DNA damage and is a therapeutic target in myeloid malignancy

AbstractPPM1D encodes a phosphatase that is recurrently activated across cancer, most notably in therapy-related myeloid neoplasms. However, the function of PPM1D in hematopoiesis and its contribution to tumor cell growth remain incompletely understood. Using conditional mouse models, we uncover a central role for Ppm1d in hematopoiesis and validate its potential as a therapeutic target. We find that Ppm1d regulates the competitive fitness and self-renewal of hematopoietic stem cells (HSCs) with and without exogenous genotoxic stresses. We also show that although Ppm1d activation confers cellular resistance to cytotoxic therapy, it does so to a lesser degree than p53 loss, informing the clonal competition phenotypes often observed in human studies. Notably, loss of Ppm1d sensitizes leukemias to cytotoxic therapies in vitro and in vivo, even in the absence of a Ppm1d mutation. Vulnerability to PPM1D inhibition is observed across many cancer types and dependent on p53 activity. Importantly, organism-wide loss of Ppm1d in adult mice is well tolerated, supporting the tolerability of pharmacologically targeting PPM1D. Our data link PPM1D gain-of-function mutations to the clonal expansion of HSCs, inform human genetic observations, and support the therapeutic targeting of PPM1D in cancer.

Associations Between Cancer Predisposition Mutations and Clonal Hematopoiesis in Patients With Solid Tumors.

Clonal hematopoiesis (CH), the expansion of clones in the hematopoietic system, has been linked to different internal and external features such as aging, genetic ancestry, smoking, and oncologic treatment. However, the interplay between mutations in known cancer predisposition genes and CH has not been thoroughly examined in patients with solid tumors. We used prospective tumor-blood paired sequencing data from 46,906 patients who underwent Memorial Sloan Kettering-Integrated Mutation Profiling of Actionable Cancer Targets (MSK-IMPACT) testing to interrogate the associations between CH and rare pathogenic or likely pathogenic (P/LP) germline variants. We observed an enrichment of CH-positive patients among those carrying P/LP germline mutations and identified a significant association between P/LP germline variants in ATM and CH. Germline and CH comutation patterns in ATM, TP53, and CHEK2 suggested biallelic inactivation as a potential mediator of clonal expansion. Moreover, we observed that CH-PPM1D mutations, similar to somatic tumor-associated PPM1D mutations, were depleted in patients with P/LP germline mutations in the DNA damage response (DDR) genes ATM, CHEK2, and TP53. Patients with solid tumors and harboring P/LP germline mutations, CH mutations, and mosaicism chromosomal alterations might be at an increased risk of developing secondary leukemia while germline variants in TP53 were identified as an independent risk factor (hazard ratio, 36; P < .001) for secondary leukemias. Our results suggest a close relationship between inherited variants and CH mutations within the DDR genes in patients with solid tumors. Associations identified in this study might translate into enhanced clinical surveillance for CH and associated comorbidities in patients with cancer harboring these germline mutations.

Clonal hematopoiesis with DNMT3A and PPM1D mutations impairs regeneration in autologous stem cell transplant recipients.

Clonal hematopoiesis (CH) is an age-related condition driven by stem and progenitor cells harboring recurrent mutations linked to myeloid neoplasms. Currently, potential effects on hematopoiesis, stem cell function and regenerative potential under stress conditions are unknown. We performed targeted DNA sequencing of 457 hematopoietic stem cell grafts collected for autologous stem cell transplantation (ASCT) in myeloma patients and correlated our findings with high-dimensional longitudinal clinical and laboratory data (26,510 data points for blood cell counts/serum values in 25 days around transplantation). We detected CHrelated mutations in 152 patients (33.3%). Since many patients (n=54) harbored multiple CH mutations in one or more genes, we applied a non-negative matrix factorization (NMF) clustering algorithm to identify genes that are commonly co-mutated in an unbiased approach. Patients with CH were assigned to one of three clusters (C1-C3) and compared to patients without CH (C0) in a gene specific manner. To study the dynamics of blood cell regeneration following ASCT, we developed a time-dependent linear mixed effect model to validate differences in blood cell count trajectories amongst different clusters. The results demonstrated that C2, composed of patients with DNMT3A and PPM1D single and co-mutated CH, correlated with reduced stem cell yields and delayed platelet count recovery following ASCT. Also, the benefit of maintenance therapy was particularly strong in C2 patients. Taken together, these data indicate an impaired regenerative potential of hematopoietic stem cell grafts harboring CH with DNMT3A and PPM1D mutations.

Clonal hematopoiesis in older patients with breast cancer receiving chemotherapy.

The expansion of hematopoietic stem cells carrying recurrent somatic mutations, termed clonal hematopoiesis (CH), is common in elderly individuals and is associated with increased risk of myeloid malignancy and all-cause mortality. Though chemotherapy is a known risk factor for developing CH, how myelosuppressive therapies affect the short-term dynamics of CH remains incompletely understood. Most studies have been limited by retrospective design, heterogeneous patient populations, varied techniques to identifying CH, and analysis of single timepoints. We examined serial samples from 40 older women with triple-negative or hormone receptor-positive breast cancer treated on the prospective ADjuVANt Chemotherapy in the Elderly trial to evaluate the prevalence and dynamics of CH at baseline and throughout chemotherapy (6 and 12 weeks). CH was detected in 44% of patients at baseline and in 53% at any timepoint. Baseline patient characteristics were not associated with CH. Over the course of treatment, mutations exhibited a variety of dynamics, including emergence, expansion, contraction, and disappearance. All mutations in TP53 (n = 3) and PPM1D (n = 4), genes that regulate the DNA damage response, either became detectable or expanded over the course of treatment. Neutropenia was more common in patients with CH, particularly when the mutations became detectable during treatment, and CH was significantly associated with cyclophosphamide dose reductions and holds (P = .02). Our study shows that CH is common, dynamic, and of potential clinical significance in this population. Our results should stimulate larger efforts to understand the biological and clinical importance of CH in solid tumor malignancies. ClinicalTrials.gov (https://clinicaltrials.gov/ct2/show/NCT03858322). Clinical trial registration number: NCT03858322.