High Incidence of Clonal Hematopoiesis in Transfusion-Dependent Thalassemia Patients

Introduction: Despite improvement in survival in patients with transfusion-dependent thalassemia (TDT), patients experience significant morbidities, including iron overload, malignancies, thromboembolic events and stroke, and cardiac complications like heart failure and arrhythmias. It is established that global chain imbalance and excess iron leads to significant oxygen stress and to the formation of oxygen free radicals resulting in an increased risk of mutations.

Clonal Hematopoiesis of Indeterminate Potential (CHIP) is characterized by the presence of somatic variants in the peripheral blood with a variant allele frequency (VAF) ≥2% in genes associated with hematologic malignancies. These variants occur more frequently with advanced age (~ 10% at age> 65 years). That said, recent data show that young patients with CHIP are at increased risk for developing not only hematological malignancies, but also coronary heart disease, cardiovascular events and stroke.

In this study we explored if TDT patients have an increased risk of clonal hematopoiesis and if this observation correlates with their underlying cardiovascular status, thromboembolic complications and history of malignancy.

Methods: Peripheral blood mononuclear cells (PBMCs) were isolated from ninety five patients with TDT just before their regular transfusion schedule (43 men and 52 women, mean age 39 years old, range 4-55 years ). 40 patients had a history of splenectomy, 32 patients had a history of cardiac disorder (13 patients with atrial fibrillation or other arrhythmias, 19 patients with valvular dysfunction). Genomic DNA was isolated from PBMCs from all patients and Next-Generation Sequencing analysis (NGS) was performed for the mutational status of 58 recurrently mutated genes in myeloid malignancies using a custom-designed Illumina sequencing panel (Illumina, San Diego, CA). Identification of mutations with a VAF ≥2% were reported after bioinformatics analysis and variant interpretation using the Varsome, ClinVar (v.2021) and Franklin databases.

Results: Fifteen of 95 patients analyzed (15.8%) displayed mutations in the genes implicated in CHIP. The age-adjusted prevalence of clonal hematopoiesis in patients with TDT vs the reported in the general population is significantly higher.

Overall, 22 somatic variants were identified in 15 patients with a median VAF of 40% (range 2.5%-52%): variants were detected in various genes including ATM, FLT3, ASXL1, MPL, SF3B1, BRAF, BTK, TP53, JAK2, RUNX1, ETV6 and EZH2.

Four patients carried variants in 4 different genes (TP53, TET2, CEBPA, NPM1) with a mean VAF of 3% (range 2,45% - 4,14%). The patient carrying the TP53 variant is a 44-year old male with a history of splenectomy and arrhythmia (ectopic atrial tachycardia). The patient carrying the TET2 mutation is 55-year old female with a history of colon cancer ten years ago, but no evidence of malignancy relapse as of today. A 5-year old male patient carried a clone in the NPM1 gene with VAF of 2.7%, with no history of splenectomy or cardiac complications. Finally, a 20 year-old male patient carried a clone in the CEBPA gene (VAF 2.7%) along with a clone in the ATM gene (VAF 50.3%). No history of splenectomy, or thromboembolic complications were noted in this patient.

Bioinformatics analysis revealed 18 variants in 11 patients with a VAF frequency within the germline range (VAF range 47-52%); germline DNA analysis is ongoing.

Seventy TDT patients (73,7%) carried the FLT3 C680T variant that is higher than the incidence reported in gnomAD exome for the European population (60.7%). Ninety three patients carried the ASXL1 T2444C variant, comparable to the observed frequency in the general population. The TET2 C100T variant was observed in 3,1% of the analyzed population compared to the 1.5% reported in the general population.

Further analysis revealed that none of the patients had a history of stroke and only two patients had a history of mitral valve regurgitation.

Conclusion: We report for the first time that patients with TDT display a significantly higher frequency of variants in genes associated with myeloid malignancies. Life-long stress in the hematopoiesis in these patients may contribute to the increased risk of clonal mutations observed, however further analysis is required to better understand the impact of these observations.

Stamatopoulos:Janssen: Research Funding; AbbVie: Research Funding. Chatzidimitriou:AbbVie: Research Funding; Janssen: Research Funding. Kattamis:Novartis: Consultancy, Honoraria, Research Funding; Chiesi: Honoraria; BMS/Celgene: Consultancy, Honoraria, Research Funding; VERTEX: Consultancy, Honoraria; ViFOR: Consultancy; IONIS: Consultancy; AMGEN: Consultancy; AGIOS Pharmaceuticals: Consultancy.