Prevalence and clinical impact of clonal hematopoiesis of indeterminate potential (CHIP) in chronic lymphocytic leukemia and richter transformation

The prevalence and the clinical impact of myeloid clonal hematopoiesis (CH) in CLL patients evaluated specifically on the myeloid compartment has not been yet evaluated. A CAPP-Seq next generation sequencing (NGS) panel of 28 genes frequently mutated in CH has been specifically designed and applied to sequence the gDNA extracted from the granulocytes of 488 newly diagnosed CLL patients. The median age of the cohort was 69.3 years, 8.9% harbored TP53 disruption and 34.3% unmutated IGHV. The median follow-up was 12.3 years. The most frequently mutated genes, as also reported in patients without CLL, were DNMT3A in 89 (26.4%) patients, followed by TET2 in 52 (15.2%) and ASXL1 in 10 (3.1%). As expected, the presence of at least one CH mutation significantly correlated with older age (p<0.001). By analyzing CH mutations in sorted CD19/CD5+ CLL cells, CD3+ T cells and CD14+ monocytes from 6 patients, CH mutations were predominantly present in the CD14+ myeloid compartment and not in the CLL cells. After a median follow-up of 12.4 years, the presence of any CH mutations associated with shorter overall survival (OS) (HR 1.36, 95% CI 1.04-1.77, p=0.023) but not with shorter time to first treatment (TTFT) in Binet A CLL (N=397) (HR 0.79, 95% CI 0.54-1.17, p=0.250). By analyzing the clinical impact of different gene mutations, TET2 mutated patients showed the strongest association with OS with a median OS of 7.9 years compared to 12.7 years for TET2 wild type patients (p=0.005). TET2 mutations (HR 1.53, 95% CI 1.09-2.16, p=0.01) maintained an independent association with shorter OS in multivariate analysis when adjusted for age, IGHV mutational status and TP53 disruption. Also, by analyzing the impact CH on Richter transformation, ASXL1 mutated patients showed an independent association with shorter time to Richter transformation when adjusted for TP53 and NOTCH1 abnormalities (HR 6.80, 95% CI 1.54-30.14, p=0.01). The analysis of longitudinal samples before and after different types of therapy showed that chemoimmunotherapy but not Bruton tyrosine kinase 4 inhibitors (BTKi) or BCL2i lead to CH clonal expansion. The impact of CH in terms of therapy toxicities was also assessed. In 30 patients treated with fixed duration venetoclax-based therapy, the presence of non-DNMT3A CH mutations (i.e. at least one CH mutation other than DNMT3A) associated with higher risk of grade >3 neutropenia during venetoclax treatment (p=0.001). In 73 patients receiving continuous treatment with BTKi, SF3B1 CH mutations associated with an increased risk of atrial fibrillation when adjusted for age and for other cardiovascular comorbidities (HR 9.75, 95% CI 2.16-44.01, p=0.003). These results suggest that CH harbors clinical relevance in CLL patients and might be considered also as a biomarker to prevent and manage therapy-related toxicities during targeted agents.