Dissecting clonal hematopoiesis in the myeloid compartment of chronic lymphocytic leukemia and Richter transformation.

The clinical and biological significance of clonal hematopoiesis (CH) has not been investigated in the myeloid compartment of chronic lymphocytic leukemia (CLL). By studying 488 newly diagnosed CLL through CAPP-seq using a 28-gene panel on granulocyte genomic DNA (gDNA), CH occurred in 231 (47.3%) patients. Cell sorting of cases that never developed Richter transformation (RT) confirmed that CH mutations, including CH-related mutations, were restricted to the myelomonocytic compartment and absent in CLL cells, as also documented by single-cell DNA sequencing. CH associated with shorter overall survival (OS) (hazard ratio [HR] 1.36, 95% CI 1.04-1.77, P = 0.023); specifically, mutations independently predicted inferior OS (HR 1.62, 95% CI 1.15-2.28, P = 0.01) after adjusting for age and for CLL-related prognostic biomarkers, namely IGHV and status. Regarding therapy-related toxicities, CH correlated with a higher incidence of Grade ≥ 3 neutropenia (P = 0.004) after venetoclax-based regimens. Sequential samples ( = 57) analysis showed that Bruton tyrosine kinase (BTK) and BCL2 inhibitors do not induce CH expansion, which was instead driven by chemotherapy. CH is significantly associated with a higher risk of second hematological malignancies only in chemo-exposed patients. Single-cell RNA sequencing of seven CH+ and six CH- CLL revealed that the T-cell compartment of CH+ patients exhibits a less exhausted phenotype, documented by lower expression of TOX, the master regulator of T-cell exhaustion, and a higher pro-inflammatory profile. CH also influenced RT, since CH mutations independently associated with higher RT risk (HR 11.19, 95% CI 4.09-30.62, P < 0.001). Overall, CH in CLL impacts survival, therapeutic toxicity, and transformation risk while also influencing the T-cell immune compartment.