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

## TL;DR

This study explores how clonal hematopoiesis in the myeloid compartment affects survival, treatment toxicity, and transformation risk in chronic lymphocytic leukemia patients.

## Contribution

The study is the first to investigate clonal hematopoiesis in the myeloid compartment of CLL and its clinical implications.

## Key findings

- Clonal hematopoiesis occurred in nearly half of newly diagnosed CLL patients and was linked to shorter survival.
- TET2 mutations independently predicted worse survival, and CH was associated with higher toxicity from venetoclax-based therapies.
- CH mutations were restricted to myelomonocytic cells and not present in CLL cells, as confirmed by single-cell sequencing.

## Abstract

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 TP53 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, TET2 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 TP53 status. Regarding therapy‐related toxicities, CH correlated with a higher incidence of Grade ≥ 3 neutropenia (P = 0.004) after venetoclax‐based regimens. Sequential samples (n = 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 ASXL1 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.