C038 | MOLECULAR AND TRANSLATIONAL IMPLICATIONS OF CLONAL HEMATOPOIESIS IN CHRONIC LYMPHOCYTIC LEUKEMIA AND RICHTER TRANSFORMATION

The translational contribution of clonal hematopoiesis (CH) in chronic lymphocytic leukemia (CLL) and Richter transformation (RT) remains insufficiently characterized. CH was analyzed by CAPP-Seq in 488 CLL patients on gDNA from granulocytes at the time of diagnosis and, in selected cases, before and after different CLL therapies. Cell sorting, single cell (sc) DNA and scRNA sequencing were also performed in cases provided with viable cells. A total of 488 patients have been sequenced (median FU 12.3y) and CH was identified in 231 (47.3%) of them. The most frequent mutation was DNMT3A in 129 (26.4%) patients, followed by TET2 in 74 (15.2%) and ASXL1 in 15 (3.1%). Cell sorting in 33 patients who never developed RT confirmed that CH was present in the myeloid compartment and not in the CLL cells. Importantly, in 5 patients, TP53 mutations were found exclusively in the myeloid compartment, therefore representing CH-related, and not CLL-related, TP53 variants (Fig. 1A). The presence of at least one CH mutation associated significantly with a shorter OS (10.8y vs 13.6y, p=0.023). Moreover, TET2 mutations retained an independent association with shorter OS (HR 1.53, p=0.01) when adjusted for age, IGHV and TP53 status (Fig. 1B). By analyzing 30 patients treated with venetoclax-based therapy, CH presence associated with a higher risk of grade >3 neutropenia (p=0.004) (Fig. 1C). In patients receiving continuous BTKi (N=73), SF3B1 CH mutations (HR 9.75, p=0.003) associated with an increased risk of atrial fibrillation when adjusted for age and other cardiovascular comorbidities (Fig. 1D). scRNA sequencing of 7 CH+ CLL compared to 6 CH- CLL (matched for FISH, IGHV and TP53 status) revealed that CH influences the transcriptomic profiles of both B and T cells (Fig. 1E). CH+ patients displayed cell pathways indicative of heightened T-cell activation and a more pro-inflammatory profile. These data suggest that T-cells of CH+ patients may exhibit a less exhausted phenotype as documented by a lower expression of TOX, the master regulator of T-cell exhaustion induction. By evaluating RT, ASXL1 mutations associated with a higher risk of RT (HR 6.80, p=0.01) (Fig. 1F) also when adjusted for TP53 and NOTCH1 status. Interestingly, in 2 patients who subsequently developed RT, scDNA sequencing identified CH mutations also in CLL cells. CH in CLL harbors potential clinical relevance for both CLL and RT, while also influencing the T-cell immune compartment.