Telomere Length Associations with Characteristics and Outcome in Patients Treated with Venetoclax-Based First-Line Combinations in the GAIA/CLL13 Study
Authors: Jebaraj Billy , Tausch Eugen , Yosifov Deyan Y. , Schneider Christof , Fürstenau Moritz , Zhang Can , Robrecht Sandra , da Cunha-Bang Caspar , Levin Mark-David , Staber Philipp Bernhard , Tadmor Tamar , Thornton Patrick , Gregor Michael , Fink Anna Maria , Fischer Kirsten , Ritgen Matthias , Hallek Michael , Kater Arnon P. , Niemann Carsten Utoft , Eichhorst Barbara F. , Stilgenbauer Stephan 
Published: December 2024

Telomeres are repetitive sequences at the ends of chromosomes that play a pivotal role in genomic stability. In the absence of maintenance mechanisms, telomeres shorten with cell proliferation. In CLL, tumor cell telomere length was described to be an important prognostic factor in various studies, but the impact of telomere length in the context of targeted treatments has not been analyzed.

Here, we studied telomere length in 917 of 926 patients (99%) from the randomized, phase 3, GAIA/CLL13 trial comparing venetoclax in combination with rituximab (RV) or obinutuzumab (GV) or with obinutuzumab and ibrutinib (GIV) vs. chemo-immunotherapy (CIT). Telomere length was analyzed on DNA from peripheral blood mononuclear cells using qPCR as previously reported (Jebaraj et al., Leukemia, 2019). The technique was validated using terminal restriction fragment length analysis (TRF; R2=0.915) and 8 samples with known TRF values were included in every qPCR run for data normalization.

Telomere lengths in this study ranged from 1.2 to 15.2 kilo bases (kb) with a median of 4 kb (CIT: 3.9, RV: 3.8, GV: 4.1, GIV: 4.4). The optimal prognostic cutoff value of telomere length of 4.17 kb was chosen for dichotomization to minimize the Akaike information criterion (AIC) value for the Cox proportional hazards regression of progression free survival (PFS; short vs. long). Categorized telomere length was significantly associated with time between diagnosis and treatment initiation (P=0.004), tumor lysis syndrome risk group (P&lt;0.001), Binet stage (P=0.006), ECOG performance status (P=0.004), serum β2-microglobulin levels (β2-MG; P&lt;0.001), serum thymidine kinase (P&lt;0.001), maximum lymph node size (P&lt;0.001) and absolute lymphocyte count (ALC; P=0.001). Telomere length did not show an association with age, gender, CIRS score and creatinine clearance.

Among genetic markers, short telomeres were significantly associated with unmutated IGHV, presence of IGLV3-21, R110 mutations and subset 2, as well as with del(11q) (all P&lt;0.001). Among gene mutations, short telomeres were significantly associated with mutated NOTCH1, SF3B1, XPO1, EGR2, NFKBIE (all P&lt;0.001) and RPS15 (P=0.005) while long telomeres were associated with mutated MYD88 (P&lt;0.001). Patients with del(17p) and/or TP53 mutations were not included in the trial. Telomere length was also associated with the CLL-IPI risk groups (P&lt;0.001).

At a median follow up of 50.8 months, 262 (28.6%) events for PFS and 48 (5.2%) events for overall survival (OS) were observed within the population with available samples. In the full cohort, short telomeres were significantly associated with shorter PFS (HR 3.06; 95% CI 2.31-4.06; P&lt;0.001) and OS (HR 3.01; 95% CI 1.54-5.91; P=0.001). Among the treatment arms, short telomere length was associated with inferior PFS with CIT (HR 3.37; 95% CI 2.03-5.61; P&lt;0.001), RV (HR 2.72; 95% CI 1.63-4.55; P&lt;0.001), GV (HR 2.69; 95% CI 1.46-4.96; P=0.002) and GIV (HR 2.55; 95% CI 1.28-5.07; P=0.008). The PFS rates at 48 months of the groups with short vs. long telomeres were 46.5% vs. 84% with CIT, 62.2% vs. 82.9% with RV, 74.4% vs. 90.1% with GV and 77.5% vs. 92.3% with GIV. Furthermore, short telomeres had a significant adverse impact on OS only with CIT (HR 5.49; 95% CI 1.25-24.06; P=0.024) but not within the venetoclax-based arms.

Multivariable analysis (MVA) was performed including all parameters significantly associated with PFS univariably (treatment arms, β2-MG, ALC, maximum lymph node size, presence of del(11q), del(13q), high karyotypic complexity (≥5 aberrations; HCKT), IGHV, NOTCH1, BIRC3, RAS/RAF, XPO1, EGR2 mutation status, and telomere length). Short telomeres (HR 1.88; 95% CI 1.35-2.62; P&lt;0.001) along with the treatment arms GV (HR 0.47; 95% CI 0.33-0.66; P&lt;0.001) and GIV (HR 0.33; 95% CI 0.22-0.49; P&lt;0.001), unmutated IGHV (HR 2.28; 95% CI 1.60-3.26; P&lt;0.001), and HCKT (HR 2.32; 95% CI 1.52-3.53; P&lt;0.001) were independent prognostic factors for PFS in the overall cohort. MVA within the venetoclax-based treatment arms RV (HR 2.72; 95% CI 1.63-4.55; P&lt;0.001) and pooled GV/GIV (HR 2.35; 95% CI 1.47-3.75; P&lt;0.001) also suggested telomere length as an independent prognostic factor for PFS.

In summary, telomere length was a prognostic factor for PFS in the full GAIA/CLL13 trial population, and with venetoclax-based regimens when analyzed within treatment arms. Furthermore, short telomere length was associated with inferior OS only with CIT.