IGLV3-21^R110 and ibrutinib treatment: Results from the double-blind, randomized, placebo-controlled GCLLSG CLL12...

IGLV3-21^R110 is a point mutation enabling autonomous B-cell receptor (BCR) signaling in chronic lymphocytic leukemia (CLL). It has been associated with shorter time to first treatment and overall survival, but its effects have not been evaluated in phase 3 clinical trials or in patients treated with Bruton tyrosine kinase inhibitors. Here, we analyzed samples from the phase 3 CLL12 study that compared ibrutinib vs. placebo in untreated early-stage CLL patients with intermediate to very high risk of disease progression, while patients with low risk of disease progression were allocated to watch-and-wait (w&w). Four detection methods (targeted next-generation sequencing, Sanger sequencing, multiplex IGLV3-21^R110-specific PCR, and flow cytometry) were compared, yielding highly consistent results. Overall, 34/515 (6.6%) patients had productive IGLV3-21 rearrangements: 5/152 (3.3%) in w&w, 15/181 (8.3%) in placebo, and 14/182 (7.7%) in the ibrutinib group. Of these, 25 were IGLV3-21^R110-positive (3/5, 12/15, and 10/14). IGLV3-21^R110 was associated with shorter event-free survival (EFS) across all arms: w&w (hazard ratio [HR] 17.03, 95% confidence interval [CI 95%]: 4.99-58.13, P < 0.001), placebo (HR 2.31, CI 95%: 1.16-4.6, P = 0.017), and ibrutinib (HR 2.99, CI 95%: 1.17-7.65, P = 0.023). Multivariable analysis identified IGLV3-21^R110 as an independent prognostic factor for shorter EFS (HR 3.18, CI 95%: 1.73-5.83, P < 0.001). Notably, IGLV3-21^R110 was associated with reduced clinical effectiveness of ibrutinib. Ca²⁺-flux and cell viability assays using patient-derived BCRs expressed in murine B-cells confirmed reduced ibrutinib efficacy in IGLV3-21^R110 cases, especially regarding inhibition of antigen-stimulated signaling. In summary, IGLV3-21^R110 is an independent prognostic factor for shorter EFS in early-stage CLL and reduces ibrutinib effectiveness clinically and in vitro.