Characterization of IGHV subgroups and their prognostic relevance in CLL

Abstract Introduction: Immunoglobulin heavy chain variable region (IGHV) somatic hypermutation (SHM) status is a strong prognostic marker in CLL. Previous studies in the chemoimmunotherapy era reported inferior outcome linked to specific IGHV stereotyped subsets, such as subset #2 associated with IGHV3-21 usage. The prognostic value of individual IGHV subgroups remains less well-understood in the targeted therapy setting. Methods We performed a retrospective analysis of patients registered on the Dana-Farber Cancer Institute CLL database between 1999 and 2025. IGHV mutation rates and subgroups were assessed by PCR of gDNA or cDNA and NGS as an alternative to PCR at CLIA-certified labs. Stereotypy data were unavailable. We used Kaplan-Meier methods to estimate overall survival (OS) from time of CLL diagnosis, event-free survival (EFS, events were defined as death, histologic transformation, or treatment initiation) from time of CLL diagnosis, time to first-line therapy (TTFT) from time of CLL diagnosis, and time from first- to second-line therapy (TT2T). Cox regression models were used to compare clinical outcomes. We defined targeted therapy as regimens including Bruton's tyrosine kinase, B cell lymphoma 2 protein, and/or phosphoinositide 3-kinase inhibitors with or without CD20 monoclonal antibody, while excluding regimens containing cytotoxic agents. Results A total of 2,989 CLL patients with IGHV data were identified. Median age at diagnosis was 60.0 years. 1,369 (45.8%) patients had unmutated (U) IGHV. Of patients with mutated (M) IGHV, the median % of mutation compared to the consensus germline IGHV sequence was 5.7%. Borderline IGHV mutation (2.01-3.00%) was found in 146 (4.9%) of patients. 260 (8.7%) of patients had more than one productive IGHV sequence. Selected IGHV subgroups for analysis were: 1-69 (11.6%), 1-2 (4.3%), 3-21 (4.1%), and 4-39 (4.0%). Certain IGHV subgroups had a skewed representation (>2-fold) of either U (90.5% of 1-69, 69.2% of 4-39) within the group, while others had a less skewed distribution of U and M-IGHV (U-IGHV in 65.6% of 1-2, 47.5% of 3-21). With a median follow-up of 77 months, U-IGHV was associated with significantly shorter OS compared to M-IGHV (p<0.05, 10Y OS: 76.7% for U-IGHV vs 91.5% for M-IGHV). Notably, patients with IGHV3-21 usage, commonly linked with inferior OS regardless of SHM status, showed a numerically shorter OS in patients with U (10Y OS 61.6%) vs. M-IGHV (10Y OS 88.8%, p=0.055). OS of patients with U and M-IGHV within the selected subgroups (1-69, 1-2, 3-21, and 4-39) were comparable to their respective SHM groups in the overall study population. Next, we conducted further analyses of 1,218 patients with a comprehensive annotation of the status of histologic transformation and treatment course. As expected, U-IGHV was associated with shorter EFS and TTFT compared to M-IGHV (5Y EFS: 32% [27%, 38%] vs 77% [73%, 81%], 5Y TTFT: 33% [28%, 39%] vs 78% [74%, 83%]). In addition, histologic transformation predominantly occurred in the U-IGHV group (17 of 19 cases). Among 343 patients who received targeted therapy as their first-line CLL therapy (1L targeted therapy), patients with U-IGHV had comparable OS and TT2T to those with M-IGHV (5Y OS: 88% [82%, 96%] vs 93% [86%, 100%], 5Y TT2T: 63% [51%, 77%] vs 83% [71%, 97%]). We analyzed three IGHV subgroups (3-21, 4-39, and 1-2) with relatively lower U:M ratios. Prognostic impact of IGHV groups in the context of targeted therapy could not be assessed due to limited numbers of patients in each IGHV group and limited duration of follow ups. Descriptively, 1 of 9 patients with IGHV3-21 progressed to receive next-line therapy at 51 months after starting 1L targeted therapy. We observed a relatively high incidence of histologic transformation (3 of 17 patients) in the IGHV4-39 group treated with 1L targeted therapy. Two of 15 patients with IGHV1-2 usage in the 1L targeted therapy group received additional lines of therapy (2 and 74 months after initial therapy). Conclusions SHM status is a robust prognostic marker in CLL associated with OS, EFS, and TTFT. Despite the lack of stereotypy information, OS by SHM status within IGHV subgroups mirrored that of the corresponding U or M-IGHV in the whole cohort. Initial treatment of CLL with targeted agents led to excellent 5-year OS of 88% for U-IGHV and 93% for M-IGHV.