Prognostic impact of specific IGHV rearrangements in younger untreated Mantle Cell Lymphoma patients is independent of p53 alterations and may be modified by ibrutinib-based regimens: Insights from the TRIANGLE trial within the MULTIPLY project

Abstract Introduction The TRIANGLE trial (Dreyling et al, Lancet 2024) compared three treatment arms in untreated, younger patients with mantle cell lymphoma (MCL): arm I (IR-CHOP/R-DHAP + ibrutinib maintenance [Im]), arm A+I (IR-CHOP/R-DHAP + ASCT + Im), and arm A (standard-of-care R-CHOP/R-DHAP + ASCT). Ibrutinib-containing regimens demonstrated superior failure-free survival (FFS) and overall survival (OS). Prior studies (Hadzidimitriou et al, Blood 2011) have shown skewed immunoglobulin (IG) repertoires in MCL, with preferential IG heavy chain (IGH) gene usage. However, large, homogeneous cohorts have not clearly linked IGHV usage or IGHV mutational status to clinical outcomes. Moreover, the interaction between biological risk factors such as TP53 aberrations and IGH repertoire is still unknown. Here, we assess the prognostic significance of IGHV repertoire after adjustment for baseline risk factors. Methods IGH clonal rearrangement analysis for minimal residual disease (MRD) was performed on bone marrow or peripheral blood samples centralized in 7 EuroMRD Network laboratories. Samples were analyzed by Sanger or amplicon-based NGS (VH-FR1/JH-3 primers) and were processed via IMGT/V-QUEST or ARResT/Interrogate to assign IGH rearrangements and germline FR1-IGHV identity. Diagnostic lymph node biopsies were assessed for p53 immunohistochemistry expression as a surrogate of TP53 alterations, scored as low (<50%) or high (≥50%). Missing baseline values were imputed by Chained Equations (MICE) model. The prognostic impact of IGHV genes and IGHV mutational status on FFS was analyzed with Kaplan-Meier curves and multivariable Cox regression adjusted for baseline prognostic factors. Results Out of the 870 enrolled patients, 560 had an available IGHV sequence for analysis. Baseline characteristics and outcomes were comparable to the remaining TRIANGLE patients and, in the selected patients, ibrutinib-containing arms had superior outcomes compared with the control arm (3y-FFS: arm A 70% vs arm A+I and I: 85%, P=0.001). The most common IGHV families were IGHV 3-21 (n=123, 22%), 4-34 (n=59, 11%) and 1-8 (n=42, 7.5%) whereas IGHD 3-3 (n=60, 11%) and IGHJ 4 (n=230, 41%) were the most frequent IGHD and IGHJ families, respectively. Univariable Cox regression focused on IGHV family usage identified the VH 3-21, 3-30, 3-48, and 3-74 genes as associated with improved FFS which were therefore grouped together, namely VHcomb patients (N=171). VHcomb patients were younger, had lower MIPI scores, and showed superior 3-year FFS compared to other families (VHother) (87% vs. 77%, P=0.002). Stratified by treatment arm, VHcomb had significantly better FFS vs. VHother in arm A (87% vs. 62%, P<0.001), but no difference was observed in ibrutinib-containing arms (87% vs. 85%, P=0.22). Interestingly, after adjusting for p53, MIPI and Ki67, VHcomb remained associated with improved FFS in arm A (Hazard ratio [HR] 0.46 [0.23-0.92], P=0.029), while no statistically significant impact was observed in arm A+I: HR 1.08 [0.55-2.13], P=0.82; but still a trend in arm I: HR 0.51 [0.23-1.13], P=0.096. Subsequently, to investigate an optimal cut-off point for FR1-IGHV gene identity, a Cox regression with restricted cubic splines was performed, identifying 97% as the best FR1-IGHV gene homology cut-off for prognostic discrimination of FFS after adjustment for MIPI, histologic subtype, Ki67, and treatment arm. Patients with FR1-IGHV gene identity > 97% (FR1-IGHV unmutated, n=448 [80%]) showed a trend towards worse FFS at later follow-up (log rank P=0.056) compared to patients with FR1-IGHV gene identity ≤ 97% (FR1-IGHV mutated, n=110 [20%]). No significant differences in FFS were observed according to FR1-IGHV mutation status after adjusting for p53, MIPI and Ki67 in multivariable analysis both in standard and ibrutinib-containing regimens. Conclusions This is the largest study investigating IGH repertoire in a prospective phase 3 trial in MCL. FR1-IGHV unmutated patients showed inferior FFS. The IGHV 3-21, 3-30, 3-48, and 3-74 rearrangements were associated with improved FFS in the chemo-immunotherapy arm, independently of p53 alterations. On the other hand, the addition of ibrutinib may potentially mitigate the prognostic impact of the IGHV families. Although requiring validation, these findings support a BCR-related prognostic role in MCL, independent from MIPI, Ki67 and p53 alterations and potentially modulated by ibrutinib.