PROGNOSTIC AND PREDICTIVE SIGNIFICANCE OF THE B-CELL RECEPTOR SIGNALING IN MANTLE CELL LYMPHOMA

Mantle cell lymphoma (MCL) is a rare subtype of Non-Hodgkin lymphoma characterized by the expansion of mature B-cells in the mantle zone of the lymph nodes. MCL presents a high clinical vari- ability, with some patients experiencing an indolent disease while others characterized by an aggressive clinical course. Recent evi- dence supports that B-cell receptor (BCR) signaling is crucial for MCL initiation and progression and is a target for therapeutic inter- vention. However, drug resistance inevitably emerges. Therefore, the definition of parameters identifying high-risk patients for aggressive disease and therapy resistance is an unmet need in MCL management. We measured the activation status of 9 BCR signaling kinases (SYK, LCK, BTK, PLCγ2, p38, ERK1/2, AKT, NF-κB p65, STAT5) in peripheral blood mononuclear cells (PBMC) from 30 MCL patients and 10 healthy donors, in the basal and anti-IgM modulated condi- tions, using phospho-specific flow cytometry. To measure phospho- rylation statuses as well as responses to external stimulation of the signaling proteins, flow cytometry data were normalized with respect to the controls and subjected to unsupervised hierarchical clustering analysis (HCA). Progression free survival (PFS) and overall survival (OS) curves were estimated using the Kaplan-Meier method and compared using the log-rank test. Univariate and bivariate models for PFS and OS were performed using Cox proportional hazard regression. BCR modulation with anti-IgM determined a heteroge- neous activation of the BCR signaling among patients’ samples, with identification of two clusters showing differential responses to BCR stimulation. The cluster comprising samples with higher BCR sig- naling response (HR) was associated with shorter survival than sam- ples grouped in the lower BCR signaling response (LR) cluster (p=0. 042 and p=0. 041 for PFS and OS, respectively). This finding was confirmed with time-to-event analyses, which showed that the MCL international prognostic index (MIPI) high-risk category together with high STAT5 response to the stimulation were significant pre- dictors of shorter PFS and OS. In addition, MIPI high-risk category combined with high SYK response predicted shorter OS. While basal BCR activation did not provide prognostic information, higher con- stitutive activation of AKT was predictive of inferior response to the Bruton’s tyrosine kinase inhibitor (BTK[/i] ibrutinib. In conclusion, we identified BCR signaling activation profiles that were associated with poorer clinical outcome and resistance to ibrutinib. This study highlighted the prognostic and predictive significance of BCR activ- ity in MCL and advanced our understanding of signaling heterogene- ity underlying clinical behavior of MCL. A future challenge is the integration of BCR signaling data with genetic signature to predict patient’s clinical behavior and drug response for a more personalized treatment approach. We thank Fondazione Italiana Linfomi (PGR Ed. 2019) for funding support.