Abstract PO-021: Modeling marginal zone lymphomagenesis
Authors: Harris Emily , Sindel Ariel , He Jian , Sabo Roy , Chesney Alden , Lai Guanhua , Mauro Adolpho , Martins Rebecca , Koblinski Jennifer , Windle Joelene , Yazbeck Victor 
Published: June 2024

Abstract
Introduction: Marginal zone lymphomas (MZL) are the second most prevalent subtype of indolent Non-Hodgkin Lymphomas (iNHL), yet lack a unique cytogenetic identifying abnormality. The B-cell receptor signaling pathway is activated in B-cell malignancy and mediates its activity mainly through the Phosphoinositide 3-kinase (PI3K), protein kinase B (Akt), mammalian target of rapamycin (mTOR) pathway. PI3K inhibitors have demonstrated impressive clinical activity in several indolent lymphomas including MZL, underscoring the pivotal role of the PI3K-AKT-mTOR (PAM) pathway in MZL pathogenesis. Furthermore, iNHL overexpress the antiapoptotic protein Bcl-2.
Methods: We developed a genetically engineered mouse model with heterozygous global knockout alleles of both the tumor suppressor genes Phosphatase and Tensin Homolog (PTEN) and Liver Kinase B1 (LKB1), resulting in heightened PAM pathway activation across all tissues. We closely monitored these mice for tumor formation via regular physical assessments over several months. Upon tumor detection, mice were euthanized, and tumors were histologically examined. For a more precise representation of B-cell biology akin to the human disease, we employed the Cre-LoxP system to create the CD19-Cre-PTENfl/fl/LKB1fl/fl and CD19-Cre-PTENfl/fl/Eµ-Bcl2.
Results: Thirty mice of global KO PTEN+/- LKB1+/- succumbed to or were euthanized due to disease progression, defined as either lymph node enlargement and/or splenomegaly. By Kaplan-Meier analysis, we saw a steady decrease in both tumor-free and overall survival after 3 months of age. Median survival time was 6 months (95% CI: 6, 8). Immunohistochemical analysis of the 51 lymph nodes revealed iNHL in 61.5% (N=32), with all of the MZL subtype. The penetrance rate was 37%. Then, we looked at the absolute B cells, and the major B subtypes in age-matched mice (N=3 per group): WT, CD19-Cre-PTENfl/fl/LKB1fl/fl, CD19-Cre-PTENfl/fl/Eµ-Bcl2. We observed the following preliminary results in the absolute B cells (23,489,812; 1,550,430; 140,476,875), Marginal zone cells (1,087,883; 452,470; 42,658,701), follicular cells (19,078,598; 203,286; 57,212,627), B1 cells (962,192; 939,386; 1,803,060), and plasma cells (211,725; 202,790; 10,531,585) respectively. Then, Kruskal-Wallis tests were used to test the main effect of these three models (WT, CD19-Cre-PTENfl/fl/LKB1fl/fl and CD19-Cre-PTENfl/fl/Bcl2) on absolute cell counts for each cell type: B cells (p=0.027), follicular (p=0.061), Marginal zone (p=0.027), B1 (p=0.43), and plasma cell (p=0.066). The test results indicate that there were statistically discernible differences in absolute cell counts among the three models for B cells and MZ.
Conclusion: Marginal zone lymphoma remains an incurable lymphoma with a dearth of reliable preclinical models. Our data provides, for the first time, evidence supporting the involvement of the PAM pathway in MZL pathogenesis, laying the groundwork for further research elucidating the disease biology and rational therapeutic strategies for this incurable malignancy.
Citation Format: Emily Harris, Ariel Sindel, Jian He, Roy Sabo, Alden Chesney, Guanhua Lai, Adolpho Mauro, Rebecca Martins, Jennifer Koblinski, Joelene Windle, Victor Yazbeck. Modeling marginal zone lymphomagenesis [abstract]. In: Proceedings of the Fourth AACR International Meeting on Advances in Malignant Lymphoma: Maximizing the Basic-Translational Interface for Clinical Application; 2024 Jun 19-22; Philadelphia, PA. Philadelphia (PA): AACR; Blood Cancer Discov 2024;5(3_Suppl):Abstract nr PO-021.