EBV-Associated Lymphoma Consortium Annual Meeting (Abstract): Submission #2

Abstract Summary One major focus of this project is to investigate the impact of LMP2A on the pathogenesis of EBV-driven lymphoma using a "humanized" mouse xenograft model. We compared mice transplanted with cord blood mononuclear cells infected with WT or LMP2A-deleted (ΔLMP2A) EBV (M81 strain). Similar to published findings, we observed that ΔLMP2A and WT initially led to similar tumor size and incidence. However, ΔLMP2A tumors failed to progress in size over time and were much less invasive, significantly decreasing mortality in those mice. In both WT and ΔLMP2A mice we observed two distinct subsets of B cells: plasmablastic (CD38hi/CD20lo) and less differentiated CD20hi/CD38lo. In pre-invasive tumors, plasmablastic cells formed capsule-like structures at the leading edge of the tumor, while the less differentiated cells clustered at the center. As tumors progressed, plasmablastic cells were the first to invade organ tissue. These findings led us to further investigate the invasive quality of these plasmablastic cells.
In RNA-Seq analysis of LCLs controlled for BCR isotype to isolate the effect of LMP2A, we found that WT LCLs upregulated many genes associated with plasma cell differentiation compared to ΔLMP2A LCLs. Published work has established a gradient of proliferation and differentiation in LCLs and identified LMP1 as the driver of proliferation. We hypothesize that LMP2A is responsible for differentiation. We believe this gradient can be explained by the bi-directional ED-L1 promoter, which drives expression of both LMP1 and LMP2B. When ED-L1 activity is high, LMP1 drives proliferation and the NF-kB pathway, and LMP2B diminishes signaling activity of LMP2A, leading to decreased differentiation. While these results clarify the impact of LMP2A on plasmablastic cell differentiation, the factor(s) regulating invasion remain unknown. Ongoing studies aim to identify the switch that regulates plasmablastic cell invasion.