Abstract LB422: Specific activation of the Epstein-Barr Virus BGLF4 locus via lowered DNA methylation in EBV-associated CNS lymphoproliferative disease

Abstract Introduction: Epstein-Barr virus positive (EBV+) central nervous system lymphoproliferative diseases (CNS-LPD) are aggressive clinical conditions with poor prognosis. We have previously reported use of a ganciclovir (GCV), zidovudine (AZT), rituximab and dexamethasone regimen (GARD) that induced complete and durable responses in patients with primary CNS post-transplant lymphoproliferative disease (PTLD). Responses were associated with detection of two GCV/AZT viral drug targets, the EBV protein kinases BGLF4 and BXLF1. These viral proteins are normally expressed in lytic phase EBV, and the molecular basis for expression in latently infected EBV+ CNS-LPD is unknown. Methods: RNA expression of EBV genes LMP1, BZLF1, BXLF1, and BGLF4 was measured in 12 CNS-LPD biopsies (n=8/12 DLBCL-type) via qRT-PCR. Mass spectrometry-based EpiTYPER assay was used to quantify DNA methylation in EBV gene promoters. Biopsies from 25 patients with systemic PTLD were used for comparison. The BGLF4 locus was investigated in detail using luciferase reporters and 5’RACE mapping of transcription start sites in 3 EBV-infected cell lines and 4 CNS-LPD biopsy samples. Overall EBV methylation was assessed in a screening assay covering 31 EBV loci. Mechanistic involvement of active demethylation via TET2 was studied in a HEK293 CRISPR-Cas9 gene knockout model under EBV (strain M81) infection. Results: Gene expression analysis of biopsy specimens showed expression of LMP1, BXLF1, and BGLF4, but not BZLF1. Expression of BXLF1 and BGLF4 was significantly higher in CNS-LPD when compared to systemic EBV+ PTLD (p=0.043 and p=0.00022, respectively). EpiTYPER data showed significantly decreased promoter methylation at BGLF4 (p=0.00013). Luciferase reporter analysis of the BGLF4 upstream sequence revealed 3 regions of promoter activity which were silenced by in vitro methylation of reporters. 5’RACE identified transcription start sites at all 3 BGLF4 promoters and detected their activity in EBV+ cell lines and CNS-LPD biopsies. By overlaying transcriptional activity, 5’RACE and DNA methylation data, we identified DNA methylation loss at single CpG dinucleotides correlated with BGLF4 expression (r2=0.73). These sites were specifically demethylated in CNS-LPD, while surrounding EBV methylation remained high. Knockout of TET2 followed by EBV infection revealed that active demethylation is required for demethylation at BGLF4 promoters. Conclusions: The molecular determinant for success of the GARD regimen in CNS-LPD has remained poorly understood, with immunohistochemical detection of BGLF4/BXLF1 as the only predictor of treatment response. Our results provide the molecular basis for expression of BGLF4 in CNS-LPD by showing decreased promotor DNA methylation. We identified specific BGLF4 methylation sites that hold promise as potential DNA biomarkers for EBV+ CNS-LPD. Citation Format: Christoph Weigel, Haley L. Klimaszewski, Selamawit Addissie, Sarah Schlotter, Fode Tounkara, James P. Dugan, Bradley M. Haverkos, Lynda Villagomez, Mark Lustberg, Pierluigi Porcu, Timothy Voorhees, Michael A. Caligiuri, Ginny Bumgardner, Christopher C. Oakes, Robert Baiocchi. Specific activation of the Epstein-Barr Virus BGLF4 locus via lowered DNA methylation in EBV-associated CNS lymphoproliferative disease [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB422.