Methylation-specific qPCR for the EBV C promoter to quantify EBV methylation

Epstein-Barr Virus (EBV) is a ubiquitous virus associated with a variety of diseases including cancers. Evidence has emerged that the C promoter is methylated in many EBV-associated malignancies, whereas in free virion DNA it is unmethylated. We have developed and evaluated a methylation-specific PCR assay for the EBV C Promoter (MSPCP) that can be applied to human biological specimens to quantify EBV methylation.

Two sets of methylation-specific primers were designed to anneal to bisulfite-converted DNA sequences with 3 CpGs in the forward primer binding site, and 2 CpGs in the reverse primer binding site. We evaluated this method in synthetic oligonucleotides, DNA extracted from cell lines, virion supernatants, and a variety of clinical specimens. EBV methylation of Cp, as measured by MSPCP, was validated with two orthogonal methods in select samples.

In contrived samples, this method had a linear range between 0-100% methylation. Application of this assay to DNA extracted from 11 formalin-fixed paraffin-embedded biopsy specimens showed high-level C promoter methylation in EBV-associated tumors (94-100%) but not in EBV-associated lymphoid hyperplasia. High-level EBV methylation was also detected in cell-free DNA extracted from the plasma of 13 patients with EBV-associated Hodgkin lymphoma. In contrast, EBV methylation was either not-detected, or detected at very low levels, in saliva from 25 adults in a general university population consistent with the presence of virion DNA.

MSPCP is a simple, rapid and accurate method that characterizes the methylation status of the EBV C promoter, which may be useful in a variety of research and clinical settings.