Characterization of a novel HHV-8-positive cell line reveals implications for the pathogenesis and cell cycle control of primary effusion lymphoma

Primary effusion lymphoma (PEL) represents a peculiar type of B cell lymphoma which associates with HHV-8 infection and preferentially grows in liquid phase in the serous body cavities. In this report, we provide the detailed characterization of a newly established PEL cell line, termed CRO-AP/6. The cell line was obtained from the pleural effusion of a HIV-positive patient with PEL. Its derivation from the tumor clone was established by immunogenotypic analysis. Detailed phenotypic investigations defined that CRO-AP/6 reflects pre-terminally differentiated B cells expressing the CD138/syndecan-1 antigen. Karyotypic studies of CRO-AP/6 identified several chromosomal abnormalities, whereas genotypic studies ruled out the involvement of molecular lesions associated with other types of B cell lymphoma. Both CRO-AP/6 and the parental tumor sample harbored infection by HHV-8. Conversely, EBV infection was present in the parental tumor sample although not in CRO-AP/6, indicating that CRO-AP/6 originated from the selection of an EBV-negative tumor subclone. The pattern of viral (HHV-8 v-cyclin) and cellular (p27(Kip1)) regulators of cell cycle expressed by CRO-AP/6, together with the results of growth fraction analysis, point to abrogation of the physiological inverse relationship between proliferation and p27(Kip1) expression. Also, both CRO-AP/6 and the parental tumor sample display biallelic inactivation of the DNA repair enzyme gene O⁶-methylguanine-DNA methyltransferase (MGMT) by promoter methylation. Overall, the CRO-AP/6 cell line may help understand cell cycle control of PEL cells, may clarify the relative contribution of HHV-8 and EBV to the disease growth and development and may facilitate the identification of recurrent cytogenetic abnormalities highlighting putative novel cancer related loci relevant to PEL.