Background:  Human polyomavirus JC (JCV) is the causative agent of the fatal demyelinating disease, progressive multifocal leukoencephalopathy (PML). Over-representation of JCV Type 2 in AIDS-PML patients, relative to its overall prevalence in the general population, has been documented. Based on in vivo observations that JCV genotypic variants may be associated with clinical progression of PML, we hypothesized that unique sequences in the JCV coding region confer enhanced replication upon JCV in glial cells.   

Methods:  Primary human fetal glial cells (PHFG) were transfected with JCV types 1A and 2B chimeras. DNA was extracted on days 5 and 10 from JCV transfected cells, and replication was measured using the DpnI replication assay. After hybridization with ³²P-labeled JCV probe the membrane was scanned on a phosphorimager. RNA was extracted from JCV-transfected PHFG cells, and 1 µg of RNA was used for cDNA synthesis. RT-PCR was performed using primers specific for JCV T antigen, VP1, and agno genes along with the housekeeping gene GAPDH. The amplicons were run on a 2% agarose gel and the ethidium bromide fluorescence was visualized after scanning using a phosphorimager.

Results:  JCV type 2B consistently replicated at a higher replication potential on days 5 and 10 when compared with type 1. Day 15 onward the replication of both JCV types was similar. To confirm the reproducibility of the data, the transfection experiment was performed 7 times using 7 independent PHFG cells derived from independent biological specimens. JCV type 2B viral transcripts bands were stronger at days 5 and 10 than type 1.

Conclusions:  Based on the in vitro data and the published in vivo data, we conclude that unique sequences in JCV type 2B coding region (early and/or late proteins) confer enhanced replication potential. Identification of these unique sequences would lead to a better understanding of the disease, to the development of diagnostic tests to facilitate clinical observations, and to the opening of roads to effective treatments.

Keywords: Porgressive Multifocal Leukoencephalopathy; JC Virus; AIDS