The curious case of the JC virus.

We have worked on the JC virus for many months to understand how this virus travels to the brain causing PML (Progressive Multifocal Leukoencephalopathy) a serious and potentially fatal infection which complicates a number of MS therapies including Tysabri, Tecfidera, Gilenya, Ocrevus and Lemtrada. This infection also complicates treatments for other autoimmune diseases, transplantation and chemotherapy; and is seen in different immune deficiencies and HIV-AIDS. There are at least 15 monoclonal antibody treatments for different conditions which are complicated by the JC virus.
 
The JC virus infects virtually all infants via the oropharynx in the first two years of life, spreading from the tonsils to the kidney and the bone marrow (where immune cells arise). The virus lies dormant for the rest of our lives except in rare instances where it spreads to the brain. The mystery has been figuring out how it gets to the brain, because there it has the potential to replicate and cause tissue damage. 
 
Two situations both have to occur to allow the virus to spread to the brain. First, one of its genes has to mutate so that it is able to grow in the brain. This may occur naturally or be caused by the cells the virus infects. Second, the immune system has to be compromised so that viral growth goes unchecked. 
 
We have known that the genes of the virus can be found in immune cells in the circulation but until now we have not understood whether this is a latent infection or whether the virus could be activated in these cells which might then transmit it the brain.
 
We first developed a method to detect viral proteins in immune cells by flow cytometry as this is a good first step to detect whether the virus is active. One of these proteins is used to turn the virus on and one to make a capsule around viral DNA initiating the process of releasing the virus. So far we have found the virus is present in every subject studied – which is remarkable because only 55% of adults have antibody immunity to the virus using a clinical laboratory test. We also could determine which type of cell is involved in this infection – the two major ones are B cells, which make antibodies, and Stem Cells. Usually JC viral proteins are found in the nucleus of an infected cell but most of these proteins are kept in the cytoplasm of immune cells bound to large multi-molecular complex. We have determined that certain activating stimuli allow the viral proteins to disassemble from this complex and move to the cell nucleus where the whole virus can be assembled leading to its release from the cell.
 
In addition, we have developed an extremely sensitive PCR assay to detect the JC viral DNA. We discovered the gene signature of the virus in virtually everyone. So the presence of the virus is significantly under-reported by presently available tests. To prove that the DNA is from the JC virus we have cloned and sequenced the detected DNA – which is definitely from this virus. When activated we see an increase in the amount of viral DNA in immune cells as well as viral DNA in the fluid in which they are cultured. We are in the process of examining whether the viral DNA discovered outside the cells is infectious. If so we have complete proof that immune cells can convey infectious virus which could then infect brain cells.