Understanding polyomavirus CNS disease - a perspective from mouse models

JC polyomavirus (JCPyV), a ubiquitous human pathogen, causes several devastating brain diseases in immune-compromised individuals. The most notable of these JCPyV-associated CNS diseases is the frequently fatal demyelinating brain disease progressive multifocal leukoencephalopathy (PML). PML, an AIDS-defining disease in the pre-cART epoch, has emerged as a life-threatening complication in patients receiving immunomodulatory agents for autoimmune and inflammatory disorders and treatment for certain hematological malignancies. Among the rapidly expanding list of PML-associated biologics, natalizumab (Tysabri®) has the highest incidence and is an ominous sequela for multiple sclerosis (MS) patients who otherwise benefit from dramatic reductions in relapses using this immunomodulatory agent. Drug withdrawal, the only therapeutic option for PML, is often complicated by a high-mortality cerebral inflammatory reaction. No anti-JCPyV agents are available. Lack of a tractable animal model of polyomavirus-induced central nervous system (CNS) disease is an acknowledged bottleneck to elucidating PML pathogenesis, immunological mechanisms that control JCPyV, in vivo evaluation of agents that inhibit polyomavirus replication in tissue culture, and uncovering early events that presage JCPyV-associated neuropathology. The natural virus-host mouse polyomavirus (MuPyV) model has recently been developed to explore mechanisms of polyomavirus-associated CNS disease. In this review, we will cover the benefits of using the MuPyV model to answer fundamental questions about innate and adaptive immune control of JCPyV, the impact of immunomodulation on JCPyV pathogenesis, and how this MuPyV CNS infection model will help improve criteria for identifying patients at risk for JCPyV-associated CNS diseases before the development of irreversible lesions.