Defining Early Stages of Polyomavirus CNS Pathogenesis and Immunity

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ABSTRACT 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 lesion 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 CNS disease is an acknowledged bottleneck to elucidating PML pathogenesis, timmunological mechanisms that control JCPyV, in vivo evaluation of agents that inhibit polyomavirus replication in tissue culture, and uncovering early events that presage irreversible JCPyV-associated neuropathology – the focus of this renewal application. Using mouse polyomavirus (MuPyV), we developed a natural virus-host model of polyomavirus-associated CNS disease. In this renewal application, we will leverage two key findings made under the parent R01 grant: (1) Mapping JCPyV-PML VP1 capsid protein mutations to MuPyV’s VP1 confers escape from virus-neutralizing antibodies (nAb) while preserving CNS tropism; and (2) STAT1-dependent innate immunity limits infection of the ventricular ependyma, a critical barrier to subsequent brain parenchymal infection. Both findings, which parallel those of JCPyV, lay the foundation for the two key questions raised in this renewal application: (1) Is the ependyma the staging ground for polyomavirus invasion of the brain parenchyma?; and (2) Does T cell deficiency open the door for outgrowth of nAb-escape virus variants? The proposed studies will make use of cutting edge advances in next-generation sequencing to uncover rare VP1 mutations in vivo, custom cryo EM image reconstruction approaches to define endogenous VP1 nAb epitopes and nAb escape mechanisms, and high-resolution 3D imaging of mouse brains to visualize viral CNS entry and spread. Findings from these studies will answer fundamental questions about innate and adaptive immune control of JCPyV and potentially improve criteria for identifying patients at risk for JCPyV-associated CNS diseases.