CD8 T Cells and STAT1 Signaling Are Essential Codeterminants in Protection from Polyomavirus Encephalopathy

Abstract

JC polyomavirus (JCPyV), a human-specific virus, causes the aggressive brain-demyelinating disease progressive multifocal leukoencephalopathy (PML) in individuals with depressed immune status. The increasing incidence of PML in patients receiving immunotherapeutic and chemotherapeutic agents creates a pressing clinical need to define biomarkers to stratify PML risk and develop anti-JCPyV interventions. Mouse polyomavirus (MuPyV) CNS infection causes encephalopathology and may provide insight into JCPyV-PML pathogenesis. Type I, II, and III interferons (IFNs), which all signal via the STAT1 transcription factor, mediate innate and adaptive immune defense against a variety of viral infections. We previously reported that type I and II IFNs control MuPyV infection in non-central nervous system (CNS) organs, but their relative contributions to MuPyV control in the brain remain unknown. To this end, mice deficient in type I, II, or III IFN receptors or STAT1 were infected intracerebrally with MuPyV. We found that STAT1, but not type I, II, or III IFNs, mediated viral control during acute and persistent MuPyV encephalitis. Mice deficient in STAT1 also developed severe hydrocephalus, blood-brain barrier permeability, and increased brain infiltration by myeloid cells. CD8 T cell deficiency alone did not increase MuPyV infection and pathology in the brain. In the absence of STAT1 signaling, however, depletion of CD8 T cells resulted in lytic infection of the choroid plexus and ependymal lining, marked meningitis, and 100% mortality within 2 weeks postinfection. Collectively, these findings indicate that STAT1 signaling and CD8 T cells cocontribute to controlling MuPyV infection in the brain and CNS injury. IMPORTANCE A comprehensive understanding of JCPyV-induced PML pathogenesis is needed to define determinants that predispose patients to PML, a goal whose urgency is heightened by the lack of anti-JCPyV agents. A handicap to achieving this goal is the lack of a tractable animal model to study PML pathogenesis. Using intracerebral inoculation with MuPyV, we found that MuPyV encephalitis in wild-type mice causes an encephalopathy, which is markedly exacerbated in mice deficient in STAT1, a molecule involved in transducing signals from type I, II, and III IFN receptors. CD8 T cell deficiency compounded the severity of MuPyV neuropathology and resulted in dramatically elevated virus levels in the CNS. These findings demonstrate that STAT1 signaling and CD8 T cells concomitantly act to mitigate MuPyV-encephalopathy and control viral infection.

Balancing Inflammation and Central Nervous System Homeostasis: T Cell Receptor Signaling in Antiviral Brain TRM Formation and Function

“…Because virus-specific CD8 T EFF also express high-affinity TCRs, we suggested that these cells were the progeny of high-affinity effectors recruited to the brain during the acute stage of infection ( 68 ). Indeed, we observed that there is a window of opportunity for immune cells, and possibly virus, to breach a blood-brain barrier rendered permeable during acute MuPyV encephalitis ( 69 ). A plausible possibility is that high-affinity TCRs enable CD8 bT RM to detect low levels of viral antigen during persistent infection ( 68 ).…”

Antibody escape by polyomavirus capsid mutation facilitates neurovirulence

“…In support of a choroid plexus-mediated route, JCPyV infects primary choroid plexus epithelial cells, and JCPyV-infected choroid plexi are found in PML brains (Corbridge et al, 2019;O'Hara et al, 2020O'Hara et al, , 2018. Both A2 and A2.V296F viruses productively infect the ependyma, and we reported ependymal infection by MuPyV under conditions of immune suppression (Mockus et al, 2020). Infection of the choroid plexus and ependyma may serve as a viral staging area for JCPyV invasion of the brain parenchyma, providing a foothold for viral dissemination in the CNS parenchyma.…”

“…Immunocompetent mice infected with MuPyV do not develop productive kidney infection when detected by immunofluorescence or immunohistochemistry (Drake and Lukacher, 1998). Stat1 -/mice depleted of CD8 + T cells develop severe systemic MuPyV infection (Mockus et al, 2020). We compared A2 and A2.V296F kidney infection in CD8 + T cell-depleted Stat1 -/mice by staining kidney sections at day 7 pi for VP1.…”

“…The thickness of the vimentin + region was quantified across six images/sample in ImageJ (NIH). Hydrocephalus was quantified by measuring the pixel area of right and left lateral ventricles and dividing by the pixel area of the total brain section (Mockus et al, 2020). For representative fluorescence and brightfield images, adjustments for brightness/contrast were done uniformly to all images in the group using LAS X (Leica).…”

Antibody Escape by Polyomavirus Capsid Mutation Facilitates Neurovirulence

“…Immunocompetent mice infected with MuPyV do not develop productive kidney infection when detected by immunofluorescence or immunohistochemistry (Drake and Lukacher, 1998). STAT1 -/mice depleted of CD8 + T cells develop severe systemic MuPyV infection (Mockus et al, 2020). We compared A2 and A2.V296F kidney infection in CD8 + T cell-depleted STAT1 -/mice by staining kidney sections at day 7 pi for VP1 and CD13, which marks proximal tubules in the kidney cortex (Guder and Ross, 1984;Van der Hauwaert et al, 2013).…”