Browsing by Subject "Poliovirus"

In the following document, I will describe two distinct strategies that poliovirus

(PV) deploys to manage host antiviral responses. In the first section, I report on a role of

the constitutive repressor of eIF2α phosphorylation (CReP) in translation of PV and the

endoplasmic reticulum (ER)-resident chaperone binding immunoglobulin protein (BiP)

at the ER. Functional, proximity-dependent labeling and cell fractionation studies

revealed that CReP, through binding of the eukaryotic translation initiation factor eIF2α,

anchors translation initiation machinery at the ER and enables protein synthesis in this

compartment. This ER site was protected from the suppression of cytoplasmic protein

synthesis by acute stress responses. I propose that partitioning of translation initiation

machinery at the ER enables cells to maintain active translation of PV during stress.

In the second section, I report that PV 2A protease cleaves all three members of

the YTHDF protein family, cytosolic N6-methyladenosine (m6A) ‘readers’ that regulate

target mRNA fate. These cleavages occurred early during infection, and preemptive

YTHDF3 depletion enhanced viral replication. This corresponded with diminished type-

I interferon (IFN) receptor (IFNAR) expression and IFN-stimulated gene induction,

while IFN production was not significantly changed. I propose that 2A protease cleaves

YTHDF proteins, in part, to interfere with IFNAR expression and antagonize the host

antiviral response.

Viruses naturally engage innate immunity, induce antigen presentation, and mediate CD8 T cell priming against foreign antigens. Polioviruses can provide a context optimal for generating antigen-specific CD8 T cells, as they have natural tropism for dendritic cells, preeminent inducers of CD8 T cell immunity; elicit Th1-promoting inflammation; and lack interference with innate or adaptive immunity. However, notorious genetic instability and underlying neuropathogenicity has hampered poliovirus-based vector applications. We devised a strategy based on the polio:rhinovirus chimera PVSRIPO, devoid of viral neuropathogenicity after intracerebral inoculation in human subjects, for stable expression of exogenous antigens. PVSRIPO vectors infect, activate, and induce epitope presentation in DCs in vitro; recruit and activate DCs with Th1-dominant cytokine profiles at the injection site in vivo. They efficiently prime tumor antigen-specific CD8 T cells in vivo, induce CD8 T cell migration to the tumor site, delay tumor growth and enhance survival in murine tumor models.

Malignant glioma formation involves an abundant inflammatory infiltrate dominated by glioma-associated macrophages and microglia (GAMM). GAMM constitutes a large portion of the glioma mass and tumor microenvironment. They are actively involved in tissue repair and immune surveillance, however in the tumor microenvironment (TME), they are subverted to promote tumor progression. The human poliovirus receptor, hCD155h, is constitutively expressed in members of the mononuclear phagocytic system and is upregulated ectopically in the neoplastic compartment of malignant gliomas (and solid cancers in general). Intratumor treatment with the highly attenuated rhino:poliovirus chimera, PVSRIPO, has a dual effect of releasing neoantigens by oncolysis and activating the GAMM component via sublethal infection, leading to a substantial but transient immune therapy effect. In a phase I clinical trial, PVSRIPO treatment resulted in 21% long-term survival with durable radiographic responses in patients with recurrent glioblastoma (Desjardins et al. New England Journal of Medicine, 2018). Therefore, studying the mechanisms of PVSRIPO immunotherapy in mouse brain tumor models to decipher contributions of viral infection to GAMM vs. malignant cells is critical to improving the therapeutic efficacy in ongoing clinical trials. We recapitulated the clinical trial scenario in an immunocompetent intracerebral mouse tumor model (CT2A-CD155) and obtained baseline and post treatment brain in a time series. Histopathology studies, combined with detailed multiplex IHC/IF and RNAseq were performed on tumor bearing brains. We found the PVSRIPO therapy induced intense engagement of the GAMM infiltrate accompanied by substantial, but transient tumor regression. There were extensive microglia activation and proliferation in adjacent brain parenchyma and even part of the contralateral cortex. This occurred against a backdrop of sustained innate antiviral inflammation and is associated with an induction of the PD-L1 immune checkpoint on GAMM. In contrast to transient antitumor effects observed after PVSRIPO monotherapy, combining PVSRIPO with PD1/PD-L1 blockade led to durable remission. Our work implicates GAMM as active drivers of inflammation and reveals broad neuroinflammatory activation of the CNS-resident myeloid compartment upon polio virotherapy of malignant glioma.