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Microglia are required for protection against lethal coronavirus encephalitis in mice.

ABSTRACT: Recent findings have highlighted the role of microglia in orchestrating normal development and refining neural network connectivity in the healthy CNS. Microglia are not only vital cells in maintaining CNS homeostasis, but also respond to injury, infection, and disease by undergoing proliferation and changes in transcription and morphology. A better understanding of the specific role of microglia in responding to viral infection is complicated by the presence of nonmicroglial myeloid cells with potentially overlapping function in the healthy brain and by the rapid infiltration of hematopoietic myeloid cells into the brain in diseased states. Here, we used an inhibitor of colony-stimulating factor 1 receptor (CSF1R) that depletes microglia to examine the specific roles of microglia in response to infection with the mouse hepatitis virus (MHV), a neurotropic coronavirus. Our results show that microglia were required during the early days after infection to limit MHV replication and subsequent morbidity and lethality. Additionally, microglia depletion resulted in ineffective T cell responses. These results reveal nonredundant, critical roles for microglia in the early innate and virus-specific T cell responses and for subsequent host protection from viral encephalitis.

SUBMITTER: Wheeler DL

PROVIDER: S-EPMC5824854 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Unlabelled: Mesenchymal stromal cells (MSCs) are being exploited as gene delivery vectors for various disease and injury therapies. We provide proof-of-concept that engineered MSCs can provide a useful, effective platform for protection against infectious disease. Venezuelan equine encephalitis virus (VEEV) is a mosquito-borne pathogen affecting humans and equines and can be used in bio-warfare. No licensed vaccine or antiviral agent currently exists to combat VEEV infection in humans. Direct antibody administration (passive immunity) is an effective, but short-lived, method of providing immediate protection against a pathogen. We compared the protective efficacy of human umbilical cord perivascular cells (HUCPVCs; a rich source of MSCs), engineered with a transgene encoding a humanized VEEV-neutralizing antibody (anti-VEEV), to the purified antibody. In athymic mice, the anti-VEEV antibody had a half-life of 3.7 days, limiting protection to 2 or 3 days after administration. In contrast, engineered HUCPVCs generated protective anti-VEEV serum titers for 21-38 days after a single intramuscular injection. At 109 days after transplantation, 10% of the mice still had circulating anti-VEEV antibody. The mice were protected against exposure to a lethal dose of VEEV by an intramuscular pretreatment injection with engineered HUCPVCs 24 hours or 10 days before exposure, demonstrating both rapid and prolonged immune protection. The present study is the first to describe engineered MSCs as gene delivery vehicles for passive immunity and supports their utility as antibody delivery vehicles for improved, single-dose prophylaxis against endemic and intentionally disseminated pathogens.SignificanceDirect injection of monoclonal antibodies (mAbs) is an important strategy to immediately protect the recipient from a pathogen. This strategy is critical during natural outbreaks or after the intentional release of bio-weapons. Vaccines require weeks to become effective, which is not practical for first responders immediately deployed to an infected region. However, mAb recipients often require booster shots to maintain protection, which is expensive and impractical once the first responders have been deployed. The present study has shown, for the first time, that mesenchymal stromal cells are effective gene delivery vehicles that can significantly improve mAb-mediated immune protection in a single, intramuscular dose of engineered cells. Such a cell-based delivery system can provide extended life-saving protection in the event of exposure to biological threats using a more practical, single-dose regimen.

Project description:There are no approved vaccines against the life-threatening Middle East respiratory syndrome coronavirus (MERS-CoV). Attenuated vaccines have proven their potential to induce strong and long-lasting immune responses. We have previously described that severe acute respiratory syndrome coronavirus (SARS-CoV) envelope (E) protein is a virulence factor. Based on this knowledge, a collection of mutants carrying partial deletions spanning the C-terminal domain of the E protein (rMERS-CoV-E*) has been generated using a reverse genetics system. One of these mutants, MERS-CoV-E*Δ2in, was attenuated and provided full protection in a challenge with virulent MERS-CoV after a single immunization dose. The MERS-CoV-E*Δ2in mutant was stable as it maintained its attenuation after 16 passages in cell cultures and has been selected as a promising vaccine candidate.IMPORTANCE The emergence of the new highly pathogenic human coronavirus SARS-CoV-2 that has already infected more than 80 million persons, killing nearly two million of them, clearly indicates the need to design efficient and safe vaccines protecting from these coronaviruses. Modern vaccines can be derived from virus-host interaction research directed to the identification of signaling pathways essential for virus replication and for virus-induced pathogenesis, in order to learn how to attenuate these viruses and design vaccines. Using a reverse genetics system developed in our laboratory, an infectious cDNA clone of MERS-CoV was engineered. Using this cDNA, we sequentially deleted several predicted and conserved motifs within the envelope (E) protein of MERS-CoV, previously associated with the presence of virulence factors. The in vitro and in vivo evaluation of these deletion mutants highlighted the relevance of predicted linear motifs in viral pathogenesis. Two of them, an Atg8 protein binding motif (Atg8-BM), and a forkhead-associated binding motif (FHA-BM), when deleted, rendered an attenuated virus that was evaluated as a vaccine candidate, leading to full protection against challenge with a lethal dose of MERS-CoV. This approach can be extended to the engineering of vaccines protecting against the new pandemic SARS-CoV-2.

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Microglia are required for protection against lethal coronavirus encephalitis in mice.

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