Year of Award

2024

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Cellular, Molecular and Microbial Biology

Department or School/College

Division of Biological Sciences

Committee Chair

Heinrich Feldmann

Commitee Members

David W. Hawman, Stephen Lodmell, Scott Wetzel, Brent Ryckman

Keywords

Antibodies, CCHFV, Nucleoprotein, RNA, TRIM21, Vaccine

Abstract

Crimean-Congo Hemorrhagic Fever Virus (CCHFV) is a negative-sense, tick-borne bunyavirus endemic to Europe, Asia, and Africa. CCHFV may cause a severe hemorrhagic disease with a case fatality rate of 5-70% and, to date, there are no widely available or highly efficacious vaccines or therapeutics. Because of its widespread distribution and lack of countermeasures, the WHO has listed CCHFV as a high priority pathogen.

Here, we report a self-replicating, alphavirus-based RNA vaccine that expresses the CCHFV nucleoprotein (repNP) and glycoprotein precursor (repGPC). Initial studies showed that repNP induces high titers of non-neutralizing anti-NP antibodies while repGPC stimulates a robust T-cell response. Further, repNP and the combined vaccine repNP + repGPC provided complete protection against CCHFV challenge, including significant decreases in viral replication, weight loss, and 100% survival. repGPC alone, however, was only partially protective with ~40% survival. We hypothesized that the lack of protection from repGPC was due to its size and complexity and thus, we narrowed down the protective epitope within repGPC to repGc-FL, expressing the full glycoprotein c. Protection from repNP + repGc-FL was highly durable, with immune responses and protection from lethal CCHFV disease fully developing as soon as two weeks and persisting up to one year post vaccination. However, despite robust T-cell responses, repGc-FL was, again, only partially protective on its own, did not induce significant neutralizing antibody responses, and did not induce immune response in non-human primates (NHPs), indicating a need to further optimize this vaccine construct. RepNP, on the other hand, was highly immunogenic in both mice and NHPs. Further studies found that repNP anti-NP antibodies primarily mediated protection through the intracellular Fc receptor TRIM21. Indeed, TRIM21 knock-out mice succumbed to lethal CCHFV disease, and we found that intracellularly delivered anti-NP antibodies could inhibit CCHFV replication in WT but not TRIM21 deficient cells. Overall, these studies not only support the continued clinical development of repNP but also, increase the understanding of protective mechanisms of non-neutralizing antibodies and inform development of much needed therapeutics for CCHFV specifically, monoclonal antibodies.

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