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Date of Award

2021

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy in Biological Sciences (PhD)

Administrative Home Department

Department of Biological Sciences

Advisor 1

Ebenezer Tumban

Advisor 2

Rupali Datta

Committee Member 1

Chandrashekhar P. Joshi

Committee Member 2

Stephen Techtmann

Committee Member 3

Marina Tanaosva

Abstract

Virus-like particles (VLPs) are empty viral shells derived from the expression of viral structural proteins such as capsid (coat) proteins in a suitable host cell. They are morphologically and structurally similar to viruses from which the coat proteins were derived, except for the fact that they lack the viral genome; thus, they are very safe. VLPs are highly immunogenic and have been used as vaccines against viruses from which the coat proteins were derived as well as vaccine platforms to develop vaccines against other infectious agents. However, VLPs derived from viruses that infect humans have some limitations; for example, pre-existing antibodies against some of these platforms already exist in the human population and can attenuate the immunogenicity of some of these platforms. As an alternative to using VLPs from human viruses, our lab used VLPs from a virus (MS2) that infects bacteria (bacteriophage) to develop a candidate vaccine against human papillomaviruses (HPVs). The candidate vaccine consisted of a mixture of two (mixed) MS2-L2 VLPs displaying a concatemer peptide from HPV16L2/HPV31L2 and a consensus peptide from HPVs. In this dissertation, we showed that immunization with mixed MS2-L2 VLPs protects mice against six HPV types; at the genital region, the VLPs protect against HPV pseudoviruses (PsVs) 5, 6, 11, 51, and 56. In the oral region, the VLPs protect against HPV PsV52. Overall, this part of the study shows that mixed MS2-L2 VLPs can protect against three HPV types associated with ~4.5% of cervical cancers, two HPV types associated with ~90% of genital warts and >90% recurrent respiratory papillomatosis; additionally, the VLPs protect against one of two HPV types associated with ~90% of HPV-associated skin cancers in patients with epidermodysplasia verruciformis. More importantly, we observed that mixed MS2L2 VLPs elicit protective antibodies that last over 9 months; furthermore, a sprayfreeze dried formulation of the VLPs is thermostable, immunogenic, and protective at room temperature for over 5 months and at 37 °C for 2 months. Given the degree of success in using bacteriophage MS2 VLPs, as a platform to develop a candidate vaccine against HPV, we also explored in this dissertation whether VLPs from other viruses (especially bacteriophages) can be developed, which could one day serve as platforms for vaccines. We assessed whether co-expression, in a thermophilic bacterium E. coli, of three coat proteins (VP11, VP16, and VP17) from a thermophilic bacteriophage, P23-77, can allow the coat proteins to assemble into VLPs. For the first time, we successfully co-expressed all three coat proteins in E. coli and observed oval structures that look like VLPs but are smaller in size compared to P23-77 virus.

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