Optimization and analysis of structure-based prion vaccines in transgenic mouse models
Creators: Fleming, Madeleine
Publisher: name: University of Alberta Library
Year: 2023

<p>Prion diseases are rare and fatal neurodegenerative disorders caused by the misfolding of the cellular prion protein (PrPC) to its infectious form (PrPSc). Until recently, the structure of PrPSc was a subject of much debate as there is evidence to support both the 4-rung β-solenoid model and published parallel in-register β-sheet (PIRIBS) cryo-EM structures. Prion diseases can be genetic, sporadic, or acquired. The most common genetic variants are genetic Creutzfeldt-Jakob Disease (gCJD), Gerstmann-Sträussler-Scheinker syndrome (GSS) and Fatal Familial Insomnia (FFI).<br>
14R1, a protein previously constructed in the Wille lab, has shown potential as a structure-based prion vaccine. This protein mimics the proposed 4-rung β-solenoid structure modified from an innocuous fungal protein, HET-s. This antigen has shown promising results as a safe and effective vaccine in transgenic mouse lines with mutations corresponding to GSS. This project aims to optimize and analyze the efficacy of 14R1 in transgenic mouse models for gCJD, GSS, and FFI. For all vaccine trials, antigen was expressed, purified, and verified by quality control measures of SDS-PAGE and TEM. The vaccine and selected adjuvant were then co-administered to young mice on a prime boost schedule. Serum was collected at the pre-immune stage and following each immunization. We then measured the antibody titre in the serum using an ELISA.<br>
Following comparison to other immunopotentiators, alum proved to be the best adjuvant in the GSS mouse line. Although immunization with 14R1 significantly delayed symptom onset and increased survival, GSS mice eventually succumb to prion disease. However, continued vaccination following the initial prime-boost schedule did not improve efficacy. Comparison of the immune response to 14R1 between mouse lines warranted investigation into immunological shortcomings and biases of each transgenic mouse model. gCJD and FFI mice, on a C57BL/6J background, had a much lower antibody titre following vaccination than the GSS mice, on an FVB background. However, the vaccine still showed efficacy in the FFI mice. gCJD mice were found to have a deficiency in a protease, cathepsin E, responsible for antigen processing. In response to the knowledge of a helper T-cell bias in gCJD mice, it was found that QS21 adjuvant was the better immunopotentiator for these mice as it significantly improved the immune response compared to alum adjuvant.<br>
Considering 14R1 as a proof of concept for rationally designed structure-based prion vaccines, new PIRIBS-based prion vaccines were designed and developed in response to emerging PrPSc cryo-EM structures. Following rational design, purification, and quality control, four vaccine constructs (P1, P2, P3a, and P4) were administered to FVB mice to assess the immune response. All PIRIBS vaccine candidates produced a large immune response, comparable to 14R1. A bridge ELISA determined that all animals immunized with P1, P2, and P3a produced antibodies which recognize PrPSc in RML-infected brain homogenate, while all animals immunized with P4 did not.<br>
Considering both 14R1 and the new PIRIBS vaccine candidates show potential PrPSc recognition, structural changes associated with prion disease becomes much more complex. Overall, these findings are an important step towards development of a prion disease vaccine for use in large animals and at-risk humans.</p>