2025 Theses Doctoral

Engineering Living Yeast as a Low-Cost and Scalable Oral Vaccine Platform

Qi, Jiaming

Vaccination has transformed humanity’s response to diseases since its creation in 1796. However, many successful vaccines are still not globally accessible to achieve herd immunity, especially during pandemics. During COVID-19, 60-80% population in developed countries was vaccinated; yet less than 20% of the population in resource-poor countries had access to vaccines. This disparity is due to the high cost of production, the limited scalability, the requirement of cold-chain transportation, and the need for trained personnel to administer vaccines. Therefore, to successfully defend against the next pandemic, new vaccine technologies are urgently needed to reduce cost, to improve scalability, and to simplify transportation and administration.

Synthetic biology has provided advanced molecular tools to engineer microorganisms with ease. Over the last 2 decades, synthetic biologists have engineered bacteria and yeasts as “living biofactories” to produce a variety of therapeutic molecules, including small molecules, peptides, antibodies, modified enzymes, vaccine antigens, and other biologics. The Cornish Lab is one of the pioneers of yeast synthetic biology, and we are currently exploring the potential of yeast in situ production and delivery of such therapeutic molecules (administering living yeast directly to the body). In this thesis, I explored the possibility of engineering living yeast as an oral vaccine vehicle that produces and delivers heterologous antigens in situ, using a synthetic biology design-build-test approach.

Chapter 1 provides background information in synthetic biology, living microbial therapeutics, mucosal immunology, and oral vaccines. Chapter 2 covers yeast engineering techniques, secretion detection, and medium-throughput screening strategies to improve yeast secretion yield. Chapter 3 describes in vitro characterizations of a secreted antigen. Chapter 4 describes in vivo testing of vaccine immunogenicity and yeast retention in mice and explores strategies to improve oral immunogenicity. Chapter 5 provides an outlook for future directions.

If successful, an oral yeast vaccine could be inexpensive to produce at large scale using conventional fermenters, with no downstream purification needed. This approach would transform our response to global pandemics, especially in resource-poor countries.