Development of a Potential Yeast-Based Vaccine Platform for Theileria parva Infection in Cattle

Abstract

East Coast Fever (ECF), caused by the tick-borne apicomplexan parasite Theileria parva, remains one of the most important livestock diseases in sub-Saharan Africa with more than 1 million cattle dying from infection every year. Disease prevention relies on the so-called “Infection and Treatment Method” (ITM), which is costly, complex, laborious, difficult to standardise on a commercial scale and results in a parasite strain-specific, MHC class I-restricted cytotoxic T cell response. We therefore attempted to develop a safe, affordable, stable, orally applicable and potent subunit vaccine for ECF using five different T. parva schizont antigens (Tp1, Tp2, Tp9, Tp10 and N36) and Saccharomyces cerevisiae as an expression platform. Full-length Tp2 and Tp9 as well as fragments of Tp1 were successfully expressed on the surface of S. cerevisiae. In vitro analyses highlighted that recombinant yeast expressing Tp2 can elicit IFNγ responses using PBMCs from ITM-immunized calves, while Tp2 and Tp9 induced IFNγ responses from enriched bovine CD8+ T cells. A subsequent in vivo study showed that oral administration of heat-inactivated, freeze-dried yeast stably expressing Tp2 increased total murine serum IgG over time, but more importantly, induced Tp2-specific serum IgG antibodies in individual mice compared to the control group. While these results will require subsequent experiments to verify induction of protection in neonatal calves, our data indicates that oral application of yeast expressing Theileria antigens could provide an affordable and easy vaccination platform for sub-Saharan Africa. Evaluation of antigen-specific cellular immune responses, especially cytotoxic CD8+ T cell immunity in cattle will further contribute to the development of a yeast-based vaccine for ECF.

Improving expression and assembly of difficult-to-express heterologous proteins in Saccharomyces cerevisiae by culturing at a sub-physiological temperature

“…S. cerevisiae has been one of the most popular heterologous expression hosts in biotechnology, and it is increasingly employed in oral vaccine development [ 10 – 16 , 37 – 41 ]. Our previous study [ 13 ] showed that the expression of LTB fused with a synthetic Dengue tetravalent antigen using S. cerevisiae was potentially useful as an oral vaccine against Dengue viruses.…”

“…In addition, its high-quality protein content and high vitamin levels distinguish S. cerevisiae as a favorable single cell organism useful for live and oral administration of pharmaceutical and feed products [ 8 , 9 ]. Furthermore, the strong adjuvant properties of yeast derivatives render it an attractive heterologous expression system for vaccine production and development [ 10 – 17 ]. A well-balanced immune response to dengue was observed when a yeast expression system was used to produce dengue virus epitope proteins [ 18 ].…”

“…This fusion protein is capable of inducing strong systematic as well as mucosal immune responses against the target antigens. However, if the availability of the antigen is limited, such as in a vaccine in which the whole yeast cell is used instead of the protein extract, the strength of the immune responses is compromised [ 10 ]. To overcome this problem, it is suggested improving the expression levels of the target antigen.…”

Characterisation of the bovine C-type lectin receptor Mincle and potential evidence for an endogenous ligand1

“…T. parva is a tick-borne hemoprotozoan that infects and transforms bovine lymphocytes (26, 27). Cow 224 had been immunised with a preparation of live T. parva sporozoites (“Infection and Treatment Method”) (28), which triggers an antigen-specific, MHC class I-restricted, cytotoxic T cell response among other immune reactions (29, 30). However, T. parva infection of cow 224 had been cleared via antiprotozoal drug treatment prior to blood sample collection and PBMC isolation for this work.…”

“…Method") (28), which triggers an antigen-specific, MHC class I-restricted, cytotoxic T cell response among other immune reactions (29,30). However, T. parva infection of cow 224 had been cleared via antiprotozoal drug treatment prior to blood sample collection and PBMC isolation for this work.…”