Molecular and antigenic properties of mammalian cellexpressed Theileria parva antigen Tp9

Authors: BASTOS, REGINALDO - Washington State University; FRANCESCHI, VALENTINA - University Of Parma; TEBALDI, GIULIA - University Of Parma; CONNELLEY, TIMOTHY - Roslin Institute; MORRISON, IVAN - Roslin Institute; KNOWLES, DONALD - Washington State University; DONOFRIO, GAETANO - University Of Parma; Fry, Lindsay

Submitted to: Frontiers in Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2019
Publication Date: 4/29/2019
Citation: Bastos, R.G., Franceschi, V., Tebaldi, G., Connelley, T., Morrison, I.W., Knowles, D.W., Donofrio, G., Fry, L.M. 2019. Molecular and antigenic properties of mammalian cellexpressed Theileria parva antigen Tp9. Frontiers in Immunology. 10. https://doi.org/10.3389/fimmu.2019.00897.
DOI: https://doi.org/10.3389/fimmu.2019.00897

Interpretive Summary: East Coast Fever (ECF) is a tick-borne disease of African cattle caused by the parasite, Theileria parva. Over one million cattle die of ECF each year, resulting in greater than 300 million U.S. dollars in annual losses. The parasite is spread to cattle by ticks, and causes disease and death when parasite-infected cells invade organs and are attacked by responding white blood cells. Currently available mechanisms of prevention are expensive and difficult to administer in the field. Thus, development of a next-generation vaccine that induces broad immune protection, is economically sustainable, and is convenient to store and administer is paramount to the long-term control of this devastating disease. The goal of this work was to test the suitability of one T. parva protein, Tp9, as a component of a protective vaccine. We found that cattle immune to T. parva exhibit a significant antibody and white blood cell response to Tp9, and conclude that Tp9 is a promising candidate vaccine antigen for T. parva.

Technical Abstract: East Cost Fever (ECF), a severe clinical syndrome caused by the tick-borne apicomplexan parasite Theileria parva, is a leading cause of morbidity and mortality in cattle of sub-Saharan Africa. A form of premunization known as the infection and treatment method (ITM) is currently the only approach available to control T. parva. Although ITM elicits acceptable levels of protection, its widespread adoption is limited by its expense, laborious production process, and antibiotic co-treatment requirement, necessitating the development of a more sustainable vaccine. To this end, efforts have been concentrated in the identification of new T. parva vaccine antigens and in the development of suitable platforms for antigen expression. In this study we investigated the molecular and antigenic properties of T. parva antigen 9 (Tp9) expressed by mammalian cells. Data indicate that Tp9 contains a non-canonical, functional secretion signal peptide. However, its secretion containing the native secretion signal peptide was minimal, suggesting that Tp9 largely remains within infected lymphocytes during natural infection. Secretion from mammalian cells increased ten-fold after the native signal peptide was replaced with the human tissue plasminogen activator secretion signal peptide (tPA). In subsequent assays, sera from all T. parva–immune cattle recognized this recombinant, secreted Tp9 protein. Additionally, PBMC from ITM-immunized cattle produced significant (p < 0.05) amounts of IFN' following ex vivo exposure to Tp9. Depletion experiments demonstrated that IFN' was primarily produced by CD4+ T cells with lesser contributions by CD8+ T cells. Data also showed that 'd T cells are not involved in the production of IFN' to Tp9. As expected, T-cell responsiveness varied between cattle of different MHC class I and class II genotypes. Collectively, these results provide rationale for further evaluation of Tp9 as a component of a T. parva subunit vaccine.