Gene gun DNA immunization of cattle induces humoral and CD4 T-cell-mediated immune responses against the Theileria parva polymorphic immunodominant molecule

Authors: Fry, Lindsay; BASTOS, REGINALDO - Washington State University; STONE, BRAD - University Of Washington; WILLIAMS, LAURA - Washington State University; KNOWLES, DONALD - Washington State University; MURPHY, SEAN - University Of Washington

Submitted to: Vaccine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2019
Publication Date: 2/16/2019
Citation: Fry, L.M., Bastos, R.G., Stone, B.C., Williams, L.B., Knowles, D.P., Murphy, S.C. 2019. Gene gun DNA immunization of cattle induces humoral and CD4 T-cell-mediated immune responses against the Theileria parva polymorphic immunodominant molecule. Vaccine. 37(12):1546-1553. https://doi.org/10.1016/j.vaccine.2019.02.009.
DOI: https://doi.org/10.1016/j.vaccine.2019.02.009

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 gene gun immunization as a means of immunizing cattle against complex diseases like T. parva. We gene-gun immunized cattle with a single T. parva protein (PIM), and assessed immune responses and degree of protection from T. parva challenge. We found that gene gun immunization elicits strong immune responses to the included antigens, especially when the antigen DNA sequence is altered to maximize its production by bovine cells. Immunization with only the PIM protein did not protect cattle from severe disease when they were challenged with T. parva. We conclude that gene gun immunization is a promising vaccine platform for complex diseases in cattle, and its use in delivering multiple antigens will be explored further in the future.

Technical Abstract: East Coast Fever (ECF), caused by the tick-borne apicomplexan parasite, Theileria parva, kills over one million cattle each year in sub-Saharan Africa. Protective immunity is comprised of humoral responses to sporozoites and cell-mediated responses to schizont-infected lymphocytes. Significant parasite genetic complexity and strain variation, pronounced immunodominance of the cellular immune response, and diversity of bovine major histocompatibility complex (MHC) loci have precluded development of a traditional T. parva subunit vaccine with population-wide efficacy. One potential solution is gene gun delivered DNA immunization, also known as particle-mediated epidermally delivered (PMED) DNA immunization, which enables highly efficient, simultaneous intradermal inoculation of multiple DNA-encoded antigens. This method has shown promise in numerous murine, porcine, primate and human viral vaccination trials, but previous investigation of bovine PMED DNA immunization is extremely limited. In this study, we utilized the T. parva polymorphic immunodominant molecule (PIM) antigen to optimize and test PMED DNA immunization in Holstein steers. Four PMED DNA- immunizations with the native T. parva PIM sequence elicited a PIM-specific antibody response in only 3/8 steers. Transfection of bovine aortic endothelial (BAE) cells with the native construct revealed minimal PIM expression in bovine cells. Mammalian codon -optimization of the PIM sequence led to abundant PIM expression by BAE cells following transfection and, after four additional immunizations with the codon-optimized PIM construct, 7/8 steers exhibited significant anti-PIM antibody responses and cell-mediated immune responses to T. parva-infected cells. Despite the robust anti-PIM immune response, there was no significant difference in disease severity between the immunized and control groups following T. parva challenge. These results indicate that gene gun immunization is an efficient vaccination strategy for cattle and that codon optimization of T. parva antigenic sequences may significantly improve protein expression in bovine cells and immunogenicity. Our results also suggest that immunization with the T. parva PIM antigen alone is insufficient to prevent ECF upon subsequent T. parva infection; however, multivalent gene gun immunization is a promising vaccine platform for T. parva and other complex pathogens in cattle.