| Summary: | Includes bibliographical references. === [Fix supervisors field.] Psittacine beak and feather disease, caused by a circovirus known as beak and feather disease virus (BFDV), is a threat to both wild and captive psittacine species. There is currently no vaccine against BFDV and safe and affordable vaccine candidates are needed to alleviate the disease burden caused by this virus. Production of the BFDV's major antigenic determinant, the capsid protein (CP), in the inexpensive and highly scalable plant expression system, could satisfy these requirements as a potential subunit vaccine. In this work, truncated CP (ÄN40 CP) was first expressed in E. coli to successfully generate anti-CP polyclonal antibodies. ÄN40 CP and full-length CP transient expression in tobacco (Nicotiana benthamiana) was optimised as fusions to elastin-like polypeptide (ELP). Fusion of CP or ÄN40 CP to ELPs of different lengths was shown to increase yield relative to unfused CP/ÄN40 CP. Free ELP and a GFP-ELP fusion could be purified by inverse transition cycling (ITC), using centrifugation and membrane filtration methods. A ÄN40 CP-ELP fusion expressed in plants could be partially purified and represents low-cost vaccine candidate against BFDV. A candidate DNA vaccine expressing ÄN40 CP was also evaluated for expression of the antigen in vitro and may prove useful in a prime-boost regimen together with one of the plant-produced vaccine candidates.
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