Protein aggregation complicates the development of baculovirus-expressed African horsesickness virus serotype 5 VP2 subunit vaccines

This paper describes the expression of a cloned African horsesickness virus (AHSV) serotype 5 VP2-gene by a baculovirus recombinant that was generated by the HAC-TO-BAC(TM) system. Immunization of horses with crude cell lysat es containing recombinant baculovirus-expressed AHSV5 VP2 did induce neutra lizing antibodies, but afforded only partial protection against virulent vi rus challenge. Further analysis of partially protective crude cell lysates revealed that baculovirus-expressed AHSV5 VP2 was predominantly present in the form of insoluble aggregates. Only approximately 10 % of VP2 was presen t in a soluble form. Immunization of guinea-pigs with aggregated and solubl e forms of AHSV5 VP2 established that only soluble VP2 was capable of induc ing neutralizing antibodies. This finding adds a new dimension to the devel opment of AHSV VP2s as subunit vaccines. Further investigation is needed to limit formation of insoluble aggregates and optimize conditions for produc ing VP2 in a form capable of inducing protective immunity.