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 BAC-TO-BAC system. Immunization of horses with crude cell lysates containing recombinant baculovirus-expressed AHSV5 VP2 did induce neutralizing antibodies, but afforded only partial protection against virulent virus 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 present in a soluble form. Immunization of guinea-pigs with aggregated and soluble forms of AHSV5 VP2 established that only soluble VP2 was capable of inducing neutralizing antibodies. This finding adds a new dimension to the development of AHSV VP2s as subunit vaccines. Further investigation is needed to limit formation of insoluble aggregates and optimize conditions for producing VP2 in a form capable of inducing protective immunity.