Expression & immunogenicity of malaria merozoite peptides displayed on the small coat protein of chimaeric cowpea mosaic virus.

ABSTRACT

BACKGROUND & OBJECTIVES: Foreign peptide sequences can be inserted into the betaB-betaC loop of the cowpea mosaic virus (CPMV) small coat protein (SCP) to yield functional chimaeric viruses. Immunisation with chimaeric CPMV elicits immune responses that protect against human immunodeficiency and mink enteritis viruses. The present study was undertaken to investigate the expression of a B cell epitope from the merozoite surface antigen-1 of the malaria parasite Plasmodium falciparum (PfMSP1) in CPMV for an epitope based vaccine. METHODS: DNA encoding a 19 aa sequence (VTHESYQEL VKKLEALEDA, termed P109), the N-terminus of the mature PfMSP1, was cloned into SCP gene yielding a chimaeric virus CPMV-P109. CPMV-P109 was propagated in cowpea plants. The immunogenicity of purified recombinant virus in rabbits was investigated. RESULTS: CPMV-P109 developed a systemically spreading infection in cowpea, with normal viral morphology. The P109 epitope was detected on CPMV-P109 by ELISA with an antiserum produced against homopolymeric P109. Immunisation of rabbits with CPMV-P109 yielded antibodies that, although were predominantly directed against virus-specific epitopes, also recognized the P109 peptide on the recombinant virus and free P109 peptide. These antibodies however, did not react with the native antigen on merozoite by immunofluorescence. INTERPRETATION & CONCLUSION: The results indicate that selecting immunodominant peptide epitopes and presenting them in a near native conformation are important for generating biologically relevant antibodies in the CPMV expression system. Further, the findings draw attention to the importance of measuring immune responses to the viral vector antigens, a preponderance of which can result in undesirable effects such as autoimmunity and hypersensitivity in immunized hosts.