Expression and immunogenicity of a liver stage malaria epitope presented as a foreign peptide on the surface of RNA-free MS2 bacteriophage capsids

We have designed a novel vaccine strategy which enables display of short pe ptides expressed from chimeras of the gene encoding the coat protein of the RNA bacteriophage MS2 and inserted foreign DNA. MS2 coat protein has a bet a-hairpin loop at the N-terminus which forms the most radially distinct fea ture of the mature capsid. The coat protein gene was modified to enable ins ertion of DNA at the central part of the beta-hairpin loop. Upon expression of the recombinant gene in E. coli, the MS2 coat protein subunits self-ass emble into capsids, each comprising 180 copies of the monomer. This system was used to produce chimeras containing a putatively protective epitope, T1 , from the immunodominant liver stage antigen-1 (LSA-1) of the malaria para site Plasmodium falciparum. The immunogenicity of the native MS2 capsid and the recombinant construct was investigated in BALB/c (H-2(d)) mice. The na tive protein appeared to elicit both humoral and cellular immune responses, observed as a predominance of type 2 cytokines but with a mixed profile of immunoglobulin isotypes. In contrast, the LSA-1 chimera stimulated a type l-polarised response, with significant upregulation of interferon-gamma, a finding which corroborates naturally acquired resistance to liver stage mal aria. These results validate RNA phage capsid display of immunogenic determ inants as a basis for the development of novel peptide vaccines and indicat e that further evaluation of MS2 coat protein as a vector for malaria epito pes is merited. (C) 1999 Elsevier Science Ltd. All rights reserved.