SURFACE DISPLAY COMPARED TO PERIPLASMIC EXPRESSION OF A MALARIAL ANTIGEN IN SALMONELLA-TYPHIMURIUM AND ITS IMPLICATIONS FOR IMMUNOGENICITY

Two different expression systems were investigated for the production of an 80 amino acid polypeptide, M3, from the C-terminus of the Plasmo dium falciparum blood stage antigen Pf155/RESA in an attenuated Salmon ella typhimurium vaccine strain, Upon expression, the malarial polypep tide was targeted either to the periplasm as a soluble fusion protein containing two IgG-binding domains (ZZ) from the staphylococcal protei n A or, to the bacterial surface as an insert within a chimeric outer membrane protein A (OmpA) derived from Escherichia coli and Shigella d ysenteriae. Both the ZZM3 and the OmpAM3 proteins were stably expresse d in the periplasm or on the surface of Salmonella, respectively. The ZZ expression system yielded 10-100 times more malarial immunogen than did the OmpA system. Live recombinant Salmonella expressing ZZM3 or O mpAM3 were used to immunize mice intraperitoneally. Both the ZZM3 and OmpAM3 genes persisted for up to three weeks in bacteria isolated from different lymphoid organs. Bacteria expressing ZZM3 induced antibodie s to M3, ZZ and to the Pf155/RESA antigen whereas, bacteria producing OmpAM3 induced similar levels of antibodies reactive with M3 but not w ith Pf155/RESA, Both recombinants induced a memory response of antibod ies reactive with both M3 and Pf155/RESA, The high levels of M3 produc ed by the ZZ expression system make it suitable for the expression of heterologous antigens in Salmonella. Nevertheless, in spite of the qua ntitative difference in M3 expression, the ZZ and OmpA constructs elic ited comparable immune responses to M3.