Recombinant meningococcal PorA protein, expressed using a vector system with potential for human vaccination, induces a bactericidal immune response.

The PorA protein of Neisseria meningitidis (subtype P1.7,16) was expressed as a recombinant protein using three vectors; pTWIN, pQE30 and pRSETA, which introduce different sized N-terminal leader sequences to the mature protein. The immunogenicity of these proteins was compared following incorporation into liposomes and ZW-micelles. All of the recombinant PorA (rPorA) preparations induced high titres of antibody that recognised the homologous PorA within the outer membrane (OM) and on the surface of meningococci. Antisera raised against liposomes and micelles containing the different rPorA proteins induced high and comparable levels of complement-mediated killing of the homologous, but not heterologous, strain. Furthermore, the bactericidal effect was greater when rPorA were incorporated into liposomes rather than detergent micelles. The minimal addition of three N-terminal amino acids in rPorA purified from the pTWIN vector represents a significant improvement over rPorA purified from vectors pQE30 and pRSETA, plus other previously purified rPorA, when considering use of these proteins in vaccines for human use.