Expression ofNeisseria meningitidisclass 1 porin as a fusion protein inEscherichia colli: the influence of liposomes and adjuvants on the production of a bactericidal immune reesponse

High level exxpression of meningococcal class 1 protein was achieved inEscherichia coliusing the p-GEMEX-1 vector, in which the protein was expressed in inclusion bodies, (IB), as a fusion with the bacteriophage T7 gene 10 capsid protein. The fusion protein (FP) was engineered with a factor Xa protease site between the gene 10 and class 1 protein, but treatment with the enzyme resulted in cleavage at additional sites within the class 1 protein. Since it was not possible to remove the leader protein, the intact FP provided an alternative antigen for immunization. Antisera raised to FP, solubilized from IB and incorporated into liposomes, generated a subtype-specific response which was weakly bactericidal for meningococci. In order to remove any possible effect ofE. coliLPS present in IB, the FP was further purified by SDS-PAGE and incorporated into liposomes, either alone ofr in combination with the adjuvants monophosphoryl lipin A or muramyl dipeptide. The incorporation of adjuvants in liposomes resulted in stimulation of the overall immune response to FP, but the resulting antisera were not bactericidal. however and effective bactericidal response was obtained with the purest preparation of FP in liposomes, without any additional adjuvants, revealing that attempts to increase further the immunogenicity of such antigens must not be at the expense of interfering with optimal protein folding