Preformulation study of the vaccine candidate P64k against Neisseria meningitidis

We have previously isolated, cloned and expressed in Escherichia coli the lpdA gene coding for a high-molecular-mass protein (P64k) common to many meningococcal strains. P64k is an outer membrane lipoamide dehydrogenase that is highly immunogenic in animals. Here we describe a preformulation study of the recombinant protein as a vaccine candidate against Neisseria meningitidis, in which six variants containing the candidate were tested. Three assays were used to identify the most suitable variant for further evaluation: percentage of adsorption, identification of P64k by SDS/PAGE, and immunogenicity in mice. All the preformulation variants studied showed more than 98% of adsorption of P64k on the aluminium gel. After desorption, P64k was also identified by SDS/PAGE in the six preformulation variants. Seroconversion was attained in all groups analysed. On the basis of these results, the most effective variant consisted of 20 microg/ml P64k plus 0.5 mg/ml aluminium hydroxide.