Safety and preliminary immunogenicity of the recombinant outer membrane protein P64k of Neisseria meningitidis in human volunteers

P64k is a meningococcal protein from Neisseria meningitidis that has been obtained by recombinant DNA technology. Recombinant P64k has been extensively characterized by physicochemical and immunological methods. Lately this protein has been found to act as a versatile immunological carrier for weak antigens in mice. In the present work, a Phase I clinical trial was carried out in healthy volunteers who received three inoculations of either placebo or recombinant P64k (20 or 50 μg). No severe adverse events occurred during the trial. Only mild adverse events in ten volunteers were observed. At I month after the third dose, 15 out of 18 volunteers (83.3%) who received the recombinant antigen had a P64k-specific antibody titre ≥ 1:100, as detected by ELISA. A fourth dose, given 9 months after the third one, elicited a potent booster immune response in P64k vaccinees. Accordingly, these P64k formulations were considered safe and immunogenic in healthy human volunteers.