Gonococcal pili: safety and immunogenicity in humans and antibody function in vitro

In a phase I clinical trial, 39 volunteers received an initial and booster subcutaneous injection of 100 or 112 microgram of a pili vaccine prepared from Neisseria gonorrhoeae strain F62 in Tris buffer with an aluminum phosphate adjuvant (alum) or 220 microgram of the F62 pili vaccine prepared in ethanolamine, with or without alum. Antibody responses were quantitated with an enzyme-linked immunosorbent assay. All four groups had significant (P less than 0.0001) responses to the vaccine preparations with peak mean antibody responses one to three weeks after the booster. Differences in antibody responses among the groups were due to the administration of alum and not to use of Tris buffer vs. ethanolamine. In vitro, postimmunization sera enhanced phagocytosis of piliated strain F62 organisms by human polymorphonuclear leukocytes; preabsorption of the sera with strain F62 pili blocked this activity. Thus, gonococcal pili given subcutaneously are immunogenic and lead to production of functional serum antibodies.