Synthesis and characterization of a Pseudomonas aeruginosa alginate-toxin A conjugate vaccine

Abstract

Alginate from Pseudomonas aeruginosa 3064 was depolymerized by controlled heating in dilute acid. The resulting depolymerized alginate (M(r) < 60,000) was covalently coupled to toxin A with adipic acid dihydrazide as a spacer molecule and carbodiimide as a linker. The resulting conjugate was composed of toxin A and depolymerized alginate at a ratio of 4: 1 and possessed an M(r) of 260,000. The conjugate was nontoxic and nonpyrogenic. While native alginate (M(r) > 640,000) given in a range of doses was poorly immunogenic in mice and rabbits, the conjugate induced high levels of antibody which bound to native alginate. Rabbits, but not mice, also producedan antitoxin immunoglobulin antibody response. Alginate derived from three other strains of P. aeruginosa competed with the homologous 3064 alginate for binding to anticonjugate antibody. This indicates that the conjugate elicits an antibody response able to recognize heterologous alginates. The serum from rabbits immunized with the conjugate was effective at promoting the uptake and killing of mucoid strains of P. aeruginosa hy human polymorphonuclear leukocytes. In contrast, immunization with native alginate did not engender an opsonic antibody response. Rabbit anticonjugate antibody also neutralized the cytotoxic potential of toxin A.