Lipid A-free polysaccharide (PS) isolated from Pseudomonas aeruginosa immunotype 5 lipopolysaccharide (LPS) was covalently coupled to toxin A via reductive amination. The PS-toxin A conjugate was comprised of 29.8% PS and 70.2% toxin A, possessed a molecular weight of > 1 X 106, was nontoxic for animals and was nonpyrogenic for rabbits at a dose of 50 tg/kg body wt when administered intravenously. The conjugate evoked only mild, transient reactions upon subcutaneous administration to human volunteers. Vaccination engendered immunoglobulin G (IgG) antibody, which neutralized the cytotoxic effect of toxin A and promoted the uptake and killing of P. aeruginosa in the presence of human polymorphonuclear leukocytes. Passively transferred IgG isolated from the serum of immunized donors was far more effective at preventing fatal P. aeruginosa burn wound sepsis than paired preimmunization serum. These studies establish the potential usefulness of such a PS-toxin A conjugate as a vaccine against P. aeruginosa.

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O-specific polysaccharide (O-PS) isolated from serotype 18 Escherichia coli lipopolysaccharide (LPS) was covalently coupled to either Pseudomonas aeruginosa toxin A (TA) or or cholera toxin (CT). The conjugates were nontoxic and nonpyrogenic. The conjugates were well tolerated on parenteral administration to human volunteers, with only mild, transient local reactions reported. Immunization engendered an IgG antibody response to both the O-PS and carrier protein. Anti-LPS antibody promoted the uptake and killing of an E. coli O18 strain bearing the K1 capsule by human polymorphonuclear leukocytes, which was complement dependent. Antibody to carrier protein neutralized the activity of native TA or CT in cell culture assays. Passively transferred IgG isolated from the serum of immunized donors provided a significant (P less than .01) degree of protection against fatal experimental E. coli O18 sepsis in mice. This study illustrates the potential use of such conjugates as vaccines against E. coli extraintestinal infections.

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