Synthesis, Characterization, and Immunological Properties of LPS-Based Vaccines Composed of O-Polysaccharides Conjugated with Recombinant Exoprotein A from <i>Pseudomonas aeruginosa</i>

Abstract

Pseudomonas aeruginosa remains one of the major pathogens affecting immunocompromised patients. LPS-based monovalent (MV) and polyvalent (PV) conjugate vaccines were prepared from the most prevalent strains of P. aeruginosa International Antigenic Typing Scheme (IATS) 6, 10, 11 and 20 to evaluate their immunogenicity and protective capacities from infection by the pathogens. Conjugation of the O-polysaccharide (O-PS) antigens of P. aeruginosa strains to the common immunogenic recombinant Exotoxin A (rEPA) supports the multi-antigenic approach for the development of a vaccine that provides cross protection against various strains of the pathogen. The O-PSs were indirectly conjugated through adipic acid dihydrazide (ADH) to rEPA by carbodiimidemediated condensation reaction. Mice were immunized with the conjugates emulsified with monophosphoryl lipid A (MPL) or Freund's adjuvant compared with conjugates without adjuvant, unconjugated mixture of rEPA and O-PS emulsified with MPL, and sterile saline. The MV and PV vaccines emulsified with MPL adjuvant elicited the highest anti-O-PS IgM and IgG antibodies. Immunization of mice with MV vaccines derived from IATS 10, 11, and 20, emulsified with MPL adjuvant provided a high level of protection against the homologous bacterial strain. Similarly, high protection was obtained when mice were immunized using PV and challenged separately with bacterial strains 10, 11, and 20, but lower protection against the IATS 6 strain. Also, high cross protection of MV vaccine derived from O-PS of IATS 10 and 20 was obtained against P. aeruginosa IATS 11 strain. The in vivo protection correlated with the level of anti-O-PS IgG in the mice serum.