Synthesis, Characterization, and Immunological Properties of LPS-Based Vaccines Composed of O-Polysaccharides Conjugated with Recombinant Exoprotein A from &amp;lt;i&amp;gt;Pseudomonas aeruginosa&amp;lt;/i&amp;gt;

Nareman F Abu-Baker,Hussein Masoud

doi:10.4236/aim.2016.64032

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.

Highlights

Pseudomonas aeruginosa is a major cause of morbidity and mortality for immunocompromised patients, especially in individuals with cystic fibrosis, severe burns, or cancer [1] [2]
The O-PS was coupled to rEPA through an acid dihydrazide (ADH) spacer by a carbodiimide-mediated condensation reaction
Conjugate vaccine is recommended for immunization over other immunogens because of its safety and its ability to elicit protective antibodies against the carbohydrate antigen

Summary

Introduction

Pseudomonas aeruginosa is a major cause of morbidity and mortality for immunocompromised patients, especially in individuals with cystic fibrosis, severe burns, or cancer [1] [2]. In these patients, P. aeruginosa is one of the most dangerous nosocomial pathogens, due to its production of several virulence factors such as exotoxin A, exoenzyme S, elastase, alginate and lipopolysaccharide (LPS) [3] [4]; emergence of multidrug resistant strains [5]; and absence of an efficient protective vaccine [2]. The serum antibodies against the surface O-PS antigen confer protective immunity against the pathogen. Since intact LPS of Gram-negative bacteria is highly toxic, and isolated O-PS molecules are poor immunogens, especially in infants, many investigators have attempted to conjugate O-PS of pathogenic bacteria to immunogenic proteins to enhance the immunogenicity of O-PS and confer protection against the pathogen [11] [12]

Methods

Results

Discussion

Conclusion