Preparation and preclinical evaluation of a novel liposomal complete-core lipopolysaccharide vaccine

Our objective is to develop a prophylactic vaccine strategy that can be eva luated for surgical and other high-risk hospitalized patients. In this pape r, we describe the preparation and preclinical evaluation of a liposomal co mplete-core lipopolysaccharide (LPS) vaccine that is nontoxic and broadly a ntigenic. Complete-core (Ra-chemotype) LPSs were isolated from four gram-ne gative bacterial strains (Escherichia coli K-12, E. coli R1, Pseudomonas ae ruginosa PAC608, and Bacteroides fragilis), mixed together to form a cockta il of complete-core LPSs, and then incorporated into multilamellar liposome s consisting of dimyristoyl phosphatidyl choline, dimyristoyl phosphatidylg lycerol, and cholesterol in a 4:1:4 molar ratio. The endotoxic activities o f these LPS-containing liposomes were less than 0.1% of the endotoxicities of the original free LPSs as measured by the Limulus amoebocyte lysate assa y. In vivo administration of liposomal complete-core LPS mixed with Al(OH)( 3) to rabbits resulted in no pyrogenicity or overt toxicity over a 7-day pe riod. In immunoblots, sera from rabbits following active immunization elici ted cross-reactive antibodies to a large panel of rough and smooth LPSs fro m numerous clinically relevant gram-negative bacteria, including E. coli (s erotypes O1, O4, O6, O8, O12, O15, O18, O75, O86, O157, and O111), P. aerug inosa (Fisher-Devlin serotypes 1, 2, and 3, which correspond to Internation al Antigenic Typing Scheme types 6, 11, and 2, respectively), Klebsiella pn eumoniae (serotypes O1, O2ab, and O3), B. fragilis, and Bacteroides valgatu s, Active immunization of mice with liposomal complete-core LPS provided pr otection against a lethal challenge with E, coli O18 LPS, The vaccine teste d was nontoxic, nonpyrogenic, and immunogenic against a wide variety of pat hogens found in clinical settings.