Synthesis of Lipooligosaccharide-Capsular Polysaccharide Conjugates for the Prevention and Treatment of Infections Caused by Acinetobacter baumannii

The proposed work will involve the synthesis of molecules designed to trigger long-lived, adaptiveimmune responses that are protective against infection caused by the Gram-negative coccobacillusAcinetobacter baumannii. There are presently no approved vaccines for A. baumannii, and there has been anincreasing incidence of infections caused by drug-resistant strains. Central Hypothesis: Covalentconjugation of synthetic portions of an Acinetobacter baumannii lipooligosaccharide (LOS) to the Bacteroidesfragilis capsular polysaccharide A1 (PSA1) will result in molecules that can trigger adaptive immune responsesselective to A. baumannii. Project Goals: Short-term goals include synthesis of A. baumannii LOS-PSA1conjugates and their injection into mice to determine their efficacy in prevention of infections caused by A.baumannii. Long-term goals include the development of a vaccine and the development of monoclonalantibodies to be used as a therapeutic. Specific Aims: Specific Aim 1: Synthesis of A. baumannii LOS coreoligosaccharides that can be conjugated to PSA1 and other carrier molecules. The success of this SpecificAim will lie in the effective implementation of synthetic strategies and completion of target molecules. SpecificAim 2: Conjugation of the A. baumannii LOS core oligosaccharides to PSA1 and subsequent injection intomice followed by studies to determine immunogenicity and protective effects against A. baumannii infection.The immunogenicity and protective effects of the LOS-PSA1 conjugates against bacterial challenge with A.baumannii will be studied. The success of this Specific Aim will lie in the effective protection of mice againstinfection by A. baumannii in which long-lived, adaptive immunity has been triggered. Specifc Aim 1 studies will involve the multistep chemical synthesis of a series of five oligosaccharideswith varying complexity and which are based on an A. baumannii LOS core structure. The 4-aryl-3-butenylthioglycosides undergoing development in our laboratory will be critical intermediates in thesesyntheses. Other key features include synthetic strategies to generate an alkoxyamine-bearing linker that willbe used to conjugate the oligosaccharides to PSA1. Specific Aim 2 studies will start with the condensation ofthe aforementioned alkoxyamine-bearing oligosaccharides with aldehydes generated through the oxidativecleavage of a diol moiety on PSA1. The resulting LOS-PSA1 conjugates will be injected into mice and themouse anti-sera will be collected subsequently. The immunogenicity of the LOS-PSA1 conjugates will bedetermined through ELISA assays to determine the nature of the antibody response as well as flow cytometryto determine if the antibodies bind to A. baumannii in addition to an assay to determine the bactericidal effectsof the sera. Pending the results of the initial serological experiments, bacterial challenge experiments in whichbacterial dissemination and survival rates in mice are determined will be conducted. Such experiments will beconducted with the most promising LOS-PSA1 conjugates based on the initial serological experiments.