Conjugation of Toll Like Receptor 7 agonist through conjugation to immunogenic proteins. Synthesis, characterization, formulation and pre-clinical evaluation

The next generation of vaccine adjuvant are represented by a wide ranging set of molecules called Toll like agonists (TLR’s). Although many of these molecules are complex structures extracted from microorganisms, small molecule TLR agonists have also been identified. However, delivery systems have not been optimized to allow their effective delivery in conjunction with antigens. Here we describe a novel approach in which a small molecule TLR agonist has been conjugated directly to antigens to ensure effective co delivery. We describe the conjugation of a relevant protein, a recombinant protective antigen from S.pneumoniae (RrgB), which is linked to a TLR7 agonist. Following thorough characterization to ensure there was no aggregation, the conjugate was evaluated in a murine infection model. Results showed that the conjugate extended animals’ survival after lethal challenge with S.pneumoniae. Comparable results were obtained with a 10 fold lower dose than that of the native unconjugated antigen. Notably, the animals immunized with the same dose of unconjugated TLR7 agonist and antigen showed no adjuvant effect. The increased immunogenicity was likely a consequence of the co-localization of TLR7 agonist and antigen by chemical binding and is was more effective than simple co-administration. Likely, this approach can be adopted to reduce the dose of antigen required to induce protective immunity, and potentially increase the safety of a broad variety of vaccine candidates