“Click” chemistry for the assembly of entirely carbohydrate-based vaccines

The immunogenicity of conjugate vaccines is affected by the type of linker used. Due to its ease of synthesis, the "click" triazole linker is now widely used, but its impact on vaccine immunogenicity remains understudied, and current findings are contradictory due to the difficulty of isolating the linker's effect. To finally quantify the effect of this linker, we have synthesized two vaccines targeting the Thomsen-nouveau (Tn) carbohydrate cancer antigen using a zwitterionic polysaccharide carrier, PS A1, with either a linker-free or triazole-based conjugation strategy. Evaluation of the triazole conjugate in C57BL/6 mice shows a 30% decrease in antibodies targeting Tn and conversely, a large immune response towards the triazole. Despite this moderate loss of antibodies, complement-dependent cytotoxicity is unaffected, hinting at limited clinical impact of the linker conjugation. The new triazole-based conjugation method allows for facile attachment of amine- and azide-bearing antigens to PS A1, largely expanding its conjugation toolbox.