Mannosylated lipopetides as model vaccines for targeting the mannose receptor

Abstract

The mannose receptor (MR) is an important component of the immune system and understanding the structural and conformational characteristics of this receptor is a key aspect of targeted vaccine design. Improved understanding of the role of carbohydrate recognition domains (CRDs) 4-7 in recognising glycosylated ligands present on the surface of pathogens such as C. albicans, P. carinii, L. donovani, and M. tuberculosis has given new insight into MR vaccine development. Initial studies identified mannan and its derivatives to be important ligands in MR targeting, providing essential knowledge about structural properties of the MR. During the last decade many attempts have been made to target this receptor for applications including vaccine and drug development.In the present study, a library of vaccine constructs comprising fluorescently-labelled mannosylated lipid dendrimers that contained the ovalbumin CD4 + epitope, OVA323-339, as the model peptide antigen were synthesised using fluorenylmethyloxycarbonyl (Fmoc) solid phase peptide synthesis (SPPS). The vaccine constructs were designed with an alanine spacer between the O-linked mannose moieties to investigate the impact of distance between the mannose units on receptor-mediated uptake and/or binding in antigen presenting cells.Mannosylated building blocks were prepared with a Lewis acid reaction and the reaction was successfully modified and monitored for a better yield. This was followed by solid phase synthesis of mannosylated peptides with an azide functional group and a fluorescent tag. Considering the presence of multi-components on the designed mannosylated peptide, different methods of preparation was used and a high yield of the final mannosylated peptides with an azide functional group and a fluorescent tag were prepared. Further, OVA323-339 lipopeptides with an alkyne functional group were prepared using microwave assisted peptide synthesis. Final vaccine structures were prepared by attaching azide and alkyne functional groups using click chemistry. The same methods were applied for the preparation of a library of control vaccine structures.In vitro uptake studies performed on macrophage (F4/80 + ) and dendritic (CD11c + ) cells showed significant uptake and/or binding for vaccine constructs containing mannose and lipid, and also for the lipopeptide vaccine construct without mannose when compared to the controls (containing no lipid, no mannose and no mannose or lipid). Further, in vitro mannan competition assays demonstrated that uptake of the mannosylated and lipidated vaccine constructs was MR mediated. To address the specificity of receptor uptake, surface plasmon resonance (SPR) was performed usingBiacore technology which confirmed a high affinity of the mannosylated and lipidated vaccine constructs towards the human recombinant MR in vitro when compared with vaccine constructs without mannose. These studies also confirmed that both mannose and lipid moieties play significant II roles in receptor-mediated uptake on APCs, potentially faci...