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 vaccine design. Improved understanding of the role of carbohydrate recognition domains 4-7 (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 the MR structural properties. The MR was found to be an early responder in immunogenic pathways. Many attempts have been made to mimic the structural properties of yeast mannan by attaching mannan or mannose to antigenic proteins or peptide epitopes. However, a more detailed understanding of the structural properties of the MR is necessary for the design of targeted vaccines. This review describes the structure of the MR and provides an overview of the use of mannosylated proteins and peptides for vaccine targeting.

Adjuvant development and understanding the physicochemical properties of particles and interpreting the subsequent immunological responses is a challenge faced by many researchers in the vaccine field. We synthesized and investigated the physicochemical properties and immunogenicity of a library of multiple epitope self-adjuvant lipopeptides in a novel asymmetric arrangement. Vaccine candidates were synthesized using a combination of solid-phase peptide synthesis and copper-mediated click chemistry. In vivo studies showed that vaccine constructs containing a single OVA CD8 T-cell epitope and two N-terminally located C16 lipid moieties were more effective at generating robust cellular immune responses compared to the same molecule containing multiple copies of the OVA CD8 T-cell epitope with or without the C16 moieties. Furthermore, attachment of the two C16 lipids to the N-terminus provoked formation of long β-sheet fibrils and was shown to induce a higher CD8 donor T-cell frequency and IFN-γ secretion, compared to vaccine constructs with an internal lipid placement. A regression analysis indicated that particle secondary structure had a significant impact on CD8 donor T-cell frequency and cytolytic activity. In addition, IFN-γ production was influenced significantly by particle shape. The findings of this research will impact the future design of a vaccine intended to elicit cellular immune responses.

Present on the surface of antigen presenting cells (APCs), the mannose receptor (MR) has long been recognized as a front-line receptor in pathogen recognition. During the past 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 labeled mannosylated lipid-dendrimers that contained the ovalbumin CD4(+) epitope, OVA(323-339), as the model peptide antigen were synthesized 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 APCs. Uptake studies performed on F4/80(+) and CD11c(+) cells showed significant uptake and/or binding for lipopeptides containing mannose, and also the lipopeptide without mannose when compared to the control peptides (peptide with no lipid and peptide with no mannose and no lipid). Furthermore, mannan inhibition assays demonstrated that uptake of the mannosylated and lipidated peptides was receptor mediated. To address the specificity of receptor uptake, surface plasmon resonance studies were performed using biacore technology and confirmed high affinity of the mannosylated and lipidated vaccine constructs toward the MR. These studies confirm that both mannose and lipid moieties play significant roles in receptor-mediated uptake on APCs, potentially facilitating vaccine development.

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...