Specific Protein Antigen Delivery to Human Langerhans Cells in Intact Skin

Abstract

Immune modulating therapies and vaccines are in high demand, not least to the recent global spread of SARS-CoV2. To achieve efficient activation of the immune system, professional antigen presenting cells have proven to be key coordinators of such responses. Especially targeted approaches, actively directing antigens to specialized dendritic cells, promise to be more effective and accompanied by reduced payload due to less off-target effects. Although antibody and glycan-based targeting of receptors on dendritic cells have been employed, these are often expensive and time-consuming to manufacture or lack sufficient specificity. Thus, we applied a small-molecule ligand that specifically binds Langerin, a hallmark receptor on Langerhans cells, conjugated to a model protein antigen. Via microneedle injection, this construct was intradermally administered into intact human skin explants, selectively loading Langerhans cells in the epidermis. The ligand-mediated cellular uptake outpaces protein degradation resulting in intact antigen delivery. Due to the pivotal role of Langerhans cells in induction of immune responses, this approach of antigen-targeting of tissue-resident immune cells offers a novel way to deliver highly effective vaccines with minimally invasive administration.

Synthesis of glycopeptides and glycopeptide conjugates

“…Specific areas of (immunological) interest these conjugates have seen use are the study of lectin mediated peptide uptake, 13,28 modulation of cytokine production 29,35 or targeting of specific cell-types. 27,36 The increased synthetic accessibility of these glycoconjugates enables the synthesis and evaluation of more variants, in turn enabling more in-depth studies of glycan function. Therefore, conjugation methods to synthesize non-natively glycosylated peptides in a facile (compared to synthesis of native structures) manner will be described in more detail.…”

“…In this synthesis, no particular care was taken to selectively produce the β-mannoside linkage in compound 30, preferring instead to separate the two diastereomers. After allyl ether deprotection (34) and introduction of the final two mannose moieties (36), the phthalimide functions were converted to the acetamides (37). To introduce the (orthogonally protected) asparagine residue, the anomeric azide was selectively reduced by hydrogenation over Lindlar catalyst to obtain the glycosyl amine.…”

Antigen targeting to dendritic cells: Still a place in future immunotherapy?

“…First attempts to study T‐cell responses induced by human skin DCs targeted via Langerin, that is, LCs, yielded equivocal data that call for more research into this (technically and logistically difficult to work with) topic [ 135 ]. A recent development of a highly specific glycomimetic ligand for Langerin represents an interesting alternative to antibody targeting for the development of novel LC‐based vaccines [ 136 , 137 , 138 ].…”

Identification of the Allosteric Binding Site for Thiazolopyrimidine on the C-Type Lectin Langerin

“…The two homologues have evolved to recognize different incoming threats based on the carbohydrate signatures and show remarkable differences in their specificity for bacterial polysaccharides. , Langerin binds to pathogen-associated carbohydrates, which in turn initiates the uptake of the exogenous particle and promotes the cross-presentation of the antigen for the subsequent immune response . Accordingly, Langerin plays a key role in the transition from innate to adaptive immunity, rendering the receptor an attractive target for targeted delivery for immunotherapeutic approaches. , Therefore, ligands with high selectivity for Langerin would be highly valuable for understanding its biology as well as for applications in targeted drug delivery.…”

“… 5 Accordingly, Langerin plays a key role in the transition from innate to adaptive immunity, rendering the receptor an attractive target for targeted delivery for immunotherapeutic approaches. 6 , 7 Therefore, ligands with high selectivity for Langerin would be highly valuable for understanding its biology as well as for applications in targeted drug delivery.…”