Donadei Agnese, Gallorini Simona, Berti Francesco, O'Hagan Derek T, Adamo Roberto, Baudner Barbara C
Mol Pharm. 2015 May 4;12(5):1662-72. doi: 10.1021/acs.molpharmaceut.5b00072. Epub 2015 Apr 20.
The potential benefits of skin delivery of vaccines derive from the presence of a densely connected network of antigen presenting cells in the skin layer, most significantly represented by Langerhans cells and dermal dendritic cells. Targeting these cells by adjuvant conjugated to an antigen should result in enhanced immunogenicity of a vaccine. Since one of the most widely used adjuvants is an insoluble salt of aluminum (aluminum hydroxide) that cannot be used for skin delivery due to reactogenicity, we focused our attention on agonists of receptors present on skin dendritic cells, including the Dectin-1 receptor. β-(1-3)-glucans, which are the most abundant components of the fungal surface, are known to activate the innate immune response by interaction with the C-type lectin-like Dectin-1 receptor. In this work we identified by rational design a well-defined synthetic β-(1-3)-glucan hexasaccharide as a Dectin-1 agonist and chemically conjugated it to the genetically detoxified diphtheria toxin (CRM197) protein antigen, as a means to increase the binding to Dectin-1 receptor and to target to skin dendritic cells. We demonstrated that the in vitro activation of the receptor was significantly impacted by the presentation of the glucan on the protein carrier. In vivo results in mice showed that the conjugation of the synthetic β-(1-3)-glucan when delivered intradermally resulted in higher antibody titers in comparison to intramuscular (i.m.) immunization and was not different from subcutaneous (s.c.) delivery. These findings suggest that weak receptor binders can be turned into more potent agonists by the multivalent presentation of many ligands covalently conjugated to the protein core. Moreover, this approach is particularly valuable to increase the immunogenicity of antigens administered via skin delivery.
通过皮肤递送疫苗的潜在益处源于皮肤层中存在紧密连接的抗原呈递细胞网络，其中最显著的代表是朗格汉斯细胞和真皮树突状细胞。通过与抗原偶联的佐剂靶向这些细胞应能增强疫苗的免疫原性。由于最广泛使用的佐剂之一是铝的不溶性盐（氢氧化铝），因其具有反应原性而不能用于皮肤递送，我们将注意力集中在皮肤树突状细胞上存在的受体激动剂，包括Dectin-1受体。β-(1-3)-葡聚糖是真菌表面最丰富的成分，已知通过与C型凝集素样Dectin-1受体相互作用激活先天免疫反应。在这项工作中，我们通过合理设计鉴定出一种明确的合成β-(1-3)-葡聚糖六糖作为Dectin-1激动剂，并将其化学偶联到经基因解毒的白喉毒素（CRM197）蛋白抗原上，作为增加与Dectin-1受体结合并靶向皮肤树突状细胞的一种手段。我们证明，葡聚糖在蛋白载体上的呈现显著影响了受体的体外激活。在小鼠体内的结果表明，与肌肉注射免疫相比，皮内递送合成β-(1-3)-葡聚糖时的偶联导致更高的抗体滴度，且与皮下递送无差异。这些发现表明，弱受体结合剂可以通过将许多配体共价偶联到蛋白核心上的多价呈现转化为更强效的激动剂。此外，这种方法对于提高通过皮肤递送的抗原的免疫原性特别有价值。
