Novel α-Galactosyl Ceramide Derivatives Enhance the Adjuvant Properties of Parenteral and Mucosal Vaccines

The rapid development of anti-microbial vaccines is an effective strategy against emerging infectious diseases, and vaccine adjuvants play an important role in enhancing the immunogenicity of vaccines. Typically, adjuvants enhance the adaptive immune response to these relatively weak antigens by promoting antigen uptake by antigen-presenting cells (APCs) or by activating the innate immune system. However, vaccine adjuvants against emerging viruses and drug-resistant bacteria are still limited, and the development of novel adjuvants is one of the challenges in vaccine development.

Constant natural killer T cells (iNKT), as a specialized T cell subset, have attracted attention due to their activation state resembling effector memory T cells. iNKT receptors (αβ-TCRs) recognize lipid and glycolipid antigens presented by CD1d on APCs. iNKT cells, upon activation, rapidly secrete Th1, Th2, and Th17 cytokines and activate NK cells, among others, to stimulate anti-tumor immune responses. The typical iNKT cell ligand is α-galactosylceramide (α-GalCer).

The synthesis of most α-GalCer analogs relies on the modification of the 6th position of the phytosphingosine, N-acyl lipid chain, and galactosyl portion. The researchers diversified derivatization of the amide bond connecting phytosphingosine to fatty acids by employing a multicomponent reaction (MCR) method that enables one-pot construction of α-GalCer derivatives with two distinct features, forming bis-amide-based scaffolds through a combination of primary amines, carboxylic acids, aldehydes, and isonitriles. The characterization of the adjuvant is altered by the groups carried by the isonitrile-hydrophobic groups, hydrophilic groups, amines, aldehydes, or carboxylic acids that can bind α-GalCer to the antigen.

Fig.1 MCR was used to construct multi-component derivatives of α-GalCer^[1].

It was shown that the novel glycolipid analogs (MGCAs) induced specific antigenic T-cells more than the conventional αGCM. compounds 18 and 20 showed a higher proliferative capacity of antigen-specific CD4+ and CD8+ T-cells. Further studies found that MGCAs significantly enhanced IgG1 and IgG2c antibody titers after inoculation via parenteral and mucosal routes. The performance of different MGCAs in Th1 and Th2 responses varies, and appropriate MGCAs can be selected to guide the immune response as needed.

Mucosal immunization experiments showed that significant IgG1 titer enhancement was obtained in the OVA+MGCAs group, and lipophilic MGCAs were effective in stimulating the Th2 response. Analysis of splenocyte supernatants showed that novel MGCAs stimulated mixed Th1/Th2 cellular immune responses and enhanced IFNγ/IL-2 and IL-5/IL-10/IL-13 secretion.

In conclusion, co-administration of novel MGCAs to the model antigen OVA significantly enhanced antigen-specific humoral and cellular immune responses, with the potential to develop effective parenteral and mucosal vaccines. It is evident that MGCAs are promising for the development of effective parenteral and mucosal vaccines. Although this is the first application of MCR in the field of vaccine adjuvants, the same strategy can be used to promote the diversification and functionalization of other adjuvant families, which can be used to fabricate multivalent structures of different adjuvants for the development of novel anti-microbial or anti-cancer vaccines.

Reference

1. Méndez Y, et al. Angew Chem Int Ed Engl, 2024, 63(1), e202310983.

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