Sugar-coating encapsulins: potential cancer immunotherapy and vaccine development

Cancer vaccines are designed to re-program the immune system to recognise antigenic markers on cancer cells, resulting in their selective clearance. Aberrantly glycosylated versions of mucin-1 (MUC1) are overexpressed on many cancers. Specifically, the truncated O-linked glycan antigens Tn (GalNAc-α1-Ser/Thr), sTn (NeuAc- α -2,6-GalNAc), and Tf (Gal-β-1,3-GalNAc), that decorate tumour-associated MUC1 are promising targets for cancer vaccine development. However, glycan antigens can suffer from low immunogenicity, and must be combined with adjuvants and/or carriers to elicit sufficient immune responses for immunotherapy (e.g. antibody production). Here, we explore encapsulin (Enc) protein nanocages as carriers for glycosylated MUC1 variants. Encs can deliver peptide antigens and elicit both humoral and cellular immune responses in vivo; and their in vivo safety has been confirmed in our lab. To exploit Encs as antigen carriers, we first glycosylated a MUC1 tandem repeat region [APDTRPAPGSTAPPAHGVTS] with Tn, sTn and Tf antigens using specific glycosyltransferases, with glycosylation then determined by mass spectrometry. These MUC1 glycopeptides were attached to recombinantly produced and purified Encs, via strained alkyneazide copper-free “Click” chemistry and attachment was confirmed by Western blot with a Tn-specific antibody.