Enhanced Immune Recognition of Cryptic Glycan Markers in Human Tumors (original) (raw)

Abnormal glycosylation is one of the hallmarks of the cancer cell and is associated with tumour invasion and metastasis. The development of tumour associated carbohydrate antigen (TACA) vaccines has been problematic due to poor immunogenicity. However when appropriate targets can be identified, passive immunisation with monoclonal antibodies (mAbs) directed against TACAs have been shown to have anti-tumour activity. Fas ligand (FasL) is a transmembrane protein which induces apoptosis in cells expressing its receptor, Fas. When grafted into mice, FasL-expressing tumour cells break immunological tolerance to self-antigens and induce antibody mediated tumour immunity. Here, five IgM mAbs were produced from mice vaccinated with FasL-expressing B16F10 mouse melanoma cells. They recognise various syngeneic and allogeneic murine tumour cell lines. One mAb, TM10, recognises a range of human tumour cell lines including melanoma, prostate and ovarian cancer. It does not bind to untransformed cells. The epitopes recognised by all the mAbs were carbohydrates expressed on proteins. Using carbohydrate microarrays, the antigenic targets of TM10 were found to be high-mannose core structures of N-linked glycans. In normal cells high mannose clusters are hidden by extensive saccharide branching but they become exposed in cancer cells as a result of abnormal glycosylation pathways. Vaccination with FasL-expressing tumours therefore enables the immune system to break tolerance to self-antigens, allowing identification of novel TACAs that can form the basis of future humoral anti-cancer therapy.