Expression of inhibitory checkpoint ligands by Glioblastoma Multiforme cells and the implications of an enhanced stem cell-like phenotype

Glioblastoma Multiforme is a highly aggressive brain malignancy commonly refractory to classical and novel chemo-, radio- and immuno-therapies, with median survival times of ~15 months following diagnosis. Poor immunological responses exemplified by the down-regulation of T-cell activity, and upregulation of immunosuppressive cells within the tumour micro-environment have limited the effectiveness of immunotherapy in GBM to date. Here we show that GBM cells express a large repertoire of inhibitory checkpoint ligands. Furthermore, GBM cells with an enhanced stem cell-like phenotype exhibit heightened levels of inhibitory checkpoint ligands, compared to non-stem cell-like GBM cells. Understanding how GBM modulates an extensive repertoire of immune checkpoint ligands and the functional consequence on immune evasion are necessary to develop effective immuno-therapeutics.