XBP1 and melanoma: In melanoma, high levels of cholesterol induce the expression of XBP1s, leading to upregulated expression of immune checkpoint molecules and inhibition of CD8+ T-cell antitumour immunity [178] (Fig. 3), while inhibition of XBP1 or a decrease in cholesterol could restore CD8+ T-cell antitumour immunity and reduce tumour progression [178].