TAP1 and neoplasm: Reversible MHC class I downregulation on tumour cells can be associated with impaired expression of a number different genes, such as genes encoding MHC class I heavy chains, β2-microglobulin, APM components including LMP-2, LMP-7, TAP-1, TAP-2 and tapasin, which can be coordinated and epigenetically regulated [7,23].