B2M and neoplasm: Knockout of TRIM21 resulted in high expression of HLA-A, B2M, TAP1 and TAP2 in SUNE1 tumour cells isolated from BALB/c nude mice (Fig. 5d) and of B2m, Tap1, Tap2, Tapbp and Earp1 in MC38 tumour cells isolated from C57BL/6 mice (Fig. 5e).