To confirm this observation at the protein level, we performed immunoblots of total cell lysates with HLA-A-, β2m-, TAP1-, TAP2-, LMP2- and LMP7-specific mAbs (Fig. 2C), revealing that HLA-A and β2m were expressed in all analyzed MCC cell lines, while TAP1 and LMP2, LMP7 expression was largely restricted to the MKL-2 cell line (Fig. 2C). This evidence concerns the gene PSMB9 and Merkel cell skin cancer.