B2M and Merkel cell skin cancer: To elucidate the mechanism(s) leading to the reduced HLA class-I expression in MCC, we analyzed gene expression data from 35 cryopreserved MCC tumors, accessible at the gene expression omnibus (GEO) database (GSE22396), for HLA-A and B2M. Surprisingly, only ~25% of tumors (n = 8) expressed low or intermediate levels of HLA-A mRNA, whereas the majority (~75%, n = 27) contained high amounts of HLA-A specific mRNA (Fig. 2A).