Racanelli et al. showed that malignant PCs from MM patient BM express reduced levels of antigen processing machinery (APM), i.e., constitutive and immunoproteasome subunits and TAP1/TAP2 transporters while protein chaperones, HLA class I and beta-2 microglobulin are increased in MM. This evidence concerns the gene B2M and Miyoshi myopathy.