B2M-inactivating mutations result in lack of MHC-I expression. (A) Diagram showing the localization and type of mutations in B2M in 7 sequenced primary cases of cHL containing these mutations. (B) Sequence analysis of DNA (top) and RNA (bottom) of the B2M gene in case 8 shows a point mutation in the start site of one allele and an out-of-frame deletion in another allele. Sequences were visualized using Integrated Genome Viewer. (C) Schematic representation of B2M together with MHC-I on the cell surface. (D) The L428 cell line was nucleofected with a plasmid encoding the wild-type B2M and a green fluorescent protein (GFP)-expressing plasmid, and flow cytometry was performed to evaluate MHC-I and B2M expression gating in the GFP+ (red) and GFP− (blue) populations.