To that end, we used liquid chromatography couple to tandem mass spectrometry (LC–MS/MS) to characterize the peptide repertoires associated with HLA-DRB1*15:01 (555 unique peptides) and HLA-DRB5*01:01 (169 unique peptides) from bare lymphocyte syndrome (BLS) transfected cells. The gene discussed is HLA-DRB5; the disease is MHC class II deficiency.