KCNU1 and cancer: The remaining nine class I peptides were reference peptides, eight of which originated from six genes (MAGEA3, MAGEA6, BRDT, DAZ1, KCNU1, and IGF2BP1) that are expressed in testis but absent from oGTEx and mTECs, with some already known as cancer/testis (C/T) antigens [29–31].