80-kDa subunit of Ku. The Ku autoantigen is a heterodimeric protein made up of 70- and 80-kDa subunits. Besides its central importance to DNA repair, Ku has a key role in a number of other fundamental cellular processes such as telomere maintenance, transcription and cell death [89]. The cell surface expressed Ku80 is detected in a variety of tumor cells, including leukemia and solid tumor cells [95]. Surface Ku contributes to adhesion and invasion of tumor cells thus potentiating tumor metastasis [59]. Here, XRCC5 is linked to leukemia.