Staining of untreated R-CLL cells showed both a cytoplasmic and nuclear distribution of pS27-Ku70 (Figure 5A), as well as a marked increase in the pS27-Ku70 level in R-CLL cells compared with S-CLL cells (immunofluorescent staining not shown). Here, XRCC6 is linked to B-cell chronic lymphocytic leukemia.