Absence of ATM in B-CLLs 33 and 34 and presence of

ATM mutation 2114insA in B-CLL 34 nontumor mononuclear cells. (A) Western blot showing complete loss of ATM in B-CLL tumors 33 and 34. N indicates normal lymphoblastoid cell line (LCL); A-T, LCL derived from an ataxia telangiectasia patient with 2 nullATM alleles; B-CLL 19 and 20, 2 tumors withoutATM mutations; B-CLL 33 and 34, tumors with 2 ATMmutations (or LOH). (B) Truncating mutation 2114insA (given as reverse sequence) in patient B-CLL 34 was present in DNA from both tumor (CD19⁺) and nontumor (CD19⁻) compartment, but not present in the buccal smear DNA. An immune system gene rearrangement could be detected only from the tumor population of patient B-CLL 34, but not from the nontumor cells, suggesting the absence of cross contamination between nontumor and tumor cells.