Southern blot analysis of the immunoglobulin heavy chain (IgH) locus in DNA from (A) LCL8664 cell line and (B) the original tumor mass from which LCL8664 cell line was derived. DNA (5 μg) was digested with Sacl and hybridized to a probe from the human IgH locus, 3' to the JH region. The arrows indicate the fragments generated from the locus in germline organization. The asterisks indicate the clonal rearrangement of the IgH locus. DNA from the tumor mass contains a large germline fragment not present in the cell line, indicative of contamination of the original necropsy sample with non-neoplastic tissue.