Somatic mutations within the untranslated regions of rearranged Ig genes in a case of classical Hodgkin's disease as a potential cause for the absence of Ig in the lymphoma cells

Hodgkin-Reed-Sternberg (H-RS) cells are clonal B cells carrying Ig gene rea rrangements, However, in situ hybridization methods failed to demonstrate I g gene expression in H-RS cells of classical Hodgkin's disease (HD). Becaus e somatic mutations rendering potentially functional Ig gene rearrangements nonfunctional were detected in some cases of the disease, it was speculate d that H-RS cells in classical Ho may have lost the ability to express anti gen receptor as a rule. Recently, we established a novel cell line (L1236) from H-RS cells of a patient with mixed cellularity subtype of HD. L1236 ce lls harbor a potentially functional V(H)1 and a potentially functional V(ka ppa)3 gene rearrangement. However, no antibody expression was detected. To show potential reasons for this lack of Ig expression, we analyzed the geno mic organization of the Ig genes and their transcription in the primary and cultivated H-RS cells of this patient. The H-RS cells were found to have s witched their isotype to IgG4, confirming their mature B-cell nature, By am plifying cDNA from L1236 cells as well as from frozen biopsy material trans cripts of the V(kappa)3 and the VH1 gene rearrangement were detected for bo th sources of cDNA. However, Northern blot hybridization of L1236 RNA faile d to demonstrate V(H)1 and V(kappa)3 transcripts, indicating only a low lev el of transcription. Sequence analysis of the promoter and leader regions o f the V(H)1 gene rearrangement from L1236 cells as well as from lymphoma-af fected tissue showed a somatic mutation in the conserved octamer motif of t he promoter region. Somatic mutations were also detected within the 3' spli ce site of the leader intron end adjacent nucleotides in the rearranged V-k appa light chain gene, leading to aberrant splicing. These mutations might prevent the generation of adequate amounts of functional Ig gene transcript s as template for translation into protein. Thus, mutations in H-RS cells t hat prevent Ig gene expression might also be located outside the coding reg ion of the Ig genes. (C) 1999 by The American Society of Hematology.