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 rearrangements, However, in situ hybridization methods failed to demonstrate Ig gene expression in H-RS cells of classical Hodgkin's disease (HD). Because somatic mutations rendering potentially functional Ig gene rearrangements nonfunctional were detected in some cases of the disease, it was speculated that H-RS cells in classical Ho may have lost the ability to express antigen 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 cells harbor a potentially functional V(H)1 and a potentially functional V(kappa)3 gene rearrangement. However, no antibody expression was detected. To show potential reasons for this lack of Ig expression, we analyzed the genomic 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 switched their isotype to IgG4, confirming their mature B-cell nature, By amplifying cDNA from L1236 cells as well as from frozen biopsy material transcripts of the V(kappa)3 and the VH1 gene rearrangement were detected for both sources of cDNA. However, Northern blot hybridization of L1236 RNA failed to demonstrate V(H)1 and V(kappa)3 transcripts, indicating only a low level of transcription. Sequence analysis of the promoter and leader regions of the V(H)1 gene rearrangement from L1236 cells as well as from lymphoma-affected tissue showed a somatic mutation in the conserved octamer motif of the promoter region. Somatic mutations were also detected within the 3' splice site of the leader intron end adjacent nucleotides in the rearranged V-kappa light chain gene, leading to aberrant splicing. These mutations might prevent the generation of adequate amounts of functional Ig gene transcripts as template for translation into protein. Thus, mutations in H-RS cells that prevent Ig gene expression might also be located outside the coding region of the Ig genes. (C) 1999 by The American Society of Hematology.