Immunoglobulin genes in multiple myeloma: expressed and non-expressed repertoires, heavy and light chain pairings and somatic mutation patterns in a series of 101 cases

Abstract

BACKGROUND AND OBJECTIVES: The available data on the immunoglobulin gene (IG) repertoire in multiple myeloma (MM) derive mainly from heavy chains; considerably less is known about light chains. We assessed in parallel IGH and IGK/IGL rearrangements in 101 MM patients so as to gain insight into: (i) IG repertoires; (ii) antigen impact; (iii) the role of receptor editing. DESIGN AND METHODS: Bone marrow aspirates were collected from all cases. IGHV-(D)-J and IGLV-J rearrangements were amplified by reverse transcriptase polymerase chain reaction (PCR). In all cases, IGKV-J rearrangements were analyzed in parallel on cDNA/genomic DNA. IGKV-KDE and IGKJ-C-INTRON-KDE were also amplified by DNA-PCR. RT-PCR products were directly sequenced. RESULTS: IGHV3 genes predominated; the IGHV4-34 gene was used in only one case. Five IGKV and five IGLV genes accounted for the majority of in-frame, transcribed IGKV-J or IGLV-J rearrangements. Taking IGKV-J, IGKV-KDE and IGKJ-C-INTRON-KDE rearrangements together, biallelic IGK locus rearrangements were detected in 22/43 k-MM cases. In l-MM, 36/42 cases had at least one rearranged IGK allele; 8/19 IGKV-J rearrangements in l-MM were in-frame. All in-frame, transcribed IGH/IGK/IGL sequences were mutated; parallel heavy/light chain analysis demonstrated a comparable impact of somatic hypermutation. INTERPRETATION AND CONCLUSIONS: Biases in IG repertoire did not seem disease-related but followed a similar pattern to that of the normal repertoire. The under-representation of the IGHV4-34 gene provides an explanation for the paucity of autoimmune phenomena in MM. Somatic mutation patterns indicate the complementary role of MM IGH/IGK/IGL sequences in antigen recognition. Finally, the frequent inactivation of productive IGKV-J joints by secondary rearrangements in MM suggests active receptor editing.