Immunoglobulin Gene Analysis in Different B cell Lymphomas With Focus on Cellular Origin and Antigen Selection

Abstract: B cell lymphoma (BCL) comprises a biologically and clinically heterogeneous group of tumors deriving from different stages of B cell development. The immunoglobulin (Ig) variable heavy chain (VH) gene rearrangement is unique for each BCL and can be used to reveal cellular origin, to study signs of antigen selection and to quantify tumor cell load.The normal counterpart of mantle cell lymphoma (MCL) has been postulated to be a naïve B cell and in hairy cell leukemia (HCL) it is considered to be a post-germinal centre B cell. We analyzed the VH gene rearrangements in 110 MCLs and 32 HCLs by PCR amplification and sequencing. Most MCLs (84%) displayed VH genes lacking somatic hypermutation (SHM), thus correlating to a naïve cell origin, whereas a subgroup (16%) showed SHM, implying derivation from a more differentiated B cell. In HCL, a majority of cases (84%) displayed SHM with signs of intraclonal heterogeneity and 16% had unmutated VH genes, thus questioning the cell of origin in HCL. Biased usage of particular VH genes was detected in both HCL (VH3-30) and MCL (VH3-21 and VH4-34), which indicates that antigen selection may be involved in lymphoma development. Furthermore, VH3-21+ MCLs showed a highly restricted V?3-19 gene use and they also had a superior outcome compared to other MCLs.Rearrangement analysis of 67 VH3-21+ chronic lymphocytic leukemia (CLL) cases from three different countries verified, regardless of geographical origin, the short and highly homologous complementarity determining region 3s and the strikingly biased usage of the V?2-14 gene (75%), as previously reported in CLL. This further supports that antigen selection by a common antigenic epitope may have occurred in VH3-21+ CLLs. In an autologous transplantation study of 30 multiple myeloma patients, we quantified the tumor content in the autografts before and after stem cell selection using clone-specific PCR. We conclude that stem cell selection reduced the number of clonal cells linearly, but purging could not totally eliminate the tumor cells from the graft, thus increasing the risk of a relapse.Altogether, our data allowed us to define new BCL subsets and to gain insights into the potential role of antigen selection in BCL development as well as the monitoring of tumor cell load using Ig gene rearrangements analysis.