Somatic diversification and selection of immunoglobulin heavy and light chain variable region genes in IgG+ CD5+ chronic lymphocytic leukemia B cells.

Abstract

SummaryChronic lymphocytic leukemia (CLL) is characterized by the clonal expansion of CD5-expressing B lymphocytes. Most studies have found that these leukemic CD5 + B cells, like their normal counterparts, use immunoglobulin (Ig) variable (V) region genes that exhibit minimal, if any, somatic diversity. These and other observations have suggested that CD5 § B cells may be incapable of generating Ig V gene diversity, and therefore may not be able to develop higher affinity binding sites that could be selected by antigen. However, most of the studies of CLL and normal CD5 + B cells have focused on IgM-producing cells. Since somatic mutations are most often seen in B cells that have undergone an isotype class switch, we analyzed the Ig heavy (H) and light (L) chain variable region genes of seven IgG + CD5 + CLL B cells to determine if somatic diversification and antigen selection had occurred. The data derived provide evidence for skewed use, somatic diversification, and antigenic selection of the Ig V region genes. Nonrandom use of both H and L chain V region genes was manifested by an overrepresentation of VH4 and V~I family genes and the underrepresentation of the JH4 gene segment. Furthermore, VH4 gene use was restricted to only two family members (4.21 and 4.18). In four of the seven cases, the V. and VL genes displayed />5% difference from the most homologous known germline counterparts. Polymerase chain reaction and Southern blot analyses performed in two of these patients demonstrated that their unique V. CDR2 and adjacent sequences were not present in their germline DNA. In addition, a significant level of diversity was seen in the rearranged DJ8 segments and at the VL-JL junctions of every patient that occurred both at the time of recombination and subsequently. The localization of replacement changes to complementarity determining regions of some patients suggested that antigen selection had occurred. Furthermore, the mutations identified in the V~ and VL genes of each individual patient were strikingly similar, both in number and location. Collectively, the data indicate that a subset of CD5 § CLL B cells can display Ig V region gene mutations. In addition, they are consistent with the notions that in some cases antigen selection of these mutations may have occurred, and that antigen stimulation may be a promoting factor in the evolution of certain CLL clones. most invariably expresses surface membrane CD5 (for a review see reference 1). Over the years, investigators have studied these cells to understand both the normal physiology of this subset of human B cells as well as the abnormal features of the B lymphocytes expanded in this disease. Studies to date suggest that the B cells that are clonally expanded in CLL use a biased set of Ig V genes (for a review see reference 2) to code for low affinity, polyreactive autoantibodies (3-5), predominantly of the IgM class. Although numerous studies have noted that these Ig V genes rarely undergo somatic mu- 1507J. Exp.

Use of V H, D and J H immunoglobulin gene segments in Brazilian patients with chronic lymphocytic leukaemia (CLL)

“…Although we found that the V H 3 family was the most frequently involved in functional rearrangements, followed by V H 4 and V H 1, in agreement with Pasqualucci et al (2000), several reports have shown V H 3 followed by V H 1 and V H 4 (Fais et al, 1998;Pritsch et al, 1999;Sakai et al, 2000;Duke et al, 2003;Vilpo et al, 2003) or V H 4 > V H 3 > V H 1 profiles (Hashimoto et al, 1995). The occurrence of V H 1 as the third most frequent family coincided with the profile of normal cells (Rassenti et al, 1995;Matsuda et al, 1998), although, in most CLL studies, it was found only V H , D and J H immunoglobulin segments in Brazilian CLL patients 645 when the V H 1-69 segment was excluded from the analyses (Oscier et al, 1997;Duke et al, 2003).…”

Different spectra of recurrent gene mutations in subsets of chronic lymphocytic leukemia harboring stereotyped B-cell receptors

“…[1][2][3][4][5] Such studies led to the discovery of quasi-identical or stereotyped BcR IGs in more than 30% of CLL patients who can be assigned to distinct subsets, each defined by a particular BcR immunogenetic motif. [6][7][8][9][10][11][12][13][14] Importantly, from both a biological and clinical perspective, evidence suggests that this classification of CLL based on BcR stereotypy is highly relevant and extends well beyond the SHM status of the BcR IG, thereby enabling the identification of homogeneous disease subgroups and, hence, overcoming the heterogeneity characteristic of CLL.…”

Intraclonal diversification of immunoglobulin light chains in a subset of chronic lymphocytic leukemia alludes to antigen-driven clonal evolution

“…19,20 A critical question in CLL biology is whether interaction with antigen is restricted to the progenitor cell (pre-transformation phase) or whether the putative antigen may continuously trigger the CLL clone and, perhaps, drive its evolution. [22][23][24][25][26][27] The experience from other types of B-cell malignancies suggests that useful hints for an ongoing interaction with antigen may be obtained through the study of intraclonal diversification (ID) within the IG genes expressed by the malignant clone. 28 With this in mind and through a recent comprehensive analysis of ID in rearranged IGHV genes from patients with CLL, we showed that although the majority of cases showed no or low levels of ID, an intense and, likely, functionally driven ID process was evident in selected cases, especially those belonging to subset 4.…”