Hashimoto S, Dono M, Wakai M, Allen S L, Lichtman S M, Schulman P, Vinciguerra V P, Ferrarini M, Silver J, Chiorazzi N
Department of Medicine, North Shore University Hospital, Manhasset, New York 11030, USA.
J Exp Med. 1995 Apr 1;181(4):1507-17. doi: 10.1084/jem.181.4.1507.
Chronic 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 VKI 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 VH and VL genes displayed > or = 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 VH CDR2 and adjacent sequences were not present in their germline DNA. In addition, a significant level of diversity was seen in the rearranged DJH 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 VH 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.
慢性淋巴细胞白血病（CLL）的特征是表达CD5的B淋巴细胞发生克隆性扩增。大多数研究发现，这些白血病性CD5+B细胞与其正常对应细胞一样，使用的免疫球蛋白（Ig）可变（V）区基因即使有体细胞多样性也极少。这些以及其他观察结果表明，CD5+B细胞可能无法产生Ig V基因多样性，因此可能无法形成可被抗原选择的高亲和力结合位点。然而，大多数关于CLL和正常CD5+B细胞的研究都集中在产生IgM的细胞上。由于体细胞突变最常出现在经历了同种型类别转换的B细胞中，我们分析了7个IgG+CD5+CLL B细胞的Ig重链（H）和轻链（L）可变区基因，以确定是否发生了体细胞多样化和抗原选择。所获得的数据为Ig V区基因的偏向使用、体细胞多样化和抗原选择提供了证据。VH4和VκI家族基因的过度表达以及JH4基因片段的低表达表明H链和L链V区基因存在非随机使用情况。此外，VH4基因的使用仅限于两个家族成员（4.21和4.18）。在7个病例中的4个病例中，VH和VL基因与最同源的已知种系对应基因的差异≥5%。对其中两名患者进行的聚合酶链反应和Southern印迹分析表明，他们独特的VH CDR2及其相邻序列在其种系DNA中不存在。此外，在每个患者重排的DJH片段以及VL-JL连接处，在重组时及随后都出现了显著水平的多样性。一些患者中替换变化定位于互补决定区，这表明发生了抗原选择。此外，在每个患者的VH和VL基因中鉴定出的突变在数量和位置上都惊人地相似。总体而言，数据表明CD5+CLL B细胞的一个亚群可以显示Ig V区基因突变。此外，这些数据与以下观点一致：在某些情况下，这些突变可能发生了抗原选择，并且抗原刺激可能是某些CLL克隆进化的促进因素。
