SOMATIC DIVERSIFICATION AND SELECTION OF IMMUNOGLOBULIN HEAVY AND LIGHT-CHAIN VARIABLE REGION GENES IN IGG(-LEUKEMIA B-CELLS()CD5(+) CHRONIC LYMPHOCYTIC)

Chronic lymphocytic leukemia (CLL) is characterized by the clonal expa nsion of CD5-expressing B lymphocytes. Most studies have found that th ese leukemic CD5(+) B cells, like their normal counterparts, use immun oglobulin (Ig) variable (V) region genes that exhibit minimal, if any, somatic diversity. These and other observations have suggested that C D5(+) B cells may be incapable of generating Ig V gene diversity, and therefore may not be able to develop higher affinity binding sites tha t could be selected by antigen. However, most of the studies of CLL an d normal CD5(+) B cells have focused on IgM-producing cells. Since som atic mutations are most often seen in B cells that have undergone an i sotype class switch, we analyzed the Ig heavy (H) and light (L) chain variable region genes of seven IgG(+)CD5(+) CLL B cells to determine i i 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 V(H)4 and VKI family genes and the underrepresentation of the J(H)4 g ene segment. Furthermore, V(H)4 gene use was restricted to only two fa mily members (4.21 and 4.18). In four of the seven cases, the V-H and V-L genes displayed greater than or equal to 5% difference from the mo st homologous known germline counterparts, Polymerase chain reaction a nd Southern blot analyses performed in two of these patients demonstra ted that their unique V-H CDR2 and adjacent sequences were not present in their germline DNA. In addition, a significant level of diversity was seen in the rearranged DJ(H) segments and at the V-L-J(L) junction s of every patient that occurred both at the time of recombination and subsequently. The localization of replacement changes to complementar ity determining regions of some patients suggested that antigen select ion had occurred. Furthermore, the mutations identified in the V-H and V-L 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 additio n, they are consistent with the notions that in some cases antigen sel ection of these mutations may have occurred, and that antigen stimulat ion may be a promoting factor in the evolution of certain CLL clones.