Ig VH1 genes expressed in B cell chronic lymphocytic leukemia exhibit distinctive molecular features

Abstract

Prior studies revealed that the leukemic B cells of patients with chronic lymphocytic leukemia (CLL) express a restricted Ig heavy chain variable region gene (VH gene) repertoire. However, this restriction needs to be re-evaluated in light of findings that the repertoire of Ig VH genes used by primary B cells of normal adults is actually more restricted than originally assumed. Because of this, we critically examined the Ig VH1 and VH7 genes expressed by leukemia cells of a random panel of patients with B cell CLL (n = 117). Forty-one (35%) had leukemia cells with functional VH1 gene rearrangements. Of these, the large majority expressed Ig VH1-69 (n = 26; 63%). The remaining leukemia cell samples expressed VH1-2 (n = 4; 10%), VH1-3 (n = 2; 5%), VH1-8 (n = 2; 5%), VH1-18 (n = 1; 2%), VH1-45 (n = 1; 2%), and VH1-46 (n = 5; 12%). Only 1 of the 117 examined (<1%) used Ig VH genes of the VH7 subgroup. We found that certain alleles of the IgVH1-69 locus are favored in CLL. Also, leukemia B cells that express VH1-69 have a distinctive use distribution of D and JH gene segments compared with that of VH1-expressing CLL B cells that do not use VH1-69 or non-neoplastic B cells that express VH1-69. Finally, the average length of the heavy chain third complementarity-determining regions (CDR3) of VH1-69-expressing leukemia cells is significantly longer than that of normal adult B cells that also express Ig encoded by VH1-69 genes. Collectively, this study indicates that the Ig expressed in CLL have distinctive molecular features that are not representative of the Ig expressed by primary B cells of normal adults.