Immunoglobulin Heavy Chain Variable Region (V_H) Genes of B Cell Chronic Lymphocytic Leukemia Cells from Lymph Nodes Show Somatic Mutations and Intraclonal Diversity Irrespective of Follicular Dendritic Cell Network

Abstract

We analyzed the immunoglobulin heavy chain variable region (V_H) gene in 4 Japanese cases of B cell chronic lymphocytic leukemia (B-CLL) with enlarged lymph nodes to clarify the presence of somatic mutations and intraclonal diversity. We also attempted to determine the role of the follicular dendritic cell (FDC) network in some proliferation centers, where tumor cells are mitotically active. Immunohistochemical studies revealed that all 4 cases showed the typical immunophenotype: CD5+, CD23+, IgM+ and IgD+. DNA was extracted from paraffin sections (lymph node) and rearranged V_Hgene was amplified by PCR. All but one exhibited a moderate number of somatic mutations, with percentages ranging from 4.1 to 9.5, and one of which indicated the effect of antigen selection on its V_Hgene. Multiple clone analysis of whole tissues showed intraclonal diversity in one case, whose V_Hgene carried a somatic mutation but the effect of antigen selection was not apparent. We further examined microdissected tissues to elucidate the relationship between FDC network and VH gene status in 2 cases. In one case, intraclonal diversity was not apparent irrespective of FDC network, however, both tumor cells around the FDC network and those apart from the FDC showed signs of intraclonal diversity in another case, suggesting that intraclonal diversity was not related to the FDC network in B-CLL. Here we demonstrate that some cases of B-CLL involved in lymph node carried mutated V_Hgenes and showed intraclonal diversity like the tumor cells in the peripheral blood. However, the significance of the FDC network in the proliferation center still remains to be resolved.

Key Words:

• B-CLL
• V_Hgene
• somatic mutation
• intraclonal diversity
• FDC network