Origin of Nodular Lymphocyte-Predominant Hodgkin's Disease from a Clonal Expansion of Highly Mutated Germinal-Center B Cells

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Abstract
The atypical cells of nodular lymphocyte-predominant Hodgkin's disease, designated lymphocytic and histiocytic (L&H) cells, have a B-cell phenotype. To clarify the clonality of these cells, we studied rearranged immunoglobulin genes for the variable region of the heavy chain (V H genes) in individual L&H cells from 11 patients with nodular lymphocyte-predominant Hodgkin's disease. We also studied the expression of immunoglobulin light chains by those cells in six of the same patients. Single CD20+ L&H cells were isolated from frozen sections by a technique of micromanipulation. The rearranged V H genes of these cells were amplified by the polymerase chain reaction (PCR), sequenced, and compared with germ-line V H genes. Immunoglobulin light-chain messenger RNA (mRNA) was detected by in situ hybridization. Of 615 L&H cells isolated from all the frozen sections, 160 yielded PCR products. In each of the 11 patients, the L&H cells that could be evaluated had identically rearranged V H genes, whether they were isolated from the same nodule, different nodules, or different blocks of tissue. All the V H sequences derived from the L&H cells were highly mutated (7.5 to 27.2 percent). In two cases the coding capacity of the V H genes was completely or partially disrupted by mutations. Intraclonal diversity was found in six cases, and monotypic immunoglobulin light-chain mRNA was found in six. The L&H cells of nodular lymphocyte-predominant Hodgkin's disease represent a monoclonal expansion of B cells. The high load of V H gene mutations and signs of intraclonal diversity suggest a relation between L&H cells and germinal-center B cells at the centroblastic stage of differentiation.