Dual genotype in cutaneous T cell lymphoma: immunoglobulin gene rearrangement in clonal T cell malignancy

Genomic DNA digests of peripheral blood lymphocytes from 13 patients with the leukemic phase of the T cell neoplasm cutaneous T cell lymphoma were studied by hydridization using probes for the constant region of the beta chain of the T cell receptor, the joining region of the immunoglobulin heavy chain gene, and the kappa and lambda light chain genes. Lymphocytes from all 13 cutaneous T cell lymphoma patients contained DNA with clonal rearrangements of the beta chain gene of the T cell receptor. In addition, DNA from 4 patients contained an immunoglobulin gene rearrangement. T cell enrichment studies of peripheral blood lymphocytes from 2 patients confirmed that the immunoglobulin gene joining region rearrangement was confined to the T cell population. These results demonstrate that cutaneous T cell lymphoma is a clonal T cell malignancy that frequently expresses a dual genotype. A multiparameter approach, including DNA probes for the beta chain of the T cell receptor, as well as the immunoglobulin genes, immunophenotyping, and cytogenetics, is valuable in the diagnosis of cutaneous T cell lymphoma.