Identification of lymphoblastic lymphoma cells using a dual assay for T cell differentiation markers

An assay that simultaneously detects two differentiation markers found in thymocytes is described. There markers include the membrane receptor for sheep erythrocytes (E) and the nuclear enzyme, terminal deoxynucleotidyl transferase (TdT). Cells are incubated with E, pelleted onto slides and then stained for TdT by an indirect immunofluorescence technique. The E-positive, TdT-positive phenotype is characteristic of the tumor cells in many cases of lymphoblastic lymphoma. Cells of this dual phenotype were not found in the peripheral blood or bone marrow of individuals without neoplastic disease. An 8-year-old-girl with lymphoblastic lymphoma is described whose peripheral blood and bone marrow smears were thought to be morphologically normal at the time of diagnosis. However, 3% of her peripheral blood and about 1% or her bone marrow mononuclear leukocytes were identified as E-positive, TdT-positive. These cells disappeared from both sites five weeks after institution of therapy, and her peripheral blood remains free of such cells nine months after diagnosis. This dual assay for E-rosette formation and TdT is a more sensitive technique than conventional morphology for the detection of tumor cells of this type. The assay may be useful in monitoring the therapy of patients with this tumor.