Single-cell immunofluorescence assay for terminal transferase: human leukaemic and non-leukaemic cells

Abstract

The characteristics of a single-cell immunofluorescence assay for terminal deoxynucleotidyl transferase (terminal transferase, TdT) is described. The data indicate that the single-cell immunofluorescence assay is highly efficient and specific for the detection of cells containing TdT. Using this assay, we have examined 124 marrow or peripheral-blood samples from 104 patients with or without haematological malignancies. Results indicate that TdT⁺ cells from 6% to 100% were found in the following patients: 34/40 samples from patients with ALL at the time of diagnosis or during relapse, 2/3 patients with acute undifferentiated leukaemia, 2/3 patients with acute myelomonocytic leukaemia, 1/24 patients with acute myeloblastic leukaemia, 1/5 patients with chronic myelocytic leukaemia (CML) in blastic crisis, and 2/2 patients with diffuse lymphoblastic lymphoma. In contrast less than 1% of TdT⁺ cells were found in 20 marrow or peripheral-blood samples from ALL patients in complete remission, 8 patients with CML in chronic phase, 2 patients with myeloma, 1 sample from a patient with Hodgkin's disease, peripheral-blood samples from 7 normal donors and marrow samples from 6 patients without haematological malignancies. TdT⁺ cells were also found in association with cells with lymphoblast morphology. The TdT⁺ cells in marrow were shown to be directly correlated with the percentage of morphological lymphoblasts, with a Spearman rank coefficient of 0·81, significant at a 0·001 level. In 2 longitudinal studies of 2 ALL patients with TdT⁺ cells at diagnosis, the percentage TdT⁺ cells also changed in parallel with the proportion of lymphoblasts. However, studies of 2 other patients with morphologically diagnosed ALL with < 1% TdT⁺ cells at diagnosis also showed < 1% TdT⁺ cells throughout the period studied, indicating a stable phenotype of blast cells in these patients. The single-cell immunofluorescence assay for TdT, which requires < 0·1% of the cells used in a conventional biochemical assay, is highly specific, and could provide a technically more efficient alternative for use in clinics as well as in experimental investigations of subpopulations of leukaemic and normal marrow cells.