Proliferation of normal and leukemic TdT+ bone marrow cells in man

Proliferative characteristics of lymphoid cells with detectable amounts of nuclear terminal deoxynucleotidyl transferase (TdT) in normal or regenerating non-leukemic bone marrow of children were assessed by sequential immunological and cytokinetic studies on single cells and compared to those of TdT+ cells in the bone marrow of children with non-T, non-B acute lymphoid leukemia (ALL) at diagnosis or in remission. The median labelling index (LI) of non-leukemic TdT+ cells was 21.3% (range 13.2 to 29.7%). The LI of non-leukemic TdT+Ia+ cells (range 18.2 to 32.6%) was always higher than that of non-leukemic TdT+Ia- cells (range 0 to 5.3%). Leukemic TdT+ bone marrow cells of children with previously untreated non-T, non-B ALL had a LI significantly (p less than 0.001) lower (median 6.1%; range 1.4 to 19.7%) than the LI of non-leukemic TdT+ cells. In patients with non-T, non-B ALL in remission neither the percentage of TdT+ cells nor the LI of TdT+ cells appeared to be useful for detecting early relapse.