Abstract

We investigated the nature of the lymphoid leukemia that developed in one of two siblings with ataxia telangiectasia. The leukemic cells were shown to be T lymphocytes. Furthermore, the neoplastic cells carried a characteristic 14q+ chromosome tandem translocation. This chromosome abnormality had been identified 11 years earlier among the patient's "normal" lymphocytes. The patient's neoplastic T lymphocytes in vitro provided helper and suppressor T-lymphocyte activity equivalent to that of normal T lymphocytes. Some neoplastic T lymphocytes bore a receptor for the Fc portion of IgM (45 per cent Tmu) whereas other carried receptors for the Fc portion of IgG (10 per cent Tgamma). All the Tmu and Tgamma lymphocytes possessed the chromosome 14 abnormality. These data suggest that neoplastic transformation occurred in an uncommitted T lymphocyte that was capable of further differentiation into the distinct pathways for help and suppression, in a lymphoid analogy of chronic myelogenous leukemia.