Analysis of CD1 molecules on thymus cells and leukemic T lymphoblasts identifies discrete phenotypes and reveals that CD1 intermolecular complexes are observed only on normal cells.

We looked at the surface expression of the three distinct human thymic cell surface differentiation antigens, CD1a, CD1b, and CD1c, that presently define the first cluster of differentiation (CD) on the cells from 34 patients with acute T cell malignancies. We also studied the expression of other T cell-restricted molecules, including the T cell receptors, on these cells. Our results confirm the extensive phenotypic heterogeneity of the cells from acute T cell malignancies, which contrast with the more limited phenotypic diversity of subacute or chronic T cell malignancies. Our study of normal children and fetal thymus cells shows that the extensive phenotypic heterogeneity of the malignant cells reflects the heterogeneity of the thymic subpopulations and shows that most of the phenotypes observed on malignant T cells have a normal counterpart, particularly in the fetal thymus. Moreover, we demonstrate that the CD1a molecules, which can form three different types of noncovalent intermolecular complexes on the surface of normal thymus cells, do not form any noncovalent intermolecular complexes on the surface of leukemic cells. We also show that CD1a molecules can form covalent intermolecular complexes with CD8 molecules on some but not all malignant cells.