Natural killer (NK) activity of cultured S100β-positive T-leukemia cells

In order to clarify the function of human S100 β- positive T-cells, S100 β-positive T-leukemia cells (S100 β TLC) were examined in vitro. S100 β TLC were obtained from the peripheral blood of a patient with S100 β-positive T-cell leukemia and enriched by an E-rosetting method. Two dimensional flow cytometric analysis indicated that the vast majority of the E-positive fraction were S100 β TLC expressing CD3 and CD8 antigens. Although S100 β TLC expressed CD3 antigen, they were negative for the α/β and γ/δ T-cell antigen receptor (TCR) defined by monoclonal antibodies (mabs) WT-31 and δ TCS-1, respectively. It was speculated that S100 β TLC initially expressed α/β TCR but lost it during malignant transformation. When S100 β TLC were cultured for 24 h, they acquired cytotoxic activity towards various NK-sensitive cell lines including K-562, Molt-3 and CEM-CCLF, but did not exhibit lysing activity towards NK-resistant cell lines including Raji, Daudi and MT-1. Despite the NK-activity of cultured S100 β TLC, they lacked the morphological features of large granular lymphocytes (LGL). S100 β TLC did not exhibit lymphokine-activated killer (LAK) activity. When S100 β TLC were cocultivated with NK-sensitive cells or NK-resistant cells, they selectively bound to NK-sensitive cells, indicating that they lysed target cells by cell-to-cell contact. The finding that S100 β TLC lacked TCR molecules and their NK activity was not inhibited by mabs reactive with the CD3-TCR complex indicated that the CD3-TCR complex was not involved in their target recognition. These findings suggest that S100 β-positive T-cells are functionally similar to NK cells. We discuss the roles of S100 β-positive T-cells in the human immune system.