Established IL‐2‐dependent double‐negative (CD4‐ CD8‐) TCRαβ/CD3+ ATL cells: induction of CD4 expression

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Abstract
Summary. We established IL‐2‐dependent T cells from an adult T‐cell leukaemia (ATL) patient whose leukaemic cells changed from CD4 single‐p‐positive in the initial phase to double‐negative (CD4‐ CD8‐) at the time of exacerbation. The cells termed SO‐4 were of ATL cell origin and showed the double‐negative TCRαβ/CD3+ T‐cell phenotype. SO‐4 cells acquired CD4 antigen expression following stimulation with concanavlin A (ConA) or immobilized anti‐CD3 antibody. The induction was inhibited by herbimycin A, an inhibitor of protein tyrosine kinase (PTK) activity. No CD4 mRNA was detectable in unstimulated SO‐4 cells but a 3.0 kb signal specific for CD4 mRNA was detected after stimulation. These findings indicate that SO‐4 cells return to their original phenotype (CD4 single‐positive) by stimulation involving PTK. The results indicate that there is a pathway of phenotypic cycling between CD4 single‐positive and double‐negative T cells.