Established IL-2-dependent double-negative (CD4^- CD8^-) TCRαβ/CD3⁺ ATL cells: Induction of CD4 expression

We established IL-2-dependent T cells from an adult T-cell leukaemia (ATL) patient whose leukaemic cells changed from CD4 single-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 concanavalin 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.