ESTABLISHED IL-2-DEPENDENT DOUBLE-NEGATIVE (CD4(-) CD8(-)) TCR-ALPHA-BETA 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 e xacerbation. The cells termed SO-4 were of ATL cell origin and showed the double-negative TCR alpha beta/CD3(+) T-cell phenotype. SO-4 cells acquired CD4 antigen expression following stimulation with concanaval in A (ConA) or immobilized anti-CD3 antibody. The induction was inhibi ted by herbimycin A, an inhibitor of protein tyrosine kinase (PTK) act ivity. 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 indica te that there is a pathway of phenotypic cycling between CD4 single-po sitive and double-negative T cells.