Phorbol ester induces interleukin-2 receptor on the cell surface of precursor thymocyte leukemia with no rearrangement of T cell receptor β and γ genes

The early event of thymocyte maturation has been analyzed using acute lymphoblastic leukemia (ALL) cells. A group of ALL cells whose cell surface phenotype was CD2 (SRBC receptor) negative and CD7 (T cell antigen) positive has been considered as precursor thymocyte ALL (pre-T-ALL). No rearrangements of the T cell receptor β-gene (TCR β) and γ-gene (TCR Γ) were found in three of four pre-T-ALL patients. Stimulation of these pre-T-ALL cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) induced only CD25 (Tac) antigen but no other T cell antigens. These findings suggest that the activation pathway of interleukin 2 (IL-2) receptor already exists in the most immature precursor thymocytes. Pre-T-ALL cells from the fourth patients showed the expression of CD3 antigen, and both TCR β and TCR γ rearrangement. TPA induced the differentiation of the more mature pre-T-ALL cells of this case in vitro, and not only CD25 (Tac) antigen but also CD4 and CD8 antigens appeared on the cell surface. The low affinity binding of ¹²⁵I-IL-2 to TPA-stimulated leukemia cells was observed in the three cases of pre-T-ALL tested, and the addition of recombinant IL-2 to TPA-stimulated cells showed no effect on cell proliferation.