INTERLEUKIN-7 SPECIFICALLY INDUCES THE B7/BB1 ANTIGEN ON HUMAN CORD-BLOOD AND PERIPHERAL-BLOOD T-CELLS AND T-CELL CLONES

B7/BB1 is a cell surface molecule and member of the Ig super family that is constitutively expressed on dendritic cells. In addition, B7 is expressed on B cells, macrophages, T cells, and T cell clones following activation. Interaction of B7 with its natural ligand CD28 is required for optimal stimulation of T cells, activated via the TCR-CD3 complex, which is thought to be due to stabilization of cytokine mRNA. Here we demonstrate that the expression of B7 on T cells can specifically be induced by IL-7. Induction of B7 expression on T cells and T cell clones requires at least 5-7 days of culture and represents a late activation event. Results of studies using T cell clones, as well as resting purified B7-T cells, demonstrate that B7 is induced on a substantial proportion of T cells after IL-7 activation and is not due to an outgrowth of pre-existing B7+ T cells. In addition, CD4+ as well as CD8+ T cells could be induced to express B7. Stimulation of purified cord blood T cells with cross-linked anti-CD3 mAb resulted in a relatively fast (48 h) induction of B7, which could not be inhibited by a neutralizing anti-IL-7 mAb, whereas no endogenous IL-7 production by activated T cells and T cell clones could be detected. Together, these results indicate that the B7 molecule can be induced on T cells by IL-7, but also by an IL-7 independent pathway involving triggering of the TCR-CD3 complex.