REQUIREMENTS FOR STIMULATION OR ANERGY INDUCTION IN ALLOREACTIVE HUMAN T-CELL CLONES

The ''two signal'' concept for T cell activation is widely accepted. S ignal 1 is commonly delivered via the antigen receptor, and signal 2 v ia accessory interactions. Delivery of both signals results in activat ion, signal 1 alone in induction of hyporesponsiveness. The nature of signal 1 in alloreactivity is not completely clear; most evidence sugg ests that a complex of foreign major histocompatibility complex molecu les and their bound peptides is recognized. Interactions between B7 (C D80) ligand and CD28/CTLA-4 receptors are currently considered the mos t important sources of signal 2. Xenogeneic cells transfected with hum an genes provide useful stimulators for dissecting signals 1 and 2 in alloreactivity. We show here that the majority of DR-specific alloreac tive T cell clones (TCC) fails to recognize Chinese hamster ovary (CHO ) cells transfected with human DR, whether or not these are cotransfec ted with genes for CD80 or LFA-3. Stimulation was not observed even in the presence of a pool of peptides isolated by low pH release from B cell line (BCL)derived DR molecules, or in the presence of synthetic p eptides corresponding to the sequences of the three most commonly iden tified endogenous peptides. Lack of recognition was observed both in f ailure to stimulate proliferation and in failure to induce anergy. How ever, one TCC was identified which responded weakly to DR(+) CHO cells , and for this clone, the presence of either CD80 or LFA-3 strongly en hanced proliferative responses. Anergy was not induced, even in the ab sence of CD80. Immobilized HLA-DR molecules purified from a BCL also f ailed to stimulate proliferation, but unlike the CHO transfectants, th ey did induce anergy. Stimulation with BCL also induced anergy if CD80 -dependent interactions were blocked with soluble CTLA-4-Ig receptor. These results are consistent with the model that DR molecules expresse d in the absence of appropriate peptide are simply not recognized by m ost alloreactive T cells, whereas DR molecules containing appropriate bound peptide are recognized as signal 1 and induce anergy. CTLA-4-Ig blocking confirms that CD80-dependent interactions can be important in preventing anergy induction, but that they are not always necessary i s illustrated by the existence of a single clone which recognized DR m olecules on CHO transfectants, giving very weak proliferation without CD80, and nonetheless no anergy induction. (C) 1994 Academic Press, In c.