Targeted delivery of anti-CTLA-4 antibody downregulates T cell function invitro and in vivo

CTLA-4 is a T cell surface molecule that binds to the costimulatory molecul es CD80 and CD86 on antigen-presenting cells and downregulates T cell funct ion. Therefore, we wanted to test whether antigen-specific activated T cell s could be inhibited through directed CTLA-4 signaling using a bispecific a ntibody (BiAb) capable of simultaneously binding to CTLA-4 and a tissue-spe cific antigen. The BiAb was prepared by linking two separate monoclonal ant ibodies against CTLA-4 and the thyroid-stimulating hormone receptor (TSHR). The mouse B cell lymphoma line M12 (H2(d)) was used to induce alloreactive T cells in CBA/J mice (H2(k)); M12 cells stably transfected with the cDNA encoding murine TSHR (mM12) were used to restimulate the alloresponse in vi tro. Results of assays for in vitro T cell proliferation, IL-2 production, and cytoxicity in the presence of BiAb demonstrated that the BiAb could inh ibit the T cell alloresponse when stimulated with mM12 cells but not with M 12 cells. This effect was dependent on binding of TSHR-bound BiAb to CTLA-4 , since the addition of soluble CTLA-4-Ig blocked the inhibitory effect. In jection of mM12 cells, along with the BiAb, not with antibodies against TSH R or CTLA-4 either separately or together, into CBA/J mice (H2(k)) downregu lated alloreactive T cell responses. Our study demonstrated that the presen ce of CTLA-4 signaling molecules on the surface of target cells can protect those cells from immune attack by antigen-specific T cells and suggested t hat a similar approach could have potential therapeutic value in transplant rejection and tissue-specific autoimmune diseases. (C) 2001 Academic Press .