Abstract: Methods for inducing antigen-specific T cell tolerance are disclosed. The methods involve contacting a T cell with: 1) a cell which presents antigen to the T cell, wherein a ligand on the cell interacts with a receptor on the surface of the T cell which mediates contact-dependent helper effector function; and 2) an antagonist of the receptor on the surface of the T cell which inhibits interaction of the ligand on the antigen presenting cell with the receptor on the T cell. In a preferred embodiment, the cell which presents antigen to the T cell is a B cell and the receptor on the surface of the T cell which mediates contact-dependent helper effector function is gp39. Preferably, the antagonist is an anti-gp39 antibody or a soluble gp39 ligand (e.g., soluble CD40). The methods of the invention can be used to induce T cell tolerance to a soluble antigen or to an allogeneic cell.

Abstract: Methods for inducing T cell tolerance to a tissue or organ graft in a transplant recipeint are disclosed. The methods involve administering to a subject: 1) an allogeneic or xenogeneic cell which expresses donor antigens and which has a ligand on the cell surface which interacts with a receptor on the surface of a recipient T cell which mediates contact-dependent helper effector function; and 2) an antagonist of the receptor which inhibits interaction of the ligand with the receptor. In a preferred embodiment, the allogeneic or xenogeneic cell is a B cell, preferably a resting B cell, and the molecule on the surface of the T cell which mediates contact-dependent helper effector function is gp39. A preferred gp39 antagonist is an anti-gp39 antibody. The allogeneic or xenogeneic cell and the gp39 antagonist are typically administered to a transplant recipient prior to transplantation of the tissue or organ.