The present invention relates to a product and process for suppressing an immune response using a T lymphocyte veto molecule capable of blocking cell surface molecules responsible for T cell activation. Disclosed is a CD4 or CD2 molecule, associated with an immunoglobulin molecule capable of binding to a major histocompatibility antigen. Also disclosed is a method to produce a T lymphocyte veto molecule, a therapeutic composition comprising a T lymphocyte veto molecule and methods to use T lymphocyte veto molecules in therapeutic processes requiring suppression of an immune response.