FR104 is a monoclonal antibody fragment, selected and optimized to target the CD28 receptor, a key receptor in effector T lymphocytes. FR104 specifically blocks the destructive function of effector T lymphocytes without blocking the regulation function of regulator T lymphocytes, thus fostering immuno-tolerance in autoimmune diseases and transplantation.
The binding of CD28, expressed on the surface of a T lymphocyte, with its B7-1 (also called CD80) or B7-2 (also called CD86) ligands expressed on the surface of an antigen-presenting cell, provides the lymphocyte with the necessary signal to its complete activation: this is a co-stimulatory signal. Co-stimulatory signals regulate lymphocyte responses. The pharmacological action of this co-stimulatory signal represents a new therapeutic pathway to regulate the immune response, in order to fight autoimmune reactions with the decrease of adverse immune responses and to avoid transplant rejection.