Anti-CD3 antibodies: towards clinical antigen-specific immunomodulation.

Current therapeutic approaches in transplantation and autoimmunity are essentially focused on immunosuppression, which is non-specific (i.e. unrelated to the antigens involved). The major drawback is their relative ineffectiveness in the long term, with the likely risk of recurrence of the pathogenic immune process once the drug is withdrawn necessitating indefinite drug administration; this has attendant problems of recurrent infections and drug toxicity. Instead, CD3-specific monoclonal antibodies possess the unique capacity to induce immunological tolerance: an antigen-specific unresponsiveness in the absence of long-term generalised immunosuppression, as is well-established in experimental models. Clinical application using humanised non-mitogenic CD3-specific antibodies is presently underway. The future challenge will be to define the modalities allowing the widespread application of this strategy through a better understanding of the underlying immune mechanisms.