T cell immunomodulation--the Holy Grail of therapeutic tolerance

The concept and practice of therapeutic tolerance has successfully been applied to animal models of autoimmunity and transplantation for more than 2 decades. Finally, there are encouraging signs of its translation to clinical practice. Short courses of anti-CD3 monoclonal antibody therapy have provided lasting benefits in recent-onset type 1 diabetes in association with evidence for the induction of immunoregulatory mechanisms. Co-stimulation blockade with abatacept (CTLA4-Ig) will soon be licensed for the treatment of rheumatoid arthritis - over the past year phase III studies have demonstrated impressive improvement in subjective and objective signs of the disease. T cell depletion is in development for several conditions, again with recent studies demonstrating evidence of immune regulation in some instances. More specific antigen-directed peptide therapies have also been applied to atopic asthma, type 1 diabetes, and adult and juvenile arthritis. The tragic sequelae of the phase I trial of TGN1412 at Northwick Park demonstrated the delicate, but unpredictable, therapeutic ratio of some T-cell-directed treatments and, in the UK, have led to new guidelines for early-phase clinical trials of immune-directed therapies.