Diagnostic concepts in clinical organ transplantation: histocompatibility testing and T cell monitoring.

Immunological rejection is still the most important problem in clinical organ transplantation requiring the lifelong immuno-suppressive treatment of the allograft recipient. The clinical success rate however can be improved by a variety of diagnostic procedures: The reduction of the histocompatibility barrier between donor and recipient by HLA-typing and organ exchange in order to obtain the best possible match; posttransplant monitoring of donor specific immune responsiveness towards donor antigens; monitoring of T-cell subsets by monoclonal antibodies and cytofluometry. T-cell subset monitoring is a rapidly developing new technique with great potential. With the presently available first generation reagents already a detailed analysis of the major T-cell population in circulation is possible, which can markedly facilitate the diagnosis of rejection and viral infection. New monoclonal antibodies, defining certain activation stages of T-cells or permitting a more refined differentiation of functionally distinct subsets will lead to increased relevance of this diagnostic approach. A particularly interesting aspect of monoclonal antibodies against T-cell differentiation antigens is their potential therapeutic use as immunosuppressive drugs with a highly selective action on defined T-cell subsets.