T cell receptor repertoire usage in allotransplantation: An overview

Lymphocytes express antigen receptors that allow the immune system to speci fically recognize antigens, In transplantation, T cells play a critical rol e in the rejection process, and different protocols inhibiting T cell-media ted alloreactivity efficiently achieve prolongation of allograft survival. T cells can interact with alloantigens by two ways, either by the "indirect " pathway that correspond to the physiological mechanism of T cell immune r ecognition, or through the "direct" pathway where they recognize alloantige ns directly on the surface of donor cells. If some T cells are specifically activated in allorecognition, one should be able to indirectly detect this "selection" by analyzing the T cell receptor usage that could be biased an d reflect the preferential amplification of alloreactive lymphocyte subsets . Nevertheless compared with disease states such as cancer or autoimmunity the T cell receptor repertoire is still largely uncharacterized. We review the current results available on T cell repertoire usage in transplantation studies involving humans or various animal models. The T cell receptor rep ertoire involved in transplantation (restricted or unrestricted) and the fe atures potentially common to alloimmune responses will be discussed.