T cell receptor repertoire usage in allotransplantation: an overview

Lymphocytes express antigen receptors that allow the immune system to specifically recognize antigens. In transplantation, T cells play a critical role in the rejection process, and different protocols inhibiting T cell-mediated 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 recognition, or through the "direct" pathway where they recognize alloantigens 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 and 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 repertoire involved in transplantation (restricted or unrestricted) and the features potentially common to alloimmune responses will be discussed.