TGFβ-dependent expression of PD-1 and PD-L1 controls CD8+ T cell anergy in transplant tolerance

CD8(+) T cell anergy is a critical mechanism of peripheral tolerance, poorly investigated in response to immunotherapy. Here, using a pancreatic islet allograft model and CD3 antibody therapy, we showed, by single cell gene profiling, that intragraft CD8(+) lymphocytes coexpressing granzyme B and perforin were selectively depleted through the Fas/FasL pathway. This step led to long-standing anergy of the remaining CD8(+) T cells marked by the absence of cytotoxic/ inflammatory gene expression also confirmed by transcriptome analysis. This sustained unresponsiveness required the presence of the alloantigens. Furthermore, tissue -resident CD8(+) lymphocytes produced TGF beta and expressed the inhibitory receptors PD -1 and PD -L1. Blockade of TGF beta downregulated PD -1 and PD -L1 expression and precipitated graft rejection. Neutralizing PD 1, PD -L1 or TGFORII signaling in T cells also abrogated CD3 antibody -induced tolerance. These studies unravel novel mechanisms underlying CD8 T cell anergy and reveal a cell intrinsic regulatory link between the TGF beta and the PD-1/PD-L1 pathways.