Alloreactive T cells temporarily increased in peripheral blood of patients before liver allograft rejection

T cells are key mediators of alloresponse during liver transplantation (LTx). However, the dynamics of donor-reactive T cell clones in peripheral blood during a clinical T-cell-mediated rejection (TCMR) episode remain unknown. Here, we collected serial peripheral blood mononuclear cells (PBMCs) samples spanning from pre-LTx to one-year post-LTx and available biopsies during the TCMR episodes from 26 rejecting patients, and serial PBMC samples were collected from 96 non-rejectors. Immunophenotypic and repertoire analyses were integrated on T cells from rejectors and longitudinally compared them to non-rejected patients. Donor-reactive T cell clone was identified and tracked by cross-matching with mappable donor-reactive TCR repertoire of each donor-recipient pair in 9 rejectors and 5 non-rejectors. Before transplantation, the naive T cell percentage and TCR repertoire diversity of rejectors was comparable to healthy control, it was reduced in non-rejectors. After transplantation, the naïve T cell percentages decreased and TCR repertoires were skewed in rejectors, the phenomenon was not observed in non-rejectors. Alloreactive clones increased in proportion in peripheral blood of rejectors before TCMR for weeks. The increase was accompanied by the naïve T cell decline and memory T cell increase and acquired an activated phenotype. Intragraft alloreactive clone tracking in pre- and post-LTx PBMC samples revealed that the pre-transplant naïve T cells were significant contributors to the donor-reactive clones, and they temporarily increased in proportion and subsequently reduced in blood at the beginning of TCMR. Together, our findings offer an insight into the dynamic and origin of alloreactive T cells in clinical LTx TCMR cases, and may facilitate disease prediction and management.