Generation of two human ISG15 knockout iPSC clones using CRISPR/Cas9 editing.

Abstract

Background and aims: T cells are the main mediators of allogeneic immune responses. Specific T cell clones can be tracked by their unique T cell receptor (TCR), but specificity and function remain elusive and have not been investigated in human liver biopsies thus far.

Methods: TCR repertoire analysis of CD4+, CD8+ and regulatory T cells of the peripheral blood and liver graft was performed in seven liver transplant recipients with either stable course (non-rejector, NR), subclinical cellular rejection (SCR) or acute cellular rejection (ACR) during an observation period from pre-transplant to six years post-transplant. Furthermore, donor-reactive T cells, identified by their expression of CD154 and GARP after allogeneic activation, were tracked longitudinally in peripheral blood and within the liver allograft.

Results: While overall clonality of the TCR repertoire did not increase in peripheral blood after liver transplantation, clonality of donor-reactive CD4+ and regulatory T cells increased and these clones accumulated within the liver graft. Surprisingly, the TCR repertoires between the liver graft and the periphery were distinct and showed only little overlap. Notably, during ACR TCR repertoires aligned suggesting either graft-specific homing or release of activated T cells from the graft.

Conclusions: This is the first study comparing TCR repertoires between liver graft and blood in patients with NR, SCR and ACR. Moreover, we attribute specificity and function to a subgroup of intragraft T cell populations. Given the little overlap between peripheral blood and intragraft repertoires future studies investigating function and specificities of T cells after liver transplantation should focus on the intragraft immune response. For this purpose, protocol biopsies of patients with normal graft function and subclinical rejection have to be taken into account.