EARLY SIGNALS OF THE TRANSITION FROM IMMUNE QUIESCENCE TO ACTIVATION IN THE LIVER ALLOGRAFT MICROENVIRONMENT AND IN THE CIRCULATION

University Of California, San Francisco, San Francisco CA

Investigators

Abstract

PROJECT SUMMARY Children with liver transplants who are maintained on low dose immunosuppression (IS) with ideal graft function according to clinical, biochemical, and histological criteria seemingly enjoy a harmonious equilibrium between the host immune system and the liver allograft. Reducing IS is a challenge that, for some but not all, precipitates alloimmune activation that can result in graft injury. Understanding the mechanisms of how allograft quiescence is sustained or lost when stressed is essential to walking the tightrope of too much versus too little IS. Achieving this balance is particularly critical for children and their families who typically face many decades of IS. Previously, we conducted prospective multicenter trials of IS withdrawal in children with liver transplants [WISP-R (NCT00320606) and iWITH (NCT01638559)]. We reported that, among allografts that appear normal by standard histological evaluation, objective quantification of inflammatory load using multiplex immunostaining accurately predicted the clinical outcome of success or failed IS withdrawal. The density of various inflammatory cell populations mapped allografts onto an alloreactivity spectrum that extended from quiescent to activated. Among inflammatory metrics, the density of immunologic synapses (iSYNs), defined as a lymphocyte interacting with an antigen-presenting cell based on positional, morphometric, and molecular metrics, was the best predictor of those who could withstand the perturbation of IS reduction and maintain allograft quiescence. These findings drive our primary hypothesis that the number and nature of interactions between intrahepatic immune cells constitutes the basis of liver allograft immunogenicity and determines whether quiescence is maintained or lost when challenged by reducing IS. iSYNAPSE proposes to conduct a multicenter, single-arm trial of 50% IS dose reduction for stable children on tacrolimus monotherapy with healthy liver allografts. Previous trials confirm that liver transplantation provides a unique context to safely study host and graft responses when their harmonious equilibrium is challenged by IS reduction. Utilizing allograft biopsies collected at the beginning and end of the trial, we will deeply characterize the liver microenvironment, precisely mapping the location, identity, state, and interactions of key immune cell subsets combining state-of-the-art technologies for tissue interrogation into a targeted and integrated multi- modal approach. These experiments will allow us to determine if the baseline phenotype and transcriptome of the lymphocytes and the antigen-presenting cells participating in iSYNs and their changes after IS is reduced differentiates participants who succeed versus fail IS reduction. Understanding the basic mechanisms of how allograft quiescence is maintained or lost in response to a discrete challenge addresses a fundamental knowledge gap in transplant immunobiology. The knowledge gained may accelerate the transition of IS management from empiricism to evidence-based with broad implications for all organ transplant recipients.