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Conferring alloantigen-specificity to ex vivo expanded CD4+CD25+FOXP3+regulatory T cells (Tregs) increases their capacity to counteract effector alloimmune responses following adoptive transfer into transplant recipients. Three strategies are currently undergoing clinical development, which involve the following: (1) expanding Tregs in the presence of donor B cells (donor alloantigen-reactive [DAR] Tregs); (2) culturing Tregs with donor cells in the presence of costimulation blockade (CSB-Tregs); and (3) transducing Tregs with an human leukocyte antigen A2–specific chimeric antigen receptor (CAR-Tregs). Our goal in this study was to assess the relative potency of each of these manufactured Treg products both in vitro and in vivo. When compared with polyclonal Tregs, all 3 manufacturing strategies increased the precursor frequency of alloreactive Tregs, and this was proportional to the overall in vitro immunosuppressive properties of the cell products. Accordingly, CAR-Tregs, which contained the highest frequency of donor-reactive Tregs, exhibited the strongest suppressive effects on a cell-per-cell basis. Similarly, in an in vivo mouse model of graft-vs-host disease, infusion of CAR-Tregs conferred a significantly longer recipient survival than any other Treg product. Our results highlighting the alloantigen-reactivity and associated immunosuppressive properties of different manufactured Treg products have implications for the mechanistic interpretation of currently ongoing clinical trials in transplantation.

The maintenance of stable allograft status in the absence of immunosuppression (IS), known as operational tolerance, can be achieved in a small proportion of liver transplant recipients, but we lack reliable tools to predict its spontaneous development. We conducted a prospective, multicenter, biomarker-strategy design, IS withdrawal clinical trial to determine the utility of a predictive biomarker of operational tolerance. The biomarker test, originally identified in a patient cohort with high operational tolerance prevalence, consisted of a 5-gene transcriptional signature measured in liver tissue collected before initiating IS weaning. One hundred sixteen adult stable liver transplant recipients were randomized 1:1 to either arm A (IS withdrawal regardless of biomarker status) or arm B (IS withdrawal in biomarker-positive recipients). Immunosuppression withdrawal was initiated in 82 participants, rejection occurred in 54 (67.5%), and successful discontinuation of IS was achieved in 22 (27.5%), but only 13 (16.3%) met operational tolerance histologic criteria (10 in arm A; 3 in arm B). The biomarker test did not yield useful information in selecting patients able to successfully discontinue IS. Operational tolerance was associated with time posttransplant, recipient age, presence of circulating exhausted CD8+T cells, and a reduced number of immune synapses within the graft.