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Migration Capacity of Thymic Regulatory T Cells can be Tuned by Expansion in Cytokine-Enriched Culture Conditions

Hoeppli, Romy E.1,5; Dijke, Esmé2,3,5; Campbell, Andrew1; West, Lori J.2,3,4,5; Levings, Megan K.1,5

doi: 10.1097/

1Surgery, University of British Columbia, Vancouver, BC, Canada; 2Pediatrics, University of Alberta, Edmonton, AB, Canada; 3Alberta Transplant Institute, University of Alberta, Edmonton, AB, Canada; 4Surgery, University of Alberta, Edmonton, AB, Canada; 5Canadian National Transplant Research Program, CNTRP, Edmonton, AB, Canada. Canadian National Transplant Research Program, CNTRP.

Introduction: Regulatory T cell (Tregs)-based therapy is a promising approach to treat allograft rejection. We have previously found that thymuses, routinely removed during pediatric cardiac surgery, are a potential source of therapeutic Tregs. To be effective, Tregs must express homing receptors for migration to inflammatory sites. For example, expression of the chemokine receptor CXCR3 on Tregs is essential to guide Tregs to locations of Th1-inflammation. We hypothesized that migration of thymic Tregs to Th1-inflammation could be fine-tuned by including cytokines in the expansion protocol.

Methods: CD4 + CD25+ Tregs were isolated from pediatric thymuses by magnetic bead-separation. Tregs were expanded with artificial antigen-presenting cells, rapamycin and IL-2. The cells were re-stimulated after 7 days without rapamycin. For Th1-polarizing conditions, IL-12 and IFN-gamma were added to cultures either during the first, second or both rounds of stimulation.

Results: Thymic Tregs cultured under Th1-polarizing conditions significantly increased CXCR3 and T-bet expression and showed >2-fold higher expansion capacity compared to Tregs cultured in neutral conditions. Expression of CXCR3 persisted even after removal of the polarizing cytokines. Importantly, Tregs cultured with Th1-inducing cytokines maintained a stable phenotype, including high FOXP3 expression and low TSDR methylation. Levels of other Treg-associated markers remained unchanged between neutrally and Th1-cultured Tregs at RNA- and protein-level. Th1-polarized Tregs did not acquire the ability to produce Th1-cell associated cytokines such as IL-2 or IFN-gamma and potently suppressed proliferation of total conventional T cells and Th1-effector T cells in vitro. In contrast to neutral cultures, expansion under Th1-conditions enabled thymic Tregs to migrate towards the CXCR3-specific chemokine CXCL10 in vitro.

Conclusions: Expansion conditions of thymic Tregs can be manipulated to specifically and stably tailor the cells’ homing capacity. The ability to direct Tregs towards specific tissues or sites of inflammation may enable optimal targeting as a therapeutic in vivo. This means that Tregs could act in a more specific manner which would reduce pan-immunosuppression often associated with polyclonal Treg administration in animal models and early clinical trials.

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