Regulatory CD4+ T cells (Treg) have the ability to migrate to allografts to exert their suppressor function and prevent rejection. However, the mechanisms of suppression utilized by Treg within allografts are unknown and may differ from those used in secondary lymphoid organs (SLO) due to acute inflammation. Thus, we investigated the mechanisms of Treg suppressor function within allografts specifically.
Methods: We adoptively transferred 2-3 x 106 effector T cells (Teff), 2-3 x 106 antigen-experienced Treg, or both to B6 mice lacking SLO (SLO-; splenectomized aly/aly or LTΒR-/-) 3-4 days after allogeneic (BALB/c) islet transplantation. Treg were sorted from congenic (B6 Thy1.1) Foxp3-reporter mice at least 30 days after donor-specific transfusion (DST) + anti-CD154 mAb treatment. Teff were harvested from wt congenic (B6 CD45.1) animals 57 days after i.p. immunization with donor splenocytes.
Results: Untreated SLO- mice, or SLO- mice receiving Treg alone failed to reject islet allografts (>100d MST; n=9 and 4 respectively). The adoptive transfer of Teff alone induced acute rejection (3d MST; n=7). However, the co-transfer of Teff + Treg led to long-term allograft survival in the majority (67%) of mice (>100d MST; n=9). Analysis of adoptively transferred CFSE-labeled Teff recovered from the graft on day 3 and 5 revealed that Treg did not affect either Teff migration or proliferation in the graft – despite the presence of Treg in significant numbers at that site, compared to the transfer of Teff alone. In order to clarify the mechanisms involved, we performed multi-photon intravital microscopy of transplanted islets under the kidney capsule of SLO- mice adoptively transferred with Teff from B6-CFP mice, with or without Cell-Tracker-Orange-stained Treg on day 2. Although the presence of Treg did not affect Teff infiltration and velocity parameters in the peri-islet area compared to the transfer of Teff alone, Treg significantly reduced intra-islet Teff infiltration.
Conclusions: Treg can suppress rejection by Teff in the allograft itself without prior activation in SLO. In addition, Treg exert intragraft suppressive activity through the inhibition of Teff function and/or Teff intra-islet migration. These results provide new insights into Treg biology and mechanisms of tolerance in transplantation.
To cite this abstract in AMA style:Camirand G. Mechanisms of Intra-Graft Regulatory T Cell Suppressor Function [abstract]. Am J Transplant. 2013; 13 (suppl 5). https://atcmeetingabstracts.com/abstract/mechanisms-of-intra-graft-regulatory-t-cell-suppressor-function/. Accessed October 23, 2020.
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