Allosuppressive Donor CD4+CD25+ Regulatory T Cells Detach from the Graft and Circulate in Recipients after Liver Transplantation

Abstract

Organ transplantation (Tx) results in a transfer of donor leukocytes from the graft to the recipient, which can lead to chimerism and may promote tolerance. It remains unclear whether this tolerance involves donor-derived regulatory T cells (Tregs). In this study, we examined the presence and allosuppressive activity of CD4+CD25+Foxp3+ Tregs in perfusates of human liver grafts and monitored the cells presence in the circulation of recipients after liver Tx. Vascular perfusions of 22 liver grafts were performed with University of Wisconsin preservation and albumin solutions. Flow cytometric analysis revealed that perfusate T cells had high LFA-1 integrin expression and had a reversed CD4 to CD8 ratio compared with control blood of healthy individuals. These findings indicate that perfusate cells are of liver origin and not derived from residual donor blood. Further characterization of perfusate mononuclear cells showed an increased proportion of CD4+CD25+CTLA4+ T cells compared with healthy control blood. Increased percentages of Foxp3+ cells, which were negative for CD127, confirmed the enrichment of Tregs in perfusates. In MLR, CD4+CD25+ T cells from perfusates suppressed proliferation and IFN-γ production of donor and recipient T cells. In vivo within the first weeks after Tx, up to 5% of CD4+CD25+CTLA4+ T cells in recipient blood were derived from the donor liver. In conclusion, a substantial number of donor Tregs detach from the liver graft during perfusion and continue to migrate into the recipient after Tx. These donor Tregs suppress the direct pathway alloresponses and may in vivo contribute to chimerism-associated tolerance early after liver Tx.

Apoptosis of CD4+CD25high T cells in response to Sirolimus requires activation of T cell receptor and is modulated by IL-2

“…We separated peripheral blood mononuclear cells (PBMCs) from healthy donors and isolated CD4 + CD25 high T cells as described previously using the Miltenyi MACS system [5,6,8,9,11,16-18, 26,27]. Cells were analyzed by flow cytometry and found to be ≥ 90% CD4 + CD25 high (Figure 1a).…”

The Liver as a Lymphoid Organ

“…The impact of liver transplantation on these cells is controversial. A perfusate of human liver was enriched in CD4 + 25 + FoxP3 + CD127 low cells, and such donor-derived Tregs were found in the circulation of liver transplant recipients, an aspect of the phenomenon of microchimerism (95). Investigators agree that, after liver transplantation in humans, the overall frequency of Tregs in the circulation falls (96,97).…”

Immunosuppression for liver transplantation

“…This may be a key point since Tregs appear to be critical for the development of liver tolerance77 78 and CD25 is known to be expressed on Tregs. Considering this, the question remains whether IL2 receptor antibodies eliminate the same Tregs that we are hoping to expand during the early post-transplant period.…”