Specific alloantigen self-control by regulatory T cells in organ transplantation: a review

TGF-β affinity-bound to a macroporous alginate scaffold generates local and peripheral immunotolerant responses and improves allocell transplantation

Enhancing vascularization of cell-transplantation devices is necessary for maintaining cell viability and integration within the host, but it also increases the risk of allograft rejection. Here, we investigated the feasibility of generating an immunoregulatory environment in a highly vascularized macroporous alginate scaffold by affinity-binding of the transforming growth factor-β (TGF-β) in a manner mimicking its binding to heparan sulfate. Using this device to transplant allofibroblasts under the kidney capsule resulted in the induction of local and peripheral TGF-β-dependent immunotolerance, characterized by higher frequency of immature dendritic cells and regulatory T cells within the device and by markedly reduced allofibroblast-specific T-cell response in the spleen, thereby increasing the viability of the transplanted cells. Culturing whole splenocytes in the TGF-β-bound scaffold indicated that the regulatory function of TGF-β is IL-10-dependent. We thus demonstrate a novel platform for transplantation devices, designed to promote an immunoregulatory microenvironment suitable for cell transplantation and autoimmune regulation.

STATEMENT OF SIGNIFICANCE

Allogeneic cell graft transplantation is a potentially optimal treatment for many clinical deficiencies. It is yet challenging to overcome chronic rejection without compromising host immunity to pathogens. We present the features and function of a cell transplantation device designed based on the principle of affinity binding of angiogenic and immunoregulatory factors to extracellular matrix in aim to achieve sustained release of these factors. We show that presentation of these factors in such manner generates the infrastructure for device vascularization and induces profound local allocell-specific tolerance, which then evokes peripheral T-cell tolerance. The tolerance is antigen specific, does not cause immune deficits and may thus serve to improve allocell survival as well as a platform to mitigate pathogenic autoimmunity.

Fragile maintenance of allograft tolerance induced by lymphocyte sequestration and co-stimulation blockade

The induction of long-term graft survival has been a goal for the last decade. Nevertheless, the issues of stable maintenance of allograft have not yet been evaluated thoroughly. Here, we studied new approaches for induction of tolerance by lymphocyte sequestration (FTY720) and co-stimulatory blockade (MR1) in skin graft model (DBA/2 to BALB/c), thus evaluating the mechanisms incorporated into the maintenance of allograft in proper function. FTY720+MR1 treatment significantly prolonged graft survival than single agent treatment did, and induced long-term graft survival in 60% of recipients expressing the up-regulation of IL-4 and FoxP3. To assess the stability of graft maintenance, we performed the second transplantation on recipients that had shown long-term graft survival. While recipients accepted the second graft from the same strain of first donor, the recipients not only rejected the third-party skin (C57BL/6) promptly but also rejected the first graft soon after the third-party skin was transplanted. The expression patterns of IL-4 and FoxP3 were changed according to the strains of second graft in lymph nodes and in the first graft. T(reg) cells from tolerant recipients effectively suppressed allo-antigen driven T cell proliferation, but T(reg) cells from recipients primed with third-party antigen had significantly hampered suppressive capacity against previously tolerant antigens. Our data indicate that the combination treatment provides effective tool for the induction of long-term graft survival, and the maintenance of allograft in proper function is an actively regulated process.

Clinical significance of monitoring circulating CD4+CD25+ regulatory T cells in kidney transplantation during the early posttransplant period

The CD4(+)CD25(+) T regulatory cells (Tregs) play an important role in immune tolerance in experimental transplantation but the clinical significance of circulating Tregs in the peripheral blood is undetermined. In 50 kidney transplant (KT) recipients, 29 healthy controls and 32 liver transplant (LT) recipients, the frequency of Tregs was measured with flow cytometry before and after transplantation. In the KT recipients, IL-10 secretion was measured with an enzyme-linked immunospot (ELISPOT) assay. The median frequency of circulating Tregs before KT was similar to that in healthy controls but significantly lower than that in LT patients before transplantation. The frequency of Tregs was significantly decreased in patients with subclinical acute rejection compared with those without subclinical acute rejection. Calcineurin inhibitors (CNIs) and anti-CD25 antibody decreased the frequency of Tregs but mTOR inhibitor did not. The frequency of donor-specific IL-10 secreting cells did not correlate with the number of Tregs. The frequency of circulating Tregs in KT recipients is strongly affected by CNIs and anti-CD25 antibody, and a low frequency of Tregs is associated with subclinical acute rejection during the early posttransplant period.

Stored red blood cell transfusion induces regulatory T cells

BACKGROUND

Allogeneic blood transfusion mediates immunosuppression in transfused recipients by an unknown mechanism. Regulatory T cells (T(regs)) are suppressive CD4(+)CD25(+)Foxp3(+) cells with a central role in immunosuppression in trauma victims, cancer patients, and transplant recipients. We hypothesized that transfusion-related immunosuppression is, in part, mediated by induction of T(regs), and this induction is attenuated with prestorage leukoreduction and accentuated with prolonged storage.

STUDY DESIGN

Packed red blood cell (PRBC) units were obtained and 50% of PRBCs were leukoreduced (LR) before routine storage for 1 day or 42 days and the supernatant was collected. Normal human peripheral blood mononuclear cells (PBMCs) were exposed to 1-day NLR, 42-day NLR, 1-day LR, or 42-day LR PRBC supernatants or to PRBC storage solution or washed PRBC supernatant +/- anti-CD3 stimulation, and analyzed by flow cytometry for Foxp3(+) T(regs) or CD25(+)-activated T cells. PRBC supernatants and cell culture supernatants were analyzed by immunoassay for interleukin (IL)-1beta, IL-2, IL-4, IL-10, interferon-gamma, tumor necrosis factor-alpha, and transforming growth factor-beta. T(reg) activity was evaluated by suppression assay.

RESULTS

All PRBC groups induced T(regs) compared with control media in anti-CD3-stimulated PBMCs, without alteration by LR or prolonged storage. PRBC supernatant did not alter nonspecific T-cell activation from control media. PRBC-induced T(regs) were suppressive, inhibiting proliferation of T-responder cells. All cytokines measured decreased with storage in LR PRBC units and no cytokines were substantially elevated in cell supernatants exposed to PRBC supernatant. PRBC storage solution did not reproduce the effects of PRBC supernatant, and washed PRBC supernatant attenuated T(reg) induction.

CONCLUSIONS

PRBC supernatant induces T(regs), but this induction is not altered by LR or prolonged storage. This induction appears to be independent of cytokines and is attenuated with washed PRBCs, implicating the plasma fraction.