CD4+CD25+ regulatory T cell therapy for the induction of donor-specific clinical transplantation tolerance

Current status of immunomodulatory and cellular therapies in preclinical and clinical islet transplantation

Clinical islet transplantation is a β-cell replacement strategy that represents a possible definitive intervention for patients with type 1 diabetes, offering substantial benefits in terms of lowering daily insulin requirements and reducing incidences of debilitating hypoglycemic episodes and unawareness. Despite impressive advances in this field, a limiting supply of islets, inadequate means for preventing islet rejection, and the deleterious diabetogenic and nephrotoxic side effects associated with chronic immunosuppressive therapy preclude its wide-spread applicability. Islet transplantation however allows a window of opportunity for attempting various therapeutic manipulations of islets prior to transplantation aimed at achieving superior transplant outcomes. In this paper, we will focus on the current status of various immunosuppressive and cellular therapies that promote graft function and survival in preclinical and clinical islet transplantation with special emphasis on the tolerance-inducing capacity of regulatory T cells as well as the β-cells regenerative capacity of stem cells.

CNI induced Th17/Treg imbalance and susceptibility to renal dysfunction in renal transplantation

Calcineurin inhibitors (CNI) prevent graft rejection by blocking interleukin-2 (IL-2), which was required for development and function of Foxp3(+)CD4(+)CD25(+) regulatory T cells (Treg). Recently, IL-2 was reported to play a part in the inhibition of Th17 cells. The renal transplantation recipient who used CNI regularly might have Th17/Treg imbalance with increased Th17 cells and decreased Treg cells, which would cause renal dysfunction even rejection. To assess the effect of CNI on Th17 cells and Treg cells, we included 123 renal transplantation recipients (101 in a stable stage and 22 with renal dysfunction) and 27 healthy volunteers. Among all the recipients, 103 recipients used CNI and 20 recipients used sirolimus without CNI. The recipients who used CNI were further classified into four groups according to the blood levels of CNI: Of all these subjects, Th17 and Treg frequencies in the peripheral blood were analyzed by flow cytometry (FCM). Serums IL-17, IL-23, IL-6, IFN-r, and TGF-β were analyzed by ELISA. The results demonstrated that the transplantation recipient treated by CNI revealed an obvious increase in peripheral Th17 frequencies and a significant decrease in Treg frequencies when compared with the sirolimus group and healthy people (P<0.05). Even more, the transplantation recipient with renal dysfunction had the highest level of Th17 cells (P<0.05) while the lowest Treg cells compared with stable recipient and healthy control, with increased serums IL-6 and IL-17. Our results indicated that CNI was associated with Th17/Treg imbalance in peripheral blood, which supported the followed generation of renal dysfunction after transplantation.

Rapamycin, unlike cyclosporine A, enhances suppressive functions of in vitro-induced CD4+CD25+ Tregs

BACKGROUND

A growing body of data shows that CD4(+)CD25(+) regulatory T cells (Tregs) can induce transplantation tolerance by suppressing immune responses to allograft antigens. However, both the generation and the suppressive capacity of CD4(+)CD25(+) Tregs can be substantially affected by different immunosuppressive drugs used in clinical transplantation. The goal of this study was to compare the effects of cyclosporine A and rapamycin on the induction and suppressive functions of human CD4(+)CD25(+) Tregs in vitro.

METHODS

CD4(+)CD25(+) Tregs were induced in two-way mixed lymphocyte reaction (MLR) in the presence of rapamycin (Treg-Rapa) or cyclosporine A (Treg-CsA). Tregs were identified in MLR cultures by flow cytometry using anti-CD4, anti-CD25, anti-CTLA-4, anti-CD122, anti-GITR mAbs and ant-PE-FOXP3 staining sets. Suppressive capacity of induced Tregs was evaluated by their capability to inhibit anti-CD3 Ab-triggered proliferation of peripheral blood mononuclear cells (PBMCs), as measured by flow cytometry. The concentration of TGF-beta1 in culture supernatants was measured by enzyme-linked immunosorbent assay.

RESULTS

Although both rapamycin and cyclosporine A suppressed the induction of CD4(+)CD25(+) Tregs during MLRs, this effect was significantly more pronounced in cells cultured with cyclosporine. On the other hand, only rapamycin significantly decreased the percentage of CD4(+)CD25(+) Tregs which expressed GITR, a negative regulator of Treg's suppressive capacity. Importantly, Treg-Rapa, unlike Treg-CsA, displayed significant suppressive activity and were capable of inhibiting the proliferation of anti-CD3 Ab-activated PBMCs. This activity was likely mediated by TGF-beta1.

CONCLUSIONS

Rapamycin, unlike cyclosporine A, does not inhibit the function of CD4(+)CD25(+) Tregs. This implies that rapamycin could contribute to the development of transplantation tolerance by promoting the induction of functional CD4(+)CD25(+) Tregs. Moreover, our results suggest that rapamycin could be combined with functional Tregs.

CD4+ CD25+ FOXP3+ regulatory T cells increase de novo in kidney transplant patients after immunodepletion with Campath-1H

Campath-1H (Alemtuzumab) is an effective immunodepletion agent used in renal transplantation. To evaluate its influence on T lymphocytes during repletion, we analyzed peripheral blood from Campath-1H-treated renal allograft recipients for the presence of FOXP3(+) regulatory T (Treg) cells. Flow cytometry demonstrated that CD4(+)CD25(+)FOXP3(+) lymphocytes increased significantly within the CD4(+) T-cell population, skewing Treg/Teff (T effector) ratios for up to several years. In contrast, Treg levels in patients treated with anti-CD25 (Basiliximab) and maintained on CsA demonstrated a sustained decrease. The increase in Tregs in Campath-1H treated patients developed independent of maintenance immunosuppression. Importantly, the increase in Tregs was not fully explained by their homeostatic proliferation, increased thymic output, or Treg sparing, suggesting de novo generation/expansion. Consistent with this, in vitro stimulation of PBMCs with Campath-1H, with or without anti-CD3, activation led to an increase in CD4(+)CD25(+)FOXP3(+) cells that had suppressive capabilities. Together, these data suggest that Campath-1H promotes an increase in peripheral Tregs and may act as an intrinsic generator of Tregs in vivo.

Resveratrol (trans-3,5,4'-trihydroxystilbene) ameliorates experimental allergic encephalomyelitis, primarily via induction of apoptosis in T cells involving activation of aryl hydrocarbon receptor and estrogen receptor

Resveratrol (trans-3,5,4'-trihydroxystilbene), a polyphenolic compound found in plant products, including red grapes, exhibits anticancer, antioxidant, and anti-inflammatory properties. Using an animal model of multiple sclerosis (MS), we investigated the use of resveratrol for the treatment of autoimmune diseases. We observed that resveratrol treatment decreased the clinical symptoms and inflammatory responses in experimental allergic encephalomyelitis (EAE)-induced mice. Furthermore, we observed significant apoptosis in inflammatory cells in spinal cord of EAE-induced mice treated with resveratrol compared with the control mice. Resveratrol administration also led to significant down-regulation of certain cytokines and chemokines in EAE-induced mice including tumor necrosis factor-alpha, interferon-gamma, interleukin (IL)-2, IL-9, IL-12, IL-17, macrophage inflammatory protein-1alpha (MIP-1alpha), monocyte chemoattractant protein-1 (MCP-1), regulated on activation normal T-cell expressed and secreted (RANTES), and Eotaxin. In vitro studies on the mechanism of action revealed that resveratrol triggered high levels of apoptosis in activated T cells and to a lesser extent in unactivated T cells. Moreover, resveratrol-induced apoptosis was mediated through activation of aryl hydrocarbon receptor (AhR) and estrogen receptor (ER) and correlated with up-regulation of AhR, Fas, and FasL expression. In addition, resveratrol-induced apoptosis in primary T cells correlated with cleavage of caspase-8, caspase-9, caspase-3, poly(ADP-ribose) polymerase, and release of cytochrome c. Data from the present study demonstrate, for the first time, the ability of resveratrol to trigger apoptosis in activated T cells and its potential use in the treatment of inflammatory and autoimmune diseases including, MS.

Spontaneous allograft tolerance in B7-deficient mice independent of preexisting endogenous CD4+CD25+ regulatory T-cells

BACKGROUND

Acute cardiac allograft rejection requires host, but not donor, expression of B7-1/B7-2 costimulatory molecules. However, acute cardiac rejection requires direct antigen presentation by donor-derived antigen presenting cells to CD4 T-cells and does not require indirect antigen presentation to CD4 T-cells. Given this discrepancy in the literature and that the consequence of allograft exposure in B7-deficient mice is unknown; the goal of the study was to examine the antidonor status of allografted B7-1/B7-2-deficient hosts.

METHODS

C57Bl/6 B7-1/B7-2-/- mice were grafted with heterotopic BALB/c hearts. Recipients bearing long-term surviving allografts were used to examine the status of antidonor reactivity in vitro and in vivo. Tolerance was examined in vivo through adoptive transfer of splenocytes from graft-bearing animals to secondary immune-deficient Rag-1-/- hosts bearing donor-type or third-party cardiac allografts and by regulatory T-cell depletion with anti-CD25 antibody.

RESULTS

When transferred to B7-replete Rag-1-/- recipients, cells from naïve B7-1/B7-2-/- mice readily initiated cardiac allograft rejection. However, splenocytes transferred from long-term allograft acceptor B7-1/B7-2-/- hosts failed to reject donor-type hearts but acutely rejected third-party allografts. In addition, such cells did not reject (donorxthird-party) F1 allografts. Finally, in vivo depletion of regulatory T-cells did not prevent long-term acceptance.

CONCLUSIONS

Results demonstrate that B7-deficient T-cells are capable of acute cardiac allograft rejection in a B7-replete environment. Importantly, results also show that B7-deficient hosts do not simply ignore cardiac allografts, but rather spontaneously develop transferable, donor-specific tolerance and linked suppression in vivo. Interestingly, this tolerant state does not require endogenous CD4+CD25+ regulatory T-cells.