Induction of immunological tolerance using monoclonal antibodies: Applications to organ transplantation and autoimmune disease

Combination of monoclonal antibodies and DPP-IV inhibitors in the treatment of type 1 diabetes: a plausible treatment modality?

Regulatory T cells (Tregs) are crucial for the maintenance of immunological tolerance. Type 1 diabetes (T1D) occurs when the immune-regulatory mechanism fails. In fact, T1D is reversed by islet transplantation but is associated with hostile effects of persistent immune suppression. T1D is believed to be dependent on the activation of type-1 helper T (Th1) cells. Immune tolerance is liable for the activation of the Th1 cells. The important role of Th1 cells in pathology of T1D entails the depletion of CD4(+) T cells, which initiated the use of monoclonal antibodies (mAbs) against CD4(+) T cells to interfere with induction of T1D. Prevention of autoimmunity is not only a step forward for the treatment of T1D, but could also restore the β-cell mass. Glucagon-like peptide (GLP)-1 stimulates β-cell proliferation and also has anti-apoptotic effects on them. However, the potential use of GLP-1 as a possible method to restore pancreatic β-cells is limited due to rapid degradation by dipeptidyl peptidase (DPP)-IV. We hypothesize that treatment with combination of CD4 mAbs and DPP-IV inhibitors could prevent/reverse T1D. CD4 mAbs have the ability to induce immune tolerance, thereby arresting further progression of T1D; DPP-IV inhibitors have the capability to regenerate the β-cell mass. Consequently, the combination of CD4 mAbs and DPP-IV inhibitor could avoid or at least minimize the constraints of intensive subcutaneous insulin therapy. We presume that if this hypothesis proves correct, it may become one of the plausible therapeutic options for T1D.

NK cells in immunotolerant organs

Organs such as the liver, uterus and lung possess hallmark immunotolerant features, making these organs important for sustaining self-homeostasis. These organs contain a relatively large amount of negative regulatory immune cells, which are believed to take part in the regulation of immune responses. Because natural killer cells constitute a large proportion of all lymphocytes in these organs, increasing attention has been given to the roles that these cells play in maintaining immunotolerance. Here, we review the distribution, differentiation, phenotypic features and functional features of natural killer cells in these immunotolerant organs, in addition to the influence of local microenvironments on these cells and how these factors contribute to organ-specific diseases.

Permanent CNI treatment for prevention of renal allograft rejection in sensitized hosts can be replaced by regulatory T cells

Recent data suggest that donor-specific memory T cells (T(mem)) are an independent risk factor for rejection and poor graft function in patients and a major challenge for immunosuppression minimizing strategies. Many tolerance induction protocols successfully proven in small animal models e.g. costimulatory blockade, T cell depletion failed in patients. Consequently, there is a need for more predictive transplant models to evaluate novel promising strategies, such as adoptive transfer of regulatory T cells (Treg). We established a clinically more relevant, life-supporting rat kidney transplant model using a high responder (DA to LEW) recipients that received donor-specific CD4(+)/ 8(+) GFP(+) T(mem) before transplantation to achieve similar pre-transplant frequencies of donor-specific T(mem) as seen in many patients. T cell depletion alone induced long-term graft survival in naïve recipients but could not prevent acute rejection in T(mem)(+) rats, like in patients. Only if T cell depletion was combined with permanent CNI-treatment, the intragraft inflammation, and acute/chronic allograft rejection could be controlled long-term. Remarkably, combining 10 days CNI treatment and adoptive transfer of Tregs (day 3) but not Treg alone also induced long-term graft survival and an intragraft tolerance profile (e.g. high TOAG-1) in T(mem)(+) rats. Our model allows evaluation of novel therapies under clinically relevant conditions.

Preferential increase in memory and regulatory subsets during T-lymphocyte immune reconstitution after Thymoglobulin induction therapy with maintenance sirolimus vs cyclosporine

BACKGROUND

Sirolimus maintenance therapy with Thymoglobulin induction is a promising regimen that may preserve renal function. Data are lacking, however, about the immunologic effects of combined Thymoglobulin-sirolimus.

METHODS

In a 12-month, prospective, randomised, open-label, single-centre pilot study, de novo deceased-donor kidney transplant patients were randomised to receive cyclosporine or sirolimus, with Thymoglobulin induction, mycophenolate mofetil and corticosteroids. Flow cytometry analysis of peripheral blood was used to evaluate immune reconstitution.

RESULTS

Nineteen patients were recruited (sirolimus 9, cyclosporine 10). Reconstitution of the CD4(+) T-lymphocyte subset was significantly lower with sirolimus versus cyclosporine over year 1, but CD8(+) reconstitution did not differ significantly between groups. The proportion of naïve CD4(+) T-lymphocytes showed an initial decrease with sirolimus versus cyclosporine. Naïve CD8(+) T-lymphocytes increased versus baseline in the cyclosporine cohort at months 1 and 3, but remained unchanged with sirolimus. Memory CD4(+) T-lymphocytes occurred more frequently in sirolimus- versus cyclosporine-treated patients during year 1. The proportion of memory CD8(+) T-lymphocytes decreased at months 1 and 3 compared to baseline in the CsA arm, but did not change in the sirolimus cohort. By month 12, the proportion of both naïve and memory CD4(+) and CD8(+) T-lymphocytes had become similar with sirolimus or cyclosporine. There were fewer naïve B-lymphocytes in the sirolimus cohort and more CD19(-)IgD(+/-)CD27(+) memory B-lymphocytes.

CONCLUSIONS

In this small population, homeostatic reconstitution after Thymoglobulin induction showed disproportionately high recovery of memory T-lymphocyte subsets during sirolimus therapy, which may explain the higher rejection rate seen with sirolimus versus cyclosporine following kidney transplantation.

Regulation of activated CD4+ T cells by NK cells via the Qa-1-NKG2A inhibitory pathway

The ability of natural-killer cells to regulate adaptive immunity is not well understood. Here we define an interaction between the class Ib major histocompatibility complex (MHC) molecule Qa-1-Qdm on activated T cells responsible for adaptive immunity and CD94-NKG2A inhibitory receptors expressed by natural-killer cells by using Qa-1-deficient and Qa-1 knockin mice containing a point mutation that selectively abolishes Qa-1-Qdm binding to CD94-NKG2A receptors. The Qa-1-NKG2A interaction protected activated CD4+ T cells from lysis by a subset of NKG2A+ NK cells and was essential for T cell expansion and development of immunologic memory. Antibody-dependent blockade of this Qa-1-NKG2A interaction resulted in potent NK-dependent elimination of activated autoreactive T cells and amelioration of experimental autoimmune encephalomyelitis. These findings extend the functional reach of the NK system to include regulation of adaptive T cell responses and suggest a new clinical strategy for elimination of antigen-activated T cells in the context of autoimmune disease and transplantation.

Regulatory T cells and T cell depletion: role of immunosuppressive drugs

Allogeneic immune responses are modulated by a subset of host T cells with regulatory function (Treg) contained within the CD4(+)CD25(high) subset. Evidence exists that Treg expand after peritransplantation lymphopenia, inhibit graft rejection, and induce and maintain tolerance. Little, however, is known about the role of Treg in the clinical setting. IL-2 and activation by T cell receptor engagement are instrumental to generate and maintain Treg, but the influence of immunosuppressants on Treg homeostasis in humans in vivo has not been investigated. This study monitored Treg phenotype and function during immune reconstitution in renal transplant recipients who underwent profound T cell depletion with Campath-1H and received sirolimus or cyclosporine (CsA) as part of their maintenance immunosuppressive therapy. CD4(+)CD25(high) cells that expressed FOXP3 underwent homeostatic peripheral expansion during immune reconstitution, more intense in patients who received sirolimus than in those who were given CsA. T cells that were isolated from peripheral blood long term after transplantation were hyporesponsive to alloantigens in both groups. In sirolimus- but not CsA-treated patients, hyporesponsiveness was reversed by Treg depletion. T cells from CsA-treated patients were anergic. Thus, lymphopenia and calcineurin-dependent signaling seem to be primary mediators of CD4(+)CD25(high) Treg expansion in renal transplant patients. These findings will be instrumental in developing "tolerance permissive" immunosuppressive regimens in the clinical setting.