Inducing CTLA-4–Dependent Immune Regulation by Selective CD28 Blockade Promotes Regulatory T Cells in Organ Transplantation

Abstract

Transplantation is the treatment of choice for patients with end-stage organ failure. Its success is limited by side effects of immunosuppressive drugs, such as inhibitors of the calcineurin pathway that prevent rejection by reducing synthesis of interleukin-2 by T cells. Moreover, none of the existing drugs efficiently prevent the late development of chronic rejection. Blocking the CD28-mediated T cell costimulation pathway is a non toxic alternative immunosuppression strategy that is currently achieved by blockade of CD80/86, the counter receptors for CD28 on antigenpresenting cells.. However interaction of CD80/86 with CTLA-4 is required for immune regulation. Therefore CD28 blockade, instead of CD80/86 blockade, might preserve regulatory signals mediated by CTLA-4 and favor immune regulation. By using monovalent antibodies, we identified true CD28 antagonists inducing a CTLA-4-dependent decreased T cell function compatible with regulatory T cell (Treg) suppression. In transplantation experiments in primates, blocking CD28 augmented intragraft and peripheral blood regulatory T cells, induced molecular signatures of immune regulation and prevented graft rejection and vasculopathy in synergy with calcineurin inhibition. These findings suggest that targeting costimulation blockade at CD28 favors CTLA-4-dependent immune regulation and promotes allograft survival.

A Monovalent Anti-Human CD28 Domain Antibody Antagonist: Preclinical Efficacy and Safety

“…Consistent with this hypothesis is a recent report by Poirier et al (20) demonstrating that a monovalent anti-human CD28 antagonist (CD28-specific single-chain Fv Ab fragment linked to a1-antitrypsin, sc28AT) synergizes with the in vitro suppressive activity of Tregs, whereas anti-CTLA-4 Ab blocks the suppression. Furthermore, treatment of nonhuman primates with sc28AT plus tacrolimus, during and following kidney or heart allograft transplantation, results in the prevention of acute rejection, attenuation of chronic rejection, and the infiltration of functional Tregs into the grafts.…”

Selective CD28 Antagonist Blunts Memory Immune Responses and Promotes Long-Term Control of Skin Inflammation in Nonhuman Primates

“…response to tuberculin; 3) peripheral regulatory T cell induction or accumulation was excluded in blood because we did not observe significant modulation of regulatory T cell numbers or frequencies, and elimination of these cells did not modify the ex vivo IFN-g response to tuberculin after treatment with FR104 as compared with control; and 4) we and others have previously reported that selective CD28 blockade induced regulatory T cell infiltrates at the site of inflammation (15,17,18,23). In this study, we did not observe important T cell infiltrates in skin biopsies after selective CD28 blockade, suggesting that if regulatory T cells directly control effector T cell activation, they would preferably be located in draining lymph nodes.…”

“…We assessed the efficiency of selective CD28 blockade in a nonhuman primate skin inflammatory model on the control of cellular and humoral memory responses and the effect on latent viral infections. It had been shown previously that CD28 blockade induces immune regulation and prevents allograft rejection or autoimmune attacks in rodents (14) and nonhuman primate (15,23,24) models. However, in these models, animals were immunologically naive toward immunizing Ags.…”

“…Sections were saturated with PBS containing 10% baboon serum, 2% normal goat and donkey serum, and 4% BSA. Sections were incubated overnight with primary Abs at 4˚C, followed by fluorescent secondary Abs as previously described (15,22). T cell infiltration analysis was performed with rabbit anti-human CD3 (Dako) and macrophages infiltration with mouse anti-human CD68 (clone KP1; Dako).…”

“…Selective CD28 blockade was described to induce immune tolerance and regulatory cells in transplant experimental models (14)(15)(16)(17)(18). We previously described that selective monovalent CD28 versus CD80/86 antagonists differentially control human effector and regulatory memory T cell activation in vitro at the immune synapse level (19).…”