CTLA4 Signals Are Required to Optimally Induce Allograft Tolerance with Combined Donor-Specific Transfusion and Anti-CD154 Monoclonal Antibody Treatment

Abstract

Sensitization to donor Ags is an enormous problem in clinical transplantation. In an islet allograft model, presensitization of recipients through donor-specific transfusion (DST) 4 wk before transplantation results in accelerated rejection. We demonstrate that combined DST with anti-CD154 (CD40L) therapy not only prevents the deleterious presensitization produced by pretransplant DST in the islet allograft model, it also induces broad alloantigen-specific tolerance and permits subsequent engraftment of donor islet or cardiac grafts without further treatment. In addition, our data strongly indicate that CTLA4-negative T cell signals are required to achieve prolonged engraftment of skin allograft or tolerance to islet allograft in recipients treated with a combination of pretransplant DST and anti-CD154 mAb. We provide direct evidence that a CD28-independent CTLA4 signal delivers a strong negative signal to CD4+ T cells that can block alloimmune MLR responses. In this study immune deviation into a Th2 (IL-4) response was associated with, but did not insure, graft tolerance, as the inopportune timing of B7 blockade with CTLA4/Ig therapy prevented uniform tolerance but did not prevent Th2-type immune deviation. While CTLA4-negative signals are necessary for tolerance induction, Th1 to Th2 immune deviation cannot be sufficient for tolerance induction. Combined pretransplant DST with anti-CD154 mAb treatment may be attractive for clinical deployment, and strategies aimed to selectively block CD28 without interrupting CTLA4/B7 interaction might prove highly effective in the induction of tolerance.

Protein Phosphatase 2A Activation Promotes Heart Transplant Acceptance in Mice

“…CTLA4, a member of the CD28 family, competes with CD28 binding to the same ligands (B7.1 and B7.2; B7 hereinafter) and delivers an inhibitory signal to T-cell activation. 70 Inhibition of this pathway has been reported to attenuate acute cardiac rejection and prolonged graft survival, 32-35 but not induce stable tolerance, 71 as CAV still developed in this model. 36 Additionally, targeted therapies directed at CTLA4 are associated with significant morbidity and side effects.…”

“…Previous studies have demonstrated that treatment with CTLA4-Ig at the time of transplant significantly prolongs heart allograft survival when compared with untreated mice (MST: 60 versus 9 d for treated and untreated recipients, respectively; P < 0.001). 31 Although previous studies have shown that inhibition of CTLA pathway mitigated acute cardiac rejection and prolonged graft survival in murine models, 32-35 CAV still occurred in the recipient animals. 36 To determine whether DT-061 could provide additional benefit in the presence of CTLA4-Ig treatment, we first examined whether DT-061 had a synergistic effect with CTLA4-Ig on transplanted heart rejection tolerance (Figure 4A).…”

A humanized IL-2 mutein expands Tregs and prolongs transplant survival in preclinical models

“…Tregs from mIL-2–treated mice had increased production of IL-10 ( Figure 7H ) and LAP, a TGF-β–associated protein ( Figure 7I ). Since CTLA-4 + Tregs are essential for allogenic tolerance ( 48 , 49 ) and immune modulation ( 50 ), we investigated the role of CTLA-4 in the mIL-2–induced prolongation of transplant survival. We used a combination of 2 non-Treg-depleting anti–CTLA-4 monoclonal antibodies (clone UC10-4F10-11 ( 49 , 51 , 52 ) and 9H10 ( 53 )) in OVA skin graft recipient mice treated with mIL-2 or control ( Figure 7J ).…”

“…The suppressive function of Tregs involves myriad mechanisms, including the secretion of immunomodulatory cytokines (e.g., IL-10), downmodulation of DCs, and coinhibitory receptor signaling through CTLA-4 with induction of indoleamine 2, 3-dioxygenase (IDO) ( 13 ). In transplantation, the expression of coinhibitory receptors and cytokines such as IL-10 has been demonstrated to be essential for Tregs’ ability to abrogate alloimmune responses ( 48 , 51 , 83 – 85 ). Equally important to increasing the number of Tregs was ensuring that their function was preserved or enhanced upon mIL-2.…”

Alloantigen Infusion Activates the Transcriptome of Type 2 Conventional Dendritic Cells

“…Alternative protocols use the infusion of “live” donor cells in combination with costimulation blockade, namely anti-CD40L, at the time of transplantation. This protocol has been repeatedly shown to produce a long-term and robust form of tolerance to murine islet ( 7 , 8 ), skin ( 9 ), and cardiac allografts ( 7 , 10 , 11 ), as well as nonhuman primate models of skin ( 12 ) and kidney ( 13 ) transplantation. Yet, the molecular response to the aforementioned donor cell alloinfusion remains poorly understood in contexts of both tolerance induction and basic cellular physiology of immune cells.…”