A Critical Role for TGF-ß/Fc and Nonlytic IL-2/Fc Fusion Proteins in Promoting Chimerism and Donor-Specific Tolerance.

BACKGROUND: Immunoglobulin-cytokine fusion molecules have been shown to be the new generation of immunomodulating agents in transplantation tolerance induction. In the present study, we tested whether immunoregulatory cytokine fusion proteins of IL-10/Fc, TGF-ß/Fc, or IL-2/Fc would enhance allogeneic bone marrow cell (BMC) engraftment and promote tolerance induction. METHODS: B6 (H2) mice were conditioned with anti-CD154 (MR1) and rapamycin (Rapa) plus 100 cGy total body irradiation (MR1/Rapa/100 cGy) and transplanted with allogeneic B10.D2 (H2) BMC. Recipients were treated with lytic IL-2/Fc, nonlytic IL-2/Fc, TGF-ß/Fc, or IL-10/Fc fusion proteins to promote chimerism to induce tolerance. RESULTS: Donor chimerism was achieved in 20% of recipients conditioned with MR1/Rapa/100 cGy. The addition of TGF-ß/Fc (5- or 10-day treatment) or nonlytic IL-2/Fc (10-day treatment) fusion proteins to the conditioning resulted in engraftment in nearly 100% of recipients. In contrast, lytic IL-2/Fc or IL-10/Fc had no effect. The combination of nonlytic IL-2/Fc and TGF-ß/Fc had a synergistic effect to promote engraftment and resulted in significantly higher donor chimerism compared with recipients conditioned with TGF-ß/MR1/Rapa/100 cGy. Engraftment was durable in the majority of chimeras and increased over time. The chimeras accepted donor skin grafts and promptly rejected third-party skin grafts. Moreover, specific T cell receptor-Vß5.½ and TCR-Vß11 clonal deletion was detected in host T cells in chimeras, suggesting central tolerance to donor alloantigens. CONCLUSIONS: Allogeneic BMC engraftment is enhanced with TGF-ß/Fc fusion protein treatment. TGF-ß/Fc and nonlytic IL-2/Fc exert a synergistic effect in promotion of alloengraftment and donor-specific transplant tolerance, significantly decreasing the minimum total body irradiation dose required.

Spontaneous resolution of acute rejection and tolerance induction with IL-2 fusion protein in vascularized composite allotransplantation.

Vascularized composite allotransplantation (VCA) has emerged as a treatment option for treating nonlife-threatening conditions. Therefore, in order to make VCA a safe reconstruction option, there is a need to minimize immunosuppression, develop tolerance-inducing strategies and elucidate the mechanisms of VCA rejection and tolerance. In this study we explored the effects of hIL-2/Fc (a long-lasting human IL-2 fusion protein), in combination with antilymphocyte serum (ALS) and short-term cyclosporine A (CsA), on graft survival, regulatory T cell (Treg) proliferation and tolerance induction in a rat hind-limb transplant model. We demonstrate that hIL-2/Fc therapy tips the immune balance, increasing Treg proliferation and suppressing effector T cells, and permits VCA tolerance as demonstrated by long-term allograft survival and donor-antigen acceptance. Moreover, we observe two distinct types of acute rejection (AR), progressive and reversible, within hIL-2/Fc plus ALS and CsA treated recipients. Our study shows differential gene expression profiles of FoxP3 versus GzmB, Prf1 or interferon-γ in these two types of AR, with reversible rejection demonstrating higher Treg to Teff gene expression. This correlation of gene expression profile at the first clinical sign of AR with VCA outcomes can provide the basis for further inquiry into the mechanistic aspects of VCA rejection and future drug targets.

Transplant tolerance: new insights and strategies for long-term allograft acceptance.

One of the greatest advances in medicine during the past century is the introduction of organ transplantation. This therapeutic strategy designed to treat organ failure and organ dysfunction allows to prolong the survival of many patients that are faced with no other treatment option. Today, organ transplantation between genetically dissimilar individuals (allogeneic grafting) is a procedure widely used as a therapeutic alternative in cases of organ failure, hematological disease treatment, and some malignancies. Despite the potential of organ transplantation, the administration of immunosuppressive drugs required for allograft acceptance induces severe immunosuppression in transplanted patients, which leads to serious side effects such as infection with opportunistic pathogens and the occurrence of neoplasias, in addition to the known intrinsic toxicity of these drugs. To solve this setback in allotransplantation, researchers have focused on manipulating the immune response in order to create a state of tolerance rather than unspecific immunosuppression. Here, we describe the different treatments and some of the novel immunotherapeutic strategies undertaken to induce transplantation tolerance.