J.D. Mezrich

The Indirect Alloresponse Impairs the Induction but not Maintenance of Tolerance to MHC Class I-Disparate Allografts

We studied the effects of indirect allorecognition on the induction and maintenance phases of tolerance in miniature swine cotransplanted with heart and kidney allografts. MHC class I‐mismatched heart and kidney grafts were cotransplanted in recipients receiving CyA for 12 days. Recipients were unimmunized or immunized with a set of donor‐derived or control third‐party MHC class I peptides either 21 days prior to transplantation or over 100 days after transplantation. T‐cell proliferation, delayed type hypersensitivity reaction (DTH) and antibody production were assessed. All animals injected with donor MHC class I peptides developed potent indirect alloresponses specific to the immunizing peptides. While untreated recipients developed stable tolerance, all animals preimmunized with donor allopeptides rejected kidney–heart transplants acutely. In contrast, when peptide immunization was delayed until over 100 days after kidney–heart transplantation, no effects were observed on graft function or in vitro measures of alloimmunity. Donor peptide immunization prevented tolerance when administered to recipients pre transplantation but did not abrogate tolerance when administered to long‐term survivors post transplantation. This suggests that the presence of T cells activated via indirect allorecognition represent a barrier to the induction but not the maintenance of tolerance.

The effects of mycophenolate mofetil on cardiac allograft survival and cardiac allograft vasculopathy in miniature swine

Background. Chronic rejection, as manifested by cardiac allograft vasculopathy, remains the leading cause of late graft failure in heart transplant recipients. Despite recent clinical trials, the efficacy of mycophenolate mofetil in preventing human cardiac allograft vasculopathy remains controversial. We investigated whether mycophenolate mofetil would prevent cardiac allograft vasculopathy and prolong cardiac allograft survival in our well-established miniature swine model of heart transplantation. Methods. Hearts disparate at the major histocompatibility complex class I locus were heterotopically transplanted into miniature swine recipients treated with a 12-day course of mycophenolate mofetil (n 3) or cyclosporine A (n 3). Allograft survival, acute rejection, and chronic rejection were monitored in the two groups. Results. Hearts transplanted with 12 days of cyclosporine were rejected between 46 and 61 days, whereas two of the three hearts transplanted with mycophenolate mofetil remained beating beyond 120 days (p 0.02). At necropsy, there was a 4.9% mean prevalence of cardiac allograft vasculopathy in the mycophenolate mofetil group as compared with 16.6% in the cyclosporine group (p 0.03). Cardiac allograft rejection and vasculopathy in the cyclosporine-treated group was associated with prominent myocardial interferon- gene expression, a finding absent in two thirds of the mycophenolate mofetil-treated swine. Moreover, the mycophenolate mofetil-treated swine failed to develop IgM or IgG alloantibodies. Conclusions. A short course of mycophenolate mofetil resulted in a longer allograft survival than a similar course of cyclosporine. Moreover, mycophenolate mofetil reduced the prevalence of cardiac allograft vasculopathy as compared with cyclosporine-treated controls. The salutary effect of mycophenolate mofetil may be related to its ability to decrease interferon- expression in the myocardium and prevent the generation of alloantibodies. (Ann Thorac Surg 2005;80:1787‐93)

Recipients of MHC class I disparate lung grafts develop T cell reactivity to donor MHC class I allopeptides in an orthotopic swine model

logical reactivity to donor antigens, followed by vascularized heterotopic heart transplantation to determine if CAV still develops in the tolerant recipient. Procedures: In mice, specific immunological nonreactivity was achieved in recipients by (1) neonatal administration of allogeneic spleen cells from F1 donors between class I mismatched donor and recipient strains, (2) acheivement of mixed chimerism by bone marrow infusion of irradiated adult recipients, (3) use of genetically immunodeficient recipients (RAG1-/or SCID). In swine, reduced reactivity was achieved through the induction of mixed chimerism. After nonreactivity was induced and verified through extended persistence of skin grafts, hearts from donors were heterotopically transplanted into the recipients. Results: Most hearts transplanted into tolerant or immunodeficeint mice developed striking vasculopathy in their coronary arteries (neonatal tolerance: 12 of 15, mixed chimeras: 15 of 23, immunodeficient recipients: 16 of 31). In contrast, isotransplants were virtually free of CAV. Three of the four transplanted swine hearts showed neointimal proliferation characteristic of CAV in 1%-6% of donor coronary arteries. Control hearts transplanted into untreated recipients across similar minor antigen barriers were acutely rejected within 44 days whereas control isografts survived indefinitely without evidence of CAV. Conclusions: Elimination of T and B cell immune responses was not sufficient to prevent the development of CAV. Other immune effectors, perhaps NK cells, could play a role in the development of CAV in this immunodeficient state. Additional results on these alternate effectors will be presented.

Regulatory cells in the maintenance phase of tolerance in miniature swine: coculture cell mediated lympholysis assay as approach for a tolerance assay

that CM/IFA-injected animals grafted with MHC class II KO hearts experienced significant prolongation of heart survival as compared to untreated mice (11 1 d vs 24 2 d). We conclude that modulation of CM response can on its own achieve graft prolongation when CD4 alloresponse is oligoclonal, i.e. mediated via indirect allorecognition. Our findings have important implications for the design of future therapies in heart transplantation.

Intracoronary interferon-γ accellerates cardiac allograft rejection in miniature swine

Purpose: The effect of interferon(IFN) on allograft rejection remains controversial. Some have proposed that IFNhas a protective effect on the microcirculation of allografts, while others have shown IFNto be deleterious. We investigated the effects of intracoronary IFNon cardiac rejection in a preclinical large animal model. Methods: MHC class I disparate hearts were heterotopically transplanted into swine treated with a 12-day course of cyclosporine (10-14mg/kg/day) (n 3). An Alzet osmotic mini-pump delivered IFNinto the coronary vasculature at a rate of 100ng/day. Control recipients were treated with a similar course of cyclosporine but without IFN(n 3). Results: Swine treated with IFNdeveloped an earlier onset of high grade acute rejection as compared to controls, and rejected their allografts in 19 days vs. 46 days for controls (p 0.02). Elastin staining of the cytokine treated allografts showed severe endothelialitis and intimal thickening as early as POD 13. Conclusion: The delivery of IFNinto the coronary circulation of cardiac allografts appears to accelerate both acute and chronic rejection. Targeting IFNin antirejection regimens may ameliorate both of these processes.