E. Welty

Selective CD28 blockade attenuates acute and chronic rejection of murine cardiac allografts in a CTLA-4-dependent manner.

Selective blockade of CD28 is a promising therapy to inhibit pathogenic alloimmunity. However, evaluation of this approach in transplantation has been very limited. Using a novel nonactivating single‐chain Fv‐based reagent (α28scFv), we have investigated the role of CD28 and cytotoxic T lymphocyte antigen 4 (CTLA‐4) in a murine cardiac transplant model. Blockade of CD28 for 2 weeks after engraftment promoted allograft survival, and significantly attenuated chronic rejection when combined with transient CD154‐blockade or calcineurin inhibition. Graft acceptance was associated with decreased alloantibody production, increased proportion of early graft infiltration by regulatory T cells and increased expression of regulatory dendritic cell genes. Blockade of CTLA‐4 during α28scFv‐based treatments led to prompt rejection in all animals and inhibited expression of forkhead box P3 (Foxp3), programmed death (PD)‐1 and 2,3‐indoleamine dioxygenase (IDO) in the graft. These results show that CD28 signaling during the first weeks after transplant is a pivotal mediator of pathogenic alloimmunity, and that selective CD28 blockade prolongs graft acceptance by at least two immunomodulatory mechanisms. Selective CD28 inhibition while sparing CTLA‐4 is thus a promising approach to inhibit pathogenic alloimmunity.

Preemptive CD20+ B cell depletion attenuates cardiac allograft vasculopathy in cyclosporine-treated monkeys

Chronic rejection currently limits the long-term efficacy of clinical transplantation. Although B cells have recently been shown to play a pivotal role in the induction of alloimmunity and are being targeted in other transplant contexts, the efficacy of preemptive B cell depletion to modulate alloimmunity or attenuate cardiac allograft vasculopathy (CAV) (classic chronic rejection lesions found in transplanted hearts) in a translational model has not previously been described. We report here that the CD20-specific antibody (alphaCD20) rituximab depleted CD20+ B cells in peripheral blood, secondary lymphoid organs, and the graft in cynomolgus monkey recipients of heterotopic cardiac allografts. Furthermore, CD20+ B cell depletion therapy combined with the calcineurin inhibitor cyclosporine A (CsA) prolonged median primary graft survival relative to treatment with alphaCD20 or CsA alone. In animals treated with both alphaCD20 and CsA that achieved efficient B cell depletion, alloantibody production was substantially inhibited and the CAV severity score was markedly reduced. We conclude therefore that efficient preemptive depletion of CD20+ B cells is effective in a preclinical model to modulate pathogenic alloimmunity and to attenuate chronic rejection when used in conjunction with a conventional clinical immunosuppressant. This study suggests that use of this treatment combination may improve the efficacy of transplantation in the clinic.

Development of a consensus protocol to quantify primate anti-non-Gal xenoreactive antibodies using pig aortic endothelial cells.

Scientists working in the field of xenotransplantation do not employ a uniform method to measure and report natural and induced antibody responses to non‐Galα(1,3)Gal (non‐Gal) epitopes. Such humoral responses are thought to be particularly pathogenic after transplantation of vascularized GalTKO pig organs and having a more uniform assay and reporting format would greatly facilitate comparisons between laboratories.

PILOT EVALUATION OF ANTI-GPIB EFFECTS ON PLATELET SEQUESTRATION IN AN EX VIVO XENOGENEIC PIG LIVER PERFUSION MODEL: 3132

L. Burdorf1, R.N. Barth2, T. Zhang3, E. Rybak4, I.I. Salles5, K. Broos6, E. Welty4, C.J. Avon7, A. Laaris4, B. McCormick2, D. Ayares8, H. Deckmyn6, A.M. Azimzadeh2, R.N. Pierson III2 1Department Of Surgery, University of Maryland, Baltimore/MD/ UNITED STATES OF AMERICA, 2Surgery, University of Maryland, Baltimore/UNITED STATES OF AMERICA, 3Surgery, Univ. of Maryland & Baltimore VA, Baltimore/MD/UNITED STATES OF AMERICA, 4Department Of Surgery, University of Maryland, Baltimore/UNITED STATES OF AMERICA, 5Department Of Haematology, Imperial College London, London/UNITED KINGDOM, 6Laboratory For Thrombosis, KU Leuven Campus Kortrijk, Kortrijk/ BELGIUM, 7Surgery, University of Maryland and Baltimore VAMHCS, baltimore/MD/UNITED STATES OF AMERICA, 8, Revivicor Inc, Blacksburg/UNITED STATES OF AMERICA

Preemptive CD20+ B cell Depletion Attenuates Cardiac Allograft Vasculopathy in CD154-Treated Monkeys.

Background Anti-CD154 monotherapy is associated with antidonor allo-antibody (Ab) elaboration, cardiac allograft vasculopathy (CAV), and allograft failure in preclinical primate cell and organ transplant models. In the context of calcineurin inhibitors (CNI), these pathogenic phenomena are delayed by preemptive “induction” B cell depletion. Methods &agr;CD154 (IDEC-131)–treated cynomolgus monkey heart allograft recipients were given peritransplant rituximab (&agr;CD20) alone or with rabbit antihuman thymocyte globulin. Results Relative to previously reported reference groups, &agr;CD20 significantly prolonged survival, delayed Ab detection, and attenuated CAV within 3 months in &agr;CD154-treated recipients (&agr;CD154 + &agr;CD20 graft median survival time > 90 days, n = 7, vs 28 days for &agr;CD154 alone (IDEC-131), n = 21; P = 0.05). Addition of rabbit antihuman thymocyte globulin to &agr;CD154 (n = 6) or &agr;CD154 + &agr;CD20 (n = 10) improved graft protection from graft rejection and failure during treatment but was associated with significant morbidity in 8 of 16 recipients (6 infections, 2 drug-related complications). In &agr;CD20-treated animals, detection of antidonor Ab and relatively severe CAV were anticipated by appearance of CD20+ cells (>1% of lymphocytes) in peripheral blood and were associated with low &agr;CD154 trough levels (below 100 &mgr;g/mL). Conclusions These observations support the hypothesis that efficient preemptive “induction” CD20 B cell depletion consistently modulates pathogenic alloimmunity and attenuates CAV in this translational model, extending our prior findings with calcineurin inhibitors to the context of CD154 blockade.