(79) - Early CD20+ B Cell Depletion Attenuates Cardiac Allograft Vasculopathy in Anti-CD154 Treated Non-Human Primate Model

Abstract

Anti-CD154 (αCD154) monotherapy is associated with the development of anti-donor alloantibodies, cardiac allograft vasculopathy (CAV), and allograft failure in preclinical primate cell and organ transplant models. Evidence suggests that peri-transplant B cell depletion may remove an efficient source of donor antigen-specific costimulation, thereby attenuating development of anti-donor alloantibodies and subsequent pathogenic phenomena. Cynomolgus monkeys underwent heterotopic intraabdominal cardiac transplantation, and recipients were treated with either αCD154 (IDEC-131, n=21), αCD20 (Rituximab, n=2), αCD154 + αCD20 (n=7), or αCD154 + αCD20 + rabbit anti-human thymocyte immune globulin (rATG, n=10). Primary graft survival was defined as time to the first rejection episode. All biopsies and explant tissue specimens were assessed for CAV using the 2005 ISHLT revised criteria. Serum BAFF (B-cell activating factor of the tumor necrosis factor family) levels were analyzed by ELISA. Combined αCD154 + αCD20 treatment significantly prolonged graft median survival time (MST >90 days), delayed anti-donor alloantibody production, and attenuated CAV compared to αCD154 monotherapy (MST 28 days, p=0.05). Addition of rATG to αCD154 + αCD20 also prolonged graft MST to >90 days, but it was associated with a 50% incidence of treatment-attributed morbidity. Incidence of severe acute rejection (>1R) and CAV severity within 90 days was reduced in αCD20 treated animals relative to reference groups (p<0.05 for both endpoints). In αCD20 treated recipients, detection of anti-donor IgM and IgG alloantibody and relatively severe CAV were anticipated by appearance of CD20 cells in peripheral blood and was associated with trough αCD154 levels <100 μg/mL. Serum BAFF levels were higher in αCD20 treated animals (d7: 3762±181pg/mL) compared to untreated controls (628±507 pg/mL) and, similarly, in combined therapy (d7: 2687±829 pg/mL) vs. αCD154 controls (371±80 pg/mL). Efficient preemptive CD20+ B cell depletion in combination with selective CD154 inhibition consistently modulates pathogenic alloimmunity and attenuates CAV in this non-human primate heterotopic heart transplantation model; however, the addition of T cell depletion to the combined therapy was associated with significant morbidity in this model.