Evidence that recipient CD8⁺ T cell depletion does not alter development of chronic vascular rejection in a rat heart allograft model

Progressive chronic vascular rejection is a central feature of indefinitely surviving WF.1L LEW/Gut (RT1¹) heart grafts transplanted to LEW (RT1¹) recipients in unmodified donor-recipient combinations. At 70 days posttransplantation, large vessels of the grafts are characterized by the presence of vasculitis, vasculitis with associated variable myointimal thickening, and occlusive myointimal thickening with minimal or absent concomitant vasculitis. To assess the potential role of CD8⁺ T cells as critical effectors of chronic vascular rejection in this model, LEW recipients of WF.1L heart grafts were effectively depleted of CD8⁺ T cells as a result of prior thymectomy and anti-CD8 (MRC 0X8) monoclonal antibody administration prior to transplantation. WF.1L heart grafts transplanted to LEW recipients that had undergone prior sham thymectomy and MRC 0X8 administration, or thymectomy and administration of antibody-free culture supernatant, provided appropriate controls. At 70 days posttransplantation, large vessels of WF.1L heart grafts in all 3 transplantation groups showed similar morphologic features, which were comparable to those observed in heart grafts of long-surviving unmodified donor-recipient pairs. This study has shown that profound selective depression of recipient CD8⁺ T cells does not alter the characteristic features of chronic vascular rejection in this rat cardiac model, and provides evidence that CD8⁺ T cells play no critical role in the initiation or development of progressive vascular damage in this setting.