Complement driven innate and adaptive autoreactivity in lung transplantation

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Abstract: Obliterative bronchiolitis (OB) is the leading cause of late death after lung transplantation (LTx) and the principle unmet obstacle to improved long-term outcomes. Increasing evidence indicates a role for recipient autoimmunity in the pathogenesis of graft rejection. Emphysema, a principle indication for LTx, has been shown to express a wide-spectrum of extracellular matrix autoreactive antibodies and T cells directed towards collagen, elastin, and decorin, the impact of which on post-Tx outcomes is unknown. Here we will utilize mouse models of emphysema, and orthopic LTx, to investigate LTx outcomes in a clinically relevant scenario. The scientific premise of these studies is to determine if pre-transplant autoreactive immunity induced by emphysema, promotes post-Tx injury that leads to exacerbated ischemia reperfusion injury (IRI) and OB. The earliest injury to the LTx occurs as a consequence of IRI, the severity of which is thought to lead to accelerated onset OB. Ischemic insult followed by reperfusion leads to the exposure of neoepitopes expressed on stressed/injured cells recognized by natural self-reactive IgM Abs, which bind and activate the C system, resulting in inflammation and injury. We have identified annexin IV as an injury-specific neoepitope expressed in ischemic transplant grafts, and have shown that this neoepitope binds natural IgM, activates C and promotes IRI. By means of an anti-annexin IV single chain Ab (B4scFv), we have validated annexin IV as a target for the therapeutic delivery of C inhibition to murine allografts. There are a number of therapeutic benefits of this neoepitope targeting approach for protection against IRI in a LTx recipient: 1. It will target the proximal event in complement activation, 2. The targeting vehicle itself contributes to therapeutic activity by blocking the binding of complement activating antibodies, and 3. Will inhibit C activation locally, which will impair T cell activation. Our working hypothesis is that pre-transplant autoreactivity to extracellular matrix targets exacerbates early graft injury, thus promoting early onset OB. We propose that neoepitope IgM graft-targeted C inhibitors will synergize to inhibit adaptive autoantibody effector functions, and reduce intragraft autoreactive T cell activity. We propose the following specific, independent, but interrelated aims. 1. Determine the complement-mediated effector functions that contribute to extracellular matrix autoreactive immunity induced acute lung graft injury. Here we will determine the isotype and phenotype of autoreactive antibodies and T cells that promote injury post transplantation and further dissect the complement effector functions that induce graft damage, and 2. In a murine model of OB, determine whether cigarette smoke-induced autoimmunity exacerbates IRI and chronic rejection following transplantation in a complement-dependent manner. We will transplant lungs into emphysematous mice (induced by cigarette smoke exposure) using allogeneic models of OB and determine whether prolonged CS exposure results in poorer outcomes, and further investigate how C-mediated inflammation and injury occurring early in the Tx process influences IRI and OB. !