Complement C5 Inhibition Reduces T Cell–Mediated Allograft Vasculopathy Caused by Both Alloantibody and Ischemia Reperfusion Injury in Humanized Mice

Abstract

Allograft vasculopathy (AV) is characterized by diffuse stenoses in the vasculature of solid organ transplants. Previously, we developed two humanized models showing that alloantibody and ischemia reperfusion injury (IRI) exacerbated T cell-mediated AV in human arterial xenografts in vivo. Here we examined a causal role for terminal complement activation in both settings. IRI, in contrast to alloantibody, elicited widespread membrane attack complex (MAC) assembly throughout the vessel wall. Both alloantibody and IRI caused early (24 h) and robust endothelial cell (EC) activation localized to regions of intimal MAC deposition, indicated by increases in NF-κB inducing kinase, a MAC-dependent activator of non-canonical NF-kB, VCAM-1 expression, and Gr-1+ neutrophil infiltration. Endothelial cell activation by alloantibody was inhibited by anti- mouse C5 mAb, but not by anti-C5a mAb or by control mAb, implicating MAC as the primary target of anti-C5 mAb. Anti-mouse C5 mAb significantly reduced alloantibody- and IRI-enhanced T cell infiltration and AV-like changes including neointimal hyperplasia as well as intraluminal thrombosis in a subset of IRI-treated arterial grafts. These results indicate that increased AV lesion formation in response to either alloantibody or IRI are dependent on complement C5 activation and accordingly inhibition of this pathway may attenuate AV.

Complement-activated interferon-γ–primed human endothelium transpresents interleukin-15 to CD8+ T cells

“…This experimental protocol avoided exposure of the adoptively transferred PBMCs to PRAs, and the groups receiving IgG-depleted sera allowed us to test the effect of MCC950 on an unmodified allogeneic T cell response to the grafts. As we described previously, the presence of human T cells in the circulation of the second set of hosts results in T cell infiltration of the graft vessel intima with expansion of the intimal area and concomitant luminal narrowing, providing a quantifiable model for human T cell-mediated graft rejection (11,31). The experiment was repeated 3 times with different donors and the results were pooled for analysis.…”

“…Successful engraftment of human CD3 + T cells, achieved in all mice in this study, was defined as 1% to 10% human CD3 + T cells engraftment relative to total murine CD45 + leukocytes before artery graft retransplantation as assessed by flow cytometry analysis of peripheral blood sampled. Retransplanted artery grafts were explanted with cuffs of mouse aorta on both ends and then interposed into the infrarenal aortae of a second recipient (31). After 14 days, retransplanted artery grafts were recovered, embedded, and snap-frozen in OCT and sectioned at 5-μm thickness.…”

Recent advances in allograft vasculopathy

“…Interestingly, these effects have been shown to be attenuated with use of an anti-C5a antibody thereby implicating MAC-dependent signaling as a key mediator of endothelial activation (59••). Such findings have the potential to be translated into new treatment strategies as has recently been demonstrated the anti-C1s complement inhibitor, shown to abrogate complement-mediated activation of human aortic ECs (60••).…”

“…Complement activation is closely associated with IRI, inducing MAC formation on the surface of the graft endothelium that ultimately results in enhanced endothelial immunogenicity mediated by activation of non-canonical NF-κB signaling. Blockade of MAC deposition through the administration of anti-C5 antibody has been recently demonstrated to result in attenuated non-canonical NF-κB signaling and diminished formation of stenotic and thrombotic AV in human coronary arteries implanted into SCID/bg mice that had previously received adoptive transfer of human T cells allogeneic to the artery (59••). …”

Comparison between iloprost and alprostadil for protection against ischemia/reperfusion injury in a rat model

“…The reperfusion of ischemic tissue can lead to catastrophic damage to cellular structures, membrane lipids, and proteins (1). Multiple interactions between free oxygen radicals, lymphocytes, cytokines, the complement system, and endothelial cells play a major role in the reperfusion process (2,3). Alprostadil (PGE1) is a vasodilator agent that has an inhibitory effect on platelet aggregation.…”