Inhibition of human serum mediated lysis of porcine endothelial cells using a novel peptide which blocks C1Q binding to xenoantibody

Compstatin, a peptide inhibitor of C3, prolongs survival of ex vivo perfused pig xenografts

Compstatin, a newly described C3-binding peptide, inhibits complement activation by blocking C3 convertase-mediated cleavage of C3. As the complement activation is an essential part of the rejection reaction, we evaluated the ability of Compstatin to delay or prevent hyperacute rejection in an ex vivo xenograft model. Pig kidneys were perfused with fresh human blood containing either Compstatin (n=6) or a control agent (n=6). Graft survival and activation of complement, leukocytes and platelets both in the fluid-phase and in the tissue were examined. The survival of the Compstatin-perfused kidneys (median, 380 min) was significantly (P=0.0036) longer than that of the controls (median, 90 min). The classical complement pathway (C1rs-C1inhibitor and C4bc) was significantly and equally activated in both groups during the first 60 min. C3 activation products increased fivefold and terminal complement complex eightfold in the control group, but no increase occurred in the Compstatin group during this period. Immunohistochemistry showed less C3 and fibrin deposition and immune electron microscopy showed less terminal SC5b-9 complement complex deposition in the Compstatin group. A significant change in total white cells, neutrophils, myeloperoxidase, and expression of the surface activation markers CD11b (CR3) and CD35 (CR1) and CD62L (L-selectin) was observed in both groups. Leukocyte activation was lower in the Compstatin group but the difference was not statistically significant. There were no differences in platelet counts, thrombospondin, soluble P-selectin or beta-thromboglobulin between the groups. We conclude that Compstatin prolongs graft survival and suggest that it may be a useful agent for attenuating hyperacute rejection by inhibiting C3 and thus terminal complement pathway activation.

Immunoglobulin prolongs survival of pig kidneys perfused ex vivo with human blood

Intravenous immunoglobulin (IVIG) (Octagam), was used to determine the effect on hyperacute rejection in an ex vivo xenograft model. Six pig kidneys were perfused with IVIG and fresh human AB blood, and six control pig kidneys were simultaneously perfused with albumin and blood from the same donation. The survival of the IVIG-perfused xenografts (median, 6.5 h) was significantly (P = 0.03) longer than the albumin-perfused xenografts (median, 3.5 h). Complement was activated in both groups. The administration of IVIG to the perfused blood resulted in immediate and significantly higher complement activation in the fluid phase as compared with the albumin group. At rejection the fluid phase complement activation was higher in the IVIG group than in the albumin group for C1rs/C1inh complexes, C4bc, Bb and TCC. At the time of rejection both the albumin and the IVIG group demonstrated interstitial tubular haemorrhage, vasculitis or necrosis of glomerular capillaries and glomerular microthrombi. IgM, C1q, C3c, C4 and fibrin were located in arteries and glomeruli and IgG in the interstitium in both groups at rejection. The fluid phase findings are consistent with a modulatory effect of IVIG on complement activation by deviating the classical pathway activation towards the fluid phase. The prolonged survival of the IVIG-perfused kidneys suggests that IVIG may be useful to dampen hyperacute rejection.