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THE EFFECT OF SOLUBLE COMPLEMENT RECEPTOR TYPE 1 ON HYPERACUTE XENOGRAFT REJECTION

In the guinea pig-to-rat model of hyperacute xenograft (Xg) rejection, the effect of complement inhibition using systemically administered soluble complement receptor type 1 (sCRl) on discordant cardiac Xg survival was investigated. In PBS-treated control Xg recipients (n=13), hyperacute rejection was rapid, with a mean Xg survival of 17±4 min. Therapy with sCRl prolonged survival of cardiac Xgs in a dose-dependent manner. A 3 mg/kg bolus of sCRl (n=4) prolonged Xg survival to 64±29 min (not significant). Increasing the sCRl dose to 5.9 mg/kg (n=4) significantly delayed Xg rejection to 71±17 min (P-0.026, log-rank test vs. control). In 10 recipients treated with 15 mg/kg sCRl, mean Xg survival was further prolonged to 189±36 min (P-0.0004) with no adverse effects. While 2 of 8 recipients receiving 60 mg/kg sCRl died with functioning Xgs at 30 and 300 min due to anastomotic bleeding, Xg survival averaged over 12 hr (747±100 min, P-0.0004) in the remaining 6 recipients. sCRl administration significantly inhibited serum complement activity in a parallel dose-dependent fashion, with the 60 mg/kg dose reducing complement activity by 95±1 and 96±1% five and 30 min following Xg reperfusion, respectively. Immunofluorescence microscopy revealed rat IgM bound to all cardiac Xgs in control as well as sCRl -treated recipients. In addition, serial histologic examination of cardiac Xgs harvested within 21 min of graft reperfusion revealed occlusive platelet aggregates within the coronary vessels as well as interstitial hemorrhage and myocardial necrosis in Xgs from control recipients, all of which were only minimally present in Xgs from recipients treated with sCRl. These studies show that complement inhibition with sCRl significantly delays hyperacute cardiac Xg rejection in this discordant model and may be an important component in a therapeutic protocol for xenotransplantation.