Prolonged discordant xenograft survival by inhibition of the intrinsic coagulation pathway in complement C6-deficient recipients.
BACKGROUND
Xenotransplantation of vascularized organs between unmodified discordant species results in hyperacute graft rejection within minutes to hours after graft reperfusion. This process is due to the presence of natural xenoreactive antibodies and complement activation, which lead to vessel injury, thrombosis, and hemorrhage. Because multiple components of the coagulation and complement cascades interact with each other, we have investigated the effects of inhibiting these systems together. The recombinant Kunitz type serine protease inhibitor (KPI-BG022) tested in these experiments inhibits factor XIIa, kallikrein, and plasmin.


METHODS
Cardiac xenografts from male Hartley guinea pigs were heterotopically grafted into male PVG rats that were either sufficient (C6[+]) or deficient (C6[-]) for the complement component C6 and thus formation of the membrane attack complex. Experimental animals received KPI 5 mg/kg intravenously before reperfusion, and control animals received saline placebo.


RESULTS
C6(+) recipients rejected their grafts hyperacutely, without a significant difference between KPI-treated (0.12+/-0.05 hours) and placebo-treated (0.13+/-0.06 hours) recipients (n = 10). As expected, C6(-) recipients showed prolonged graft survival (17.65+/-3.45 hours, n = 5). However, a single intravenous bolus of KPI before releasing the clamps further delayed graft rejection in C6(-) recipients (46.2+/-3.3 hours; n = 5). Histologic examination at 2, 6, and 12 hours after transplantation showed platelet aggregation and inflammatory infiltrates were significantly decreased in KPI-treated (C6[-]) recipients. However, intragraft hemorrhage was apparent at 6 and 12 hours.


CONCLUSIONS
We conclude that in vivo inhibition of the intrinsic clotting cascade by functional inactivation of factor XIIa has a synergistic effect with inhibition of membrane attack complex formation in preventing hyperacute discordant xenograft rejection.
Jakobs
F M
FM
Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205-2196, USA.
Davis
E A
EA
White
T
T
Sanfilippo
F
F
Baldwin
W M
WM
D000818:Animals; D001779:Blood Coagulation Factors / Q000037:antagonists & inhibitors*; D003183:Complement C6 / Q000172:deficiency*; D006084:Graft Rejection / Q000188:drug therapy*; D006085:Graft Survival; D006168:Guinea Pigs; D016027:Heart Transplantation; D008297:Male; D018375:Neutrophil Activation; D010455:Peptides; D010940:Plant Proteins; D051381:Rats; D014183:Transplantation, Heterologous; D014361:Trypsin Inhibitors / Q000627:therapeutic use*
D001779:Blood Coagulation Factors; D003183:Complement C6; C053865:Kunitz-type protease inhibitor, plant; D010455:Peptides; D010940:Plant Proteins; D014361:Trypsin Inhibitors