Low molecular weight dextran sulfate prevents complement activation and delays hyperacute rejection in pig-to-human xenotransplantation models

Dextran sulfate of 5000 molecular weight (DXS 5000) is known to block compl ement activation as well as the intrinsic coagulation cascade by potentiati on of C1 inhibitor. The effect of DXS 5000 on hyperacute rejection (HAR) wa s tested in pig-to-human xenotransplantation models. For in vitro testing, a cytotoxicity assay was used with the pig kidney cell line PK15 as target cells and fresh, undiluted human serum as antibody and complement source. E x vivo pig lung perfusion was chosen to assess DXS 5000 in a physiologic mo del Pig lungs were perfused with fresh, citrate-anticoagulated whole human blood to which 1 or 2 mg/ml DXS 5000 were added; the lungs were ventilated and the blood de-oxygenated. Pulmonary vascular resistance (PVR) and blood oxygenation (Delta pO(2)) were monitored throughout the experiment. Autolog ous pig blood and human brood without DXS 5000 served as controls. In the P K15 assay DXS 5000 led to a complete, dose-dependent inhibition of human se rum cytotoxicity with an average IC50 of 43 +/- 18 mug/ml (n=8). Pig lungs perfused with untreated human blood (n = 2) underwent HAR within 105 +/- 64 min, characterized by increased PVR, decrease of Delta pO(2), and generali zed edema. Microscopically, capillary bleeding as well as deposition of hum an antibodies, complement and fibrin could be observed. Addition of DXS 500 0 (n=4) prolonged lung survival to 170 +/- 14 min for 1 mg/ml and 250 +/- 4 2 min for 2 mg/ml, and PVR values as well as edema formation were comparabl e to control lungs that were perfused with autologous pig blood (n=2). Acti vation of complement (activation products in serum, deposition on lung tiss ue) and the coagulation system (fibrin monomers) were significantly diminis hed as compared to human blood without DXS 5000, Binding of anti-Gal antibo dies was not influenced, and in vitro experiments showed no evidence of com plement depletion by DXS 5000. In conclusion, DXS 5000 is an efficient comp lement inhibitor in pig-to-human xertotransplantation models and therefore a candidate for complement-inhibitory/anti-inflammatory therapy - either al one or in combination with other substances - and warrants further investig ation.