Immunodepletion in Xenotransplantation

Abstract

Xenograft transplantation is perhaps the most immunologically difficult problem in transplantation today. An overwhelming hyperacute rejection reaction (HAR) occurs within minutes of organ implantation. Preformed antibodies are thought to initiate this process. We used a pig-to-dog renal xenograft transplant model and investigated methods of decreasing the severity of hyperacute rejection. Female pigs weighing 15-20 kg were used as donors. Recipients were mongrel dogs weighing 15-25 kg. Experimental dogs were all given a number of treatments of IgG depletion using an antibody removal system (Dupont-Excorim). This machine immunoadsorbs plasma against a column containing immobilized staphylococcal protein A, which is known to bind the IgG Fc receptor. An 84% reduction in the IgG levels and a 71% reduction in IgM levels was achieved. Postoperative assessment was made of urine output, time to onset of HAR, and histopathological examination of the rejected kidneys. Although cross-matches between donor lymphocytes and recipient sera remained strongly positive in the treated dogs, there was a two-to fourfold reduction in the titers. The time to onset of HAR was prolonged in the experimental group, and the urine output was increased slightly. The histopathologic changes in the experimental group generally showed signs of HAR, but of less intensity than in the nonimmunodepleted control group. KeywordsImmunoadsorption; xenotransplantation; immunodepletion; hyper-acute rejection Currently, one of the major limitations in renal transplantation involves the large number of sensitized dialysis patients. Blood transfusions, prior transplants, or multiple pregnancies can all play an etiologic role, but result in an identical situation. These highly sensitized patients, who have antibodies to most or all HLA antigens, are rendered immunologically untransplantable. At present there is no effective means of dealing with this problem, and these patients can spend years on transplant waiting lists. Materials and Methods ImmunodepletionMale or female mongrel dogs weighing between 15 and 25 kg were anesthetized with pentothal, intubated, and maintained on a ventilator with 40% oxygen, ketamine 1.5 mg/kg every 1-2 h intravenously, and pancuronium 0.05-0.1 mg/kg every 1-2 h intravenously. Cutdowns in the neck on both the carotid artery and the external jugular vein were made and the vessels cannulated with 13-gauge Quinton-Scribner shunt cannulas. Arterial blood was fed into a Haemonetics V-50 plasmapheresis unit, which separates the red blood cells from the plasma. Citrate was used as an anticoagulant. The plasma was then fed into the immunoadsorption system which contains two columns of protein A attached to Sepharose CL-4B (Immunosorba A) in parallel (Figs 3 and 4). The CITEM 10 (Excorim KG, Lund, Sweden/Dupont) is a computer-controlled device which controls the flow of plasma and various regeneration solutions over the two columns. While plasma was run across one column, the adsorbed IgG and IgM were eluted from the other c...

Prevention of hyperacute xenograft rejection in orthotopic xenotransplantation of pig hearts into baboons using immunoadsorption of antibodies and complement factors

“…Many strategies for removal of XNAb and complement depletion [28] were investigated, including plasma exchange, plasmapheresis, xenogeneic organ perfusion and the use of haptens like aGall-3Gal-fragments and penicillamine [3]. Plasma exchange and organ perfusion result in a loss of coagulatory and plasma proteins and are therefore clinically unattractive.…”

The Influence of Baseline Expression of Human Decay Accelerating Factor Transgene on Graft Survival and Acute Humoral Xenograft Rejection

“…Many studies have shown that HAR following discordant xenotransplantation of vascularized organs is due to preformed antibodies in the recipient interacting with antigens on the vascular endothelium of the donor organ. This further activates both the endothelium and the complement cascade (21)(22)(23)(24)(25). A major area of research has been developing methods to inhibit this activation process, either by removing the preformed antibodies or by inhibiting complement activation (26 -28).…”

A Primate Model for Discordant Pig to Primate Kidney Xenotransplantation Without Hyperacute Graft Rejection

“…This reaction has been classi ed as hyperacute xenograft rejection (HAR) [3,4]. Current therapeutic strategies for abrogation of HAR include pretransplant antibody absorption by speci c or nonspeci c extracorporeal column perfusion [5][6][7], ex vivo donor solid organ perfusion, the administration of substances interfering with complement activation, or even the genetic alteration of donor organs by, for example, transgenic introduction of recipient type regulators of complement activation [8].…”