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Because of the current organ shortage, ABO-incompatible (ABOi) transplantations have been increasingly performed in recent years. The results seem comparable to those of compatible transplantations, but there have also been reports of increased side effects possibly because of the desensitization therapy. To address an increase in severe infectious complications, we compared the outcomes of 48 ABOi transplant recipients to outcomes of 96 matched ABO-compatible (ABOc) controls transplanted at Heidelberg University Hospital from August 2005 to April 2018. Over a follow-up period of 8 years, ABOi transplant recipients had comparable graft and patient survival as well as graft function compared with ABOc patients. T-cell-mediated and antibody-mediated rejections were not different between groups. In ABOi transplant recipients, urosepsis (22.9% vs. 8.5%; P = 0.019) and pneumonia with opportunistic pathogens (8.3% vs. 1.0%, P = 0.025) appeared more frequently. As a consequence, a significantly higher number of deaths from infection have been observed after ABOi transplantations (6.3% vs. 0%, P = 0.010). High-titer recipients (isoagglutinin titer of ≥1:256) showed a higher incidence of BK virus replication and postoperative bleeding complications. ABO-incompatible transplantations can be performed with results that are not different from results after ABOc transplantations. However, an increased rate of serious infectious complications must be taken into account.

During pig-to-primate xenotransplantation or perfusion of porcine organs with human blood, a xenogeneic coagulopathy with consecutive development of thrombotic microangiopathy (TMA) can be observed. The aim of this study was to elucidate the influence of the reduction of xenoreactive natural antibodies on the coagulopathy using an ex vivo perfusion system. Thirteen perfusion experiments using landrace wild-type porcine kidneys were performed in three different experimental groups: autologous, xenogeneic, and immunoadsorption. During and after perfusion, blood and tissue samples were collected to assess markers of coagulation, complement, inflammation, and endothelial activation. Immunoadsorption prior to perfusion did not prolong perfusion time (174 min ±28) compared to xenogeneic (182 min ±22) experiments, whereas autologous perfusion was possible for maximum of 240 min in all experiments. Activation of coagulation was similar comparing perfusions after immunoadsorption (D-Dimer 24 186 μg/l ±5813; TAT 566 μg/l ±34) to xenogeneic (D-Dimer 22 175 μg/l ±7826, TAT 600 μg/l ±0) experiments. But antibody-mediated complement activation was reduced in the immunoadsorption group. TNF-alpha and markers of endothelial cell activation were lower in the immunoadsorption group compared to the xenogeneic experiments. In this ex vivo perfusion model, we observed that marked removal of xenogeneic antibodies can reduce complement activation via the classical pathway as well as endothelial cell activation and inflammation. Immunoadsorption cannot prevent the activation of the terminal complement cascade and coagulation.

In times of organ shortage, transplantation over the blood group A/B and HLA antibody barriers helps increasing the living donor pool in kidney transplantation. Waiting times are reduced while patient survival may be improved. By desensitization, both blood group A/B as well as HLA antibodies are eliminated from the patient's circulation using plasmapheresis, double filtration plasmapheresis or selective or unselective immunoadsorption. In addition, antibody production and posttransplant antibody rebound are prevented by powerful immunosuppression and induction therapy with or without B-cell eliminating anti-CD20 antibody rituximab. Death-censored graft survival does not appear to be impaired after ABO incompatible kidney transplantation. This article is protected by copyright. All rights reserved.

Summary Pretransplant removal of antiblood group ABO antibodies is the cornerstone of all current ABO-incompatible (ABOi) transplantation programmes. In our protocol, plasmapheresis (PP) is performed with a plasmafilter followed by immunoadsorption (IA) of anti-ABO antibodies. The bleeding complications of this technique are not known. We analysed the data of all 65 consecutive ABOi kidney transplantations between March 2006 and October 2013 and compared these with matched 130 ABO-compatible (ABOc) kidney transplantations. Cases differed from controls in the pre-operative regimen, which included IA-PP and rituximab, tacrolimus, mycophenolate mofetil, prednisone and immunoglobulines. Data on platelet count, blood loss and red blood cell (EC) transfusions during 48 h postoperatively were collected. ABOi patients received EC transfusions more frequently than controls (29% vs. 12%, P = 0.005). Intra-operative blood loss was higher (544 vs. 355 ml, P

Summary Protocols for recipient desensitization may allow for successful kidney transplantation across major immunological barriers. Desensitized recipients, however, still face a considerable risk of antibody-mediated rejection (AMR), which underscores the need for risk stratification tools to individually tailor treatment. Here, we investigated whether solid phase detection of complement-fixing donor-specific antibodies (DSA) has the potential to improve AMR prediction in high-risk transplants. The study included 68 sensitized recipients of deceased donor kidney allografts who underwent peritransplant immunoadsorption for alloantibody depletion (median cytotoxic panel reactivity: 73%; crossmatch conversion: n = 21). Pre and post-transplant sera were subjected to detection of DSA-triggered C4d deposition ([C4d]DSA) applying single-antigen bead (SAB) technology. While standard crossmatch and [IgG]SAB testing failed to predict outcomes in our desensitized patients, detection of preformed [C4d]DSA (n = 44) was tightly associated with C4d-positive AMR [36% vs. 8%, P = 0.01; binary logistic regression: odds ratio: 10.1 (95% confidence interval: 1.6–64.2), P = 0.01]. Moreover, long-term death-censored graft survival tended to be worse among [C4d]DSA-positive recipients (P = 0.07). There were no associations with C4d-negative AMR or cellular rejection. [C4d]DSA detected 6 months post-transplantation were not related to clinical outcomes. Our data suggest that pretransplant SAB-based detection of complement-fixing DSA may be a valuable tool for risk stratification.

With the advent of novel therapies to directly intervene with B cell immunity and complement activation, antibody-mediated kidney allograft rejection (AMR) has come into the focus of transplant immunologists. Intravenous immunoglobulin, rituximab, bortezomib, and eculizumab have been used to treat patients with acute AMR, apart from the standard treatment of antibody removal with plasma exchange or immunoadsorption and steroid pulses. This article describes the experimental rationale and summarizes the still limited clinical experience with these novel therapies in the transplant setting. Results with the standard treatment for acute AMR, including intense plasmapheresis, intravenous immunoglobulins, and steroids are good with a graft survival of 80% at 18 months. In contrast, patients suffering from chronic AMR have significant irreversible damage in their grafts with substantially impaired graft survival. Thus, the authors propose a step-wise escalation of therapy in refractory cases of acute AMR and advocate an urgent need for controlled therapeutic trials for acute and chronic AMR not to inflict unnecessary harm on our patients by uncontrolled polypragmasy.

Living donor kidney transplantation in crossmatch-positive patients is a challenge that requires specific measures. Ten patients with positive crossmatch results (n = 9) or negative crossmatch results but strong donor-specific antibodies (DSA; n = 1) were desensitized using immunoadsorption (IA) and anti-CD20 antibody induction. IA was continued after transplantation and accompanied by HLA antibody monitoring and protocol biopsies. After a median of 10 IA treatments, all patients were desensitized successfully and transplanted. Median levels of mean fluorescence intensity (MFI) of Luminex-DSA before desensitization were 6203 and decreased after desensitization and immediately before transplantation to 891. Patients received a median of seven post-transplant IA treatments. At last visit, after a median follow-up of 19 months, 9 of 10 patients had a functioning allograft and a median Luminex-DSA of 149 MFI; serum creatinine was 1.6 mg/dl, and protein to creatinine ratio 0.1. Reversible acute antibody-mediated rejection was diagnosed in three patients. One allograft was lost after the second post-transplant year in a patient with catastrophic antiphospholipid syndrome. We describe a treatment algorithm for desensitization of living donor kidney transplant recipients that allows the rapid elimination of DSA with a low rate of side effects and results in good graft outcome.

Antibody-mediated rejection (AMR), which is commonly caused by preformed and/or de novo HLA alloantibodies, has evolved as a leading cause of early and late kidney allograft injury. In recent years, effective treatment strategies have been established to counteract the deleterious effects of humoral alloreactivity. One major therapeutic challenge is the barrier of a positive pretransplant lymphocytotoxic crossmatch. Several apheresis- and/or IVIG-based protocols have been shown to enable successful crossmatch conversion, including a strategy of peritransplant immunoadsorption for rapid crossmatch conversion immediately before deceased donor transplantation. While such protocols may increase transplant rates and allow for acceptable graft survival, at least in the short-term, it has become evident that, despite intense treatment, many patients still experience clinical or subclinical AMR. This reinforces the need for innovative strategies, such as complementary allocation programs to improve transplant outcomes. For acute AMR, various studies have suggested efficiency of plasmapheresis- or immunoadsorption-based protocols. There is, however, no established treatment for chronic AMR and the development of strategies to reverse or at least halt chronic active rejection remains a big challenge. Major improvements can be expected from studies evaluating innovative therapeutic concepts, such as proteasome inhibition or complement blocking agents.

We have intentionally performed heart transplantation in a 5-year-old child, despite the most unfavourable risk factors for patient survival; the presence of high level of antibodies against donor's human leucocyte antigen (HLA) class I/II and blood group antigens. Pretransplant treatment by mycophenolate mofetil, prednisolone, tacrolimus, intravenous immunoglobulin, rituximab, protein-A immunoadsorption (IA) and plasma exchange reduced antibody titres against the donor's lymphocytes from 128 to 16 and against the donor's blood group antigen from 256 to 0. The patient was urgently transplanted with a heart from an ABO incompatible donor (A(1) to O). A standard triple-drug immunosuppressive protocol was used. No hyperacute rejection was seen. Antibodies against the donor's HLA antigens remained at a low level despite three acute rejections. Rising anti-A(1) blood group antibodies preceded the second rejection and were reduced by two blood group-specific IAs and remained at a low level. The patient is doing well despite the persistence of donor-reactive antibodies.

Acute humoral rejection (AHR) is currently perceived as an immunological reaction against donor antigens mediated by complement-binding antibodies. C4d, a split product of complement activation and bound to endothelial cells of the peritubular capillaries, is used as a diagnostic marker for AHR. We report on three patients with biopsy-proven acute humoral rejection who were treated initially with plasmapheresis (PS). As two of the patients did not recover renal function, and biopsy showed persistent C4d staining after PS, immunoadsorption (IAS) was additionally performed on them. In all patients, renal function recovered, and follow-up biopsies in two patients showed complete disappearance of C4d, 29 days and 58 days after transplantation and only minimal residual C4d deposits in one patient 48 days after transplantation. We conclude that successful treatment of AHR is followed by complete resolution of serological and histological markers of AHR, displayed by the disappearance of C4d.

Transplantation of a living donor kidney is in general the best treatment option for patients with end-stage renal disease. Two major advantages as compared to transplantation with a deceased donor kidney are the avoidance of waiting time and the superior results in terms of renal function and graft survival. In some patients who are lucky enough to have a person in their neighborhood who are willing to donate a kidney, the transplantation cannot be performed directly because there is ABO blood type incompatibility between donor and recipient, or because of a positive lymphocyte crossmatch, based on the presence of donor-specific antibodies. During recent years, several strategies have been developed to enable transplantation in these cases. A first approach is to use a living donor kidney exchange program, which can result in successful matches in more than half of the crossmatch-positive couples [1]. With the incorporation of kidneys from nondirected, anonymous donors in such an exchange program, domino-paired chains of transplantations can be set up, which end with the transplantation of a living donor kidney to a recipient from the waiting list [2]. However, for a substantial number of recipients, these exchange programs do not result in a successful donor–recipient match. In these cases, desensitization strategies to reduce the titer of ABO blood group antibodies or anti-HLA antibodies can be employed. Desensitization techniques are based on the extracorporeal removal of antibodies, treatment with intravenous immunoglobulins, and on immunosuppressive therapy. Since these procedures carry additional risks for the transplant recipient, desensitization treatment should ideally be reserved for recipients who cannot be served with a donor kidney after several rounds of matching in a (multicenter) exchange program. Unfortunately, kidney exchange programs are not allowed by legislation in every country. In this issue of Transplant International, Morath et al. present the results of living donor kidney transplantation in nine crossmatch-positive patients with peritransplant immunoadsorption (IA) and induction therapy with the anti-CD20 antibody rituximab [3]. Three patients also underwent pretransplant plasmapheresis. In one additional patient with a negative crossmatch but high titers Correspondence L. B. Hilbrands, Department of Nephrology, Radboud University Nijmegen, PO Box 9101, 6500, HB Nijmegen, The Netherlands. E-mail: l.hilbrands@nier.umcn.nl

Depletion of anti-pig xenoantibodies reduces cell cytotoxicity of human serum to pig endothelial cells and lymphocytes. The aim of this study was to test, in a pig kidney xenoperfusion model, the ability of soluble alpha Gal terminated disaccharides to prevent the hyperacute rejection process in an organ. Porcine kidneys were perfused with whole human blood lacking saccharide and blood supplemented with Gal alpha 1-3GAL, Gal alpha 1-2Gal and lactose. Parameters evaluated were, urine production, renal blood flow, vascular resistance, renal clearance, blood cell counts, xenoantibody titers, complement activation and histopathology. The blood flow was higher in the Gal alpha 1-3Gal (155 +/- 31 ml/min x 100 g-1 kidney tissue) group compared to Gal alpha 1-2Gal (138 +/- 16), lactose (92 +/- 78) and controls (69 +/- 16), When calculated as percent of the blood flow value at 1 min, the blood flow at 30 min was 157% for the Gal alpha 1-3Gal and for 187% the Gal alpha 1-2Gal. The corresponding values for the lactose and control groups were 102% and 74%, respectively. Urine production in the lactose/control groups was lower (0.7 ml/min x 100 g-1 kidney tissue) compared to Gal alpha 1-3Gal (3.0) and Gal alpha 1-2Gal (3.7). Urine sodium excretion was reduced in the lactose/control groups, compared to the Gal alpha alpha 1-groups during the perfusions. An increase in urine potassium excretion was found in the Gal alpha alpha 1-groups while a reduction occurred in the lactose/control experiments. An initial 40-50% reduction in platelet count was observed in all groups while the leukocyte count showed a continuous decrease. Immunohistochemistry revealed less deposition of IgM, IgG, C3 and C1 q in the Gal alpha alpha 1-saccharide groups compared to the lactose/control groups. Soluble Gal alpha a1-disaccharides improved both functional and histological parameters. However, significant pathological changes were still present indicating that this approach to inhibit HAR must be used in combination with additional therapeutic approaches such as solid phase xenoantibody immunoadsorption and blocking of complement activation.

In xenotransplantation long ischemic time of grafts is supposed to have a marked influence on hyperacute rejection (HXR). We investigated the influence of different cold ischemic times on HXR of ex vivo "working pig hearts" perfused with human blood. Xenoreactive natural antibodies (XNAb) as a trigger of HXR were eliminated by Ig-Therasorb immunoadsorption (IA). Explanted Landrace pig hearts of group G1 and group G3 (with additional IA) underwent 4 h of cold ischemia prior to xenoperfusion. Control groups G2 and G4 (with IA) were kept ischemic for only 46.6 +/- 15.8 and 51.2 +/- 4.2 min, respectively. Ischemic time prolonged the perfusion time in our working heart model (G1: 356 +/- 46.1 min; G2: 125 +/- 31 min; P < 0.05). IA had no additional impact on perfusion time but was effective by itself. The heart weight increased fourfold more in G2 as compared to the other groups. IA without ischemia significantly improved cardiac output in G4 (G3: 198.8 +/- 15.4 mL/min; G4: 338.5 +/- 16.0 mL/min). Coronary flow in G2 was significantly lower than in G1 (G1: 157.9 +/- 9.15 mL/min; G2: 59.4 +/- 20.1 mL/min). Histological signs of HXR (light and electron microscopy) could be found in G2 in contrast to the other groups. Parameters of serological damage showed a minimum in G4 and the maximum in G2. In G1 XNAb were nearly equally eliminated immediately after the start of xenoperfusion as in IA groups G4 and G3. Four hours of ischemic time showed beneficial effects in preventing HXR, possibly caused by changes of the endothelial cell surface (for example, glycosylation or loss of alpha1-3Gal epitopes with a hapten effect).

Transplantation across the ABO barrier is sometimes done in cases of emergency, such as acute liver failure, but is also carried out in elective cases, e.g. kidneys from living donors. Reducing the recipient anti-A/B antibody titres is often necessary in ABO-incompatible kidney transplantation. This is usually done by the use of techniques such as plasmapheresis and protein A- or sepharose-linked anti-human Ig immunoadsorption. A new ABO immunosorbent with synthetic A- or B-trisaccharide carbohydrate epitopes linked to a sepharose matrix has been tested. Columns made of this material have been tested in vitro with plasma from A- and B-individuals, assessed for antibody reduction capacity, flow characteristics, biocompatibility, and unspecific protein adsorption. The columns have a high capacity for ABO antibody removal, reducing titres by three to seven steps in one passage. We noted a high biocompatibility, with no unspecific protein adsorption, no activation of coagulation factors, and a low activation of complement, no immune complex formation and no cytotoxicity towards cultured mammalian L929 cells.