Clinical characteristics of thrombotic microangiopathy following ABO incompatible living donor liver transplantation

The outcomes of thrombotic microangiopathy after liver transplantation: A nationwide survey in Japan

BACKGROUND

Although thrombotic microangiopathy (TMA) is recognized as one of the poor-prognosis factors after liver transplantation, the precise outcome of TMA is unclear. We sought to elucidate the factors affecting the outcome of TMA after liver transplantation in Japan, based on the data from a nationwide survey.

METHODS

One hundred cases of post-transplant TMA were accumulated from 17 Japanese centers of which two cases were excluded because the cause of death was obviously not related to TMA (recurrence of original diseases as primary sclerosing cholangitis and hepatocellular carcinoma), and the remaining 98 cases were enrolled in this study. The patient survival after the development of TMA and the factors that affected the patients' outcomes were retrospectively analyzed.

RESULTS

All cases were living-donor liver transplant cases, and the 1-, 3-, and 5-year patient survival rates after transplantation were 66.9%, 64.6%, and 62.2%, respectively. In a multivariate analysis, the requirement of renal replacement therapy during TMA treatment was the only factor that was significantly related to poor outcome after the development of TMA.

CONCLUSION

The outcomes of TMA were generally poor. The progression of renal dysfunction despite intensive treatment might be the only factor related to the poor prognosis after the development of TMA.

Analysis of the prevalence of systemic de novo thrombotic microangiopathy after ABO-incompatible kidney transplantation and the associated risk factors

OBJECTIVES

To analyze the prevalence of systemic de novo thrombotic microangiopathy in ABO-incompatible kidney transplantation and risk factors associated with this condition.

METHODS

A total of 201 patients who received living-donor kidney transplantation (114 patients with ABO-identical kidney transplantation and 87 patients with ABO-incompatible kidney transplantation) were retrospectively analyzed. Systemic de novo thrombotic microangiopathy was diagnosed clinically according to the presence of thrombocytopenia with microangiopathic hemolytic anemia and pathological findings of thrombotic microangiopathy. Anti-A and anti-B antibodies were purified from human plasma, and these antibodies' bindings to human kidney were investigated in vitro.

RESULTS

ABO-incompatible kidney transplantation was a significant risk factor of systemic de novo thrombotic microangiopathy (odds ratio 55.9, 95% CI 1.8-8.9, P < 0.001) after transplantation. Multivariate logistic regression analysis showed that non-use of mycophenolate mofetil, pretreatment immunoglobulin G antibody titer ≥64-fold and pretransplant immunoglobulin M antibody titer ≥16-fold were significant risk factors for systemic de novo thrombotic microangiopathy in ABO-incompatible kidney transplantation. Microvascular inflammation of 1-h post-transplant biopsy could be observed more frequently in thrombotic microangiopathy patients than in non-thrombotic microangiopathy patients. Anti-A and anti-B antibodies purified from human plasma showed a strong in vitro reaction against human kidney when the antibody titer was ≥16-fold.

CONCLUSIONS

Antibody titer should be decreased to ≤16-fold until the day of ABO-incompatible kidney transplantation by desensitization therapy including mycophenolate mofetil. The 1-h biopsy results might help to diagnose systemic de novo thrombotic microangiopathy.

Feasibility of Monotherapy by Rituximab Without Additional Desensitization in ABO-incompatible Living-Donor Liver Transplantation

BACKGROUND

Rituximab is a cornerstone in the regimens of desensitization for ABO-incompatible living-donor liver transplantation (ABO-i LDLT) that makes this modality an acceptable option for liver transplantation. Plasmapheresis (PP) to reduce anti-ABO antibody titer and local infusion (LI) therapy were practiced as the strategies for desensitization before the application of rituximab and were reported as additional treatments. The aim of this study was to clarify the feasibility of monotherapy by rituximab without any additional desensitization treatments in ABO-i LT.

METHODS

Forty patients receiving ABO-i LDLT with rituximab were enrolled in this retrospective study. The patients were divided into 2 groups: the rituximab with pretransplant PP and posttransplant LI (RPL) group (n = 20) and the rituximab monotherapy (RM) without any additional treatment group (n = 20). The groups were then compared in terms of the rates of patient survival, antibody-mediated rejection (AMR), and infection.

RESULTS

The 1-, 3-, and 5-year patient survival rates were 85%, 85%, and 85% in the RPL group and 89%, 80%, and 80% in the RM group, respectively. There was no significant difference in patient survival between the 2 groups. There were no episodes of AMR in either group. The RM group had a lower rate of fungal and viral infections than the RPL group.

CONCLUSIONS

Pretransplant rituximab without additional treatments yielded satisfactory outcomes comparable to that with additional treatments, such as PP and LI.

Feasibility of using marginal liver grafts in living donor liver transplantation

Liver transplantation (LT) is one of the most effective treatments for end-stage liver disease caused by related risk factors when liver resection is contraindicated. Additionally, despite the decrease in the prevalence of hepatitis B virus (HBV) over the past two decades, the absolute number of HBsAg-positive people has increased, leading to an increase in HBV-related liver cirrhosis and hepatocellular carcinoma. Consequently, a large demand exists for LT. While the wait time for patients on the donor list is, to some degree, shorter due to the development of living donor liver transplantation (LDLT), there is still a shortage of liver grafts. Furthermore, recipients often suffer from emergent conditions, such as liver dysfunction or even hepatic encephalopathy, which can lead to a limited choice in grafts. To expand the pool of available liver grafts, one option is the use of organs that were previously considered “unusable” by many, which are often labeled “marginal” organs. Many previous studies have reported on the possibilities of using marginal grafts in orthotopic LT; however, there is still a lack of discussion on this topic, especially regarding the feasibility of using marginal grafts in LDLT. Therefore, the present review aimed to summarize the feasibility of using marginal liver grafts for LDLT and discuss the possibility of expanding the application of these grafts.

Recent advances in ABO incompatible liver transplantation

Liver transplantation has become the best way to cure patients with end-stage liver disease. Due to the shortage of donor organs worldwide and being unable to obtain matched donor liver, most patients with severe hepatic failure lose the chance of operation or even die. As a result, ABO incompatible (ABO-I) liver transplantation has become a choice to save the endangered life. However, compared with ABO compatible liver transplantation, ABO-I liver transplantation is more prone to cause severe antibody mediated rejection (AMR), biliary complications, infection, thrombotic microangiopathy, and acute kidney injury. Consequently, its clinical application is limited. In recent years, with the progress of AMR prevention strategies such as immunoabsorption, plasmapheresis, rituximab, splenectomy, intravenous immunoglobulin, and graft perfusion, the clinical efficacy of ABO-I liver transplantation has been significantly improved, although it still faces the challenge of how to prevent and control AMR and postoperative complications.

Von Willebrand Factor Deposition and ADAMTS-13 Consumption in Allograft Tissue of Thrombotic Microangiopathy-like Disorder After Living Donor Liver Transplantation: A Case Report

BACKGROUND

Thrombotic microangiopathy (TMA) pathogenesis after living donor liver transplantation (LDLT) is thought to be caused by release of unusually large von Willebrand factor multimers (UL-vWFMs) resulting from sinusoidal endothelial cell damage and induction of platelet adhesion and aggregation. A decrease in a disintegrin-like and metalloproteinase with thrombospondin type 1 motifs-13 (ADAMTS-13) that cleave UL-vWFMs might cause excessive UL-vWFMs activity and result in platelet thrombus formation. However, this phenomenon has not undergone a full pathologic assessment.

PROCEDURES

A 60-year-old man was diagnosed with hepatitis C-related end-stage cirrhosis. His son was the donor, and he underwent LDLT. On postoperative day 44, his laboratory findings met most TMA diagnostic criteria, and he was diagnosed with TMA-like disorder (TMALD). Localization of CD42b as a platelet marker, vWF, and ADAMTS-13 in allograft tissue of this patient were evaluated using immunohistochemistry.

RESULTS

CD42b expression was observed as platelet aggregates attached to hepatocytes or within the hepatocyte cytoplasm, a morphology called extravasated platelet aggregation (EPA). vWF expression was observed mainly as deposited compact clusters, and ADAMTS-13 expression resembled distinct dots throughout the liver tissue.

CONCLUSION

These findings suggest that EPA indicated sinusoidal endothelial cell damage followed by detachment, and vWF deposition resulted from UL-vWFM oversynthesis. ADAMTS-13 might be consumed in the allograft tissue to cleave UL-vWFMs, but ADAMTS-13 levels might be insufficient to cleave all the deposited UL-vWFMs. We present the case of an LDLT recipient diagnosed with TMALD using blood tests, which showed the presence of TMA pathogenesis in the allograft.

Dysfunction in Patients With Small-for-Size Grafts After Living Donor Liver Transplantation

The relationship between postoperative percentage fall of platelet (PLT) counts and graft dysfunction after living donor liver transplantation (LDLT) in recipients with small-for-size (SFS) graft has not been fully evaluated. We retrospectively studied 50 adult-to-adult LDLT recipients with a graft-to-recipient weight ratio of <0.8% between 1999 and 2011. Graft dysfunction was defined as the presence of hyperbilirubinemia, coagulopathy, or ascites on 3 consecutive days during the first postoperative week. Each clinical sign of dysfunction was assigned 1 point. Postoperative percentage fall in PLT counts, graft dysfunction score, and postoperative complications according to the Clavien-Dindo classification were investigated. Overall, 31 patients (62%) exhibited a PLT count fall of more than 50%, and 19 (38%) patients exhibited a PLT count fall of less than 50% at postoperative day (POD) 3. Receiver operating characteristic curve analysis indicated that at POD 3, the cutoff value of PLT count fall was 56% for a graft dysfunction score of 2 or 3 (sensitivity, 70%; specificity, 63.3%). Fourteen of 20 patients (70%) with a dysfunction score of 2 or 3 and 11 of 30 patients (37%) with a dysfunction score of 0 or 1 showed a fall in PLT count >56% at POD 3 (P = 0.021). Grade 2 to 5 complications were more observed in patients with a dysfunction score of 2 or 3 than in patients with a dysfunction score of 0 or 1 (P < 0.001). The fall of PLT count at POD 3 >56% is an ominous sign that can predict the graft dysfunction after LDLT in recipients with SFS graft.

Living donor liver transplantation for patients immunized against human leukocyte antigen

BACKGROUND/PURPOSE

The clinical features and perioperative management of liver transplant recipients who are already sensitized against human leukocyte antigen (HLA) prior to transplantation are not yet clear.

MATERIALS AND METHODS

Medical records of living donor liver transplant recipients were reviewed and clinical features of the patients possessing anti-HLA antibodies were studied.

RESULTS

Among the 470 consecutive living donor liver transplant recipients, 6 patients (1.3%) had preformed anti-HLA antibodies. A review of the postoperative courses of these patients revealed that the problems included platelet transfusion refractoriness (PTR) due to immune-mediated destruction of platelet and thrombotic microangiopathy (TMA). PTR was observed in patients with anti-HLA class I antibodies and only HLA-matched platelet concentrate (HLA-matched PC) relieved thrombocytopenia. Intravenous gammaglobulin had an additive effect to HLA-matched PC in some cases, and platelet transfusion from close relatives might be a substitute for HLA-matched PC in life-threatening situations. Although the etiology of TMA is unremarkable, the incidence was high (67%, 4/6) compared with that in patients who were not sensitized against HLA (5.6%, 26/464; p < 0.01). Of the four patients, three were complicated with late-onset TMA.

CONCLUSIONS

Considering these clinical features, careful preparation and postoperative management are needed for liver transplant candidates with anti-HLA antibodies.

Lessons and insights from ABO-incompatible lung transplantation

With ABO blood group incompatibility (ABOi) between donor and recipient becoming a part of mainstream living-donor renal transplantation, the applicability of ABOi to other areas of transplantation is being reconsidered. Here we present a case of inadvertent ABOi lung retransplantation managed successfully with initial plasmapheresis, antithymocyte globulin and intravenous immunoglobulin; and subsequently with oral cyclophosphamide and sirolimus in addition to tacrolimus and prednisolone. Interestingly, in the setting of solid levels of tacrolimus and sirolimus, the patient developed a fatal thrombotic microangiopathy of uncertain origin subsequent to the cessation of cyclophosphamide at 9 years posttransplant. It is apparent that ABOi lung transplantation can result in surprisingly successful long-term outcomes. Low pretransplant antibody titers likely aid this and, in pediatric neonatal or infant cases, this may not be uncommon. We must proceed cautiously as there are significant risks. Understanding the monitoring, prevention and treatment of lung transplant antibody-mediated rejection, while avoiding the long-term complications of overimmunosuppression, will be the keys to the success of future cases.

Transnational validation of the Australian algorithm for virtual crossmatch allocation in kidney paired donation

An independent pool of 16 incompatible live donor-recipient pairs registered at the Vienna transplant unit was applied to test whether virtual crossmatch allocation used in the Australian kidney paired donation (KPD) program reliably predicts negative crossmatches. High resolution HLA data were entered into the computer-matching algorithm and allocation was performed excluding any DSA>2000MFI. CDC and flow crossmatch data of recipients against any of the donors were available for 112 crossmatch combinations. The computer program identified 19 possible pairings in 2-way or 3-way chains in multiple combinations. The top ranked combination included one 3-way and two 2-way ABO-compatible chains. Where crossmatches were available all recipients were CDC crossmatch negative with the computer-matched donor. Excluding allocation of KPD donors in the presence of DSA>2000MFI had a negative predictive of 99.9% for CDC and 96.4% for flow crossmatch. In the 12 pairings with ⩾1 DSA against crossmatched donors there was a negative CDC and flow crossmatch. These results show excellent correlation between matching using virtual crossmatch and actual crossmatch results. Using the 2000MFI cut-off the number of potentially unacceptable CDC and flow crossmatch positive pairings identified by virtual crossmatching is low, but some potential crossmatch negative pairings are missed.

Behavior of ADAMTS13 and Von Willebrand factor levels in patients after living donor liver transplantation

INTRODUCTION

Thrombotic microangiopathy (TMA) is one of the important complications occurring after liver transplantation (LT), and it is suggested that a Von Willebrand factor (VWF) and ADAMTS13 may play an important role in the onset of TMA and poor outcome after LT.

MATERIALS AND METHODS

In 81 patients after living donor LT (LDLT), 17 patients who had both severe thrombocytopenia and hemolytic anemia with fragmented red cell were diagnosed as TMA- like syndrome (TMALS) and 10 patients died.

RESULTS

ADAMTS13 activities were slightly low, and plasma levels of VWF and VWF propeptide (VWFpp) antigens and the ratio of VWFpp/VWF were significantly high before LDLT. ADAMTS13 activities were significantly reduced from day 1 to day 28 after surgery, and plasma levels of VWF antigen slightly decreased on day 1 and plasma levels of VWFpp continued to be high. The ratio of VWFpp/VWF was significantly high on day 1 after surgery. The mortality was high in the patients with TMALS and the frequency of TMALS was high in non-survivors. VWF levels were significantly low and the ratio of VWFpp/VWF was significantly high in those with TMALS on day 1 after surgery. The ADAMTS13 activity was significantly low, and the VWFpp and the VWFpp/ADAMTS13 ratio were significantly high in non-survivor on day 28 after surgery.

CONCLUSION

These findings suggest that VWF and ADAMTS13 might therefore play an important role in the onset of TMA and poor outcome after LT. The VWFpp may therefore be a more useful marker for the diagnosis of TMALS than VWF.

Successful sirolimus rescue in tacrolimus-induced thrombotic microangiopathy after living-related liver transplantation

TMA is a rare complication of tacrolimus. Disruption of endothelial cells, platelet aggregation, and intravascular mechanical fragmentation of red cells are core mechanisms of injury; however, exact pathways of toxicity are not clear. The clinical presentation may vary but TMA is a potentially life-threatening condition usually demanding aggressive treatment. We present the case of TMA in a child after living-related liver transplantation (LRLTx) on tacrolimus-based immunosuppressive regiment successfully converted to sirolimus.

Thrombotic microangiopathy after living-donor liver transplantation

Thrombotic microangiopathy (TMA) is an infrequent but severe life-threatening disorder in solid organ transplant recipients. Few studies of TMA in living donor liver transplant (LDLT) recipients, however, have been reported. We investigated the clinical characteristics and prognostic factors of TMA after LDLT. Among 393 adult LDLT recipients, 30 patients (7.6%) were identified to have TMA. The 1-, 3- and 5-year survival rates of these patients were lower (60.6%, 52.5% and 47.7%, respectively) than those of patients without TMA (93.0%, 89.0% and 87.3%, respectively). Multivariate analysis confirmed that reduced administration of fresh frozen plasma and sensitization against HLA are closely related with TMA (odds ratio [OR]: 2.6 and 16.1, respectively). However, a review of the cases revealed that individual responses to treatment varied considerably and the main etiologies were difficult to determine. A comparison of the clinical factors suggested that late onset (>30 days), poor response to treatment and delayed diagnosis and/or treatment are associated with a poor outcome. Because the prevention of TMA in LDLT patients is difficult, early diagnosis and initiation of intensive therapies may be crucial to improve the prognosis.

Acute renal endothelial injury during marrow recovery in a cohort of combined kidney and bone marrow allografts

An idiopathic capillary leak syndrome ('engraftment syndrome') often occurs in recipients of hematopoietic cells, manifested clinically by transient azotemia and sometimes fever and fluid retention. Here, we report the renal pathology in 10 recipients of combined bone marrow and kidney allografts. Nine developed graft dysfunction on day 10-16 and renal biopsies showed marked acute tubular injury, with interstitial edema, hemorrhage and capillary congestion, with little or no interstitial infiltrate (≤10%) and marked glomerular and peritubular capillary (PTC) endothelial injury and loss by electron microscopy. Two had transient arterial endothelial inflammation; and 2 had C4d deposition. The cells in capillaries were primarily CD68(+) MPO(+) mononuclear cells and CD3(+) CD8(+) T cells, the latter with a high proliferative index (Ki67(+) ). B cells (CD20(+) ) and CD4(+) T cells were not detectable, and NK cells were rare. XY FISH showed that CD45(+) cells in PTCs were of recipient origin. Optimal treatment remains to be defined; two recovered without additional therapy, six were treated with anti-rejection regimens. Except for one patient, who later developed thrombotic microangiopathy and one with acute humoral rejection, all fully recovered within 2-4 weeks. Graft endothelium is the primary target of this process, attributable to as yet obscure mechanisms, arising during leukocyte recovery.

Thrombotic microangiopathy-like disorder after living-donor liver transplantation: A single-center experience in Japan

AIM: To investigate thrombotic microangiopathy (TMA) in liver transplantion, because TMA is an infrequent but life-threatening complication in the transplantation field.

METHODS: A total of 206 patients who underwent living-donor liver transplantation (LDLT) were evaluated, and the TMA-like disorder (TMALD) occurred in seven recipients.

RESULTS: These TMALD recipients showed poor outcomes in comparison with other 199 recipients. Although two TMALD recipients successfully recovered, the other five recipients finally died despite intensive treatments including repeated plasma exchange (PE) and re-transplantation. Histopathological analysis of liver biopsies after LDLT revealed obvious differences according to the outcomes. Qualitative analysis of antibodies against a disintegrin-like domain and metalloproteinase with thrombospondin type 1 motifs (ADAMTS-13) were negative in all patients. The fragmentation of red cells, the microhemorrhagic macules and the platelet counts were early markers for the suspicion of TMALD after LDLT. Although the absolute values of von Willebrand factor (vWF) and ADAMTS-13 did not necessarily reflect TMALD, the vWF/ADAMTS-13 ratio had a clear diagnostic value in all cases. The establishment of adequate treatments for TMALD, such as PE for ADAMTS-13 replenishment or treatments against inhibitory antibodies, must be decided according to each case.

CONCLUSION: The optimal induction of adequate therapies based on early recognition of TMALD by the reliable markers may confer a large advantage for TMALD after LDLT.

Impact of thrombocytopenia on survival of baboons with genetically modified pig liver transplants: clinical relevance

A lack of deceased human donor livers leads to a significant mortality in patients with acute-on-chronic or acute (fulminant) liver failure or with primary nonfunction of an allograft. Genetically engineered pigs could provide livers that might bridge the patient to allotransplantation. Orthotopic liver transplantation in baboons using livers from alpha1,3-galactosyltransferase gene-knockout (GTKO) pigs (n = 2) or from GTKO pigs transgenic for CD46 (n = 8) were carried out with a clinically acceptable immunosuppressive regimen. Six of 10 baboons survived for 4-7 days. In all cases, liver function was adequate, as evidenced by tests of detoxification, protein synthesis, complement activity and coagulation parameters. The major problem that prevented more prolonged survival beyond 7 days was a profound thrombocytopenia that developed within 1 h after reperfusion, ultimately resulting in spontaneous hemorrhage at various sites. We postulate that this is associated with the expression of tissue factor on platelets after contact with pig endothelium, resulting in platelet and platelet-peripheral blood mononuclear cell(s) aggregation and deposition of aggregates in the liver graft, though we were unable to confirm this conclusively. If this problem can be resolved, we would anticipate that a pig liver could provide a period during which a patient in liver failure could be successfully bridged to allotransplantation.

Decreased ADAMTS13 levels in patients after living donor liver transplantation

INTRODUCTION

Thrombotic microangiopathy (TMA) is a complication occurring after liver transplantation (LT), and an unusually large multimer (ULM) of Von Willebrand factor (VWF) and ADAMTS13 may play an important role in the onset of TMA during LT.

MATERIAL AND METHODS

Eight-one patients underwent living donor LT (LDLT). Seventeen of those patients had both severe thrombocytopenia and hemolytic anemia with fragmented red cells and were diagnosed as TMA- like syndrome (TMALS).

RESULTS AND CONCLUSIONS

A significant reduction of ADAMTS13 and an increase of VWF were observed in the patients with TMALS. The ADAMTS13 activity in patients after LDLT was significantly reduced from day 1 to day 21, and it was significantly low in those with TMALS at day 14 and 28. The VWF levels in patients with LDLT were significantly high, and the VWF/ADAMTS13 ratio was significantly increased in patients at 7, 14 and 28 days after LDLT, especially in patients with TMALS at day 14 and 28 after LDLT. High molecular weight multimers of VWF were observed to have increased in patients with LDLT, and the high molecular weight multimers of VWF were further increased in those with mild TMALS but they decreased in those with severe TMA. These findings suggest that ULM- VWF and ADAMTS13 might be associated with the onset of TMA after LT.

Thrombotic microangiopathy after ABO-incompatible living donor liver transplantation: a case report

Thrombotic microangiopathy (TMA) has rarely been reported in the setting of liver transplantation. Herein we have reported a successful case of TMA after ABO-incompatible living donor liver transplantation (LDLT) treated with plasma exchange and high-dose intravenous gamma-globulin infusion. A 50-year-old woman was diagnosed with hepatitis C virus-related cirrhosis. We performed an ABO-incompatible LDLT (group B to O) with preoperative plasma exchange to reduce the anti-B hemagglutinin titers to 1:8. The immunosuppressants consisted of tacrolimus, mycophenolate mofetil, and steroid. On postoperative day (POD) 8, her anti-B hemagglutinin titer suddenly increased to 1:64. The serum lactate dehydrogenase (LDH) level was grossly elevated (1518 IU/L). On POD 13, we suspected infection of an intra-abdominal hematoma (Serratia marcescens) which was drained surgically. On day 5 after the reoperation, thrombocytopenia developed with a platelet count of 3 x 10(4)/mm3. A peripheral blood film showed severe red blood cell (RBC) fragmentation. Thus, we made a clinical diagnosis of TMA and reduced the tacrolimus dose. We started intensive daily plasma exchange (4 L/d) with fresh frozen plasma and high-dose intravenous gamma-globulin infusions. One week thereafter, thrombocytopenia improved with reduced transfusion requirements. The peripheral blood film showed normal RBC morphology. The serum LDH returned to baseline levels. Four factors were considered to have caused TMA in this case: the prescription of tacrolimus, ABO-incompatible liver transplantation, bacterial infection, and surgical stress. These factors may have all contributed by causing significant endothelial injury and TMA.

Removal of blood group A/B antigen in organs by ex vivo and in vivo administration of endo-beta-galactosidase (ABase) for ABO-incompatible transplantation

BACKGROUND

ABO incompatibility in organ transplantation is still a high risk factor for antibody-mediated rejection, despite the progress in effective treatments. We have explored the possibility of using the enzyme to remove the blood type A/B antigen in organs.

METHODS

Recombinant endo-beta-galactosidase (ABase), which releases A/B antigen, was produced in E. coli BL-21. Human A/B red blood cells (RBC) were digested with ABase, and subjected to flow cytometric analysis after incubation with human sera. Purified recombinant ABase was intravenously administered to a baboon. Biopsies were taken from kidney and liver before and 1, 4 and 24 h after in vivo administration. Excised baboon kidneys were perfused with cold UW solution+/-purified recombinant ABase and preserved at 4 degrees C. Biopsies were taken before and 1 and 4 h after ex vivo perfusion. The change in A/B antigen expression was analyzed by immunohistochemical study.

RESULTS

ABase removed 82% of A antigen and 95% of B antigen in human A/B red blood cells, and suppressed anti-A/B antibody binding and complement activation effectively. ABase was also found to remain active at 4 degrees C. In vivo infusion of ABase into a blood type A baboon demonstrated a marked reduction of A antigen expression in the glomeruli of kidney (85% at 1 h, 9% at 4 h and 13% at 24 h) and the sinusoids of liver (47% at 1 h, 1% at 4 h and 3% at 24 h) without serious adverse effects. After ex vivo perfusion and cold storage of excised baboon kidney (blood type B) with ABase, the expression levels of B antigen in glomeruli were reduced to 49% at 1 h and 6% at 4 h.

CONCLUSIONS

This alternative approach might be useful for minimizing antibody removal and anti-B cell immunosuppression as an adjuvant therapy in ABO-incompatible kidney, liver and possibly heart transplantation.