Evidence of immune tolerance to blood group antigens in a case of ABO-incompatible pediatric liver transplantation

Challenge to ABO blood type barrier in living donor liver transplantation

ABO incompatible living donor liver transplantation has the potential to expand the donor pool for patients with end stage liver diseases on the expense of challenges to overcome immunological barriers across blood type. There is a profound impact of age on incidence and severity of antibody mediated rejection (AMR). Even children older than 1 year have chances of AMR; children aged 8 years or older have risks of hepatic necrosis similar to adult liver recipients. The mechanism of AMR is based on circulatory disturbances secondary to inflammation and injury of the vascular endothelium caused by an antibody-antigen-complement reaction. The strategy to overcome ABO blood type barrier is based on both pre-transplant desensitization and adequate treatment of this phenomenon. Nowadays, rituximab is the standard means of desensitization but unfortunately an insufficient aid to treat AMR. Because of low incidence (less than 5% in the rituximab era), in practice of AMR only some case reports about the treatment of clinical AMR are available in the literature. Initial experiences revealed that the proteasome inhibitor, bortezomib might be a promising treatment based on its capacity to deplete plasma cell agents. Although ABO blood type barrier has been counteracted in 95% of patients by applying "rituximab-desensitization", many issues, such as prediction of high-risk patients of infection and AMR and secure treatment strategies for evoked AMR, remain to be resolved.

Low Titers of Antidonor ABO Antibodies After ABO-Incompatible Living Donor Liver Transplantation: A Long-Term Follow-Up Study

Background

The ABO blood-type barrier in kidney and liver transplantation has been overcome by aggressive treatments such as B cell depletion using rituximab. However, the long-term effects of ABO-incompatible liver transplantation (ABO-I LTx) on immunological status have not previously been studied. Here, we assessed whether long-term immune hyporesponsiveness against ABO blood-group antigens was retained.

Methods

We recruited 81 patients, 75 patients who had survived ABO-I LTx without retransplantation and 6 patients who had survived after retransplantation using blood type-compatible grafts. The time between ABO-I LTx and outpatient visits for blood sampling for this study ranged from 1.1 to 16.8 years. We also evaluated patients' backgrounds and postoperative therapies.

Results

Overall, antidonor ABO antibody titers in the 75 patients without retransplantation decreased during long-term follow-up. In the subset of 40 patients with blood type O, anti-nondonor ABO antibody titers did not decrease and were significantly higher than antidonor ABO antibody titers. In addition, long-term antidonor ABO antibody titers were significantly lower in pediatric patients than in adult patients. In the 6 patients who were retransplanted with blood type–compatible grafts, antidonor ABO antibody immunoglobulin G titers remained low, but IgM titers increased slightly long after removal of the ABO-incompatible graft.

Conclusions

These findings suggest that donor-specific hyporesponsiveness remains after ABO-I LTx, particularly in pediatric patients. Long-term persistence of blood antigens may contribute to this donor-specific hyporesponsiveness.

The Role of Liver Sinusoidal Endothelial Cells in Induction of Carbohydrate Reactive B Cells Tolerance Through the Programmed Death 1/Programmed Death Ligand 1 Pathway

BACKGROUND

A spontaneous tolerance of B cells responding to blood group antigens frequently develops in ABO-incompatible pediatric liver transplantation (LT). Liver sinusoidal endothelial cells (LSECs), which exclusively express blood group antigens in the liver, possess a capacity to induce alloantigen-specific tolerance. In this study, we elucidated the role of LSECs in the tolerance induction of blood group antigen-reactive B cells after ABO-incompatible LT using mice that lack galactose-α(1,3)galactose (Gal) epitopes resembling blood group carbohydrate antigens.

METHODS

Using adoptive transfer of LSECs from wild type (WT) C57BL/6J mice to congenic α1,3-galactosyltransferase gene knockout (GalT) mice, we established orthotropic GalT → GalT LSEC chimera mice. Anti-Gal Ab (antibody) production was evaluated after immunization of GalT → GalT LSEC chimera mice with Gal rabbit RBC.

RESULTS

Adoptive transfer of LSECs isolated from WT GalT mice via the portal vein resulted in persistent engraftment of Gal LSECs in congenic GalT mouse livers. Only when GalT mice were splenectomized before LSEC inoculation, the GalT → GalT LSEC chimera lost the ability to produce anti-Gal Abs. The administration of blocking monoclonal Abs (mAbs) against programmed death ligand 1 to the splenectomized GalT → GalT LSEC chimera resulted in the recovery of anti-Gal Ab production.

CONCLUSIONS

These findings suggest that LSECs take a part in tolerization of immature but not mature B cells specifically for Gal. Furthermore, the programmed death 1/programmed death ligand 1 pathway likely plays a crucial role in the mechanisms underlying spontaneous tolerization of B cells responding to ABO-blood group antigens in LT.

Production of anti-ABO blood group antibodies after minor ABO-incompatible bone marrow transplantation in NOD/SCID/gamma(c)(null) mice

ABO incompatibility is a barrier for solid organ transplantation, but not for hematopoietic stem cell transplantation. To investigate tolerance induction, we enrolled patients who had undergone minor ABO-incompatible (O into A group, n = 6) and ABO-identical (O into O group, n = 4) bone marrow transplantation (BMT). None of the six O into A patients were positive for recipient-specific (anti-blood group A) isohemagglutinins, whereas all four O into O patients were. Peripheral blood mononuclear cells (PBMCs) were engrafted into NOD/SCID/gamma(c)(null) (NOG) mice, followed by sensitization of blood group A red blood cells. Anti-blood group A antibodies (Abs) in the sera of the patients and the human PBMC-engrafted NOG mice were measured by enzyme-linked immunosorbent assays. Anti-blood group A Abs in the patients' sera were significantly correlated with anti-A isohemagglutinin titers (p < 0.01). In the human PBMC-engrafted NOG mice, anti-blood group A Abs were significantly lower in the O into A group than in the O into O group (p < 0.05), despite ex vivo restimulation of B cells. The results of this study suggest that long after receiving minor ABO-incompatible BMT, B cells derived from newly engrafted donor precursor cells were induced tolerance to recipient-specific antigens.

Current progress in ABO-incompatible liver transplantation

BACKGROUND

ABO-incompatible (ABOi) living donor liver transplantation (LDLT) in adult patients has been controversial because of the high risk of antibody-mediated rejection (AMR) mediated by preformed anti-ABO antibodies. However, outcomes have recently improved owing to various treatment advances.

MATERIALS AND METHODS

This review article describes the history and current progress in ABOi liver transplantation, mainly from the viewpoint of the Japanese experience.

RESULTS

The typical clinical manifestations of AMR are hepatic necrosis and intrahepatic biliary complication. The outcomes of early ABOi LDLT were poor, especially in older children and adult cases. Since we first introduced portal vein infusion therapy into adult ABOi LDLT in 1998, local graft infusion therapy has emerged in Japan as a crucial breakthrough to overcome the ABO blood group barrier. From 2003, rituximab prophylaxis has been widely used with local graft infusion, and has resulted in markedly improved patient survival. The novel approach of intravenous immunoglobulin induction may become another option to suppress AMR. Continued patient enrollment and controlled trials will allow further validation of these treatments.

CONCLUSIONS

The outcome of ABOi LDLT is now similar to that of blood-type-matched transplantation in Japan. However, infection is the major cause of morbidity and mortality after ABOi LDLT. Thus, evaluation of the patients' immune status and adjustment of immunosuppression will be the way forward in the future.

Current status of liver transplantation across ABO blood-type barrier

Outcomes of ABO-blood type incompatible liver transplantation have recently improved owing to various treatments. The typical clinical manifestations of antibody mediated rejection (AMR) are hepatic necrosis and intrahepatic biliary complication (IHBC). The prognosis of AMR is poor. AMR is the result of circulatory disturbance which is caused by injury to the endothelium due to an antibody-antigen-complement reaction. Diffuse C4d staining in the portal capillaries and periportal areas in severe AMR. Since natural antibodies against A/B carbohydrate determinants are likely to develop as a result of exposure to environmental bacteria that express similar determinants, the B-1 lineage has been speculated to be the major population of B-cell types responding to A/B determinants. Calcineurin inhibitors block B-1 cell differentiation. Rituximab can be used to deplete both cells that are producing IgM antibodies and those that have already differentiated into B-1 cells. Mycophenolate mofetil is required to inhibit the production of IgG subclass of antibodies. The outcome is now similar to that of blood-type-matched transplantation. However, there are still issues to be solved in order to further improve the outcome via a decrease of infection.

The persistent elimination of B cells responding to blood group A carbohydrates by synthetic group A carbohydrates and B-1 cell differentiation blockade: novel concept in preventing antibody-mediated rejection in ABO-incompatible transplantation

We demonstrated a novel strategy for specific and persistent inhibition of antibody (Ab) production against blood group A or B carbohydrate determinants necessary for successful ABO-incompatible transplantation. Similar to human blood group O or B individuals, mice have naturally occurring Abs against human blood group A carbohydrates in their sera. B cells with receptors for A carbohydrates in mice belonging to the CD5+CD11b+B-1a subset have phenotypic properties similar to those of human B cells. These cells could be temporarily eliminated by injecting synthetic A carbohydrates (GalNAcα1–3, Fucα1–2Gal) conjugated to bovine serum albumin (A-BSA) and anti-BSA Abs. In mice that received the injection of A-BSA/anti-BSA Abs, the serum levels of anti-A IgM were reduced, but immunization with human A erythrocytes resulted in increased serum levels of anti-A Abs. When combined with cyclosporin A (CsA) treatment, which blocks B-1a cell differentiation, and treatment with A-BSA/anti-BSA Abs, the serum levels of anti-A Abs were persistently undetectable in the mice even after the immunization. B cells with receptors for A carbohydrates were markedly reduced in these mice. These results are consistent with the hypotheses that treatment with A-BSA/anti-BSA Abs temporarily depletes B cells responding to A determinants, and CsA treatment prevents the replenishment of these cells.