Anti-donor immunoglobulin G subclass in liver transplantation

Cellular and Molecular Crosstalk of Graft Endothelial Cells During AMR: Effector Functions and Mechanisms

Graft endothelial cell (EC) injury is central to the pathogenesis of antibody-mediated rejection (AMR). The ability of donor-specific antibodies (DSA) to bind C1q and activate the classical complement pathway is an efficient predictor of graft rejection highlighting complement-dependent cytotoxicity as a key process operating during AMR. In the past 5 y, clinical studies further established the cellular and molecular signatures of AMR revealing the key contribution of other, IgG-dependent and -independent, effector mechanisms mediated by infiltrating NK cells and macrophages. Beyond binding to alloantigens, DSA IgG can activate NK cells and mediate antibody-dependent cell cytotoxicity through interacting with Fcγ receptors (FcγRs) such as FcγRIIIa (CD16a). FcRn, a nonconventional FcγR that allows IgG recycling, is highly expressed on ECs and may contribute to the long-term persistence of DSA in blood. Activation of NK cells and macrophages results in the production of proinflammatory cytokines such as TNF and IFNγ that induce transient and reversible changes in the EC phenotype and functions promoting coagulation, inflammation, vascular permeability, leukocyte trafficking. MHC class I mismatch between transplant donor and recipient can create a situation of "missing self" allowing NK cells to kill graft ECs. Depending on the microenvironment, cellular proximity with ECs may participate in macrophage polarization toward an M1 proinflammatory or an M2 phenotype favoring inflammation or vascular repair. Monocytes/macrophages participate in the loss of endothelial specificity in the process of endothelial-to-mesenchymal transition involved in renal and cardiac fibrosis and AMR and may differentiate into ECs enabling vessel and graft (re)-endothelialization.

Immunological Role of IgG Subclasses

The loss of tolerance to self-antigens is the unequivocal "red line" of autoimmunity: both development of autoreactive T and B cells and production of polyclonal autoantibodies represent seminal keys to the pathogenesis of protean autoimmune diseases. Most of these autoantibodies are immunoglobulins G (IgG), functionally distinguished in four subclasses named IgG1, IgG2, IgG3, and IgG4, due to structural differences in the hinge and heavy chain constant regions. Different studies analyzed serum levels of IgG subclasses in the course of different disorders, showing that they might have a pathogenic role by regulating interactions among immunoglobulins, Fc-gamma receptors, and complement. To date, the mechanisms promoting different IgG subclasses distribution during the natural history of most autoimmune diseases remain somewhat unclear. Evidence from the medical literature shows that the serum IgG profile is peculiar for many autoimmune diseases, suggesting that different subclasses could be specific for the underlying driving autoantigens. A better knowledge of IgG subsets may probably help to elucidate their pathological task, but also to define their relevance for diagnostic purposes, patients' personalized management, and prognosis assessment.

Bidirectional graft-host hematological traffic in liver transplantation

The highly complex immuno-hematological system of the recipient has to rebalance itself when the liver is replaced with a graft that has its own system. This gives us an opportunity for observation. Here we consider the graft-to-recipient direction with passenger lymphocyte syndrome (PLS) as well as the recipient-to-graft direction with Factor VIII (FVIII) inhibitors, paroxysmal nocturnal hemoglobinuria (PNH) and graft endothelial replacement with liver transplantation. PLS extends beyond the ABO blood groups to any situation where the donor has been sensitized to a recipient antigen. PLS directed against ABO or minor blood group antigens is usually self limiting whereas Rhesus (Rh) PLS persists with life threatening immune hemolysis. Human platelet antigen (HPA) 1A PLS results in life threatening immune thrombocytopenia. Treatments of severe PLS may include reduction in immunosuppression, anti-B-cell therapy, plasmapheresis and splenectomy. Liver transplantation into recipients with FVIII inhibitors has been difficult. Donors with acquired hemophilia may transmit the capacity to make FVIII inhibitors by PLS and should be avoided. Patients with PNH have been transplanted successfully but a considerable cost in the continued use of high dose eculizumab. We speculate that combined bone marrow and liver transplantation would be a better option for recipients with FVIII inhibitors or PNH. Replacement of liver graft endothelium with recipient cells is common and may explain relative transplant tolerance that is believed to occur with liver transplantation.

The impact of alloantibodies directed against the second donor on long-term outcomes of repeat liver transplantation

Background

Despite reports that associate donor specific antibody (DSA) with rejection after liver transplantation, grafts are still allocated according to blood group (ABO) but not human leukocyte antigen (HLA) compatibility, possibly due to the absence of an easily discernible clinical association between adverse recipient outcome and DSA. Re-transplantation provides a test environment where the presence of preformed DSA is prevalent and its effect on outcome should be apparent.

Methods

All patients undergoing a second liver transplantation with available pre-operative serum were included with the exception of ABO incompatible or multiple organ transplants. Banked sera were tested for anti-HLA antibodies with Luminex-based solid phase assays. Anti-HLA antibodies to the second donor (D2SA) were determined using antibodies specificity and HLA typing of 2nd liver donor.

Results

Preformed HLA antibodies directed to second liver transplantation (D2SA) were found in 31 (39%) of the 79 patients that were included in the study. Primary and re-transplantation characteristics were similar in both subgroups except first graft survival which was significantly shorter in recipients who are negative for D2SA. Mean survival of the second graft was similar in D2SA+ and D2SA- cohorts [8.55 (range, 0.01-24.74) vs. 7.56 (range, 0-23.53) years respectively, P=0.574]. Mean patient survival after 2nd liver transplantation was similar in D2SA+ and D2SA- cohorts [9.11 (range, 0.01-24.74) vs. 8.10 (range, 0-23.53) years respectively, P=0.504]. Subgroup univariate analysis demonstrated no detrimental effect of class, locus, or strength of D2SA on survival of the second liver transplant. In multivariate cox regression model, neither class I D2DSA (HR =1.101, P=0.92) nor class II D2SA (HR =1.74, P=0.359) were significant risks of graft failure.

Conclusions

Presence of D2SA was not found to be associated with inferior outcomes in this retrospective cohort study of liver re-transplantation suggesting that changes to the allocation system are not required.