Detection of Intragraft Anti-Blood Group A and B Antibodies Following Renal Transplantation

Early Thrombotic Microangiopathy After ABO-Incompatible Living Donor Kidney Transplantation

Introduction

Although long-term graft survival is comparable with that of ABO-compatible (ABOc) renal transplantation, the risk of antibody-mediated rejection (ABMR) following ABO-incompatible (ABOi) transplantation is higher and can occur as an early thrombotic microangiopathy (TMA).

Methods

We designed a retrospective multicenter study, including all patients who presented with a TMA (histological and/or biological) after an ABOi transplantation (< 1 month) and compared with matched controls who had a favorable initial course with a normal biopsy.

Results

Between 2013 and 2022, 375 ABOi kidney transplants were performed and 23 patients (6.1%) developed TMA (median: 1 day, interquartile range [IQR]: 0-3 days). Twenty-one patients (91.3%) had biological TMA. Among 23 early graft biopsies, histological evidence of active TMA was found in 17 cases (80.9%). All patients received treatment: 20 of 23 received at least 1 session of plasmapheresis and 19 of 23 received at least 1 injection of eculizumab. Eight early graft losses (30.4%) occurred (median: 7 days, IQR: 3-16 days). IgG and IgM anti-blood group antibody (ABGA) levels (peak and last pregraft assay) were significantly higher in the TMA group (peak: P = 0.01 for IgG and P = 0.0006 for IgM; last assay before kidney transplantation [KT]: P < 0.0001 for IgG and P = 0.0003 for IgM). A level ≥ 1/8 for IgG and ≥ 1/4 or IgM before transplantation were significantly and independently predictive of the occurrence of TMA. No other predictive factors were found.

Conclusion

TMA after ABOi transplantation is not a rare phenomenon and is associated with a poor prognosis in nonresponders-to-treatment patients. ABGA titer performed by hemagglutination is an imperfect marker of the occurrence of such a phenomenon.

ABO-incompatible living kidney transplantation

ABO-incompatible living kidney transplantation is nowadays a routine procedure to expand living donor pool. The past decades have seen the evolution of desensitization protocol and immunosuppression regimen. Despite increased bleeding events, infectious complications, and rejection episodes reported in some studies, favorable graft and patient survival rate are now achieved, regardless of various protocols among transplant centers. Several issues such as the usage of rituximab and standardization of blood group antibody titration remain to be settled. The deposition of C4d is no longer the histopathologic hallmark of antibody-mediated rejection, which have inspired innovative strategies of peripheral molecular screening and the improvement of histological diagnosis of AMR (antibody-mediated rejection). The better understanding of the underlying mechanism might facilitate the distinction and therapeutic schemes of AMR.

The Role of Major Histocompatibility Complex in Organ Transplantation- Donor Specific Anti-Major Histocompatibility Complex Antibodies Analysis Goes to the Next Stage

Organ transplantation has progressed with the comprehension of the major histocompatibility complex (MHC). It is true that the outcome of organ transplantation largely relies on how well rejection is managed. It is no exaggeration to say that to be well acquainted with MHC is a shortcut to control rejection. In human beings, MHC is generally recognized as human leukocyte antigens (HLA). Under the current circumstances, the number of alleles is still increasing, but the function is not completely understood. Their roles in organ transplantation are of vital importance, because mismatches of HLA alleles possibly evoke both cellular and antibody-mediated rejection. Even though the control of cellular rejection has improved by recent advances of immunosuppressants, there is no doubt that antibody-mediated rejection (AMR), which is strongly correlated with donor-specific anti-HLA antibodies (DSA), brings a poor outcome. Thus, to diagnose and treat AMR correctly is a clear proposition. In this review, we would like to focus on the detection of intra-graft DSA as a recent trend. Overall, here we will review the current knowledge regarding MHC, especially with intra-graft DSA, and future perspectives: HLA epitope matching; eplet risk stratification; predicted indirectly recognizable HLA epitopes etc. in the context of organ transplantation.