Definition of permissible and immunogenic HLA antigens based on epitope analysis of the HLA specific antibodies produced in sensitized patients

Abstract

The goal of this study was to develop an accurate protocol whereby detection of acceptable HLA-A and -B mismatches is based on epitope analysis of HLA class I specific antibodies detected in the serum of highly sensitized patients awaiting a kidney retransplant. A total of 400 serum samples from 44 highly sensitized patients with panel reactive antibodies (PRA) of > or = 60% were collected during a 3-year follow-up period. All patients had been sensitized from a previous graft. In order to define the specificities of the HLA class I specific antibodies, two techniques were used in parallel: the antihuman globulin augmented complement-dependent cytotoxicity (CDC) technique and an enzyme-linked immunoabsorbent assay (ELISA) technique. Epitope identification was based on class I HLA antigen sequencing, where the unique epitope configuration on one HLA antigen represented the private epitope of the specific HLA antigen, and epitopes shared by more than one HLA antigen represented public determinants. The epitope prediction for the immunogenic HLA epitopes was based on an MHC database. For each highly sensitized patient, antibody specificities against actual and 'at risk' epitopes were defined. Following epitope analysis, all HLA antigens that did not express the actual and/or 'at risk' immunogenic epitopes were considered as acceptable mismatches of epitope analysis. The cytotoxicity of highly sensitized patients was determined using two different panels of selected, separated T lymphocytes. HLA class I specific IgG antibodies against 69 actual and 86 'at risk' epitopes were detected. In all patients, a large number of acceptable mismatches were defined. These included a large number of HLA antigens, corresponding to both HLA-A and -B loci. Our study introduces an accurate protocol for the detection of acceptable mismatches in highly sensitized patients. According to this protocol, the detailed description of immunogenic HLA specific epitope targets, against which HLA class I specific antibodies are directed, is a useful tool for the detection of acceptable mismatches in highly sensitized patients. This may lead to reduced production of HLA class I specific antibodies and, consequently, improved graft survival.

Using Genetic Variation to Predict and Extend Long-term Kidney Transplant Function

“…13 This algorithm was particularly useful in interpreting sera antibody reactivity patterns against HLA panels in highly sensitized patients to determine donors with acceptable mismatches and has been incorporated into Eurotransplant's clinical protocol for highly sensitized patients, resulting in shorter waiting times for donor kidneys and graft survival rates comparable to those seen in nonsensitized patients. [14][15][16][17][18] There is debate, however, over whether using split HLA matching or HLAMatchmaker provides improvements over broad HLA matching in clinical practice. Kidney transplant outcome data reported to United Network for Organ Sharing and Eurotransplant registries suggested HLA matching of amino acid triplets improved graft survival compared to serologically define broad level HLA typing.…”

Antibody‐reactive epitope determination with HLAMatchmaker and its clinical applications

“…Permissible and immunogenic HLA antigens can be determined from epitope analyses of HLA‐specific antibodies in sensitized patients (36). HLAMatchmaker is a useful tool in the analysis of serum antibody reactivity of sensitized patients and the identification of potential donors with acceptable mismatches (8, 30, 37–39).…”