Multi-array antibody screening in detecting antibodies to mismatched HLA in patients awaiting a second transplant

Effective identification of HLA specificities to which a prospective transplant recipient has antibodies depends on how effective the most sensitive assay is in detecting these antibodies. To ascertain the assay’s efficacy, the results of antibody screening of patients on the waiting list for a second transplant were studied. A commercially available panel of fluoro-coded microbeads coated with multiple and single purified class I or II HLA antigens was used with flow cytometry to detect antibodies in human serum (LABScreen, One Lambda, Canoga Park, Calif, USA). A total of 112 HLA-A, B, and DR mismatches between donors and recipients were present among 34 patients. Antibodies to 56% of the mismatches were detected with 67% of the HLA-A, 38% of the HLA-B, and 63% of the HLA-DR mismatches detected, respectively. Thirty percent of the patients had antibodies to all of the mismatched HLA, 43% had antibodies to some, and 27% did not develop antibodies to any of the mismatched antigens. Among patients who developed antibodies to all of the mismatched HLA, 60% had had a transplant nephrectomy. Only 11% of patients who had no antibodies detected to mismatched HLA had had a transplant nephrectomy and 44% of them were still on immunosuppression. Using the Matchmaker program developed by Duquesnoy, the latter group of patients had a sufficient number of triplet mismatches that could have resulted in an antibody response. All of the undetected antibodies had been identified in other patients in this group. The assay used in this study to detect antibodies is considered the most sensitive one available. Nonetheless, antibodies to slightly less than half of the mismatched HLA antigens were not detected. It appears that the assay system is capable of detecting the antibodies, since in other patients with the same mismatched HLA, antibodies were detected. It is likely that the recipients could develop antibodies since there was a sufficient degree of disparity in the HLA of donors and recipients. Antibodies were more likely to be detected when there had been a transplant nephrectomy and the absence of immunosuppression. There was no way of knowing whether we were missing detecting antibodies or if they were not present. The results of this study have important implications with respect to utilizing “unacceptable antigens” in an allocation system for patients awaiting a second transplant.