DETERMINATION OF ACCEPTABLE HLA MISMATCHES IN HIGHLY SENSITIZED PATIENTS BY sHLA-ELISA INHIBITION.
Carin A. Koelman, Els van Beelen, Marian D. Witvliet, Ilias I.N. Doxiadis, Frans H.J. Claas. Leiden University Medical Center, Leiden, The Netherlands
Background: Acceptable HLA mismatches (AM) are determined for highly sensitized patients to increase the chance to be transplanted. The disadvantage of the current procedures is that the antibody reactivity of the patients sera are tested against HLA antigens expressed on cells or HLA antigens isolated from cell lysates. Therefore, two (homozygous for HLA-A and -B) to four (heterozygous for HLA-A and -B) different HLA Class I antigens are present in the test. This might cause that reactivity towards non-acceptable mismatches mask the determination of acceptable mismatches.
Methods: recently we observed that the detection of soluble HLA (sHLA) class I antigens is inhibited by HLA specific antibodies. In the present study, inhibition of sHLA-specific ELISAs (anti sHLA-A2, -B7, -B12) was evaluated as a tool to determine AM. The results were compared with current determination of AM (which is CDC and/or FACS).
Results: In case of AM determined by the conventional methods, sera from the patients were not interfering in these ELISAs, whereas in case of non-AM (thus specific antibodies) a significant inhibition was observed in the majority of the cases. In case of the non-AM, 20 of the 24 cases showed a significant inhibition of the test, while in case of AM (8 out of 8) no inhibition was observed, indicating the lack of specific antibodies.
Conclusions: In highly sensitized patients, the introduction of sHLA-specific ELISAs are of additional and confirmatory value for the determination of acceptable mismatches. The major advantage of this approach is that the antibody reactivity is tested against single antigens only.