HLA TYPING FOR SOLID ORGAN TRANSPLANTATION: DNA VS SEROLOGY?
IM Buyse, J Ruth, S Warnell, BD Kahan and RH Kerman. University of TX Medical School, Houston, Texas

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Until the recent introduction of DNA typing procedures, serological typing has been the method of choice to identify HLA class I and class II antigens for solid organ transplantation. The solid organ transplantation setting requires reporting of serologically identified antigens, allows little or no sample batching and may impose a time restriction. Over the past few years, molecular HLA class II low resolution genotyping, using sequence-specific primers (SSP), has proven to be robust and accurate, allows for serology-equivalent results without concern for cell viability, antibody crossreactivities, and can be performed within the allowed time-frame in the clinical setting. With the sequence identification of HLA class I alleles, molecular SSP class I typing assays have also recently been introduced. In order to develop an adequate typing strategy, we evaluated the typing results for 87 patients using a commercial low-resolution SSP AB/DR tray and multiple serological ABC trays. Although SSP typing offered very accurate, robust, and fast results, the following weaknesses were identified; as a result of increasingly complex sequence patchwork patterns (as more alleles are identified) for both class II but especially for class I alleles, combinations of groups of alleles, sometimes crossing serological borders corresponded to particular primer reactivity patterns. In addition, with an increasing number of novel alleles not defined serologically, a typing result possibly included a blank allele serologically since no translation was possible. Therefore, in our opinion, combining the DNA results with serology rather than with high resolution DNA typing would be most effective. We decided against typing by serology only for previously stated reasons. We thus analyzed our serological data to find a single tray that would complement our DNA results resolution-wise, and identified a monoclonal tray to be the best candidate. In summary, we believe that the combination of both DNA and serology typing methodologies, rather than the sole usage of either technology, offers an adequate typing strategy for solid organ transplant HLA typing laboratories. Indeed, the complementation of DNA (SSP low resolution) AB/DR typing with I serological monoclonal class I tray combines accuracy and robustness with actual antigen identification in a cost-effective manner. In rare cases where a class II typing cannot be identified unambiguously, combining the result with a serological class II tray was also proven effective.