EFFICACY AND CLINICAL RELEVANCE OF ELISA-BASED CROSSMATCHING (XM) RELATIVE TO THE COMPLEMENT-DEPENDENT CYTOTOXICITY (CDC) XM

Abstract

453 The XM is utilized to identify transplant candidates with no serologically detectable anti-donor antibody (Ab) reactivity in order to select donor-recipient pairings for successful graft outcomes. Disadvantages of CDC XM methods are the requirements for complement and viable target cells, detection of Ab against non-HLA antigens, and subjective scoring. A recently developed ELISA XM procedure (Cross-Sta®, SangStat Medical Corp.) uses donor HLA captured onto ELISA plates to detect donor-specific anti-HLA class I Ab, and is therefore theoretically devoid of these flaws. We compared results between our standard anti-human-globulin (AHG)-enhanced CDC XM and Cross-Stat on 148 pre-Tx sera from 61 renal allograft recipients that were all negative (NEG) for anti-donor IgG Abs by AHG-CDC XM, and 362 sera from 170 potential Tx patients that were either AHG-CDC IgG-XM positive (POS) or Neg against the same donors. Seventy-eight samples gave "indeterminant" (IND) results by Cross-Stat. For the remaining 426 samples there was a significant correlation between AHG-CDC and Cross-Stat results (χ2=39.09, p<0.001). As a consequence of the high frequency of Cross-Stat False Neg results relative to AHG-CDC Tru Pos results, "Sentivity" of the Cross-Stat method was 58%. For sera which gave False Neg results, however, repeat AHG-CDC XMs were still Pos after platelet-absorption, indicating the presence of non-HLA antibodies, which are not detectable by Cross-Stat (and whose role in allograft survival is not well defined). The frequency of False Pos results by Cross-Stat relative to AHG-CDC XM Tru Pos results yields a"Positive Predictive Value" for Cross-Stat of 39%. However, flow cytometry XM results usually substantiated the Cross-Stat results, indicating that this discrepancy may be due to greater sensitivity of Cross-Stat for anti-HLA Ab detection. Among 37 Cross-Stat Neg vs. 10 Cross-Stat Pos primary cadaveric renal allograft recipients (all AHG-CDC IgG-XM Neg), there was not a statistically significant difference in the overall graft survival times of 50.1 months (follow-up to 59.3) vs. 45.5 months (follow-up to 64.0). Thus, preliminary results indicate that in sera devoid of AHG-CDC XM detectable anti-donor reactivity, the ELISA identified anti-HLA Abs are not clinically deleterious to primary recipients. Given the important theoretical advantages of ELISA-based XM methods over the CDC XM, however, further testing of the clinical relevance of the Cross-Stat is warranted.Table