This single-center study showed that in the AM program DDA detected by SA, and not by less-sensitive methods, may be related to acute rejection episodes but is not detrimental to long-term graft outcome. These findings question the increasing use of more-sensitive screening techniques for the allocation of organs.

In Luminex bead-based screening assays, color-coded microspheres coated with human leukocyte antigens (HLA) are used to identify both complement-binding and non-complement-binding HLA class I and II antibodies in recipient sera. Many laboratories rely on their specificity detection and use the information obtained for allocation of donor organs. A donor-specific crossmatch in the Luminex technique (LumXm) is for that reason desirable. A LumXm, in which the actual donor HLA are coated onto specific capture beads, was tested for 88 pre- and posttransplant sera of 18 recipients. The results were compared with previously published flow cytometric crossmatch (FCXm) results for the same donor-recipient combinations. All sera were also examined by Luminex single antigen (SA) tests. Class I LumXm detected 24 of 27 T-cell positive FCXm (89%) and class II 15 of 22 B-cell positive FCXm (68%). Sensitivity of LumXm for class I and II was 89% and 68% and specificity was 98% and 97%, respectively. Discrepant LumXm results were obtained in 13 sera of nine patients (15%). In general, based on SA testing, FCXm showed false-positive results for class I and LumXm gave false-negative and positive results for class II. The LumXm test was proven not to react with recipient sera containing DQ antibodies only, also DP detection was insufficient. The validity of the LumXm has been shown for class I, but its value for class II is uncertain. HLA-DR is most probably correctly identified, the validity for DQ and DP is doubtful.

Human leukocyte antigen (HLA)-DP is considered a target for humoral immune response in clinical transplantation. This study analyses the incidence of HLA-DP antibodies in renal patients. Development and epitope specificity of donor-specific antibodies (DSA) and non-DSA (NDSA) were examined. Pre- and posttransplant sera of 338 patients were screened for HLA-DP antibodies using the luminex single antigen assay. Positive patients, partners and/or kidney donors were HLA-DP typed by sequence-specific oligonucleotides. Potential epitopes were mapped by comparing the amino acid sequences of HLA-DP hypervariable regions (HVR) A-F of recipient, partner and/or donor. Specificities in the sera were aligned to deduce the HVR motif responsible for the antibodies. HLA-DP antibodies were detected in 14% of the patients (48/338). Before transplantation, the antibodies were shown in 23% (10 females and 1 male) and 77% were found after transplantation (30 in patients after the first, 7 after the second graft). Specificities were never restricted to individual mismatched antigens; broad HLA-DP sensitization was found as a rule. A single HVR mismatch was present in 80% of the DSA and in 79% of the NDSA. No HLA-DPA specific antibodies were found. Our findings confirm that HLA-DP antibodies are specific for epitopes shared by different HLA-DP antigens, indicating that only a restricted number of mismatched epitopes are recognized by the recipients immune system. Matching for immunogenic HLA-DP epitopes for renal transplantation seems to be functionally more relevant than classical matching at the allelic level.

Donor-directed HLA antibodies after transplantation were demonstrated in 81% of first transplant recipients, all of whom were DDA negative by LSA before transplantation. The majority of the antibodies was found after transplantectomy. These findings may have to be taken into consideration in the allocation of organs of marginal donors such as older or nonheart beating kidneys.

The clinical significance of the presence of donor-specific anti-human leucocyte antigen (HLA) antibodies (DSA) prior to renal transplantation detected solely by solid-phase techniques remains unclear. This study was designed to determine the clinical relevance of the recently introduced bead-based Luminex donor-specific crossmatch (LumXm). A group of 165 patients transplanted between 1997 and 2001 were tested. Of 165 recipients transplanted with a negative complement-dependent cytotoxicity crossmatch, 32 proved to have a positive Luminex crossmatch. Sixteen were positive for class I, 15 were positive for class II, 1 was both class I and II positive and 133 recipients were negative. Acute rejection (AR)-free survival for all recipients was 77%, and there was no difference in AR-free survival between LumXm-positive and LumXm-negative recipients. Overall graft survival after a median follow-up time of 8 years was 56%. Recipients with a positive class I LumXm had worse long-term graft survival (P = 0.006). In recipients with a positive class I LumXm, 5-year graft survival was 41% vs 70% in negative patients and 10-year graft survival was 27% vs 56%. Positivity for class II LumXm was not a significant risk factor for graft failure (P = 0.7). In conclusion, pretransplant DSA detected by the LumXm had no impact on AR episodes. Class II LumXm positivity proved no significant risk factor for graft failure, but the value of the class II LumXm is questionable. A positive class I LumXm resulted in worse long-term graft survival compared with a negative one.