Advances in Pretransplant Donor-Specific Antibody Testing in Solid Organ Transplantation: From Bench to Bedside

Establishment of calculated panel reactive antibody and its potential benefits in improving the kidney allocation strategy in Taiwan

BACKGROUND/PURPOSE

Renal transplant candidates who are highly sensitized to human leukocyte antigens (HLAs) tend to wait longer to find a matched donor and have poor outcomes. Most organ-sharing programs prioritize highly sensitized patients in the allocation scoring system. The HLA sensitization status is traditionally evaluated by the panel-reactive antibody (PRA) assay. However, this assay is method dependent and does not consider the ethnic differences in HLA frequencies. A calculated PRA (cPRA), based on a population's HLA frequency and patients' unacceptable antigens (UAs), correctly estimates the percentage of donors suitable for candidates. The Taiwan Organ Registry and Sharing Center does not prioritize sensitized patients. We propose that the incorporation of the cPRA and UAs into the renal allocation program will improve the local kidney allocation policy.

METHODS

We established a cPRA calculator using 6146 Taiwanese HLA-A, -B, -C, -DR, and -DQ phenotypes. We performed simulated allocation based on the concept of acceptable mismatch for 76 candidates with cPRA values exceeding 80%.

RESULTS

We analyzed 138 waitlisted renal transplant candidates at our hospital, and we determined that the concordance rate of the cPRA and PRA for highly sensitized (%PRA > 80%) candidates was 92.5%, which decreased to 20% for those with %PRA < 80%. We matched 76 highly sensitized patients based on acceptable mismatch with the HLA phenotypes of 93 cadaver donors. Forty-six patients (61%) found at least one suitable donor.

CONCLUSION

The application of the cPRA and acceptable mismatch can benefit highly sensitized patients and reduce positive lymphocyte cytotoxicity crossmatch.