FREQUENCY OF POSITIVE CROSSMATCHES IN HLA CREG-MATCHED POTENTIAL RENAL TRANSPLANT RECIPIENTS. VA Lazda, Histocompatibility Laboratory, Regional Organ Bank of Illinois, Chicago, IL.

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One proposed benefit of CREG matching is the likelihood of a negative crossmatch with donors for sensitized potential recipients. We analyzed the frequency of positive crossmatches for these patients (current PRA > 10%) when there were no CREG mismatches with a crossmatched donor. The 9 CREG groups adopted for the UNOS voluntary CREG matching variance were used. Actual crossmatch results for a 3 month period (74 cadaver donors) were examined. T-cell crossmatches were performed using a 4-wash antiglobulin-enhanced cytotoxicity test (AHG-CDC) using two most current sera. A total of 747 donor/recipient crossmatch results were selected from the database - all had a zero-CREG mismatch with the donor (0-A,B mismatched pairs were excluded). The frequency of positive crossmatches correlated with PRA levels (Table). Positive crossmatches were significantly more common with certain donor mismatches, e.g.,

HLA-A2, and rare with others, e.g., A30, B8, B42.

We conclude that despite a zero-CREG mismatch positive crossmatches do occur, especially in highly-sensitized patients. Antibody formation against the HLA "private" epitopes within a CREG is a likely explanation, with some epitopes, e.g., A2 being more immunogenic.