FLOW-CYTOMETRY PRA, A NEW TEST THAT IS HIGHLY CORRELATED WITH GRAFT-SURVIVAL

IgM antibodies present in the recipient sera are not necessarily harmful to the outcome of the graft. However, one primarily measures IgM with panel-reactive antibody (PRA) determined by microcytotoxicity. In order to develop a potentially more correlative PRA measurement, we have utilized the flow cytometer to measure IgG antibody to a panel of lymphocytes representing HLA antigens. This was accomplished by measuring the median channel shift associated with the patient's serum antibody binding to pooled target cells. The correlation between flow PRA and graft outcome was analyzed in 59 regraft recipients using current serum prior to transplantation. The PRA was determined by both cytotoxicity and flow cytometry. One-year follow up was available on all transplant recipients with 62% 1-yr actuarial graft survival. Cytotoxic PRAs were divided into greater than 10% and less than or equal to 10%, with a 72% vs 70% graft survival at 6 months and 62% vs 62% 1 yr graft survival, respectively. Flow cytometry PRA was divided into greater than 10 and less than or equal to 10 channel shift with 63% vs 86% graft survival at 6 months, and 53 vs 79% 1 yr graft survival respectively (p < 0.05 for both time intervals). Serum creatinine levels were concomitantly lower at 1 and 3 months in the flow PRA-negative recipients. Flow PRA was a simple, rapid test which eliminates "false" positives due to IgM and detects non-complement fixing IgG, which occurred in 25% of the samples. Flow PRAs were significantly correlated with graft survival and represented a new test which can be utilized as an in vitro correlate for immune response in the transplant candidate.