Donor-specific antibodies after transplantation by flow cytometry: relative change in fluorescence ratio most sensitive risk factor for graft survival.

BACKGROUND

There is no consensus on the role of donor-directed antibodies after renal transplantation detected by complement-dependent cytotoxicity (CDC) or by flow cytometry (FC).

METHODS

Therefore, antibody formation was studied by FC and correlated with clinical course in a group of patients who received transplants between 1983 and 1993. All had a negative current CDC crossmatch and were treated with cyclosporine. Current and posttransplant sera from 143 donor-recipient combinations were studied retrospectively. Antibodies were considered present in FC if the fluorescence ratio between serum and negative control was > 2.65.

RESULTS

Of 143 patients, 17 (11.9%) were found to be positive in the posttransplant FC crossmatch and 126 (88.1%) were negative. Of the positive patients, 3 were already positive in the current FC crossmatch, whereas 14 demonstrated a positive posttransplant FC crossmatch after a negative current FC crossmatch. It was noteworthy that, from 16 patients with a positive current FC crossmatch, 13 turned negative in the posttransplant crossmatch. In 113 recipients (79%), both pre- and posttransplant FC crossmatches were negative. The development of a positive FC crossmatch after transplantation was a significant risk factor for graft survival in Cox regression analysis (P = 0.01). The results were also studied as relative change in fluorescence ratio (RCFR). RCFR was determined by classifying the recipients in quartiles according to their change in flow cytometric value from current to posttransplant serum. Quartiles were defined as follows: quartile 1, decrease > 10%; quartile 2, decrease 0-10%; quartile 3, increase > 0-30%; and quartile 4, increase > 30%. RCFR proved to be the only significant risk factor for graft survival (odds ratio for quartile 4 vs. quartile 1, 3.27; P < 0.02). More rejections were shown for increasing quartile numbers (P < 0.001).

CONCLUSIONS

Classification of patients by RCFR detected more patients with unfavorable clinical outcome (25% vs. 11%) than by FC crossmatch.