Preliminary Results of [ 99m Tc]OKT3 Scintigraphy to Evaluate Acute Rejection in Renal Transplants F.P.P. Martins, S.A.L. Souza, R.T. Gonçalves, L.M.B. Fonseca, and B. Gutfilen ABSTRACT Allograft rejection can be classified as humoral or cellular mechanisms. Accurate diagnosis of acute rejection remains a formidable challenge in renal transplantation. The need to avoid unnecessary immunosuppressive therapy to treat this complication has led to a continued search for improved diagnostic methods to evaluate and identify postoperative episodes. Here we evaluated the use of [ 99m Tc]OKT3 scintigraphy to diagnose acute rejection in renal transplants. Among 22 patients undergoing renal transplant, we observed an increased [ 99m Tc]OKT3 kidney uptake with the passage of time in patients with rejecting allografts. These findings agreed with those of biopsies. We suggest the [ 99m Tc]OKT3 scans may be useful for the monitoring of renal transplants to detect acute rejection. T RANSPLANTATION HAS REVOLUTIONIZED the treatment of end-stage renal disease by being more cost-effective than hemodialysis and showing a lower morbidity rate and an improved quality of life. Despite high graft and patient survival figures, a variety of parenchymal complications can threaten the transplant in the postoper- ative period, including rejection episodes, acute tubular necrosis, or cyclosporine toxicity. 1,2 An acute rejection episode (ARE) occurrs in 20% to 30% of grafts. The occurrence of an ARE may be the single most important event determining the short- (1-year) and long- term (5-year) graft survival. Among those grafts afflicted, roughly equal proportions have single versus multiple ARE. The first ARE typically occurs within 6 months of trans- plantation, indeed, often within the first 5 weeks. 1,3 Not uncommonly, empiric antirejection therapy is admin- istered prior to a final diagnosis by a confirmatory histolog- ical report. Thus, there is an urgent need for a specific and sensitive noninvasive diagnostic method to detect acute rejection. 3,4 The differential diagnosis of graft dysfunction is achieved by the clinical history, sonographic and Doppler findings, renal arteriography, scintigraphy, magnetic resonance im- aging, and positron-emission tomography. Despite the use of these diagnostic tools, the histological examination is considered the gold standard to establish the diagnosis and guide the therapy. However, biopsy procedures are invasive and associated with complications. 5–7 OKT3 is an antibody that is particularly effective to reverse or prevent rejection episodes in renal transplant patients, since it causes the depletion of peripheral CD3- positive T cells, which are responsible for many allograft failures due to rejection episodes. 8 So the aim of this study was to evaluate the use of this antibody labelled with Tc-99m as a noninvasive diagnostic tool for early rejection diagnosis. PATIENTS, MATERIALS, AND METHODS All recipients of primary renal allografts were eligible for entry into the study, which was approved by the Commitee for the Protection of Human Research Subjects. We analyzed 22 patients who gave informed consent without exclusion criteria. Twenty-two healthy volunteers constituted the control group. OKT3 was labeled with technetium-99m according to the tech- nique developed by Martins and Gutfilen. 8 Briefly, OKT3 (300 L) was incubated for 10 minutes with 2-mercaptoethanol (2-ME, exogenous chelator). SnCl 2 was added to the solution for another 10, minute incubation. Tc-99m (370 MBq) was incubated for 20 minutes. Filtration via a Milipore 0.45  separated unbound Tc-99m and colloid from [ 99m Tc]OKT3. The total activity of the From the Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil. Supported by Fundação José Bonifácio/UFRJ (FUJB), Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ), Conselho Nacional do Desenvolvimento Cientı´fico e Technológico (CNPq). Address reprint requests to Prof Bianca Gutfilen, Universidade Federal do Rio de Janeiro, 21941-590 Rio de Janeiro, RJ Brazil. E-mail: bgutfilen@hucff.ufrj.br 0041-1345/04/$–see front matter © 2004 by Elsevier Inc. All rights reserved. doi:10.1016/j.transproceed.2004.09.085 360 Park Avenue South, New York, NY 10010-1710 2664 Transplantation Proceedings, 36, 2664 –2667 (2004)