Flow cytometric evaluation of cytotoxic peripheral blood lymphocytes in acute renal graft rejection.

The presence of the S6F1+ epitope on the surface of CD8+ lymphocytes is believed to be uniquely representative of cytotoxic subpopulations. A preliminary study was conducted to evaluate the CD8+ S6F1+ peripheral lymphocytes by flow cytometry in patients undergoing renal allograft biopsy for allograft dysfunction. Lymphocytes, obtained at the time of biopsy, were analyzed by flow cytometry with CD8-FITC/S6F1-RD1 as the test monoclonal antibody and MsIgG-RD1/MsIgG-FITC as internal control. A 100% increase in S6F1+ cells over internal control was considered to be positive result. The results were correlated with the histopathologic findings in 14 instances of allograft dysfunction occurring 26.5 +/- 11.6 days posttransplantation. The histopathologic diagnosis was acute cellular rejection in eight cases, acute tubular necrosis in four, and cyclosporine nephrotoxicity in two. Flow cytometric detection of an increase in S6F1+ cells yielded a sensitivity of 87.5% and a specificity of 83.3% for the diagnosis of acute rejection. It would appear that the use of a monoclonal antibody to detect increases in the number of CD8+ S6F1+ peripheral lymphocytes is a valuable test for the detection of acute allograft rejection in the initial period after transplantation.