The OKT3 immunosuppressive effect. In situ antigenic modulation of human graft-infiltrating T cells.

OKT3 exerts its in vivo immunosuppressive effects by inducing major peripheral T cell depletion as well as antigenic modulation of the T3/Ti T cell receptor complex. Modulated cells, which reversibly lose the expression of the CD3 T cell receptor molecular complex but still share the CD4 and CD8 antigens, have been shown to be functionally immunoincompetent. Antigenic modulation is maintained as long as significant OKT3 serum levels are present. Cells infiltrating renal allografts from seven OKT3 treated patients were studied by double immunofluorescence to assess whether antigenic modulation could affect cells located in profound organs such as renal allografts. Needle biopsies were obtained in patients given OKT3 (5 mg/day) for at least 10 consecutive days in association with conventional immunosuppressive drugs for treatment of a rejection episode (5 cases) or prophylactically (2 cases). In all patients at the time of biopsy, CD3 positive cells were absent from the circulation, significant OKT3 serum levels were present, and neither IgG nor IgM anti-OKT3 antibodies were detected. Infiltrating cells were double-labeled using a combination of either anti-CD3 and anti-CD4 or anti-CD3 and anti-CD8 monoclonal antibodies. Following 7-14 consecutive days of treatment, all patients given OKT3 for a rejection episode showed a significant decrease in the number of graft-infiltrating lymphocytes. Importantly, all T cells still infiltrating the allograft were CD3-CD4+ or CD3-CD8+ cells, which is exactly the same phenotypical pattern of CD3 circulating modulated T cells. In 6 out of the 7 patients, this phenotypical pattern was associated with clinically normal graft function. These results further underline the fact that antigenic modulation is an important mechanism mediating the immunosuppressive effect of OKT3 both in peripheral blood and in renal allografts.