The role of OKT3 in clinical transplantation.

OKT3 is a murine monoclonal anti-T cell antibody that is directed to CD3, a five-chain molecular complex found in association with the T cell receptor for antigen. OKT3 was the first monoclonal antibody to be used in organ transplantation and during the past 10 years there has been extensive experience of its use both for preventing and treating rejection in organ transplantation. OKT3 blocks T cell function by modulating CD3 and the T cell receptor from the T cell surface. A reaction to OKT3 results from cytokines released when OKT3 first reacts with T cells. This reaction is generally mild but can be severe. First rejections following kidney transplantation are reversed in approximately 95% of cases. Steroid-resistant rejections are also susceptible to OKT3 but in only approximately 75% of cases. When used for prophylaxis, OKT3 completely blocks rejection in 95% of patients and significantly delays the onset of rejection in those who do reject. Antibodies to OKT3 are produced in approximately 75% of patients receiving it. However, seldom are the antibodies to OKT3 present in high titer and only in those cases is successful re-use of OKT3 prevented. As is the case with all potent immunosuppressive drugs, the use of OKT3 is associated with increased viral, specifically cytomegalovirus, infections. However, it appears that reduction of concomitant immunosuppression decreases the incidence of severe infections. Unquestionably, OKT3 has been a useful addition to the immunosuppression used for organ transplantation. In addition, its use has stimulated research on other monoclonal antibodies for use in organ transplantation.