Variations in serum OKT3 concentration based upon age, sex, transplanted organ, treatment regimen, and anti OKT3 antibody status

An essential parameter of the efficacy of OKT3 therapy is serial determinations of serum OKT3 levels. We hypothesized that precise monitoring of these levels would optimize treatment protocols. Therefore, enzyme-linked immunosorbent assay (ELISA) technology was utilized to measure OKT3 serum concentrations daily during 263 OKT3 treatment courses in recipients of solid organ grafts. Patient characteristics were: Mean age 33 years (0.1–71), 147 male/116 female, 134 kidney/82 liver/47 heart, 122 prophylaxis/141 rejection, and 213 conventional dosing/50 increased dosing. Mean OKT3 levels were higher in women than in men at all time points from day 1 to day 14, reaching the greatest difference between groups on day 7 (849 versus 598 ng/ml, p = 0.004). Patients receiving OKT3 as a component of a prophylactic protocol had higher levels than those receiving the drug for treatment of rejection from day 1 to day 6, with the greatest difference between groups occurring on day 1 (678 versus 333 ng/ml, p < 0.00001). However, from day 7 to day 14 patients receiving OKT3 prophylactically had lower mean OKT3 levels than did those receiving OKT3 for rejection, with the greatest difference between groups occurring on day 11 (555 versus 784 ng/ml, p < 0.05). Liver transplant recipients had significantly higher OKT3 levels than did kidney or heart transplants at all time points. However, more liver patients required increased OKT3 doses to modulate peripheral blood CD3⁺ cells to <25/mm³. Kidney recipients had higher levels than did heart recipients. Children <10 years of age had higher OKT3 levels than did older patients at all time points. Pediatric-age patients required increased doses of OKT3 more frequently than did adults. Patients who were anti-OKT3 antibody negative before OKT3 had significantly higher OKT3 concentrations during treatment than did patients who were anti-OKT3 antibody positive before treatment. Patients who developed anti-OKT3 antibodies following treatment had significantly lower OKT3 levels than did those who did not develop antibodies, the greatest difference between groups occurring at the end of therapy. In conclusion, differences in OKT3 serum levels based upon age, sex, transplant type, treatment regimen, and anti-OKT3 antibody status indicate that monitoring will optimize treatment protocols.