Immunologic monitoring with Orthoclone OKT3 therapy

Muromonab-CD3 monoclonal antibody (Orthoclone OKT3) was used 146 times in 123 transplant recipients to treat or prevent rejection. Reversal and prevention of rejection were evaluated 1 week and 1 year after OKT3 therapy. Eighty-one percent (73 of 90) of the rejection episodes in kidney transplant patients were reversed with 67% of these grafts functioning at 1 year. Eighteen of 20 (90%) rejection episodes in liver transplant recipients were reversed, as were 11 of 13 (85%) heart transplant rejection episodes. Only one of five pancreas transplant episodes were reversed. OKT3 was used prophylactically in 18 transplant recipients (13 kidney, four heart, one liver). Immunologic monitoring (lymphocyte subsets, serum OKT3 levels, and antimurine antibodies) was performed during and after OKT3 therapy. Antimurine antibody formation rate was 28% (26 of 94 patients monitored). OKT3 therapy resulted in a rapid depletion of CD3+ cells from the peripheral circulation (less than 20/mm3) and trough serum OKT3 levels of greater than 800 ng/ml by the third day of therapy in all transplant types. Twenty-three patients (14 kidney, five liver, three heart, and one pancreas) were retreated with OKT3; reversal of rejection occurred in 87% of patients (13 of 15) with no antimurine antibodies and in 83% of patients (five of six) with a low antibody titer but did not occur in the two patients with a high antibody titer. Retreatment of patients with no anti-OKT3 antibody resulted in a depletion of CD3+ cells from the peripheral blood, but it took longer than in patients treated with OKT3 for the first time. Similarly, serum OKT3 levels increased slower in retreated patients compared with first treatment. In retreatment patients with a low titer antimurine antibody, often it was necessary to increase the dose of OKT3 to achieve adequate serum OKT3 levels and to deplete CD3+ cells. Antimurine antibody developed de novo in four of the 15 antibody negative patients (27%) who were retreated. Overall, OKT3 was an effective agent in reversing and preventing rejection in solid organ transplantation with few severe side effects and a low mortality. Retreatment with OKT3 should not be considered unless the antibody status of the patient is known. Development of low titer antibodies does not preclude successful retreatment with OKT3. Alternate antirejection therapy, however, should be used in patients with high titer antimurine responses.