Effects of the malononitrilamide FK778 on immune functions in vitro in whole blood from non-human primates and healthy human volunteers.

BACKGROUND: FK778, a malononitrilamide analog of leflunomide, is currently being investigated for use in clinical transplantation. METHODS: Whole blood from cynomolgus monkeys (n=4) and healthy human volunteers (n=4) was incubated with different concentrations of FK778 and stimulated with mitogens in culture medium. Lymphocyte proliferation was assessed by tritium-labeled thymidine incorporation and by flow-cytometric analysis of expression of proliferating cell nuclear antigen on cells in S/G(2)M phase. Flow cytometry was also used to assess expression of T and B lymphocyte activation surface antigens and production of intracellular cytokines by T cells. RESULTS: Not only lymphocyte proliferation, but also expression of various T cell surface antigens (CD25, CD11a, CD95, CD154) was suppressed by FK778. Fifty percent effective concentration values for the different immune functions were lower in human blood than in blood from cynomolgus monkeys. CONCLUSIONS: FK778 inhibits multiple immune functions. Their flow cytometric evaluation can be used to assess the effects of the drug in vivo.