Potential of monoclonal antibodies to improve therapeutic monitoring of cyclosporine.

We show that monitoring of cyclosporine by immunoassay could be improved by using monoclonal antibodies (MAbs) of restricted specificity instead of polyclonal antisera that recognize both unmodified cyclosporine and its metabolites. MAbs with high affinity for cyclosporine have been prepared and characterized. We tested their ability to discriminate between native cyclosporine and its metabolites in indirect solid-phase enzyme immunoassay with a set of cyclosporine metabolites modified at residues 1, 4, 6, and 9 (corresponding to the six known sites of metabolism of cyclosporine). All the metabolites tested were detected by MAb1 at least 15- to 1000-fold less well than unmodified cyclosporine. A second MAb recognized unmodified cyclosporine and most of its metabolites equally well. Both MAbs retained their activity when coupled to alkaline phosphatase and could therefore be used in a direct solid-phase enzyme immunoassay.