Stephen J. LeGrue

Immunopharmacological monitoring of cyclosporin A-treated recipients of cadaveric kidney allografts

Twelve cadaveric kidney allograft recipients, who were established preoperatively to be strong responders, were treated with cyclosporin A (Cy A) and subjected to postoperative monitoring of drug levels and immune performances. The Cy A-treated recipients were compared with 72 historical (36 strong and 36 weak immune responders) and 18 current, strong responder, azathioprine-treated control patients. Estimation of Cy A levels in plasma and whole blood revealed that 75% of the drug at trough and 44% at peak was cell bound. Concomitant radioimmunoassay (RIA) and high performance liquid chromatography (HPLC) determinations on whole blood yielded concordant values. Trough levels above 200 ng/ ml in plasma and 600 ng/ml in whole blood were associated with toxic manifestations. Although absolute peak levels were not helpful, calculation of peak to trough ratios yielded values which when less than 3.0 predicted toxicity. Post-transplant immune monitoring showed administration of Cy A to be associated with fewer (1) rejection episodes; (2) nonspecific immune events; and (3) donor-specific in vitro reactions than were observed after treatment with azathioprine. Although the activity of peripheral blood mononuclear cells as natural killers of K562 target cells was not affected by Cy A treatment, their capacity to suppress the generation of a third-party mixed lymphocyte culture was enhanced to the same degree as cells from azathioprine-treated patients. Enumeration of peripheral blood lymphocyte T cell subpopulations using monoclonal xeonoantisera revealed (1) the total number of T cells to be unaffected by administration of either Cy A or azathioprine and (2) a reduction in the ratio of helper-inducer to suppressor-cytotoxic cells specificially in Cy A-treated recipients compared with normal individuals, hemodialysis patients, or azathioprine-treated recipients. Although pharmacological monitoring of blood levels may be useful to discern patients at high risk for toxic complications, the achievement of maximal therapeutic efficacy may depend upon identifying and quantitating the cellular target responsible for the disruption of immune homeostasis observed during Cy A administration.

Isolation and in vitro characterization of a novel immunosuppressive cyclosporine metabolite.

A novel metabolite (M-E) was identified by high-performance liquid chromatography in the serum of cyclosporine-treated renal transplant recipients during a second wave of immunosuppressive activity after disappearance of the initial wave due to the direct effect of CsA. M-E was identified in human serum and porcine bile both by HPLC and by a preparative thin-layer chromatography (TLC). It demonstrated homogeneity with characteristic retention times on C8 and C18 column HPLC systems using a variety of elution systems, and distinctive TLC mobility (Rf 0.35). Metabolite E (M-E) was documented to be a CsA metabolite by radioactive tracer studies, by crossreactivity with a polyclonal sheep antibody in radioimmunoassay, and by the presence of a characteristic mass spectrum. Further, in vitro immunosuppressive assays documented effects of M-E similar to those of CsA. The relative activity of M-E versus CsA was quantitated by potency ratios: for inhibition of normal human mixed lymphocyte culture reactions, the ratio was 0.79 +/- 0.23. Interindividual differences were observed in patient susceptibility to MLR inhibition not only by CsA, as previously reported by others, but also by M-E. There was a lesser effect of M-E compared with CsA in inhibiting proliferation of, and IL-2 generation by, C3H murine splenocytes stimulated with concanavalin A: the potency ratios for both systems were about 0.5, possibly reflecting an interspecies variability in generation of or susceptibility to M-E. These studies suggest that heretofore unidentified metabolites--including, but not limited to, M-E--may play an important role in the immunosuppressive effect of CsA in man.