Estimation of individual sensitivity to cyclosporin in children awaiting renal transplantation

Background. Optimal immunosuppressive drug therapy requires that efficacy be balanced against toxicity. We have performed in vitro assays of cyclosporin (CsA) efficacy in children awaiting renal transplantation. Methods. Peripheral blood mononuclear cells (PBMC) from 13 children awaiting renal transplantation and 10 healthy paediatric controls (‘responders’) were incubated in the presence of CsA (0–250 ng/ml). Irradiated PBMC from a parent (prospective live donor) were cultured with those of the child in the presence of interleukin 2. Europium‐labelled, non‐irradiated phytohaemagluttinin‐stimulated target cells from the parent were added to the culture after 7 days incubation. Target cell lysis was quantified by time resolved fluorometry. CsA‐mediated inhibition of target cell lysis was calculated and used to compare individual responses to the drug. Two‐colour flow cytometry was performed to identify activated subsets of lymphocytes at varying concentrations of CsA. Results. Wide inter‐individual variations in per cent lysis and per cent inhibition were observed in patients and controls. Immunophenotyping indicated expansion of CD8+ and CD25+ lymphocyte subsets following allo‐stimulation that was inhibited by increasing concentrations of CsA. Eight out of 13 patients and four out of 10 controls were ‘sensitive’ to CsA in vitro in that they achieved 50% inhibition of cell lysis (IC50) at low concentrations of the drug (