Genetic Polymorphisms in ABCB1 Influence the Pharmacodynamic Effects of Tacrolimus on T Cells

Abstract

Background: Tacrolimus (TAC) has a large interindividual variability in pharmacokinetics and quantification of its effect is difficult. TAC is a substrate of P-glycoprotein (P-gp; encoded by ABCB1), an efflux-pump which is expressed more on CD8+ T cells than on CD4+ T cells. Single-nucleotide polymorphisms (SNPs) are associated with interindividual differences in P-gp activity and hence may influence intralymphocytic TAC concentrations and efficacy, especially in CD8+ T cells. Here we studied the influence of SNPs in ABCB1 and of verapamil-induced P-gp inhibition on the biological effect of TAC on T cells. Methods: The influence of ABCB1 genotypes (3435CC/high pump-activity, CT, TT/low pump-activity) was studied in T cells of 16 healthy volunteers using P-gp-mediated rhodamine efflux (2 hours). The intracellular IL-2 expression in T-cell populations was measured after PMA/iono stimulation of whole blood by use of flowcytometry, in the presence of 10 ng/mL TAC and 40 nM verapamil. In addition, the relationship between ABCB1 SNPs, TAC-levels and ex vivo induced IL-2 production was studied in 37 TAC-treated renal transplant patients. Results: The mean rhodamine efflux was higher in CD8+ T cells compared to CD4+ T cells: 40% vs. 16%, respectively (P< 0.001). In healthy volunteers with the CC genotype 50% (95%-CI: 46-53%) of CD8+ T cells effluxed rhodamine which was significantly higher compared to the TT genotype (mean 39%; 95%-CI: 30-46%; P< 0.05). In the presence of the P-gp inhibitor verapamil, rhodamine was effluxed by only 0.8% of CD8+ T cells (95% CI: 0.3-1.4%), while TAC did not influence the efflux of rhodamine (mean 38%; 95%-CI: 35-42%). Blockade of P-gp by verapamil in the presence of TAC decreased the percentage of intracellular IL-2 producing CD8+ T cells by 14% suggesting an increased pharmacodynamic effect of TAC through prolonged intralymphocytic accumulation. In TAC-treated renal transplant patients with the CC genotype, verapamil reduced the percentage of IL-2 producing CD8+ T cells by 22% whereas no effect of verapamil was found in patients with the TT genotype. Moreover, the ratio TAC C0versus % IL-2 producing CD8+ T cells in CC genotype patients was significantly higher (P< 0.05) compared to TT genotype patients, showing that in CC-genotype patients, TAC has a smaller pharmacodynamic effect. Conclusion: Genetic polymorphisms in ABCB1 influence the P-gp activity of CD8+ T cells and the immunosuppressive effect of TAC in kidney transplant recipients.