ABCB1 genotypes predict cyclosporine-related adverse events and kidney allograft outcome

Update on the clinical pharmacogenomics of organ transplantation

Organ transplantation suffers from a static graft and patient survival rate, and a high incidence of serious adverse drug effects. The pharmacogenomics of organ transplantation has emerged only recently and is complementary to the immunogenetic information that has accumulated over the past decade. Gene polymorphism studies have focused on the genes that interact across the group of immunosuppressants, including ciclosporin, tacrolimus, sirolimus and corticosteroids. The polymorphisms that hold the most potential for use in a drug selection algorithm are in genes CYP3A5, ABCB1, IMPDH1 and IMPDH2, and cytokines and growth factors. Gene-expression arrays have led to gene-expression testing, such as the use of AlloMap((R)) with heart transplant patients. The expanded use of gene-expression assays, proteomics and drug selection algorithms in organ transplantation will progress slowly and may be outpaced by drug test co-development programs for new transplant drugs. In the future, clinical pharmacogenomics will be a routine part of patient care for organ transplant patients.

Cyclosporine, tacrolimus and sirolimus retain their distinct toxicity profiles despite low doses in the Symphony study

BACKGROUND

Reducing side effects of immunosuppressive regimens has become a priority in transplantation medicine because of the large number of patients and grafts that succumb to infection in the short term and cardiovascular disease in the long term. The Symphony study was a 12-month prospective, randomized, open-label, multi-centre, four parallel arm study that aimed to evaluate the safety and efficacy of low-dose immunosuppressive regimens compared with a standard-dose regimen in renal transplant recipients. This sub-analysis focuses on specific toxicities observed with the low-dose regimens.

METHODS

Adult patients (n = 1645) scheduled to undergo renal transplantation received low-dose cyclosporine (CsA), tacrolimus (Tac) or sirolimus (SRL) in addition to daclizumab induction or standard-dose cyclosporine without induction. All patients received mycophenolate mofetil and corticosteroids. We evaluated the incidence of adverse events (AEs), tested specific group differences and assessed the relationship of selected AEs with drug levels.

RESULTS

The four arms had similar incidences of AEs, but serious AEs were more common with low-dose SRL and led to more discontinuations. Infections were the most common AEs, with the highest incidence in the standard-dose CsA group, in particular, cytomegalovirus (CMV) infections. Low-dose Tac had the most reports of new-onset diabetes, leucopenia and diarrhoea. Low-dose SRL negatively influenced triglycerides, wound healing, lymphocele and anaemia. We found only weak relationships between specific AEs and drug levels.

CONCLUSIONS

Despite the low doses, CsA, Tac and SRL retained distinct and different toxicity profiles. These findings may be of relevance for tailoring specific immunosuppressive regimens to patients with particular needs.

Donor age and renal P-glycoprotein expression associate with chronic histological damage in renal allografts

The contributions of donor kidney quality (partially determined by donor age), allograft rejection, and calcineurin inhibitor nephrotoxicity on the progression of histologic damage of renal allografts are not completely defined. Moreover, the determinants of individual susceptibility to calcineurin inhibitor nephrotoxicity are not known but may include variability in drug transport and metabolism. In a prospective cohort of 252 adult renal allograft recipients treated with a combination of tacrolimus, mycophenolate mofetil, and corticosteroids, we studied 744 renal allograft biopsies obtained regularly from time of transplantation for 3 yr. We assessed determinants of histologic evolution, including tacrolimus exposure, renal P-glycoprotein (ABCB1) expression, and polymorphisms in the CYP3A4, CYP3A5, and ABCB1 genes. Within the first 3 yr after transplantation, we noted a progressive increase in interstitial fibrosis, tubular atrophy, glomerulosclerosis, and vascular intimal thickening. Older donor age, absence of P-glycoprotein expression at the apical membrane of tubular epithelial cells, and combined donor-recipient homozygosity for the C3435T variant in ABCB1 significantly associated with increased susceptibility to chronic allograft damage independent of graft quality at implantation. Changes in graft function over time reflected these associations with donor age and ABCB1 polymorphisms, but it was acute T cell-mediated and antibody-mediated rejection that determined early graft survival. In conclusion, the effects of older donor age reach beyond the quality of the allograft at implantation and continue to be important for histologic evolution in the posttransplantation period. In addition, ABCB1 genotype and expression of P-glycoprotein in renal tubular epithelial cells determine susceptibility to chronic tubulointerstitial damage of transplanted kidneys.