Iain MacPhee

Biomarkers of Tolerance in Kidney Transplantation: Are We Predicting Tolerance or Response to Immunosuppressive Treatment?

We and others have previously described signatures of tolerance in kidney transplantation showing the differential expression of B cell–related genes and the relative expansions of B cell subsets. However, in all of these studies, the index group—namely, the tolerant recipients—were not receiving immunosuppression (IS) treatment, unlike the rest of the comparator groups. We aimed to assess the confounding effect of these regimens and develop a novel IS‐independent signature of tolerance. Analyzing gene expression in three independent kidney transplant patient cohorts (232 recipients and 14 tolerant patients), we have established that the expression of the previously reported signature was biased by IS regimens, which also influenced transitional B cells. We have defined and validated a new gene expression signature that is independent of drug effects and also differentiates tolerant patients from healthy controls (cross‐validated area under the receiver operating characteristic curve [AUC] = 0.81). In a prospective cohort, we have demonstrated that the new signature remained stable before and after steroid withdrawal. In addition, we report on a validated and highly accurate gene expression signature that can be reliably used to identify patients suitable for IS reduction (approximately 12% of stable patients), irrespective of the IS drugs they are receiving. Only a similar approach will make the conduct of pilot clinical trials for IS minimization safe and hence allow critical improvements in kidney posttransplant management.

The Pharmacogenetics of Immunosuppression for Organ Transplantation

Transplantation has transformed the treatment of patients with organ failure in a number of clinical settings, and immunosuppressive drug therapy is fundamental to its success. However, all the drugs in current use have a narrow therapeutic index. Under-dosing can lead to rejection, while over-dosing increases the risks of infection, malignant disease, and serious drug-specific adverse effects, including diabetes mellitus, nephrotoxicity, hypertension, and hyperlipidemia.Heterogeneity in the pharmacokinetics of these drugs makes initial dose determination difficult, as there is a poor correlation between dose and blood concentration. This results in difficulties in achieving target blood concentrations early after transplantation, which are important for reducing the rate of immunological rejection. This problem is compounded by the observation that neither drug dose nor drug blood concentration accurately predict clinical efficacy or toxicity.The main determinant of heterogeneity in dose requirements is intestinal absorption of the active drug. The oxidative enzymes, cytochrome P450 (CYP) 3A4 and CYP3A5, and the drug efflux pump P-glycoprotein (P-gp) in enterocytes regulate this process. Most substrates for the P-gp pump are also substrates for the CYP3A enzymes. An efficient barrier to xenobiotic absorption is formed by the CYP enzymes and P-gp, and by the two systems working synergistically. Genetic polymorphisms have been reported for the genes associated with the expression of the CYP3A enzymes and P-gp. Genotyping patients for CYP3A genes has the potential to aid the establishment of optimal dosage regimens for transplant patients.Genetic polymorphism of the multiple drug resistance gene-1 (MDR1, also known as ABCB1) [3435C/T] and the CYP3A5 genes (CYP3A5*1, CYP3AP1*1) have the greatest potential to influence the pharmacokinetics of immunosuppressants. Homozygosity of the T allele of the MDR1 3435C/T polymorphism has been associated with reduced enterocyte expression of P-gp resulting in increased drug absorption. The presence of the CYP3A5*1 allele is necessary for the production of a fully catalytic CYP3A5 protein, and also influences the ratio of CYP3A4 : CYP3A5 as well as the overall CYP3A catalytic activity. The CYP3A4 : CYP3A5 ratio may, in turn, influence the pattern of drug metabolites formed. Heterogeneity in the production of active and inactive metabolites has implications for both the pharmacokinetics and pharmacodynamics of these drugs.Gene frequencies and drug dose requirements differ between ethnic groups. Ethnic differences in dose requirements for immunosuppressants have been discussed widely. However, ethnicity is a rather crude marker for genotype. Pharmacogenetic typing offers the possibility of significant improvement in the individualization of immunosuppressive drug prescribing with reduced rates of rejection and toxicity.

Dose-finding Study of Peginesatide for Anemia Correction in Chronic Kidney Disease Patients

BACKGROUND AND OBJECTIVESnPeginesatide is a synthetic, PEGylated, investigational, peptide-based erythropoiesis-stimulating agent. We report the first assessment of its efficacy and safety in correcting renal anemia in a population of 139 nondialysis chronic kidney disease patients.nnnDESIGN, SETTING, PARTICIPANTS, & MEASUREMENTSnChronic kidney disease patients who were not on dialysis and not receiving treatment with erythropoiesis-stimulating agents in the 12 weeks before study drug administration were sequentially assigned to one of 10 cohorts; cohorts differed in starting peginesatide dose (different body weight-based or absolute doses), route of administration (intravenous or subcutaneous), and frequency of administration (every 4 or 2 weeks).nnnRESULTSnAcross all cohorts, 96% of patients achieved a hemoglobin response. A dose-response relationship was evident for hemoglobin increase. Comparable subcutaneous and intravenous peginesatide doses produced similar hemoglobin responses. Rapid rates of hemoglobin rise and hemoglobin excursions >13 g/dl tended to occur more frequently with every-2-weeks dosing than they did with every-4-weeks dosing. The range of final median doses in the every-4-weeks dosing groups was 0.019 to 0.043 mg/kg. Across all cohorts, 20% of patients reported serious adverse events (one patient had a possibly drug-related serious event) and 81% reported adverse events (11.5% reported possibly drug-related events); these events were consistent with those routinely observed in this patient population.nnnCONCLUSIONSnThis study suggests that peginesatide administered every 4 weeks can increase and maintain hemoglobin in nondialysis chronic kidney disease patients. Additional long-term data in larger groups of patients are required to further elucidate the efficacy and safety of this peptide-based erythropoiesis-stimulating agent.

Does pharmacogenetics have the potential to allow the individualisation of immunosuppressive drug dosing in organ transplantation

The immunosuppressive drugs used in organ transplantation have a narrow therapeutic index, with rejection occurring as a consequence of underdosing and infection, malignancy and a number of drug-specific side effects with excessive dosing. Significant heterogeneity in the dose of drug required to achieve therapeutic blood concentrations adds to the complexity of the problem, which has been partly resolved by therapeutic drug monitoring. Single nucleotide polymorphisms have been identified in genes encoding metabolic enzymes, drug efflux pumps and drug targets for most of the drugs in widespread use. A pharmacogenetic approach to immunosuppressive drug prescribing remains to be tested. Based on current evidence, the most promising strategy would be use of the cytochrome P450 3A5 expresser genotype to guide initial dosing with tacrolimus.

Long‐ and short‐term outcomes in renal allografts with deceased donors: A large recipient and donor genome‐wide association study

Improvements in immunosuppression have modified short‐term survival of deceased‐donor allografts, but not their rate of long‐term failure. Mismatches between donor and recipient HLA play an important role in the acute and chronic allogeneic immune response against the graft. Perfect matching at clinically relevant HLA loci does not obviate the need for immunosuppression, suggesting that additional genetic variation plays a critical role in both short‐ and long‐term graft outcomes. By combining patient data and samples from supranational cohorts across the United Kingdom and European Union, we performed the first large‐scale genome‐wide association study analyzing both donor and recipient DNA in 2094 complete renal transplant‐pairs with replication in 5866 complete pairs. We studied deceased‐donor grafts allocated on the basis of preferential HLA matching, which provided some control for HLA genetic effects. No strong donor or recipient genetic effects contributing to long‐ or short‐term allograft survival were found outside the HLA region. We discuss the implications for future research and clinical application.

UK Renal Registry 17th Annual Report: Appendix B Definitions and Analysis Criteria

The take-on population is defined as all patients over 18 who started renal replacement therapy (RRT) at UK renal centres and did not have a recovery lasting more than 90 days within 90 days of starting RRT. The treatment timeline is used to define take-on patients as follows. If a patient has timeline entries from more than one centre then these are all combined and sorted by date. Then, the first treatment entry gives the first date of when they received RRT. This is defined as a ‘start date’. However, in the following situations there is evidence that the patient was already receiving RRT before this ‘start date’ and these people are not classed as takeon patients:

UK Renal Registry 15th Annual Report: Appendix A The UK Renal Registry Statement of Purpose

1. Executive summary 2. Introduction 3. Statement of intent 4. Relationships of the UK Renal Registry 5. The role of the UK Renal Registry for patients 6. The role of the UK Renal Registry for nephrologists 7. The role of the UK Renal Registry for Trust managers 8. The role of the UK Renal Registry for commissioning agencies 9. The role of the UK Renal Registry in national quality assurance schemes 10. References and websites

Appendix E Methodology for Estimating Catchment Populations of Renal Centres in England for Dialysis Patients

Providing accurate centre-level incidence and prevalence rates for patients receiving renal replacement therapy (RRT) in the UK has been limited in the past by the difficulty in estimating the catchment population from which the RRT population was derived. One reason for this is that the geographical boundaries separating renal centres are relatively arbitrary and dependent upon a number of factors including referral practice, patient choice and patient movement. Previously, incidence and prevalence rates have been calculated at Local Authority/Primary Care Trust/Health Board level where denominator data were available, but not at renal centre level. Previous UK Renal Registry (UKRR) Annual Reports have suggested an estimate of the size of the catchment populations. These were extrapolated figures originally derived from data in the 1992 National Renal Survey undertaken by Paul Roderick. The purpose of this appendix is to present an estimate of the dialysis catchment population for all renal centres in England. The document also contains a methodological description and discussion of the limitations of this estimate. These catchment population estimates have been used in this report (chapter 1: UK RRT Incidence in 2009: national and centre-specific analyses) to calculate RRT incidence rates by renal centre, rather than only by Primary Care Trust/HB.

Steroid regulation: An overlooked aspect of tolerance and chronic rejection in kidney transplantation.

Steroid conversion (HSD11B1, HSD11B2, H6PD) and receptor genes (NR3C1, NR3C2) were examined in kidney-transplant recipients with operational tolerance and chronic rejection (CR), independently and within the context of 88 tolerance-associated genes. Associations with cellular types were explored. Peripheral whole-blood gene-expression levels (RT-qPCR-based) and cell counts were adjusted for immunosuppressant drug intake. Tolerant (nu202f=u202f17), stable (nu202f=u202f190) and CR patients (nu202f=u202f37) were compared. Healthy controls (nu202f=u202f14) were used as reference. The anti-inflammatory glucocorticoid receptor (NR3C1) and the cortisol-activating HSD11B1 and H6PD genes were up-regulated in CR and were lowest in tolerant patients. The pro-inflammatory mineralocorticoid gene (NR3C2) was downregulated in stable and CR patients. NR3C1 was associated with neutrophils and NR3C2 with T-cells. Steroid conversion and receptor genes, alone, enabled classification of tolerant patients and were major contributors to gene-expression signatures of both, tolerance and CR, alongside known tolerance-associated genes, revealing a key role of steroid regulation and response in kidney transplantation.

Appendix F Additional Data Tables for 2010 Incident and Prevalent Patients

Abrdn 76 24 L Rfree 74 11 15 Airdrie 88 13 L St.G 75 13 12 Antrim 95 5 LWest 89 2 8 B Heart 81 16 3 Leeds 72 19 9 B QEH 75 19 6 Leic 67 20 13 Bangor 81 19 Liv Ain 94 6 Basldn 94 6 Liv RI 57 30 13 Belfast 87 8 4 M Hope 55 31 14 Bradfd 83 14 3 M RI 65 21 14 Brightn 72 28 Middlbr 83 12 5 Bristol 79 11 11 Newc 65 17 18 Camb 63 11 26 Newry 90 10 Cardff 73 19 8 Norwch 74 26 Carlis 76 24 Nottm 66 27 6 Carsh 85 8 7 Oxford 65 21 14 Chelms 62 38 Plymth 69 27 4 Clwyd 92 8 Ports 65 26 9 Colchr 100 Prestn 83 14 3 Covnt 71 23 6 Redng 52 38 10 Table F.1.2. Number of patients per treatment modality at 90 days (incident cohort 1/10/2009 to 30/09/2010)