Following kidney transplantation one of the most frequent complication is acute rejection, defined by certain clinical characteristics and histological evidence of insufficient control of the immune response. Genetic variability offers a possible explanation for the inter-individual differences on the clinical course post-transplant. Single-nucleotide polymorphisms (SNPs) located in genes involved in immune responses and in the pharmacokinetics/pharmacodynamics of immunosuppressive drugs are associated with allograft rejection. Therefore in this study key SNPs in specific target genes were analysed in kidney transplant recipients:
• 3 SNPs related to drug transporter ABCB1/MDR-1 (or permeability glycoprotein), that influences the pharmacokinetics of the immunosuppressant calcineurin inhibitors, like Tacrolimus
• 10 SNPs connected to Inosine MonoPhosphate DeHydrogenase (IMPDH2), direct target of the immunosuppressive mycophenolic acid (MPA)
• 4 SNPs in the MPA metabolizing Uridine Diphosphate Glucuronosyltransferase 1A9 (UGT1A9) enzyme
• 1 SNP in the proinflammatory cytokine Tumor Necrosis Factor-alpha (TNF-alpha) and
• 1 SNP in the anti-inflammatory cytokine Interleukin-10 (IL-10) gene.
Our aim is to determine the SNPs profiles of five important genes associated with the acute rejection event in kidney transplant patients.
The study protocol is the following: recruitment in study groups, blood sample and clinical data collection, molecular analysis of 19 SNPs, statistical analysis.
Currently, a total number of 220 individuals are included in our study: 41 transplant patients with acute rejection in the Case, 109 transplant patients without acute rejection in the Control I and 70 healthy blood donors in the Control II group. Analyzing the clinical characteristics there are statistically significant differences regarding the gender (p = 0.0028) and the age (p = 0.0123) distribution between the three experimental groups. Individuals in the Control II group were little younger than in the two other groups (Case: 50 (42-62) vs Control I: 55 (48-62) vs Control II: 49 (41-54). In our study more male (103) patients needed transplantation than female (47) patients. Moreover this gender difference is also noted when acute rejection happens (36 male vs 5 female cases).
The observed allele frequencies are in line with ones reported from Europe indicating that the studied population in the Control II group is representative.
Our results show that all SNPs for IMPDH2, with the exception of rs11706052, are not polymorphic. Other groups have published similar results hypothesizing that those SNPs found in public, online databases (Ensembl) are artefacts of previous, not so accurate sequencing techniques.
All polymorphisms are in Hardy-Weinberg equilibrium, except the rs1045642 of ABCB1 in the Case group.
Analysis of allele and genotype frequencies and trend test were performed between Case vs Control I; Transplant group (Case+Control I) vs Control II; Case vs Control II. Comparing the group of all transplant patients and healthy individuals, our result is suggesting that a G/G genotype of rs1800872 belonging to IL10 gene more probably leads to chronic kidney disease (CKD), as it has been shown in previous works.
Patients holding a C allele in rs1045642 or an A in rs2032582, both SNPs of ABCB1, are more prone to develop an adverse event after transplantation. Since ABCB1 is a drug efflux pump, SNPs modifying the effectiveness of the pump may compromise the success of the immunosuppressive therapy or lead to cytotoxicity.
Thus, screening for ABCB1 polymorphisms rs1045642 and rs2032582 before transplantation would help clinicians to better personalize therapy.
However, all calculations need to be repeated after reaching the adequate number of patients estimated with the sample size test (69 patients/group) to correctly verify our results. The molecular analysis of the missing samples is in progress thanks for a collaboration with the Department of Nephrology in Udine
