Impact of the MHC-encoded HLA-DMA, DMB, and LMP2 gene polymorphisms on kidney graft outcome

Gene polymorphisms and transplantation

The influence of gene polymorphisms in key immunoregulatory molecules on the clinical course post-transplant has become an area of active research, since it offers a possible explanation for the heterogeneity in outcomes between individuals. Several groups have now investigated the association of polymorphisms in molecules--including cytokines, cytokine receptors, adhesion molecules and costimulatory molecules--that participate in the immune response to an allograft. Several interesting observations have been made that would suggest that genetic variability influencing allograft survival reaches beyond that of the MHC molecules.

Cytotoxic T-lymphocyte antigen 4 gene polymorphisms and susceptibility to acute allograft rejection

BACKGROUND

Cytotoxic T-lymphocyte antigen 4 (CTLA4) has been shown to play a critical role in the down-regulation of the immune response. We retrospectively examined the association between acute rejection and two polymorphisms in the CTLA4 gene, the dinucleotide (AT)n repeat polymorphism in exon 3 and the single nucleotide polymorphism A/G at position 49 in exon 1, in a cohort of liver and kidney transplant recipients.

METHODS AND RESULTS

A total of 207 liver and 167 renal transplant recipients were analyzed. In the case of the (AT)n repeat polymorphism we found an increased incidence of acute rejection in association with allele 3 and 4 in both liver and kidney (P=0.002 and 0.05, respectively). In addition, in liver transplant recipients, allele 7 was associated with acute rejection independent of ethnicity (P<0.05). Allele 1 was less frequently observed in African American as compared with Caucasian liver and kidney transplant recipients, with a frequency of 33.8% and 69%, respectively (P<0.0001). Those patients with allele 1 had a tendency toward a lower rate of rejection at 42% versus 57.8% (P=0.058), suggesting a potential protective effect of allele 1. Analysis of the A/G single nucleotide polymorphism demonstrated no association between either allele and the incidence of acute rejection in the patients studied.

CONCLUSION

These initial observations provide the necessary basis to further investigate the risk stratification of transplant recipients based on specific CTLA4 gene polymorphisms.

The importance of genetic polymorphisms in renal transplantation

Genetic variations including single nucleotide polymorphisms, dinucleotide repeats and microsatellites have been identified in a number of genes encoding cytokines, cytokine receptors, chemokines and their receptors, adhesion molecules. Several of the polymorphisms are located in the promoter region of the gene, affect transcription or translation, and not infrequently determine the level of expression of the protein product. An interesting and testable hypothesis for the clinical heterogeneity and differential responsiveness in allograft recipients is genetic variation. These nucleotide sequence variations, polymorphisms located in genes contributing to immune repertory and in genes responsible for drug metabolism, are excellent candidates for the differential clinical phenotype.

HLA-DMA allele polymorphism: no impact on kidney allograft outcome

The purpose of this study was to analyze the association of HLA-DMA alleles with rejection episodes and early graft loss (EGL) in renal transplant recipients. One hundred and eighty four HLA-DMA alleles were retrospectively analyzed by DNA sequence analysis in 92 kidney transplant recipients. The gene frequencies of HLA-DMA *0101, *0102, *0103 and *0104 were found to be similar in all recipients, regardless of rejection vs non rejection episodes and EGL incidence. In conclusion, HLA-DMA allele polymorphism did not impact renal allograft outcome.