HSP70-hom Gene Polymorphism as a Prognostic Marker of Graft-Versus-Host Disease

Review of Genetic Variation as a Predictive Biomarker for Chronic Graft-Versus-Host-Disease After Allogeneic Stem Cell Transplantation

Chronic graft-versus-host disease (cGvHD) is one of the major complications of allogeneic stem cell transplantation (HSCT). cGvHD is an autoimmune-like disorder affecting multiple organs and involves a dermatological rash, tissue inflammation and fibrosis. The incidence of cGvHD has been reported to be as high as 30% to 60% and there are currently no reliable tools for predicting the occurrence of cGvHD. There is therefore an important unmet clinical need for predictive biomarkers. The present review summarizes the state of the art for genetic variation as a predictive biomarker for cGvHD. We discuss three different modes of action for genetic variation in transplantation: genetic associations, genetic matching, and pharmacogenetics. The results indicate that currently, there are no genetic polymorphisms or genetic tools that can be reliably used as validated biomarkers for predicting cGvHD. A number of recommendations for future studies can be drawn. The majority of studies to date have been under-powered and included too few patients and genetic markers. Like in all complex multifactorial diseases, large collaborative genome-level studies are now needed to achieve reliable and unbiased results. Some of the candidate genes, in particular, CTLA4, HSPE, IL1R1, CCR6, FGFR1OP, and IL10, and some non-HLA variants in the HLA gene region have been replicated to be associated with cGvHD risk in independent studies. These associations should now be confirmed in large well-characterized cohorts with fine mapping. Some patients develop cGvHD despite very extensive immunosuppression and other treatments, indicating that the current therapeutic regimens may not always be effective enough. Hence, more studies on pharmacogenetics are also required. Moreover, all of these studies should be adjusted for diagnostic and clinical features of cGvHD. We conclude that future studies should focus on modern genome-level tools, such as machine learning, polygenic risk scores and genome-wide association study-transcription meta-analyses, instead of focusing on just single variants. The risk of cGvHD may be related to the summary level of immunogenetic differences, or whole genome histocompatibility between each donor-recipient pair. As the number of genome-wide analyses in HSCT is increasing, we are approaching an era where there will be sufficient data to incorporate these approaches in the near future.

Genomic studies of GVHD-lessons learned thus far

GVHD remains the most significant complication of hematopoietic SCT, despite advances in HLA matching and the identification of risk various factors. To account for the variation in the incidence and severity of this disease, many genetic association studies have been performed in order to explore the role of immunoregulatory gene polymorphisms. These genes include those that encode cytokines, chemokines, and costimulatory molecules. Polymorphisms in other classes of genes such as those involved in drug metabolism, protein folding, and DNA replication have also been studied. In this review, we address the current knowledge of the role of genetic polymorphisms in GVHD. We also discuss the potential pitfalls inherent in genetic association testing and alternative strategies to address these problems.

Evaluation of published single nucleotide polymorphisms associated with acute GVHD

Candidate genetic associations with acute GVHD (aGVHD) were evaluated with the use of genotyped and imputed single-nucleotide polymorphism data from genome-wide scans of 1298 allogeneic hematopoietic cell transplantation (HCT) donors and recipients. Of 40 previously reported candidate SNPs, 6 were successfully genotyped, and 10 were imputed and passed criteria for analysis. Patient and donor genotypes were assessed for association with grades IIb-IV and III-IV aGVHD, stratified by donor type, in univariate and multivariate allelic, recessive and dominant models. Use of imputed genotypes to replicate previous IL10 associations was validated. Similar to previous publications, the IL6 donor genotype for rs1800795 was associated with a 20%-50% increased risk for grade IIb-IV aGVHD after unrelated HCT in the allelic (adjusted P = .011) and recessive (adjusted P = .0013) models. The donor genotype was associated with a 60% increase in risk for grade III-IV aGVHD after related HCT (adjusted P = .028). Other associations were found for IL2, CTLA4, HPSE, and MTHFR but were inconsistent with original publications. These results illustrate the advantages of using imputed single-nucleotide polymorphism data in genetic analyses and demonstrate the importance of validation in genetic association studies.

Immunoregulatory gene polymorphisms and graft-versus-host disease

Graft-versus-host disease (GVHD) remains a significant complication that greatly enhances morbidity and mortality associated with hematopoietic stem cell transplantation. Key immunoregulatory molecules have been implicated in the pathogenesis of GVHD, but the mechanisms by which these molecules affect the incidence and severity of GVHD have not been fully elucidated. The effects of genetic polymorphisms in immunoregulatory molecules, including cytokines, costimulatory and adhesion molecules, pharmacogenes and growth factors, have been shown to play a central role in GVHD. The results of these polymorphism studies contribute to the identification of predictive risk factors for GVHD based on individual polymorphism makeup. This review summarizes investigations of genetic polymorphisms in immunoregulatory molecules significantly associated with GVHD over the last 5 years.

Investigating cellular stress responses--a multidisciplinary approach from basic science to therapeutics--report on the EuroSciCon (European Scientific Conferences) meeting

The meeting on "Investigating cellular stress responses--a multidisciplinary approach from basic science to therapeutics" was held in London on 13 October 2006. The purpose of this 1-day meeting was to bring together European scientists investigating the immune biology of stress proteins and their potential clinical applications. The main topics included: the role of heat shock proteins (Hsps) in bacterial infections; the role of Hsps with a molecular mass of about 70 kDa in cancer therapy and in prediction of the clinical outcome following allogeneic hematopoietic stem cell transplantation; the quality and duration of stress as a danger signal for the initiation of a stress response; the mechanism of Hsp-protein interaction; and Hsp export from tumor cells in secretory granules.

Association of HSP70-hom genetic variant with prostate cancer risk

Because of the importance of androgens to prostate cancer (PCa) development, several candidate genes along androgen pathway have been under intensive study. Given the role of the molecular chaperone HSP70 in the regulation of the androgen receptor (AR) transactivation function, we first chose to explore the association between the HSP70-hom functional genetic variant (+2437 T > C) and prostate cancer risk by genotyping DNA samples from 101 unselected PCa patients and 105 healthy men. There was a trend towards lower frequency of TC and CC genotypes among patients when compared with healthy controls, however the difference did not reach the statistical significance (TC genotype: OR = 0.53, P = 0.05; CC genotype: OR = 0.42, P = 0.16). Moreover, individuals carrying at least one C allele have a statistically significant lower susceptibility for PCa (OR = 0.51 (0.26-0.97); P = 0.02). Since some factors may influence tumor progression rather than initiation, we also examined the relationship between the HSP70-hom polymorphism and the clinical characteristics of the malignancy at the time of diagnosis. The stratified analysis of the genotypes with the clinical stage and tumor grade showed that there was no significant difference in the risk estimates according to prognostic indicators of PCa disease in our population study. This is the first report on the studies of HSP70 SNPs in PCa and our data suggest that this genetic variant may be a genetic marker for PCa susceptibility in Tunisians.