Role of Pharmacogenetics in Hematopoietic Stem Cell Transplantation Outcome in Children

Impact of Glutathione S-Transferase Polymorphisms on Busulfan Pharmacokinetics and Outcomes of Hematopoietic Stem Cell Transplantation

BACKGROUND

Busulfan (Bu) is an alkylating drug used in many preparative regimens before hematopoietic stem cell transplantation (HSCT). It is conjugated in the liver mainly by glutathione S-transferase isoenzyme A1-1 ( GSTA1 ). Genetic polymorphisms in these isoenzymes may affect the pharmacokinetics of Bu and the clinical outcomes of HSCT. This study aimed to assess the impact of glutathione S-transferase ( GST ) genetic polymorphisms on the clearance of Bu and the clinical outcomes of patients undergoing HSCT.

METHODS

This single-center retrospective study included patients who received IV Bu before HSCT at Sultan Qaboos University Hospital (SQUH), Oman from January 2003 to October 2016. Genotyping for polymorphisms was performed for GSTM1 , GSTT1 , GSTA1 , and GSTP1 . Each GST polymorphism was analyzed for its impact on Bu clearance and HSCT outcomes.

RESULTS

A total of 135 patients were included. The mean Bu clearance was 3.7 ± 0.98 mL/min/kg. Patients with GSTA1 A-513G heterozygosity (AG) were found to have a higher incidence of graft loss ( P = 0.006). Homozygous double null of GSTM1 and GSTT1 was associated with a higher incidence of acute graft versus host disease ( P = 0.04). Double non-null GSTM1 and GSTT1 and non-null GSTM1 increased the risk of mortality ( P = 0.034 and 0.021, respectively).

CONCLUSIONS

GST genotyping before HSCT may predict HSCT outcomes. The results of this preliminary retrospective study need to be confirmed in a larger prospective study.

Effect of physical exercise on the functional capacity of children and adolescents submitted to transplantation of hematopoietic stem cells-A systematic review with meta-analysis

Previous studies have shown beneficial effects of physical exercise (PE) in adults submitted to hematopoietic stem cell transplantation (HSCT). Conduct a systematic review about the effects of PE on the functional capacity of children and adolescents submitted to HSCT. The studies were searched in the databases MEDLINE (via PubMed), Central Register of Controlled Trials (Cochrane CENTRAL), EMBASE, LILACS, and Evidence Database in Physical Therapy (PEDro) (CRD42018080093). Two independent reviewers performed the article selection, data extraction, and methodological quality assessment. Randomized and nonrandomized clinical trials comparing PE with usual treatment in children and adolescents aged 3-18 years were included. The risk of bias was assessed using the Cochrane Collaboration tool and ROBINS-I tool, and the overall quality of the evidence was determined by the GRADE system. We included three studies with 91 patients. PE improved the functional capacity assessed by the timed up and down stairs test (MD -1.23 [95% CI, 2.27 to -.20, I2 = 0%]), but there was no significant effect in the six-minute walk test (MD 44.63 [95% CI, -20.86 to 110.13, I2 = 83%]). The benefits regarding quality of life and peripheral muscle strength of these individuals were not clearly demonstrated, but positive responses were observed in relation to the analyzed data. None of the studies evaluated the fatigue. The limitations found were the high heterogeneity between studies, as well as the sample size and the low methodological rigor. PE might be favorable to improve the functional capacity of children and adolescents treated with HSCT. However, further studies are needed to clarify the best PE program.

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.