A meta-analysis of the effects of interleukin-6 -174 G>C genetic polymorphism on acute graft-versus-host disease susceptibility

Association of recipient and donor interleukin 6 polymorphisms 174 and 597 with outcome after allogeneic hematopoietic stem cell transplantation in children

Purpose

The success of allogeneic hematopoietic stem cell transplantation (HSCT) is compromised by complications such as infection, relapse, and graft-versus-host disease (GVHD). The investigation of non-HLA immunogenetics, particularly of cytokines, could identify predictors of an unfavorable outcome after allogeneic HSCT. In this study, we examined the impact of single nucleotide polymorphisms (SNPs) within the promoter region of interleukin 6 (IL6) on the development of GVHD after pediatric allogeneic HSCT.

Methods

In this retrospective analysis, we included 320 pediatric patients with a median age of 10 years who underwent an allogeneic HSCT and their respective donors. We used TaqMan real-time polymerase chain reaction to analyze the SNPs IL6-174 (G/C) and IL6-597 (G/A). The IL6-174 polymorphism was examined in 300 recipients and 295 donors. The IL6-597 polymorphism was analyzed in 299 recipients and 296 donors. We investigated the influence of the IL6-174 and IL6-597 polymorphisms on overall survival, event-free survival, relapse incidence, transplant-related mortality, and the occurrence of GVHD.

Results

G polymorphism at position 174 of the recipient IL6 gene was associated with a higher incidence of acute GVHD (GG vs. GC/CC; P = 0.024). Patients with IL6-597 GG genotype developed acute GVHD more frequently than individuals with an A allele (GG vs. GA vs. AA; P = 0.013). IL6-174 GG homozygous recipients had a more frequent occurrence of chronic GVHD (GG vs. GC/CC; P = 0.049). We observed a significant increased risk of chronic GVHD in recipients with IL6-597 GG genotype (GG vs. GA vs. AA; P = 0.043). Polymorphisms of donors did not affect the incidence of acute GVHD and chronic GVHD. In multivariate analysis, the IL6-174 and IL6-597 SNPs were independent significant risk factors for acute GVHD (P = 0.030; P = 0.007, respectively) as well as for chronic GVHD (P = 0.045; P = 0.015, respectively). In addition, older age at time of transplantation turned out to be a significant risk factor for chronic GVHD (P = 0.003).

Conclusion

Our study identified the IL6-174 and IL6-597 GG genotypes of pediatric allogeneic HSCT recipients as genetic risk factors for the development of acute GVHD and chronic GVHD. After evaluations in further studies, these findings could implicate the adjustment of prophylactic measures to reduce the occurrence of acute GVHD and chronic GVHD.

A single-nucleotide polymorphism in the human ENTPD1 gene encoding CD39 is associated with worsened graft-versus-host disease in a humanized mouse model

Regulatory T cells (Tregs) protect against graft-versus-host disease (GVHD), a life-threatening complication of allogeneic hematopoietic stem cell transplantation. The ectoenzyme CD39 is important for increasing the immunosuppressive function of Tregs. The rs10748643 (A → G) single-nucleotide polymorphism (SNP) in intron 1 of the human ENTPD1 gene is associated with increased proportions of CD39⁺ Tregs. This study aimed to determine whether the rs10748643 SNP corresponded to increased proportions of CD39⁺ Tregs in an Australian donor population, and whether this SNP influences clinical GVHD in a humanized mouse model. Donors were genotyped for the rs10748643 SNP by Sanger sequencing, and the proportion of CD39⁺ T cells in donor peripheral blood was determined by flow cytometry. Donors encoding the G allele (donors^AG/GG ) demonstrated higher proportions of CD39⁺ CD3⁺ CD4⁺ CD25⁺ CD127^lo Tregs, but not CD39⁺ CD3⁺ CD8⁺ T cells or CD39⁺ CD3⁺ CD4⁺ conventional T cells, compared with donors homozygous for the A allele (donors^AA ). NOD-SCID-IL2Rγ^null mice were injected with human peripheral blood mononuclear cells from either donors^AA (hCD39^AA mice) or donors^AG/GG (hCD39^AG/GG mice). hCD39^AG/GG mice demonstrated significantly greater weight loss and GVHD clinical scores, and significantly reduced survival, compared with hCD39^AA mice. hCD39^AG/GG mice showed significantly higher hCD4⁺ :hCD8⁺ T-cell ratios than hCD39^AA mice, but displayed similar proportions of CD3⁺ hCD4⁺ hCD25⁺ hCD127^lo Tregs and hCD39⁺ Tregs. However, the proportion of human Tregs corresponded to survival in hCD39^AA mice, but not in hCD39^AG/GG mice. This study demonstrates that donors encoding the G allele show higher percentages of CD39⁺ Tregs, but cause worsened GVHD in humanized mice compared with donors homozygous for the A allele.

Interleukin-6 in Allogeneic Stem Cell Transplantation: Its Possible Importance for Immunoregulation and As a Therapeutic Target

Allogeneic stem cell transplantation is associated with a high risk of treatment-related mortality mainly caused by infections and graft-versus-host disease (GVHD). GVHD is characterized by severe immune dysregulation and impaired regeneration of different tissues, i.e., epithelial barriers and the liver. The balance between pro- and anti-inflammatory cytokine influences the risk of GVHD. Interleukin-6 (IL-6) is a cytokine that previously has been associated with pro-inflammatory effects. However, more recent evidence from various autoimmune diseases (e.g., inflammatory bowel disease, rheumatoid arthritis) has shown that the IL-6 activity is more complex with important effects also on tissue homeostasis, regeneration, and metabolism. This review summarizes the current understanding of how pro-inflammatory IL-6 effects exerted during the peritransplant period shapes T-cell polarization with enhancement of Th17 differentiation and suppression of regulatory T cells, and in addition we also review and discuss the results from trials exploring non-selective IL-6 inhibition in prophylaxis and treatment of GVHD. Emerging evidence suggests that the molecular strategy for targeting of IL-6-initiated intracellular signaling is important for the effect on GVHD. It will therefore be important to further characterize the role of IL-6 in the pathogenesis of GVHD to clarify whether combined IL-6 inhibition of both trans- (i.e., binding of the soluble IL-6/IL-6 receptor complex to cell surface gp130) and cis-signaling (i.e., IL-6 ligation of the IL-6 receptor/gp130 complex) or selective inhibition of trans-signaling should be tried in the prophylaxis and/or treatment of GVHD in allotransplant patients.