Toll-like receptor genetic variations in bone marrow transplantation

Tools for optimizing risk assessment in hematopoietic cell transplant - What can we get away with?

Unrelated allogeneic hematopoietic cell transplant (HCT) is a critical modality to treat hematologic malignancies. The current objective of donor selection is to match donor and recipient at the HLA (human leukocyte antigen) peptide-binding region which should lower the risk of graft-versus-host disease. However, depending on the patient's ethnicity/race, finding a matched donor is challenging, especially for HLA-DPB1 which is due to the weak linkage disequilibrium between HLA-DPB1 and the other HLA class II loci. Recent evidence, on the molecular level, has shown that certain HLA mismatches carry lower clinical risk. More specifically, there is an increasing understanding of polymorphisms of the innate and adaptive immune systems and their impact on transplant outcomes, allowing us to expand our "toolkit" for optimization of donor selection in HCT. Therefore, in this review we discuss matching strategies based on comparing donor and recipient polymorphisms that may influence innate and adaptive immune response genes in allorecognition and the role of single nucleotide polymorphisms in non-HLA genes that have the potential for providing additional tools to refine risk stratification.

Trained Innate Immunity in Hematopoietic Stem Cell and Solid Organ Transplantation

Although significant progress has been made to improve short-term survival of transplant patients, long-term acceptance of allografts in solid organ and hematopoietic stem cell (HSC) transplantation is still a significant challenge. Current therapeutics for preventing or treating allograft rejection rely on potent immunosuppressive drugs that primarily target T cells of the adaptive immune response. Promising advances in transplant immunology have highlighted the importance of innate immune responses in allograft acceptance and rejection. Recent studies have demonstrated that innate immune cells are capable of mediating memory-like responses during inflammation, a term known as trained innate immunity. In this process, innate immune cells, such as macrophages and monocytes, undergo metabolic and epigenetic changes in response to a primary stimulus with a pathogen or their products that result in faster and more robust responses to a secondary stimulus. There is also some evidence to suggest that innate immune cells or their progenitors may be more anti-inflammatory after initial stimulation with appropriate agents, such as helminth products. Although this phenomenon has primarily been studied in the context of infection, there is emerging evidence to suggest that it could play a vital role in transplantation rejection and tolerance. Mechanisms of training innate immune cells and their progenitors in the bone marrow are therefore attractive targets for mediating long-term solid organ and HSC transplant tolerance. In this review, we highlight the potential role of proinflammatory and anti-inflammatory mechanisms of trained innate immunity in solid organ and HSC transplantation.

Perfluorooctanoic acid-induced immunotoxicity via NF-kappa B pathway in zebrafish (Danio rerio) kidney

Perfluorooctanoic acid (PFOA) is widely used in industrial production due to its stable chemical structure and hydrophobic and oleophobic characteristics. PFOA has been frequently detected in environmental media and organisms, leading to increased health risks. There is a lack of information about the immunotoxicity of aquatic organisms induced by PFOA, and the molecular mechanisms remain unclear. In this study, LC-MS analysis proved that PFOA can accumulate in the kidney of zebrafish. In the 0.05 mg/L PFOA treatment group, the accumulation of PFOA in the kidney after 21 days of exposure significantly increased by 79.89%, compared to 14 days of exposure. And a hydropic endoplasmic reticulum, swelling of mitochondria and vacuolization were observed in kidney immune cells of zebrafish. The Toll-like receptor 2 (TLR2)/myeloid differentiation factor 88 (myd88)/NF-κB (P65) pathway was activated when PFOA exerted its effects, which led to regulation of antibody expression; RT-PCR results showed that the mRNA expression level of interleukin-4 (IL-4) decreased in a dose-dependent manner, decreasing to 29.6% of the control level in the 1 mg/L PFOA group after 21 d of exposure. According to triangle plot analysis, immunoglobulin exhibited a notable stress response to PFOA at an early phase; a high concentration of PFOA may disrupt the immune system of zebrafish. Third-order polynomial fitting analysis showed that the high-mRNA-expression regions of IL-4 and antibodies were partially consistent. The results indicated that PFOA could affect antibodies by increasing the concentrations of proinflammatory cytokines. Changes in antibody levels further influenced the expression of other cytokines, which eventually caused disorders in the zebrafish immune system. This study expands the understanding of PFOA-induced immunosuppression and suggests that toxicity mechanisms should be considered for further health risk assessment of emerging pollutants.

Donor UNC-93 Homolog B1 genetic polymorphism predicts survival outcomes after unrelated bone marrow transplantation

UNC-93 homolog B1 (UNC93B1) is a key regulator of toll-like receptors (TLRs), pattern recognition receptors that sense invading pathogens and manage the innate immune response and deliver them from the endoplasmic reticulum to their respective endosomal signaling compartments. Several types of TLRs are known to contribute to the inflammatory process after allogeneic hematopoietic stem cell transplantation (SCT), so UNC93B1 might play integral roles there. We investigated the influence of the UNC93B1 single-nucleotide polymorphism (SNP) rs308328 (T>C) on transplant outcomes in a cohort of 237 patients undergoing unrelated HLA-matched bone marrow transplantation (BMT) for hematologic malignancies through the Japan Marrow Donor Program. The donor UNC93B1 C/C genotype was associated with a better 3-year overall survival than the donor UNC93B1 C/T or T/T genotype. An analysis of the UNC93B1 rs308328 genotype may therefore be useful for selecting the donor, estimating the prognosis, and creating therapeutic strategies after allogeneic SCT.

Donor Heme Oxygenase-1 Promoter Gene Polymorphism Predicts Survival after Unrelated Bone Marrow Transplantation for High-Risk Patients

Heme oxygenase-1 (HO-1), an intracellular enzyme that catalyzes the degradation of heme into biliverdin, free iron, and carbon monoxide, exerts anti-inflammatory and cytoprotective effects against endothelial cell injury. The HO-1 promoter gene has one important single-nucleotide polymorphism (SNP) rs2071746 (-413A>T) that is functional, and the A allele has been reported to be associated with higher HO-1 expression levels than the T allele. We investigated the influence of the HO-1 rs2071746 SNP on the transplant outcomes in 593 patients with hematological malignancies undergoing unrelated, human leukocyte antigen (HLA)-matched, T-cell-replete bone marrow transplantation (BMT) through the Japan Donor Marrow Program. In patients with high-risk diseases, the donor A/A or A/T genotype was associated with better 5 year overall survival (35% vs. 25%; p = 0.03) and 5 year disease-free survival (35% vs. 22%; p = 0.0072), compared to the donor T/T genotype. These effects were not observed in patients with low-risk diseases. The current findings therefore indicate that HO-1 rs2071746 genotyping could be useful for selecting donors and tailoring transplant strategies for patients with high-risk hematologic malignancies.

Infection Complications in Hematopoietic Stem Cells Transplant Recipients: Do Genetics Really Matter?

Hematopoietic stem cell transplantation (HSCT) is a highly advanced technique that offers a potential cure for an increasing number of life-threatening diseases. Enormous progress achieved in the last decade, including the refinement of donor selection and advancements in patient supportive care, had significantly improved transplant outcomes; however, invasive infections, graft-vs.-host disease (GVHD) and other serious complications still represent a major source of morbidity and mortality in HSCT recipients. The damage of anatomical barriers due to pre-transplant conditioning, a severely damaged immune function and a profound disruption in the composition of gut microbial commensals (gut microbiota) are alterations inherent to the transplant procedure that are directly implicated in the development of invasive infections and other HSCT complications. Although HLA-matching represents the most important genetic predictor of transplant outcomes, genetic variants in non-HLA genes, especially single nucleotide polymorphisms (SNPs) of genes encoding proteins associated with the immune response to tissue injury and pathogen infection have also been proposed as additional risk factors implicated in the occurrence of HSCT complications. Furthermore, although the microbiota composition is affected by several factors, recent evidence suggests that certain host genetic variants are associated with an altered composition of the gut microbiome and may, therefore, predispose some individuals to invasive infectious complications. This article summarizes the current understanding of the influence that genetic variants in non-HLA genes have on the development of infectious complications in HSCT recipients.