Advances in the genomics of allogeneic haemopoietic stem cell transplantation

Polymorphisms of cytokine and innate immunity genes and GVHD

In the last 10 years, non-HLA genotypes have been investigated for their potential roles in the occurrence and severity of graft-versus-host disease (GVHD) as well as for their contribution to overall transplant-related mortality, infectious episodes, and overall survival. This chapter will review the latest results of cytokine gene polymorphisms between patient and donor which may cause the production of high or low levels of cytokines during the three-stage process of the GVHD 'cytokine storm'. More recent investigations into innate immunity and the interaction with subsequent downstream cytokine production and ultimate tissue damage are discussed. The potential of these non-HLA genetics to aid in predicting GVHD and post-transplant survival and the relevance of this information to the clinic are reviewed.

Haematopoietic stem cell transplantation: can our genes predict clinical outcome?

Haematopoietic stem cell transplantation (HSCT) is currently the only curative treatment for many patients with malignant and non-malignant haematological diseases. The success of HSCT is greatly reduced by the development of complications, which include graft-versus-host disease (GVHD), relapse and infection. Human leukocyte antigen (HLA) matching of patients and donors is essential, but does not completely prevent these complications; non-HLA genes may also have an impact upon transplant outcome. Polymorphisms within genes that are associated with an individual's capability to mount an immune response to alloantigen and infectious pathogens and/or response to drugs (pharmacogenomics) are all currently being studied for their association with HSCT outcome. This review summarises the potential role of non-HLA polymorphisms in predicting HSCT outcome, from studies on retrospective transplant cohorts of HLA-identical siblings and matched unrelated donors. The clinical relevance and interpretation of non-HLA genetics, and how these could be used alongside clinical risk factors in HSCT, are also discussed.

Risk assessment in haematopoietic stem cell transplantation: Pre–transplant patient and donor factors: non-HLA genetics

Non-HLA genetics involving the study of single-nucleotide polymorphisms (SNPs) and microsatellites of cytokine and cytokine receptor genes, and as well as genes associated with response to infection and therapeutic drugs, are currently being studied for associations with diseases, including autoimmune disease, cancer and solid-organ transplant rejection. This chapter will summarize the potential role of non-HLA genetics in predicting outcome of haematopoietic stem-cell transplantation (HSCT) and how genotyping for non-HLA genes may give insight into the immunobiology of HSCT complications, including GvHD and infectious episodes. Future directions - including the role of pharmacogenomics, use of the research results for individualized medicine, and interpretation of data - will also be discussed.

Beyond HLA: the significance of genomic variation for allogeneic hematopoietic stem cell transplantation

The last 2 years have seen much excitement in the field of genetics with the identification of a formerly unappreciated level of “structural variation” within the normal human genome. Genetic structural variants include deletions, duplications, and inversions in addition to the recently discovered, copy number variants. Single nucleotide polymorphisms are the most extensively evaluated variant within the genome to date. Combining our knowledge from these studies with our rapidly accumulating understanding of structural variants, it is apparent that the extent of genetic dissimilarity between any 2 individuals is considerable and much greater than that which was previously recognized. Clearly, this more diverse view of the genome has significant implications for allogeneic hematopoietic stem cell transplantation, not least in the generation of transplant antigens but also in terms of individual susceptibility to transplant-related toxicities. With advances in DNA sequencing technology we now have the capacity to perform genome-wide analysis in a high throughput fashion, permitting a detailed genetic analysis of patient and donor prior to transplantation. Understanding the significance of this additional genetic information and applying it in a clinically meaningful way will be one of the challenges faced by transplant clinicians in the future.

Cytokine Gene Expression in Peripheral Blood Mononuclear Cells and Alloreactivity in Hematopoietic Cell Transplantation with Nonmyeloablative Conditioning

Cytokines are thought to play an important role in the pathophysiology of graft-versus-host disease (GVHD). To study the relationship between cytokines and GVHD, we obtained peripheral blood mononuclear cells (MNCs) from 21 patients with hematologic malignancies and their HLA-identical sibling donors before and sequentially after hematopoietic cell transplantation (HCT) with nonmyeloablative conditioning. The MNCs were cultured for 72 hours either alone or in mixed lymphocyte cultures with irradiated MNCs of recipient, donor, or HLA-mismatched third-party origin. The gene expression of interleukin (IL)-2, IL-4, IL-10, IL-18, tumor necrosis factor alpha, and transforming growth factor beta in each culture was then measured by real-time quantitative reverse transcriptase-polymerase chain reaction. The composition of the responder MNCs differed between patients and donors and changed after HCT, with a possible influence on the results. Early after transplantation (day +14), the IL-10 messenger RNA (mRNA) level in response to recipient or donor antigens was higher in patients who did not develop clinically significant acute GVHD when compared with the level in patients who subsequently developed acute GVHD grades II to IV (P = .005 and P = .004, respectively). The IL-10 mRNA level on day +14 was highly correlated with the pretransplantation mRNA level of the recipient MNCs but not with the level of the donor MNCs; this suggests that the IL-10 mRNA detected on day +14 originated from responder cells of recipient origin. A higher IL-10 mRNA level was found in MNCs obtained before transplantation from recipients whose disease progressed or relapsed after the transplantation when compared with the level in patients whose disease did not progress or relapse (P = .03). In conclusion, a high IL-10 gene expression in the recipient MNCs may be related to a reduced incidence of acute GVHD grades II to IV and a reduced graft-versus-tumor effect after HCT with nonmyeloablative conditioning.

Genomic Polymorphism and Allogeneic Hematopoietic Transplantation Outcome

Polymorphisms in genes that encode antigen-presenting molecules, antigen receptors, and immune mediators are crucial determinants of the risk of complications after allogeneic hematopoietic cell transplantation (allo-HCT). Matching for HLA alleles remains the cornerstone of donor selection, and recent studies are refining our understanding and use of HLA typing in allo-HCT. High-resolution allelic HLA matching generally improves transplant outcome but may limit the donor pool and delay transplantation. Allelic mismatches may be permissible in certain circumstances without compromising outcome. There is growing interest in the role of natural killer (NK) cell-mediated immunity in allo-HCT. NK cells express an array of activating and inhibitory killer cell immunoglobulin-like receptors (KIR), and NK cell activation is negatively regulated by KIR interaction with HLA class I molecules. In haploidentical transplants, NK cell alloreactivity in the graft-versus-host direction can be predicted by the HLA class I and KIR genotypes of donor and recipient and has been associated with potent graft-versus-leukemic effects and low rates of graft-versus-host disease. KIR genotype and expression may influence transplantation outcomes in both HLA-matched and -mismatched transplants. Graft-versus-host disease and major infection remain problematic despite HLA matching, and there is mounting evidence that polymorphisms in non-HLA immune mediators and host defense genes influence the risk of these complications. The importance of non-HLA genomics in nonmyeloablative transplants is poorly understood and is under investigation. These findings suggest that tissue typing for allo-HCT is entering an exciting era in which both HLA and non-HLA genomic data may be used in a more sophisticated fashion to select donors, stratify risk, identify novel therapeutic targets, and ultimately improve outcome for allo-HCT recipients.