Cambridge BRC

Transplantation - Recent Highlights

Section: 
Transplantation

Role of MHC proteins and NK receptors in transplantation

MHC genes and molecules & NK receptors

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Regulation of MHC class I and class II and their ligands in transplantation

MHC genes and molecules

We study the human major histocompatibility complex (MHC) and related loci. This key cluster of genes encodes the most polymorphic proteins in the human genome. MHC class I and class II play a pivotal role in alerting the rest of the immune system to disease. The MHC is associated with more diseases than any other region of the genome, including most autoimmune conditions, infections, cancers, drug-sensitivity and, interestingly, Parkinson's disease and schizophrenia.

NK receptors

Like some MHC genes, the NK receptors are part of extensive gene families. They are involved in activating, or inhibiting NK cells and some T cells. We are studying the organisation of the NK-receptor gene families, particularly KIR, their polymorphism and association with disease.

The aim is to understand the genetic and functional consequences of interactions of the receptors with different MHC class I molecules. We are investigating the roles of MHC molecules and their ligands in transplantation and ways in which they may be manipulated to promote transplantation tolerance on tissue or stem cells whilst at the same time initiating anti-leukaemia effects. To facilitate

this we have developed a novel high-throughput KIR typing system. We are in discussion with Craig Taylor regarding marketing KIR typing as a national service.

Regulation of MHC class II

Recently, mechanisms have been uncovered for post-translational regulation of MHC class II expression. We have shown that the HLA-DRA chain, as well as the DRB, chain is modified by polyubiquitination. Several viruses are known to modulate MHC class I levels by influencing their ubiquitination. We showed for the first time that Salmonella specifically down-modulates MHC class II at the cell surface by ubiquitination. These bacteria also manipulate natural killer cell responses in order to avoid immune recognition. As dendritic cells mature into professional antigen presenting cells surface MHC class II expression is increased by down-regulating ubiquitination. Several pathogens regulate MHC antigen presentation through enhancing ubiquitination of both class I and class II molecules. Understanding the mechanisms controlling surface class II expression may provide novel targets for small molecules capable of controlling surface MHC expression. Therapeutic control of MHC class II ubiquitination may restrict the initiation of adaptive immune responses in transplanted tissues and stem cells.

Sub-theme leads: John Trowsdale and Craig Taylor

Pluripotent stem cells as a source of cells and tissues for transplantation, and to enable new insights from modeling human disease

Research continues to focus on the early stages of development of pluripotent human embryonic stem cells (hESCs) to determine the conditions that maintain pluripotency and induce differentiation in chemically defined conditions. hESCs rely on Actividin-Nodal signalling to maintain pluripotency but paradoxically such signaling may also induce mesoendodermal differentiation. We have recently shown that Smad-interacting protein 1 (SIP1) limits the mesendoderm-inducing effects of Activin-Nodal signaling without inhibiting the pluripotency-maintaining effects exerted by SMAD2/3. In turn, Activin-Nodal signaling cooperates with NANOG, OCT4, and SOX2 to control the expression of SIP1 in hESCs, thereby limiting the neuroectoderm-promoting effects of SIP1. These results reveal the mechanisms by which Activin-Nodal signaling acts through SIP1 to regulate the cell-fate decision between neuroectoderm and mesendoderm in the progression from pluripotency to primary germ layer differentiation.

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A major thrust within this sub-theme is to realise the translational potential of induced pluripotent stem cells (iPS cells) and their differentiated cell types, not only as a source of cells and tissue for transplantation, but as models for understanding mechanisms of disease. Somatic cells can be reprogrammed into iPS cells by overexpressing combinations of factors such as Oct4, Sox2, Klf4, and c-Myc but reprogramming is slow and stochastic. We have identified senescence as an important barrier to reprogramming and shown that expression of the four reprogramming factors triggers senescence by up-regulating p53, p16(INK4a), and p21(CIP1). Induction of DNA damage response and chromatin remodeling of the INK4a/ARF locus are two of the mechanisms behind senescence induction. Crucially, ablation of different senescence effectors improves the efficiency of reprogramming, suggesting novel strategies for maximizing the generation of iPS cells.

The power of iPS cells as models for human disease is exemplified by our recent success in the area of metabolic liver disease. Dermal fibroblasts from patients with various inherited metabolic diseases of the liver were used to generate patient-specific human iPS cell lines that were differentiated into hepatocytes using a novel 3-step differentiation protocol in chemically defined conditions. The resulting cells exhibited functional properties of mature hepatocytes and cells generated from patients with 3 of the inherited metabolic conditions studied (alpha1-antitrypsin deficiency, familial hypercholesterolemia, and glycogen storage disease type 1a) were found to recapitulate key pathological features of the diseases affecting the patients from which they were derived. The simple and effective platform for hepatocyte generation from patient-specific human iPS cells is proof of principle that it is possible to model diseases whose phenotypes are caused by pathological dysregulation of key processes within adult cells. Collaborations have now been initiated with investigators within several of the different themes within the BRC to use iPS cells to model human diseases that result from pathological disturbances within a variety of other cell types.

Sub-theme leads: Roger Pedersen and Ludovic Vallier

Evaluating novel targets for therapeutic intervention in tissue injury

Research relating to the role of TNF and its receptors has demonstrated the independent regulation and differential functions of TNFRs in myocardium, consistent with TNFR1-mediated tissue injury and cell death and TNFR2-mediated repair. These results are being translated into potential novel therapeutic approaches to reducing graft loss through a number of strategies. Peptides which may act as TNF receptor selective agonists and antagonists are being designed based on existing knowledge of TNF-TNF receptor interactions, in collaboration with Professor Shankar Balasubramanian Department of Chemistry, University of Cambridge. These peptides are currently being tested in receptor binding assays.

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Research relating to the role of TNF and its receptors has demonstrated the independent regulation and differential functions of TNFRs in myocardium, consistent with TNFR1-mediated tissue injury and cell death and TNFR2-mediated repair. These results are being translated into potential novel therapeutic approaches to reducing graft loss through a number of strategies. Peptides which may act as TNF receptor selective agonists and antagonists are being designed based on existing knowledge of TNF-TNF receptor interactions, in collaboration with Professor Shankar Balasubramanian Department of Chemistry, University of Cambridge. These peptides are currently being tested in receptor binding assays.

In addition, selective TNF receptor antagonists are being tested using in vivo models in collaboration with colleagues at Yale University as part of an academic-commercial partnership. The potential role of TNF in promoting cell growth in malignancy has also been investigated in collaboration with Professor David Neal (Cancer theme). Studies in renal cell carcinoma have demonstrated that TNF, acting through TNFR2, is an autocrine growth factor for renal cell carcinoma, acting via Enothelial/epithelial tyrosine kinase-VEGFR2 cross-talk, providing insights that may inform a more effective therapeutic approach to this disease.

Sub-theme lead: John Bradley

Evaluating novel approaches for assessing organ function and viability before and after transplantation, predicting transplant outcome and testing novel immunosuppressive agents

There have been several significant achievements over the last 18 months within this sub-theme. Research has continued to inform the use of kidneys donated for organ transplantation after cardiac death, providing information on the influence of donor malignancy, kidney disease and timing of cardiac death on outcome that has aided planning and resourcing of organ recovery after cardiac death and helped maximise donor numbers. In addition, studies have clarified the optimum methods of storing organs after retrieval. Andrew Bradley (PI) and Chris Watson (CI) were recently awarded a programme grant from the NIHR to improve access to and outcomes after kidney transplantation.

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There have been several significant achievements over the last 18 months within this sub-theme. Research has continued to inform the use of kidneys donated for organ transplantation after cardiac death, providing information on the influence of donor malignancy, kidney disease and timing of cardiac death on outcome that has aided planning and resourcing of organ recovery after cardiac death and helped maximise donor numbers. In addition, studies have clarified the optimum methods of storing organs after retrieval. Andrew Bradley (PI) and Chris Watson (CI) were recently awarded a programme grant from the NIHR to improve access to and outcomes after kidney transplantation.

Also under this subtheme, significant progress has been made in the development of a prototype probe for evaluating the fat content of livers prior to transplantation. Fatty donor livers perform poorly following organ transplantation and the novel probe (developed in conjunction with the photonics and sensors group within the Department of Engineering) promises to provide for the first time an objective way to estimate the fat content of a donor liver prior to transplantation. The most recent prototype has been shown to be effective in pre-clinical studies and is now undergoing full clinical evaluation. We continue to evaluate a variety of novel immunosuppressive strategies in clinical transplantation and in conjunction with Ken Smith and colleagues we have recently highlighted an important limitation to the use of B cell depletion as an induction strategy at the time of kidney transplantation.

Sub-theme leads: Chris Watson and Andrew Bradley

Cell-fate decisions between neuroectoderm and mesendoderm in human pluripotent stem cells

The Improving Outcomes in Transplantation theme continues to elucidate the mechanisms involved in determining cell fate. Human embryonic stem cells (hESCs) rely on Activin-Nodal signalling to maintain their pluripotency, but Activin-Nodal signalling is also known to induce mesendoderm differentiation. Work supported by the NIHR Cambridge Biomedical Research Centre and the Medical Research Council has identified the mechanisms by which Activin-Nodal signalling acts through SIP1 to regulate the cell-fate decision between neuroectoderm and mesendoderm in the progression from pluripotency to primary germ layer differentiation.

[Read more...]

The Improving Outcomes in Transplantation theme continues to elucidate the mechanisms involved in determining cell fate. Human embryonic stem cells (hESCs) rely on Activin-Nodal signalling to maintain their pluripotency, but Activin-Nodal signalling is also known to induce mesendoderm differentiation. Work supported by the NIHR Cambridge Biomedical Research Centre and the Medical Research Council has identified the mechanisms by which Activin-Nodal signalling acts through SIP1 to regulate the cell-fate decision between neuroectoderm and mesendoderm in the progression from pluripotency to primary germ layer differentiation.

See Transplantation Key Publications