In the autumn of 2010 we made the following awards to:
Dr Stuart Tangye and Dr Umamainthan Palendira Garvan Institute, Darlinghurst, NSW, Australia. £40,000 over two years.
The most critical and perplexing feature of XLP is the extreme vulnerability to infection with the herpes virus Epstein Barr virus (EBV). While >90% of healthy individuals are infected with EBV, most remain asymptomatic, unaware they have contracted the virus. The ~25% of normal individuals affected by EBV infection develop infectious mononucleosis (“glandular fever”), a self-limiting illness that resolves within several months. In stark contrast, exposure of XLP patients to EBV is life-threatening. Here, XLP patients develop severe infectious mononucleosis characterised by uncontrolled activation of immune cells, causing gross and often-fatal damage to the liver and bone marrow. Unlike EBV infection, XLP patients generate normal immune responses to other viruses – including other herpes viruses (herpes simplex, varicella zoster, cytomegalovirus). This striking observation informs us that signalling in immune cells through pathways that utilize SAP – the protein encoded by SH2D1A, which is mutated in XLP – is fundamental for the generation of successful anti-EBV immune responses, and that no redundant pathways exist to compensate for SAP deficiency. Thus, in order to improve the outcomes of XLP patients, it is absolutely critical to identify the exact mechanisms deployed for host protection against EBV infection.
We propose that the central defect in XLP is the inability of SAP-deficient immune cells to respond appropriately to the type of cell that is specifically infected by EBV, that being B cells. Thus, we plan to identify the molecular defect(s) underlying the impaired response of SAP-deficient immune cells to B cells. Identifying key intermediates in the SAP signalling pathway required for the efficient recognition and destruction of EBV-infected B cells will reveal molecules that could be targeted to improve anti-EBV immune responses in XLP patients.
Dr. Andrew L. Snow, Department of Pharmacology, Uniformed Services University of the Health Services, United States of America. £40,000. Awarded over one year.
Effective adaptive immunity depends upon rapid and controlled clonal T cell expansion to respond to pathogens without inflicting damage to “self” tissues. Restimulation-induced cell death (RICD) is a self regulator mechanism that curbs excessive T cell expansion by triggering apoptosis of T cells upon repeated engagement of the T cell receptor (TCR). Our recent work revealed that XLP1 patients T cells deficient for SLAM-associated protein (SAP) demonstrate impaired RICD, which likely contributes to life-threatening accumulations of activated T cells in XLP1 patients, particularly in response to Epstein-Barr virus (EBV) infection . Indeed, both SAP and the SLAM family receptor protein NTB-A are required for optimal RICD of human T cells. However, the biochemical links between SAP, NTB-A, and TCR-induced signaling pathways remain poorly understood.
This project aims to elucidate the molecular functions of SAP, NTB-A, and other SLAM family receptors that influence TCR signaling and RICD sensitivity for activated T cells. Aim 1 builds upon past work and new preliminary data that suggests a previously unrecognized network of biochemical communication between SAP, NTB-A, and components of the TCR signaling machinery such as LCK and SHP-1. Aim 2 will deduce how other SLAM receptors influence RICD by modulating SAP-dependent signals through NTB-A and the TCR. Detailed characterization of these molecular interactions will advance our understanding of aberrant T cell signaling and function in XLP patients, and perhaps expose new therapeutic targets for controlling harmful T cell hyperproliferation.
Dr Stuart Tangye and Dr Umamainthan Palendira Garvan Institute, Darlinghurst, NSW, Australia. £30,000 over two years. Awarded 2007.
X-linked lymphoproliferative disease (XLP) is an inherited disease. The gene defect results in the absence of a protein that is involved in signalling through numerous receptors on the surface of white blood cells. These receptors may be crucial for the function of cytotoxic T lymphocytes, a population of white blood cells that are important for anti-viral immune responses and for tumour clearance. One major problem for XLP patients is their increased sensitivity to infection with Epstein Barr Virus (EBV), a virus which causes asymptomatic infection in the majority of the population, but can occasionally cause self-limiting infectious mononucleosis (Glandular fever). Exposure to EBV is often fatal in XLP patients and even those who survive acute virus infection often go on to develop further complications such as lymphoma, a cancer of immune cells. We aim to investigate why XLP patients are particularly susceptible to infection with EBV. We will achieve this by characterising the differences in the function of cytotoxic white blood cells collected from XLP patients and from healthy individuals. We will also determine why XLP patients are able to respond to common viruses such as Influenza virus. This study will provide a greater understanding of why XLP patients are particularly susceptible to one particular virus, which causes widespread tissue damage of often death in these patients. The findings from this study may aid in the development of new treatmentsltherapies for XLP patients.
"We have been addressing the question of why patients with XLP are so exquisitely and uniquely sensitive to infection with Epstein Barr virus (EBV) - a virus that is relatively harmless when it infects healthy individuals. All viruses are incapable of surviving on their own – they need to infect an appropriate host cells which then provides all of the 'machinery' necessary for the virus to replicate and survive. EBV infects B cells, which are a type of immune cell.
What we have discovered is that the cells of the immune system that are responsible for detecting and killing viruses and virus-infected cells are unable to properly recognise the cells that become infected with EBV – i.e. B cells. In contrast, the killer cells in XLP patients are completely normal in their ability to recognise different types of virus-infected cells, such as skin cells (which become infected with viruses such as influenza), and other immune cells which can be infected with viruses such as cytomegalovirus (which is related to EBV).
Overall, the answer to why XLP patients succumb to EBV infection is elegant in its simplicity – EBV infects B cells, and XLP killer cells fail to interact with B cells in a normal manner. If EBV infected other types of cells, it is likely that there would be a compensation mechanism whereby the killer cells would be able to control EBV infection. These findings are also relevant to the development of lymphoma in XLP patients. Lymphoma affects ~30-40% of XLP patients, and most of the lymphomas that develop arise from malignant B cells. Since the immune cells that are involved in recognising virus-infected cells and destroying them are also responsible for detecting cancer cells. Thus, since the XLP killer cells are inefficient at recognising B cells, it is highly likely that this contributes to the high incidence of B-cell lymphoma in XLP."
Kim Nichols, MD Children’s Hospital of Philadelphia, United States of America. £72,550 Awarded over two years, June 2008 - June 2010.
Our laboratory is studying proteins that regulate the activity of T lymphocytes, white blood cells that are essential in the immune response against specific pathogens, such as viruses. By identifying molecules that control host protective mechanisms, we hope to develop improved therapies for patients suffering from severe virus infections and virus-associated cancers. We have made progress by studying X-linked lymphoproliferative disease (XLP), a rare and often fatal immunodeficiency characterized by a decreased ability to control Epstein-Barr virus infection, a reduced production of specialized proteins known as antibodies and an increased risk to develop lymphoma. Previously, we identified SHZDlA, the gene that is abnormal in XLP patients. SHZDlA encodes for a protein known as SAP, which regulates the functions of T lymphocytes. Recently, we observed that SAP is required for the development of a potent but poorly understood subset of T lymphocytes known as natural killer T (IVKT) cells. Currently, our research is focused on understanding how SAP controls NKT cell development and establishing whether this adaptor regulates mature NKT cell functions. We are also examining how the absence of IVKT cells contributes to the abnormal antiviral immune responses that occur in XLP patients and SAP-deficient mice. These studies will increase our understanding of NKT cell biology and may provide insights into how LIKT cells can be expanded and activated to enhance host immunity.
Sylvain Latour, Christelle Lenoir and Stéphanie Rigaud Inserm Unit 768, Hôpital Necker-Enfants Malades, Paris, France. €55,000 over two years. Awarded 2007.
The X-linked lymphoproliferative syndrome (XLP) or Purtilo syndrome is a rare inherited immunodeficiency that is characterized by an inappropriate immune response to Epstein-Barr virus (EBV) infection. Mutations in the genes SAP and XIAP underlie most of the patients with familial XLP disease. We have recently established that both XIAP and SAP deficiency lead to a specific defect in a particular lymphocyte subpopulation, the NKT lymphocytes.
The aim of this proposal is : There is a significant number of patients presenting an EBV-associated lymphoproliferative syndrome (diagnosed as an XLP-like disease) that are not carrying mutations in SAP nor XIAP. In these patients, the genetic origin of the condition is unknown suggesting that other genes may account for the pathology in these patients. The identification of the gene defect (s) that cause these related syndromes will be undertaken. This study will help identify people who may suffer from XLP-like conditions.