Liver Immunology group
Lab head: Patrick Bertolino
Location: The Liver Immunology Group, Centenary Institute
Liver Immunology: The liver has fascinating immunological properties. In animal models of transplantation, livers grafted across MHC barriers do not result in rejection and are able to prevent rejection of a different organ from the same donor, suggesting that the liver has induced donor-specific tolerance. This bias toward tolerance is advantageous in transplantation as it promotes graft acceptance. However, it can be detrimental when pathogens infecting the liver, such as malaria, Hepatitis B and C viruses, induce tolerance and evade immune responses, leading to chronic infection. Understanding how the liver induces tolerance will reveal new strategies to boost immune responses to clear liver pathogens, or to increase the survival of solid organ transplants.
Research in the group:Our group is recognized internationally for contributions to this field. Using a variety of transgenic mouse models, we were the first to demonstrate that naïve CD8 T cells can be directly activated in the liver. We have now evidence that the liver can also support activation of naïve CD4 T cells. These are unique findings, as it was thought that naïve T cells could only be activated in lymphoid organs. We showed that unlike CD8 T cells activated in lymphoid tissues, liver-activated T cells die by apoptosis, leading to tolerance. The fate of CD4 T cells activated in the liver is totally unknown. Recently, we discovered a different mechanism that the liver uses to delete liver-activated CD8 T cells. This mechanism was very efficient, resulting in rapid clearance of T cells within a few hours. T cells were found to invade hepatocytes (the main liver cells), and were subsequently degraded within lysosomal compartments. This is a novel cellular phenomenon, which will open up new ways to understand immune cell regulation by the liver. The three projects available in our group for 2013 will use a new generation of recombinant adeno-associated virus (AAV) vectors able to transduce 100% of mouse hepatocytes in vivo. These recently developed vectors represent new powerful tools to investigate the phenotype, function and fate of T cells activated intrahepatically.
Project 1: Role of TCR affinity in shaping CD8 T cell responses to liver antigens
Primary supervisor: Patrick Bertolino
Background and aims: Using a recombinant AAV that efficiently expresses ovalbumin (OVA) in all hepatocytes, we have recently shown that OT-I CD8 T cells that express a transgenic TCR specific for SIINFEKL, a high affinity OVA-derived epitope, were efficiently retained and activated in the liver before being deleted. Although this observation is critical to explain how the liver is able to tolerise high affinity T cells, we do not know if low affinity T cells would be tolerised the same way. We have generated 5 different rAAV vectors, each expressing a different OVA variant containing one point mutation in the OVA sequence encoding for the SIINFEKL peptide. These variants give rise to altered peptide ligands (APLs) able to bind as efficiently to the MHC Class I molecule but generate p:MHC complexes recognised with different affinities by the OT-1 transgenic TCR. We have demonstrated that T cell retention in the liver as well as activation is affinity-dependent. The role of affinity in T cell function (CTL activity) and deletion by degradation in hepatocytes is unknown.
1. Determine whether OT-I T cells activated by the different APLs mature into efficient CTLs
2. Determine whether OT-I T cells activated by the different APLs similarly enter into hepatocytes and whether they are degraded in lysosomes in the same way
3. Investigate the role of CD4 T cells in helping low and high affinity CD8 T cells.
Expected outcomes: We expect that T cells activated by low affinity APLs will not differentiate into efficient CTLs and will not be deleted as efficiently as T cells activated by high affinity peptides. We predict that T cells activated by APLs will accumulate in the liver without inducing hepatic damage.
Why is this project important? The T cell repertoire normally consists of T cells with a range of affinities. Studying the behavior of both low and high affinity responses will give a more comprehensive picture of T cell responses to liver antigens. As this low affinity interaction in the liver has not yet been investigated, the work has potential to be published in a high impact factor journal, and give important insights relevant to future interventions to manipulate the balance between tolerance and immunity.
Techniques you will learn for the project: This project will give you experience in mouse handling and organ harvesting; multicolour flow cytometry; immunohistochemistry; and confocal microscopy.Experience in these techniques are invaluable for a career in immunology research. You will use recombinant AAV vectors that are currently in clinical trials for gene therapy in a range of conditions. There is potential for both projects to evolve into a PhD research project for the right candidate.
Discipline: Infectious diseases and Immunology
Co-supervisors: David Bowen
Keywords: Liver, Transgenic mouse models, T-cells