We investigate immune mechanisms of defence against viral pathogens and cancerous (transformed) cells.
Understanding these processes will help to:
- Better understand molecular mechanisms that govern the immune system.
- Identify genetic predisposition to haematological malignancies.
- Design novel therapeutic approaches to prevent life-threatening complications of bone marrow stem cell transplantation.
Cytotoxic lymphocytes (CL) carry an arsenal of highly toxic effector molecules, which upon their release rapidly kill undesirable target cells. This process of target cell recognition and destruction by CLs is called immune surveillance. The breakdown of that process due to various genetic or acquired factors leads to a greater predisposition to cancer and increased susceptibility to viral infections, which in extreme cases can also lead to severe dysregulation of the immune system. Despite decades of research into the mechanisms that govern CL activity and the killing of target cells, these aspects of immunology are yet to be fully understood.
The Trapani laboratory has a long-standing interest in elucidating the mechanisms and regulation of CL activity, with the major focus of our studies being key cytotoxic molecules: pro-apoptotic proteases, granzymes and a pore-forming protein, perforin (PRF). Once released into the synaptic cleft between a CL and a target cell, granzymes and PRF synergistically induce rapid apoptotic death of the unwanted cell.
What we have shown
By dissecting the role of components of CLs (individually and in combination), we have shown the mechanisms underlying apoptotic activity of granzymes, particularly their role in the mitochondrial death pathway. As this may be counteracted by the anti-apoptotic molecule BCL-2, which is overexpressed in many cancers, we are now developing strategies aimed at neutralising its activity and thus making a cancer cell more sensitive to immune surveillance.
Pore-forming PRF is critical for the cytotoxic activity of CLs that maintains immune surveillance of cancer and viral infections in experimental animals. In a recent breakthrough, we have demonstrated the role of PRF in maintaining immune homeostasis and protection against viral infections in humans. We found that partial PRF deficiency predisposes individuals to haematological malignancies, atypical infections and delayed onset of the immunoregulatory disorder familial haemophagocytic lymphohistiocytosis. Our studies have revealed previously unappreciated genetic regulation of PRF expression, and we are currently investigating its role in pathologies.
Our research directions
In contrast to the everyday protective role, PRF-dependent CL activity leads to life-threatening tissue damage, which is particularly evident in:
- Xenograft rejection.
- A frequently fatal complication of bone marrow transplantation, resulting in graft-versus-host disease, where cells in the gut and skin are attacked by the immune system.
- Autoimmunity such as type I diabetes, where pancreatic beta cells are targeted and killed by CLs.
- Cerebral malaria, where CLs cause inflammation in the brain.
One of the directions of our research is the development of novel therapeutic strategies to alleviate undesired effects of CL activation through the temporary targeted inhibition of PRF activity.
Opening avenues for further research
Our research group has also led the world in studies into the molecular mechanisms of PRF pore formation. We have developed experimental strategies that have allowed dissection of critical elements of the PRF mechanism and provided insight into PRF synergy with granzymes. Most recently, together with our collaborators at Monash University and Birkbeck College in London, we have resolved the x-ray crystal structure of the PRF monomer and the three-dimensional reconstruction of the entire PRF pore by cryo-EM. This has opened avenues for further research into PRF mechanism and provided the framework for the rational design of regulators of PRF function.
Voskoboinik I, Whisstock JC, Trapani JA (2015). Perforin and granzymes: function, dysfunction and human pathology. Nat Rev Immunol.15(6):388-400.
Jenkins MR, Rudd-Schmidt JA, Lopez JA, Ramsbottom KM, Mannering SI, Andrews DM, Voskoboinik I, Trapani JA (2015). Failed CTL/NK cell killing and cytokine hypersecretion are directly linked through prolonged synapse time. J Exp Med.212(3):307-17.
Spicer JA, Lena G, Lyons DM, Huttunen KM, Miller CK, O'Connor PD, Bull M, Helsby N, Jamieson SM, Denny WA, Ciccone A, Browne KA, Lopez JA, Rudd-Schmidt J, Voskoboinik I, Trapani JA (2013). Exploration of a series of 5-arylidene-2-thioxoimidazolidin-4-ones as inhibitors of the cytolytic protein perforin. J Med Chem.56(23):9542-55.
Susanto O, Stewart SE, Voskoboinik I, Brasacchio D, Hagn M, Ellis S, Asquith S, Sedelies KA, Bird PI, Waterhouse NJ, Trapani JA (2013). Mouse granzyme A induces a novel death with writhing morphology that is mechanistically distinct from granzyme B-induced apoptosis. Cell Death Differ.20(9):1183-93.
Law RH, Lukoyanova N, Voskoboinik I, Caradoc-Davies TT, Baran K, Dunstone MA, D'Angelo ME, Orlova EV, Coulibaly F, Verschoor S, Browne KA, Ciccone A, Kuiper MJ, Bird PI, Trapani JA, Saibil HR, Whisstock JC (2010). The structural basis for membrane binding and pore formation by lymphocyte perforin. Nature.468(7322):447-51. (equal corresponding author)
Baran K, Dunstone M, Chia J, Ciccone A, Browne KA, Clarke CJ, Lukoyanova N, Saibil H, Whisstock JC, Voskoboinik I, Trapani JA (2009). The molecular basis for perforin oligomerization and transmembrane pore assembly. Immunity.30(5):684-95.
Chia J, Yeo KP, Whisstock JC, Dunstone MA, Trapani JA, Voskoboinik I (2009). Temperature sensitivity of human perforin mutants unmasks subtotal loss of cytotoxicity, delayed FHL, and a predisposition to cancer. Proc Natl Acad Sci USA.106(24):9809-14.