Learning how breast cancer cells evade the immune system

Cancer cells have ways to evade the human immune system, but research at Diamond could leave them with nowhere to hide

The human immune system has cells that can attack invading pathogens, protecting us from bacteria and viruses. These cells are also capable of killing cancer cells, but they don't. Cancer cells have evolved defence mechanisms that protect them from our immune system, allowing them to survive and replicate, growing into tumours that may then spread through the body. Dr Vadim Sumbayev, together with an international team of researchers, has been working in collaboration with Dr Rohanah Hussain and Prof Giuliano Siligardi of Diamond's B23 beamline to investigate these defence mechanisms. Their previous work at Diamond led them to conclude that the immune receptor Tim-3 and the protein it naturally binds to, galectin-9, play a role in allowing acute myeloid leukaemia (AML) cells escape the human immune system. In work recently published in Frontiers in Immunologythe team investigated the role of the Tim-3-galectin-9 complex in human breast cancer. They found that breast tumours express significantly higher levels of Tim-3 and galectin-9 than healthy tissue, with the result suggesting that both proteins are expressed by the same cells. Further experiment showed that a wide range of different cancers express detectable amounts of both Tim-3 and galectin-9.

Immune surveillance and avoidance

The human immune system has two kinds of cells that can attack pathogens, natural killer (NK) cells and cytotoxic T lymphocytes. Although these cells are capable of recognising and killing cancer cells, they don't. Human cancer cells operate a variety of molecular mechanisms that allow them to escape our immune systems, allowing the disease to progress.
Dr Sumbayev's team focus on understanding the molecular mechanism by which cancer cells evade the human immune system. In this work, they sought to understand one of the biochemical pathways leading to galectin-9, which cancer cells use to avoid immune surveillance. 
Acute myeloid leukaemia (AML) cells operate an immunosuppressive pathway using the T cell immunoglobulin and mucin domain-containing protein 3 (Tim-3) and its natural ligand, galectin-9. Galectin-9 kills cytotoxic T lymphocytes and impairs the activity of natural killer (NK) cells. Soluble Tim-3 affects the production of a protein needed for the activation of both NK cells and cytotoxic T lymphocytes. 
However, the molecular mechanisms that allow cancer cells to escape host immune surveillance remain poorly understood. With a growing body of evidence suggesting that some solid tumours also use Tim-3 and galectin-9 and to evade host immune attack, the researchers studied the activity of this pathway in breast and other solid and liquid tumours. 

Synchrotron Radiation Circular Dichroism (SRCD) Spectroscopy

At Diamond, the team used SRCD spectroscopy to investigate the point at which the pathway begins. AML cells trigger the pathway using the neuronal receptor latrophilin 1 (LPHN1) and its ligand fibronectin leucine-rich transmembrane protein 3 (FLRT3). 
Dr Sumbayev explained: 

Access to Diamond is crucial to our research. The sensitivity that synchrotron radiation allows cannot be replicated using other techniques, and it allows us to really see what's happening to the proteins, even small details.

The researchers found that primary breast tumours expressed galectin-9, Tim- 3 and FLRT3, as well as two protein variants of LPHN - LPHN2 and LPHN3. Using SRCD spectroscopy, the team were able to prove the interaction between FLRT3 and LPHN2 that triggers the immune suppressive pathway in breast cancer cells.
Their work showed that breast tumours express significantly higher levels galectin-9 and Tim-3 than healthy breast tissue and suggests that both proteins are expressed by the same cells.
Using a model, the team were able to show that lymphocytes can attack breast cancer cells when galectin-9 is disabled.
The team then investigated nine more types of cancer and found their results applicable everywhere. Tim-3 and galectin-9 are far more active in cancer cells.
These findings demonstrate the activity of the Tim-3-galectin-9 biochemical pathway in several types of human cancer cells, as well as its possible role in the suppression of the immune system response. 
The ultimate goal of this research is now to find the best way to disable the Tim-3-galectin-9. This could lead to therapies that allow our immune systems to attack cancer, reducing the need for more toxic treatments such as chemotherapy and radiotherapy, which have severe side-effects for patients.
Dr Sumbayev and his team are already planning another visit to Diamond, for the next stage in this vital research.
To find out more about the B23 beamline, or to discuss potential applications, please contact Principal Beamline Scientist Giuliano Siligardi: giuliano.siligardi@diamond.ac.uk

Related publication:

Yasinska IM et alThe Tim-3-Galectin-9 Pathway and Its Regulatory Mechanisms in Human Breast CancerFrontiers in Immunology 10, 1594 (2019). DOI: 10.3389/fimmu.2019.01594.