5th Nov 2019
5th Nov 2019
Curated by Dr Govinda Sharma
Beware, cancer! Thanks to a newly developed technology we are gaining insights into how immune cells can spot cancer cells that try to play hide and seek. This achievement is an important step in making anti-tumour immunotherapy more precise.
In 10 seconds? Antigens, the chemical ‘signals’ on the surfaces of all our cells, help the immune system tell friend from foe. A new method sifts through a huge number of them and flags up those that can call an immune response allowing our self-defence system to deal with tumours. (Read the science)
What is the finding? T cells, the soldiers of our immune system, can recognize and fight tumours, but only if they can sense a certain type of chemical signal, called an antigen, that informs a T cell to attack. So, it is important to find antigens needed to allow them to recognise the enemy. We have developed a new way to identify antigens that can elicit a T cell reaction. It works by scanning through massive numbers of potentially existing antigens to find the ones that actually cause response from T cells. This new technology will enable scientists to develop new T cell-based medicines. (Read the paper)
How was the method developed? We took advantage of a key feature of T cells: their ability to target infected or mutated cells with a toxic molecule called granzyme B in an extraordinarily focused way. When a T cell decides to kill a target cell, it delivers granzyme B only to the target without harming surrounding healthy cells. Using this natural feature, we developed a method to isolate cells marked for destruction. These targets are identified by fluorescence-activated cell sorting, or FACS, and the antigens they carry are revealed by DNA sequencing. Knowing the antigens that are at the heart of the interactions between T cells and tumour cells is important because it then allows researchers to appropriately stimulate the right T cells to treat cancer with. (Read more about classical methods)
What do T cells do? They are a specialized type of immune cells, on constant patrol around the body, looking out for foreign invaders or cells that have gone rogue and could form tumours. T cells do this by inspecting different antigens, using unique proteins of their own called T cell receptors (TCRs). Antigens signal to T cells whether the inspected host cell represents normal “self” tissues or has become “non-self” – that is, infected by foreign pathogens or harbours harmful cancer mutations. If a foreign or mutated antigen is discovered by a T cell, it initiates a response that is aimed at clearing out the offending antigen-bearing target. (Read about a way T cells discover antigens)
Is it that simple? Unfortunately, no. The molecular interactions by which T cells interact with antigens are very complex. So, decoding the identities of the antigens that trigger their responses has been a major challenge in understanding the role of immunity in disease. However, the potential payoff of being able to speak the language of T cells is enormous. For example, it would give scientists the ability to engineer or otherwise direct T cells against known tumour antigens, providing a powerful means to perform precision cancer therapy. (Read more)
So, why is this better than what we’ve had before? The innovation of this approach is that very large sets of candidate antigens can be simultaneously tested in parallel. In fact, we can test up to a thousand times more candidate antigens than any other current method can handle. Thus, we are getting a better insight into how to make safer, more effective cancer immunotherapies. (More on T cell recognition patterns)
What does it mean for the future? This is a key step forward because it increases our ability to find tumour-fighting T cells that could be used in therapeutic cell products. Cancer immunotherapy is based on enabling T cells to go to war against tumours – and it has shown some promising results to-date – but it doesn’t work for everyone at the moment. New antigen targets are needed so that new therapies can be designed to help a larger chunk of the patient population. (Read why immunotherapy merited the Nobel Prize in Medicine in 2018)
What we have now: T cell therapy can yield results but it has its limits
Last year, a long-time sufferer of Non-Hodgkin Lymphoma was given the all clear after receving a relatively new therapy, called CAR T. In this procedure, T cells are removed from the patient's blood sample and modified by inserting a gene for an immune receptor that can redirect the reactivity of the T cells towards the tumour. Technicians then grow these cells and infuse them into the patient.
The 66-year old woman received a type of synthetic immune receptor called chimeric antigen receptor (or CAR). But many other types of immune receptors could be used to guide cell therapies, including naturally occurring T cell receptors (TCRs) like the ones that already exist inside of every person!
A key advantage of TCRs is that these receptors can “see” many more potential targets, including those that exist inside of a cell, than CARs, which are restricted to only seeing targets that naturally occur on the outer surface of a cell.
Post-Doctoral Fellow at Canada's Michael Smith Genome Sciences Centre, researching novel methods for high-throughput, function-based T-cell antigen screening. Govinda is currently in the process of forming a biotech company to use the technology described in this digest pave the way for immune cell therapies in cancer.