Immunotherapy has been heralded as a lasting cure for cancer. What exactly is it — and does it really have the potential to change the way we treat the disease?
What is immunotherapy?
It is a treatment that relies on the patient’s own immune system to identify and destroy cancerous cells.
Other treatments like radiotherapy, chemotherapy and surgery remove tumours by physically attacking them with radiation, drugs or the scalpel but they can also cause substantial damage to neighbouring healthy cells which may have serious consequences for the person with the tumour.
Using the patient’s own immune system against cancer is like opting to remove a splinter with tweezers rather than a kitchen knife, as some immune cells can pinpoint the specific location of a tumour by recognising molecules called antigens that molecularly flag up that a cell is abnormal and needs to be removed.
The catch is that there are over 200 different types of cancer. To add to the challenge, the tumours associated with these cancers are complex masses of abnormal cells that can vary considerably and look molecularly very different from each other and even from one end to the other.
What’s more, some tumours can produce proteins which disrupt the way immune cells locate antigens. So, while the immune cells may be theoretically good at spotting and remembering tumour-related antigens they are effectively trying to locate lots of visible and invisible differently shaped abnormal needles in a haystack of needles.
(There is hope, though. Recent research found that a patient’s immune cells were able to identify unique protein markers in lung tumours even as these tumours evolved over time. Although the immune cells had failed to kill the tumour, it seemed they were capable of spotting the abnormal cells, raising the possibility of a therapy designed to target this universal marker.)
How does it work?
Immunotherapy is designed to improve, restore and support the immune system’s ability to locate and destroy these abnormal cells. There are lots of different ways to do this, and there are a large number of ongoing clinical trials exploring different methods to boost the immune system.
One method is to use monoclonal antibodies which can latch on to the cancer cell and disrupt the way these cells hide from the immune system. The same antibodies can also be adapted to locate specific tumour antigens and deliver a drug directly to the tumour. Alternatively, the antigens can deliver a radioactive molecule to either kill the cells or help doctors locate where the tumour is growing.
Other methods include: non-specific immunotherapies which may boost immune cell production or reduce the growth of abnormal cells, cancer vaccines which train the immune cells to recognise specific cancers either before they develop or to fight them as they grow, and oncolytic virus therapy which uses genetically modified viruses to kill cancer cells.
Will immunotherapy replace other treatments?
‘The short answer is no, it’s not going to replace other therapies, I think what it will do is add another element to the pillars of treatments we already have,’ says Emma Smith, Cancer Research UK’s science communications manager.
Smith explains that for some diseases, like testicular cancer, the current treatments are already very effective and will not change. She suggests that immunotherapy may be key to tackling cases where standard treatments don’t work or when the cancer comes back after treatment.
‘That’s where immunotherapy is really looking exciting, because even with cancers that are very advanced or genetically complex, immunotherapy can be a very powerful weapon,’ she says.
Smith adds that it is important to remember that there are still side effects that come with immunotherapy and it does not work for everyone — one in five patients with advanced skin cancer have a long-lasting response to immunotherapy.
She says: ‘We’re still at the start of really understanding immunotherapy, drilling down into how it works, who should receive it, who is it going to work for, why doesn’t it work for everyone, and what types of cancers will it be effective against. We’re still at the very tip of these discoveries. It’s such an exciting field and there is going to be a lot more to come over the next five to 10 years.’