- CAR T-cell therapy uses a patient's own immune cells to attack a tumour.
- This is very effective on blood cancer, but less effective on solid tumours.
- Scientists have engineered T cells that can be activated by a pulse of blue light when they are near the tumour.
Scientists have engineered immune cells that switch on when exposed to blue light and have used them to destroy skin tumours in mice.
Developed by bioengineers at the University of California, San Diego, the light control system is a promising new breakthrough in a cancer treatment known as chimeric antigen receptor (CAR) T-cell therapy.
This therapy involves modifying a patient’s own T cells – a type of white blood cell that play a key role in the immune system – to treat their cancer.
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The T cells are collected from the patient and then genetically engineered to express special receptors on their surface that recognise the foreign substances (antigens) produced by tumour cells. The engineered T cells are then infused back into the patient, where they find and attack the targeted antigens.
Although this approach has been successful at treating some types of blood cancer and lymphoma, it doesn’t work so well on solid tumours. This is partly because healthy cells can also express antigens similar to those of cancer.
“It is very difficult to identify an ideal antigen for solid tumours with high specificity so that CAR T cells only target these diseased tumour sites without attacking normal organs and tissues,” said Dr Peter Yingxiao Wang, who led the team behind the project. “Thus, there is a great need to engineer CAR T cells that can be controlled with high precision in space and time.”
To achieve this, Dr Wang and colleagues created a ‘switch’ inside the engineered T cells that only turns on when exposed to one-second pulses of blue LED light. This light is shined on the site of the tumour and causes two proteins inside the T cell to bind together, triggering the expression of the special, cancer-fighting receptor.
Using this technique, the researchers were able to reduce tumour size in mice by between eight and nine times without harming healthy tissue. In the future, the team hopes to test this new therapy on patients with melanoma.
Reader Q&A: How does radiation kill cancer if it causes cancer?
Asked by: Odysseus Ray Lopez, US
It’s rather like the way guns can be used to commit crime, or stop it.
Radiation causes cancer because its high-energy photons can cause breaks in the DNA strands in your cells. Cells can repair this damage up to a point, but sometimes the repair isn’t perfect and leaves some genes defective. If the break affects one of the many tumour-suppressing genes in your DNA, that cell can become cancerous.
But cancer cells are also more vulnerable to radiation than ordinary cells. Part of what makes them cancer cells is their ability to divide rapidly and this normally means that some of the DNA ‘spellcheck’ mechanisms are turned off.
So when a cancer cell suffers a break in a DNA strand, it’s less likely to repair it correctly. Depending where the break occurs, it might either kill the cell outright, or make it reproduce more slowly.
Radiation therapy uses a focused beam that is aimed at just the part of the body with the tumour, and the dose is carefully calculated to cause the minimum collateral damage to healthy cells. Even so, radiation therapy does very slightly increase your chances of developing a second cancer.
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