Tumours in several people with an advanced form of skin
cancer have completely disappeared after treatment with one of three drugs that
force tumour cells out of hiding. The patient's own immune system can then
recognise the cancer and destroy it.
Cancer cells should normally be spotted by T-cells –
immune cells that recognise and destroy foreign material in the body. But
tumour cells evolve a way of hiding themselves from T-cells by sprouting a
surface molecule called a ligand. The ligand binds to and activates a receptor
on the T-cell called PD-1. When PD-1 is activated the T-cell fails to recognise
the cancer cell as foreign, fooling the immune system into mistaking tumours
for normal tissue.
Wolchok says that what makes the antibody therapies so
exciting is that unlike conventional cancer treatments, such as radio and
chemotherapy, they work by reviving the power of the patient's own immune
system – something that has evolved to efficiently dispose of infectious,
foreign or abnormal tissue. "They treat the patient, not the tumour,"
he says.
Earlier this year, one person with acute lymphoblastic
leukaemia was cured
in just eight days after their T-cells were engineered to attack any cell
with a surface molecule called CD19, which is unique to the cancerous cells.
In 54 of 135 people with advanced melanoma – the most
deadly form of skin cancer – tumours more than halved in volume after treatment
with the first of the antibody therapies, called Lambrolizumab. Tumours
disappeared altogether in six of the 57 people who were given the highest dose
of this drug, developed by Antoni
Ribas of the University of California at Los Angeles and colleagues.
Results were equally impressive with Nivolumab, a second
antibody drug. Tumours more than halved in size and significantly decreased in
number in 21 of 53 people with advanced melanoma who took the drug alongside
another drug. Cancer vanished completely within 12 weeks in three of the 17
people who received the highest dose.
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