Several news outlets carried a story this week regarding very promising results of cancer vaccines trials. This was a very small trial (on just three patients) who had an aggressive and late-stage skin cancer known as melanoma. In all three patients the cancers stopped growing, and they were alive and well at the time of publication. In spite of the low number of patients, this study provides a tantalising glimpse of a brand new form of cancer therapy.
So how would these vaccines work? The aim is to teach the patient’s own immune system that cancer cells are bad. That way, our own bodies could potentially mount a natural and effective response, free of the side-effects of conventional chemotherapy. Myriam has previously posted a great blog on how the immune system works (which can be found here), so I’ll stick to the basics.Our immune system recognises invaders or abnormal growths by reading what molecules are sticking out from the surface of cells. These molecules are known as antigens. If the immune system recognizes a cell's antigens as being foreign or abnormal, it will mount an immune-response to clear it from our system. The key is to correctly differentiate foreign antigens from normal, and this is the responsibility of a group of “teacher” immune cells which differentiate friend from foe and teach the other immune cells to do the same. These teacher cells include cells known as “dendritic cells”, which were used in this study.However, cancer cells are problematic for these “teacher” cells. Because cancers arise from a cell that was once healthy, they are sometimes not recognised as being abnormal, and as a result the immune system isn’t alerted to the problem.What these scientists did was to analyse the cells in a biopsy of the patient’s tumour to understand what molecules (antigens) are sticking out from the surface of only the cancer cells. The next step was to train the teaching cells (dendritic cells) to see these specific antigens as foreign. These newly-educated dendritic cells were then put back into the patient’s blood, where they could teach other immune cells to attack the tumour. Encouragingly, after the dendritic cells were infused back into the patients, they mounted a massive immune response to the tumour. It remains to be seen whether this presents a long term solution to these people’s cancers, but it is an exciting “proof of principle” study.This is a very promising new therapy for cancer. It has the potential to be very specific to the tumour and hence have very few side effects. Large scale use of such technology is still quite a few years away, but his is a very exciting step along that path.
