Search This Blog

Friday, 5 April 2013

T Cell Therapy for Leukaemia - Why is this news?

In a recent report in The New England Journal of Medicine, the authors explain how two child patients were treated with a new technique. In both, their leukaemia was cleared and one of them remains in remission. The technique has previously had some success on a small group of adults.
News of medical research does not usually cover successes in just one or two patients - so why did the researchers go public on this?
In solid cancers you can never be sure that there are no cancer cells left in the body but in leukaemia you can be much more certain. It is no longer a case of looking at slides through a microscope - the latest techniques and equipment can scrutinise large numbers of blood cells and detect the presence - or absence - of cancerous cells.
There are many different kinds of leukaemia, each relating to a particular kind of blood cell. The nursery for blood cells is the red bone marrow and it is here that leukaemia cells are produced before they are released into the circulation. This red bone marrow is essential to life. It not only replaces red blood cells but all the white blood cells that make up the immune system. Without it, fatal anaemia and infection are inevitable.
Doctors can categorise the various leukaemias very accurately these days. For some patients the prognosis is good. For others, the only hope is a stem cell (bone marrow) transplant. These two young patients were suffering from relapsed Acute Lymphoblastic Leukaemia (ALL).
A stem cell transplant is usually the treatment of last resort. It uses brutal chemotherapy to kill all the red bone marrow, diseased and healthy. Then there is an infusion of blood stem cells, gathered from a closely matched donor. These then set up home in the bone marrow cavities and rebuild the blood producing tissue. It is a risky and arduous process. For some it fails to work and for others the treatment itself proves fatal.
Medical researchers sometimes use what they call translational research, which they also refer to as "bench to bedside research". Scientific advances in the lab are tried out on small groups of volunteers. These are patients who have little to lose - maybe a stem cell transplant has already failed - and they are willing to take the risk of acting as guinea pigs.
Translational research is quite different to a controlled trial - it is, literally, trying out something that they think should work to see what happens. This paper is an example of translational research - hence the tiny numbers. The progress of research like this is slow. Suitable patients are rare. By publishing this early success, researchers can share knowledge and perhaps find other patients who would benefit.
 We have long had the tantalising knowledge that immune cells known as T cells (or T lymphocytes) can destroy cancer cells in the lab - but often fail to do so in the body. One of the reasons for this failure is that the immune cells cannot recognise the cancer cells as something alien to the body. Store detectives deal with a similar problem: shoplifters tend to look like honest shoppers.
In the experimental treatment two child patients were treated with a kind of gene therapy in which T cells were genetically altered in the lab and put into the patient's body. The technique teaches the T cells the exact molecular pattern they need to attack and harnesses their killing power. It's like giving store detectives a photograph of a professional shoplifter.
There was a serious reaction to the treatment - the children's immune systems reacted violently to the rapid dying-off of cancer cells (tumour lysis syndrome). But both went into remission with no trace of the ALL cells. One of them subsequently started producing a slightly different kind of leukaemia cell but the other seemed to be remaining clear.
Such new forms of treatment may in time prove to be less dangerous and more effective than the current approach, which involves strong chemotherapy drugs. For sick children and their parents in particular, a shorter and less arduous course of treatment would be a great step forward.

Chimeric Antigen Receptor-Modified T Cells for Acute Lymphoid Leukemia," New England Journal of Medicine, Online March 25, 2013. To appear in print April 18, 2013.

Science Daily article: