The main issue is that for this to work, you need to know specifically what antigen you're targeting on the tumor cells. Think of the antigen as a unique tag that the immune system can use to differentiate cells (a "natural key" if you will). In the majority of cancers we haven't got a clue as to what we should use as for an antigen (though it's not an insurmountable probelem). However, with leukemia they can use CD-19 which is found exclusively on the surface of normal and cancerous B-cells. The last thing you want is an antigen that "looks" like something common, so CD-19 apparently fits the bill there as well. If you choose something non-specific, then the immune system can go after all kinds of other tissue that you don't want it to which could very likely kill the patient.
All that being said, targeted therapy like this is probably the future of cancer treatment, but it's going to take tremendous effort to work out all the kinks. The immune system is ferociously complex, and is still poorly understood. However, it does have the advantage of being battle tested throughout evolution.
Thanks for the reply. Just while you're here, I was wondering if I could ask another question. Am I right in thinking that they used the HIV virus to 'program' the white blood cells? And if so, in the future might it be possible to reprogram the cancer cells themselves? Perhaps the virus could 'patch' the broken/missing DNA?
As you can tell, I'm horrifically ignorant on the topic but I would be grateful if you could indulge me :)
While it may be possible in theory to patch/fix the cancer cells, you'd need a virus that can target them specifically. In the case of using HIV here, it's because it's so efficient at getting into the immune system that it can be used as a vector to reprogram it. I've got to imagine that other "super viruses" could be used in a similar manner if they also target things so well.
simcop2387 is right in that the biology here gives them a leg-up on what would otherwise be an even more difficult problem. The whole class of lentiviruses (of which HIV is part) are useful for delivering genes to target cells. In this case, HIV is very good at finding T-cells which are exactly what whas needed here to trigger the immune response.
You are correct that they are using the HIV virus to reprogram the T-cells. They basically are making them express a very specific protein on their surface which allows them to seek out the tumor cells. When they find one, that protein is "wired up" to the cells' ordinary immune system genes that do their thing as they normally would.
Basically, the T-cell is like a hit man. It shows up, punches a bunch of holes in the target cell's membrane. Then it dumps a bunch of enzymes in there that go in and break important stuff. Once the chaos reaches a certain point, the target cell decides all is lost and it pushes the big, red "self destruct" button and goes through programmed cell death (apoptosis).
The actual work to make the viral vector and test it in mice was published in a study in 2009, so this new article is news because it's the follow-up where things were done in humans the first time (and they actually worked). From looking over the literature, apparently people have been trying this for some time but it has been failing for one reason or another.
All that being said, targeted therapy like this is probably the future of cancer treatment, but it's going to take tremendous effort to work out all the kinks. The immune system is ferociously complex, and is still poorly understood. However, it does have the advantage of being battle tested throughout evolution.