A really alluring/tantalizing thing is to get our own immune system to more effectively fight cancer. The desire is to have a specific, devoted type of immune cell that hunts out and kills any other cells that are not perceived as healthy. Fortunately, we do have that kind of cell circulating through our blood that shoots first and asks questions later. the Natural Killer cell. The Natural Killer (NK) cell is a foreboding and awesome name for part of our immune system. These cells are just as their name implies, they’re natural killers ready to annihilate any other cell that looks at them the wrong way. The NK cell is a rather ancient part of immune systems that have been with us for a long time. This part of the immune system is old enough that there’s actually quite a bit of evolutionary differences between us and close mammalian relatives like mice. Their specialty is to survey for cancerous and virally infected cells that pose a threat to other cells in the neighbourhood.

There’s an involvement of NK cells in attacking tumor cells and it’s not entirely clear how they’re doing this. Unique to NK cells is a protein on its surface that is used to sense and detect diseased cells (Ly49 in mice and killer-cell immunoglobulin-like receptors (KIR’s) in humans). It’s only very recently being appreciated that NK cells will develop specific recognition for particular cells to attack even after a lot of time between being exposed to its target. It’s a kind of immune cell memory. This isn’t uncommon for immune cells to develop lasting memories to certain pathogens and cells. The whole half of the immune system called the adaptive immune system is geared towards memorizing and responding to pathogens our body has been exposed to previously. That’s what our immunity is. It’s why we typically only get chicken pox once. And it’s the rationale behind getting vaccinated. Vaccines are a way for us to educate our immune system to recognize a disease without having to actually contract the disease. And it’s why certain vaccinations happen annually like getting the flu shot every year. The influenza virus naturally changes very rapidly and to prevent massive outbreaks of flu we need to have our immune systems regularly “studying” how the virus changed.

Back to NK cells. The odd thing is that we don’t have a very good idea as to how NK cells are developing memory. It was originally thought that these cells were on a hair-trigger and if any other cell didn’t present the right identification to say “friendly cell” NK cells would waste them and then move on to question another cell. But it seems that there is some kind of memory being formed, NK cells will better attack tricky and hiding diseased cells that are cancerous or infected with virus that have been encountered before. But it’s not by the same mechanism as other ways to educate other parts of the immune system.

So, NK cells have some way to form memories of diseased cells that they’re to attack, they attack tumor cells in the body, and the purpose of vaccines is to educate immune cells on what to attack – so why don’t we make vaccines for cancer?

Well, that’s actually what many researchers are wanting to achieve and are actively working towards. There’s still a few hurdles to overcome, though. The biggest problem to solve first is how memory is being formed. The most straight forward way that our immune systems develop memory is by exposure to the pathogen. Particular cells in the immune system will swallow these up, chew them up, and then present chewed up pieces of the pathogens proteins as example to other cells of the immune system that are more efficient at killing pathogens and educate them that “when you encounter this kill it”.

In the case of NK cells it seems that this isn’t the case, at least not it’s not as simple as that. A lot of the sample cellular machinery used to educate NK cells is involved but not in the same way and it’s a mechanism that’s much more subtle and involves more cellular machinery that we don’t really know much about at the moment.

It seems to be a very finely balanced system, though. NK cells are always ready to “shoot first and ask questions later”. Cells in the body being examined by NK cells need to have a few pieces of “i.d.” to get the okay from NK cells and be allowed to move along. Often cancer cells are sneakily able to present this i.d. and not get caught so then how NK cells can catch these cancer cells sometime and not others suggests there’s still more going on than we’ve been able to figure out so far.

There’s not much of a nice, neat, clean story to wrap up on the biology of NK cells here, unfortunately. These are still a very curious cell and we are barely getting to know them. But there’s a lot of potential here because we do know that these are an active member of the immune system that in part clears tumor cells from the body. A lot of work is going into understanding them better as we could one day be able to better educate our immune system to tackle cancer, especially in the elderly where cancer is more prevalent and the immune system’s not as sharp or potent anymore.

Here and here are a couple recent reviews that summarize our current understanding of NK cells and their roles in fighting disesase.