One disease a lot of folks are focused on in brain cancer. Certainly not a monolithic entity– but scientists are working on viruses against them all. One of the viruses on the front lines against cancer is herpes.
Maybe this is why:
Its that damn immune system getting in the way.
Not in the way you might think– Its not anti-HSV antibodies neutralizing the anti-cancer viruses, or anti-HSV cytotoxic T-cells— It is Natural Killer cells that are preventing HSV-based anti-brain-cancer strategies from reaching their potential.
NK cells are not part of your adaptive immune response– they are part of the innate immune system. They are not specific for Virus A or Bacteria B, but instead recognize broad patterns of ‘wrongness’. If they see something that is ‘wrong’, they kill it.
In this case, the cancer cells, when infected with the anti-cancer HSV, produces a couple ‘SOMETHING IS WRONG!!’ signals. So NK cells mosey on up into the brain and kill the cancer cells.
Well, ‘YAY!’, right? The NK cells are killing the tumor… and the whole point of this exercise is to kill the tumor… so…
The problem is, the NK cells kill the HSV infected tumor cells before the tumors can produce babby viruses. If left to its own devices, the HSV would continue to replicate in, infect, and kill the tumor cells until ALL the tumor cells were dead. Once the tumor is gone, the HSV will functionally ‘starve to death’. No HSV, no cancer.
But the NK cells break the cycle. It kills the infected tumor before more viruses can be made, so the virus goes ‘extinct’ before the tumor. Once the HSV is ‘dead’, the NK cells leave. They dont kill the tumor. No HSV, but the cancer is still there.
So what does this mean for HSV-based anti-cancer therapies?
The scientists in this paper generated mice that lacked the ability to transmit the ‘SOMETHING IS WRONG!!!’ signal between infected tumors and NK cells, and the mice lived longer, the HSV therapy worked. But that is an entirely unhelpful approach for humans.
The good news is, they identified at least two reasons for why this therapy hasnt worked as well in humans. Now we have at least two targets for improving this therapy. Maybe it will be as simple (hah) as as throwing in some siRNA into your GMO HSV. Maybe some anti-‘SOMETHING IS WRONG!!!’ antibodies. Who knows what solution will end up working the best. But its a hellovalot easier to solve a problem when you know what the problem is.