The impetus of the study was thrombosis in cancer patients. It’s well known that thrombosis is common in cancer patients, it can occur in up to 20% of patients with certain cancers. We have made the observation, as well as others have as well, that the risk of thrombosis may be further increased in patients who are treated with immune checkpoint inhibitors which are now a common drug in the cancer armamentarium. So our goal was to define how this occurs.

What we did is actually we developed a mouse model where we actually grow tumours in mice and then we treat these mice with immune checkpoint inhibitors and we find that the mice that are treated with immune checkpoint inhibitors develop larger blood clots in our experimental thrombosis model. So there are different ways this can occur, for example, we find that the tumours have more tissue factor, we find that there seems to be activation of neutrophils with release of these things called neutrophil extracellular traps, or NETs.

But we also find activation of something called the contact system, which is one of the coagulation pathways and we determined this by measuring the cleavage of a certain component of that pathway called kininogen. We can detect this in blood and plasma, actually both in the mice and in patients.

So we don’t know how the contact activation system becomes activated and one of the things we found in a previous study, just without immunotherapy, was that patients with cancer have elevated levels of these small things called extracellular vesicles which are tiny particles derived from cells. We find that these vesicles are coded with something called polyphosphate and polyphosphate can activate this contact system.

Polyphosphate is very interesting, it’s present in all organisms. We know how it’s produced in bacteria, in yeast, but actually the pathway by which it is produced in mammalian cells and in humans is entirely unknown. However, it is known that there’s one enzyme called IP6 kinase that seems to contribute in some way. So low levels of IP6 kinase, or IP6K, are associated with lower levels of polyphosphate but we don’t know how it works.

So we wondered whether IP6K may be involved in the release of these polyphosphate-coded extracellular vesicles. We actually found in our mouse model that there’s really the same number of extracellular vesicles in the blood in mice that are either treated with control IgG or treated with the immune checkpoint inhibitors. But if we specifically measure the levels of these polyphosphate-coded extracellular vesicles, those are actually increased about twelve-fold in the immune checkpoint treated mice. We also detect these in patients, as I’ve mentioned.

So, again, this is a work in progress. What we really need to know is how exactly polyphosphate is synthesised and how it’s added, how it becomes attached, to these extracellular vesicles. So, again, it’s a work in progress, we need to do some further work on the animal model. But I think it’s one of the few findings showing regulation of IP6 kinase in mammalian cells.