What is graft versus host disease or GVHD? Graft versus host disease is a manifestation of the fact that we've essentially taken the immune system and replaced it with somebody else's immune system. And so that new immune system, the whole idea of the transplant is that it recognizes your leukemia as something that's foreign and attacks it. The problem is that it can also recognize normal parts of your body as something that's foreign and attack them. And the sort of three most common areas or three most common manifestations of graft versus host disease early after a bone marrow transplant are a rash on the skin, abnormal liver function tests, and diarrhea from the new immune system attacking the lining of the gut. It turns out that the frequency with which patients get graft versus host disease after a bone marrow transplant depends a little bit on what medicines are given as prophylaxis. So what medicines we give to prevent patients from getting graft versus host disease. And here at Johns Hopkins, we use something called post-transplant cyclophosphamide, which seems to greatly reduce the risk of having serious graft versus host disease. And so patients generally, it's probably somewhere between 10 and 20 percent of patients get really serious graft versus host disease when they've had post-transplant cyclophosphamide. And we hope it's closer to 10 percent in general. A higher percentage than that of patients get less severe graft versus host disease, sometimes even just a rash that doesn't require treatment. And the interesting thing is that actually it's been shown in a number of studies that having a little bit of graft versus host disease is actually a good thing because it indicates that this new immune system is working, that it's recognizing things as being foreign. And so for patients that have graft versus host disease after a bone marrow transplant, they're a lot less likely to relapse. And for patients that have a little bit of graft versus host disease, they're not that likely to have serious complications from it.