T+41 GVHD: What good is it?

BOX SCORE
Element	Current	Std. Range	Trend
Hemoglobin	10.6	13-17	v
Platelets	153	140-375	v
ANC	3490	1800-8300	^

If a little bit is good, then a lot is better, right? I mean, I'm thinking about raises at work, and apple pie, and time with friends and family, and vacation times. But does this truism always hold true? Let's see if we can figure this out. 

Yesterday at my clinic visit, I had to report that I have discovered a rash that involves my scalp and neck and back. There's not much of a rash, but it does involve some bumpy skin and redness. And Dr. Meyers has told us right along that it is normal to get rashes after bone marrow transplant (BMT). She said that it is a sign of graft versus host disease (GVHD). 

Now GVHD is one of the hazards of putting someone else's DNA into your body. The graft DNA doesn't recognize the host DNA and decides it needs to be removed. It's something like an allergic reaction, where the body mounts a furious battle against an allergen like pollen or eggs or any of the myriad kinds of allergies that people suffer. We think of allergies as terrible things, and they can prove to be anything from mildly annoying to life threatening. One thing they do, though, is to verify that the immune system is functional, or in the case of severe allergies, dysfunctional, a situation that doctors call hypersensitivity. 

As Dr. Meyers explains it to us, the rash is a sign that GVHD is occurring, and in one way that is good, because it indicates the new immune system is functioning. Part of the idea behind BMT is that the new, healthier immune system will seek out any remaining host bone marrow cells and any leukemia cells and destroy them. This function, by definition, is a good thing. It's supposed to happen. So, a little GVHD is a good thing. 

A lot of GVHD, on the other hand, can lead to the new immune system attacking other cells in the body, and like an anaphylactic allergic reaction, it can be life threatening. This, you may imagine, is not a good thing. The trick is to get enough GVHD to destroy the bad cells (cancer producing host marrow cells, leukemia cells, etc.) but not enough GVHD to do harm to healthy host cells and systems. 

One  reason that we are staying close to OHSU this summer is so that the medical team can keep close tabs on GVHD and control it with medications. Now that I have incurred a rash, it is pretty clear that, not only are the transplanted stem cells taking over and replacing my bone marrow, as I reported in my last post, but they are also beginning to supply immune responses. These immune responses are necessary, if I am ever to be out of quarantine and living in a world that is full of potential health risks that the immune system is designed to combat. On the other hand, an undisciplined immune system can cause all kinds of havoc. 

People sometimes get what are called autoimmune diseases. Some you may have heard of include psoriasis, rheumatoid arthritis, lupus, Chrohn's disease. These can be debilitating problems for many people. In simplistic terms, they are caused by the immune system attacking certain tissues in the human body unnecessarily. Why that happens I can't say, but when it does it can be devastating. 

GVHD is a hazard, if it becomes unchecked, just as autoimmune diseases are. Did you ever visit anyone who was devoted to a pet dog and raved about what a wonderful addition the dog was to the family? And did you ever realize that this angel of canine virtue was mainly good at jumping up on people, barking unnecessarily, digging in the yard, and sniffing crotches? In other words, Fido was untrained and undisciplined. You don't want to be around Fido, do you?

Well, I don't want to be around an undisciplined immune system, where GVHD is out of control, and my medical team does not want that either. I mean think how bad they would look if I croaked! Consequently, the team is gradually training my new immune system to realize that only my old, sick marrow cells and any stray leukemia cells need to be dealt with. Everything else is off limits, except things like germs and viruses that I may encounter and from which I need protection.

Think of a well trained dog. Especially think of a well trained working dog, like a herding dog that is trained to bring in the sheep, or a drug sniffing dog, trained to find illicit drugs for his master. Even a well trained pet dog, who sits and stays and stops barking on command is an example that may be compared to a BMT that is under control to provide appropriate immune responses and make new blood cells, without annoying, and perhaps, dangerous side effects. 

So, if a little is good, is a lot better? In the case of GVHD, I vote NO! A little GVHD  to rid me of leukemia and diseased marrow cells is a good thing, but a lot of GVHD I can do without! You are, of course, welcome to disagree, but I hope you will see it my way.