After talking with the doctor yesterday, I thought I would share some of the ideas behind the transplant ...
I am having a "reduced intensity" transplant. In a "normal" transplant, the host bone marrow is totally wiped out using very strong chemo drugs and full body radio therapy, before the donor cells are injected. However, at my age, the risks of doing this to me outweigh the benefits. Instead, I will have a much gentler chemo regime before the donor cells are injected, combined with immune suppressant treatment. The immune suppressants work both on my residual immune system, to stop it attacking the donor cells, and on the donor cells immune system to suppress it attacking my body. The latter if called "graft versus host" disease (GVHD), and attacks mainly the skin, the kidneys and the liver. However, the real "trick" with reduced intensity transplant is to get the new immune system to attack the host's leukaemia cells, known as "graft versus leukaemia effect". For a while I will have two immune systems; it is intended the stronger donor system will kill off the weaker host system. One of the ways the transplant can fail is if this does not happen, however even in this case they can take some mature White cells from Harry and inject them into me to give the new immune system a boost.
After the initial transplant, and the time in hospital afterwards until the donor cells embed in the bone marrow, the next 100 days are key. It is a balancing act between graft versus host disease and graft versus leukaemia effect, effectively training the new immune system. The immune suppressant drug levels are varied based on weekly or biweekly blood samples. The main drug is called cyclosporine; a drug discovered 40 years ago, and still nothing better has been discovered! It is a difficult drug to use, affecting different people differently, and getting the dose right is apparently quite tough. With this drug the new immune system can be trained, literally, to do the right thing. If I get too much GVHD they increase the cyclosporine dose, which suppresses the immune system. Then the dose is gradually lessened again and the immune system knows not to attack me again, otherwise it gets more cyclosporine!
Note that it is the anti viral part of the immune system that is suppressed, whereas until now I have been concerned about bacterial infection, post transplant it is viruses that I need to worry about.
During this 100 days post transplant it is likely that I will be readmitted to hospital for one reason or another, for example a viral infection or a flare up of GVHD. One very common cause is an attack of cytomegalovirus or CMV. CMV affects about 60% of the population, lying dormant and causing no issues, until your immune system is suppressed. Luckily, both Harry and I are CMV negative, which is a real bonus post transplant. I will attend a weekly clinic, and the hospital will provide transport for me to and from the clinic.
Finally, one strange effect of the original treatment and transplant, is that the "memory" of the donor immune system is erased. We all know about this but so take it for granted - the immune system memory knows about viruses it has killed before and enables it to kill new occurrences. This is why we are vaccinated as kids. Well, my new immune system will have no memory, so after it has properly bedded in, and I am off the cyclosporine, I will be vaccinated against all the common diseases like measles, mumps and so on. And of course, as I have blogged before, my blood type will change to be the same as my brother's. Furthermore, my blood will have his DNA! One of the ways they tell if the graft has taken is to take the DNA of my blood after three months. They hope it will be all Harry's, and none of mine.
I think the whole process and it's various outcomes are fascinating.
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