Is my DNA different now?
Photo: Brothers Dean (left) and Dan (right) – Dean received a stem cell transplant using cells donated by Dan.
In a stem cell transplant, a core part of you is (partially) replaced – your immune system.
The donor cells that set up shop in your bone marrow start churning out a brand new set of blood and immune cells, which travel throughout your body to help fight infections and cancer.
But these donated cells, thriving in their brand new environment, have a mostly different set of DNA within them compared to the rest of your cells. Although some of their immune system genes will be at least partially matched to yours, the rest of the genes in these cells will be forever different to the other cells in your body.
This is a normal part of the stem cell transplant process, but is still a unique situation that most humans will never experience. So, what does it mean to have two different sets of DNA in your body?
Do your genes changes after a transplant?
DNA carries all the information the body needs to function properly. It’s like a set of codes that tells each individual cell how to do its specific job.
Blood stem cells from a donor will contain the donor’s DNA – and will pass this DNA on to all the blood and immune cells that they create. Ideally, they’ll happily live in your bone marrow producing cells your whole life, so you’ll always have at least a bit of donor DNA in your body.
Because you probably still have some blood cells of your own remaining after your transplant, you’ll experience ‘chimerism’ – which in this case means you’ll have some blood cells containing your DNA, and some blood cells containing your donor’s DNA, living alongside each other. The number of donor cells compared to your cells can be measured as a percentage – the degree of chimerism within your body. So if half your blood cells are donor cells and half are your own, you’ll have 50% chimerism.
Most of the time, your clinical team will be hoping for 100% donor chimerism – meaning that your entire immune system is now made up of donor cells. 100% donor chimerism is usually the aim because it’s associated with a lower chance of relapse. However, it may take months or years to reach this stage, and it isn’t necessarily a bad thing if you don’t have 100% chimerism.
The effects of chimerism
High chimerism means the donor cells are situated within your body and doing their jobs. It’s a biologically unusual situation though, outside of stem cell transplants, so it produces some quirks!
Even though the new DNA in your body is confined to cells of the immune system, the fact that your new immune system is working to a different set of instructions can produce unpredictable effects.
One common change patients experience is brand new allergies – since the unique characteristics of the immune system determines your allergies. Patients have reported new allergies to medications or foods, or conditions like asthma and eczema.
"The impact these allergies have had on my life have, at times, been debilitating. At their worst, and for many years, I was covered head to toe in eczema and hives, exhausted through lack of sleep due to severe itching and raised histamine levels, and then groggy during the day due to the amount of antihistamines I had to take.
“But as my immune system and I have grown together and I’ve learned what to avoid, things have really improved. It’s also reassuring that my new immune system IS so responsive! I was given a stem cell transplant for a reason – to protect me – and my new immune system is doing that. The allergies, I now know, is my immune system showing strength, and I find that if I eat cleanly, and exercise a reasonable amount, my immune system is happy – which means I am too.”
Alan Thorpe, stem cell transplant recipient who developed an antibiotic and nut allergy following a cord blood transplant.
This can also go the other way – with patients losing their previous allergies. However there have also been case reports of people keeping their old allergies even with 100% donor chimerism, or of a patient developing a brand new allergy despite the donor not having that allergy; showing just how mysterious the immune system still is.
Beyond allergies, patients have also reported changes in food preferences and tastes after a transplant. We’ve even heard from one patient who reported enjoying Country music after his transplant, when previously he never listened to it! Unfortunately, there’s currently no medical evidence that changes in taste or personality can be linked to the donor’s cells themselves – some suggest it’s more likely that these changes are linked to the side-effects of medications or the psychological impact of prolonged hospital stays and intense treatments.
“I was lucky that my brother, Martin, matched and was my donor.
“After the transplant I couldn’t bear to have HP sauce, which I had loved before. I had gherkins one day and realised that I loved them – would never have eaten them before. If they had previously been on my plate, I wouldn’t have touched them.
“I contacted my brother to see if he liked them and he said that he loved them.
“Luckily my taste for HP sauce returned…”
Val McGeough, stem cell transplant recipient
Crime scene conundrum
Another quirk of chimerism is that a blood test will likely detect donor DNA rather than your own – or a mix of the two. This could potentially provide a bit of a puzzle for any scientist or health professional analysing your blood, but they would quickly figure out that a stem cell transplant is the culprit of any unusual results.
Sometimes people ask what would happen if a stem cell transplant recipient’s blood was found at a crime scene – would the donor be mistakenly identified? Thankfully we haven’t heard of any cases of a donor being mistakenly imprisoned based on forensics evidence, but there have been several cases of a forensics team recognising the DNA signature of a stem cell transplant (essentially DNA from two different people) from crime scene samples.
Listen to a podcast interview with our senior medical officer Dr Tania Dexter for IFLScience.
Could I pass my donor's genes on to my children
There is an important distinction between DNA that’s in the normal, everyday cells in your body (called ‘somatic’ cells), and DNA in the cells that pass your genes on to your children (known as ‘germ’ cells – sperm and eggs). If the DNA in your somatic cells changes, you won’t pass those changes on to your children. Only changes in your germ cells have the potential to influence your child’s genetics.
So, barring some kind of medical miracle, there’s no way for the DNA from a stem cell donor to sneak into your germ cells and change your family genetic line!
We look at how a stem cell transplant could affect your fertility on our patient information pages here.
So what does having different DNA in my blood mean for me?
Ultimately, having donor DNA in your body makes you a particularly unique human – a chimera. Your donor’s cells have given your body a chance to recover from disease and develop a brand new immune system. You’re still undoubtedly you, just with an uncommon upgrade that may change how you feel about gherkins …
Further resources
See these resources from our Patient Information team for more information: