My lab works on transplantation and how your body and immune system responds to a transplanted tissue. The answer to your question is yes, a body definitely changes following a transplant, and it is due to differences in the DNA between the recipient and the donor.

Primarily, the host always has an immune response to the transplanted tissue because it recognizes those differences, so most people are on very strong drugs called immunosuppressants, which block the immune system from killing the transplanted tissue, for the rest of their lives. This is bad because then the patient is also not responding to normal infections. In addition, many times the transplanted tissues contain what are called blood forming stem cells, which are the cells that make your blood. The donor stem cells can begin to make blood, and the recipient actually has blood made from them, and is now a 'chimera', made of tissues of two individuals.

After an organ transplant, the body will change due to the function of the organ. The function of the organ is instructed by the DNA in cells that make up the organ. DNA is contained within the nucleus of the cells in your body. The exception is red blood cells that do not have a nucleus (and so do not have DNA. A blood transfusion can include only red blood cells which would mean that no new DNA would be added to your body. The addition of the organ will change your body (hopefully for the better) and the effect on your body is most likely not reversible. The DNA in the cells of the transplanted organ will NOT be added to the DNA in the cells of your other organs.

Interesting question. The key to understanding the answer is to remember that DNA stays in the nucleus of the cell. So if you get a kidney transplant, and someone took a DNA sample of your kidney, it would have the donor’s DNA. But the rest of your DNA would still be yours. Well, almost all of it. There will be some cells in the kidney, like blood cells or damaged kidney cells. The DNA from these may end up in your blood stream, but the DNA won’t move into other cells.

Your red blood cells don’t have any nuclei when they mature, but your white blood cells do. These days blood is usually separated into different components based on what a patient needs. They can even take just a particular component of the blood from a donor. (When I give platelets--which are fragments of a specific cell and help blood to clot— they put the red and white blood cells and the plasma right back into me.) So let’s say you got a transfusion of red cells, then they did a DNA test on your blood. The only cells with DNA at all would be the few white cells. There might be a few cells in the sample that had the donor’s DNA, but most would be your own.

Here’s an interesting thing, though. Blood cells are made in bone marrow. Some people have diseases like leukemia that may need to be treated by destroying a person’s own bone marrow, and replacing it with donor bone marrow. This person will then be making blood cells with the donor’s DNA. This has been a plot point in some mysteries. The rest of the person’s tissues would still have their own DNA.

When a person gets an organ transplant, they need to find a donor with similar DNA. Why do you think that’s important?

Well, you're better than you were before, if you needed a transfusion or an organ transplant; so you wouldn't want to be the same as before.

1. Yes, some of the other DNA can stay in your body: DONOR DNA IS DETECTED IN RECIPIENT BLOOD FOR YEARS AFTER KIDNEY TRANSPLANTATION USING SENSITIVE FORENSIC MEDICINE METHODS. You can read here

2. You don't even need to have a transplant to have different types of DNA in your body. Here are some strange stories: Read here

3. Maybe I have DNA from my son in my brain! Scientists autopsied the brains of 59 dead women and found Y [male] chromosomes in 37 of the women! They think it got there when they were pregnant with their sons! Read here

This question doesn't have a simple answer.
If the DNA of the transplanted blood and tissue is too different from your own, then your immune system will conclude that it's an invading infection and will try to destroy it. The resulting internal warfare can even kill you. For this reason, doctors are very careful to make sure that the blood or other tissue being donated is genetically compatible with the recipient.

If the tissue being transplanted is bone marrow, then your blood will be changed because bone marrow is what makes new blood. If it's a blood transfusion, then the transplanted blood will remain while it's still in you, but will be flushed out of your body as blood is constantly being replaced from your bone marrow and you will go back to what you were before. If it's anything else, then the transplanted organ will be new, but the rest of your body will not.

All of the cells in a person's body contain the same genetic code because they originated from the same founder cell way back in fertilization. Each time cells divide, they transfer a copy of the genetic code to a daughter cell. Whenever our bodies need new cells, cell divisions occur and pass along our genetic information. However (and this is very important), not all of the cells in our body are capable of dividing.

Cancers occur when cells that should never divide begin dividing uncontrollably. Evolution has given us a delicate balancing act - if we don't have enough dividing cells, we can't regenerate dying cells in important organs, but if we have too many, the consequences are extremely dangerous. This is why we have small populations of pluripotent cells specific to each organ that generate cells only when needed.

Red blood cells (RBCs), the important component of blood transfusions , are made in bone marrow, where stem cells divide to create new RBCs. Because stem cells are not transferred in a donation, the RBCs given to the patient will not divide and continue to spread donor DNA. (Additionally, RBCs are a unique type of cell because they actually lack a nucleus!)

However, some patients do need bone marrow transplants, especially following treatment for cancer. As mentioned before, cancer occurs when stem cells go crazy - therefore, treatments like radiation and chemotherapy are used to stop cell division that has gotten out of control. This treatment is effective at killing cancer cells, but it also kills healthy stem cells like those in bone marrow. Sometimes patients have their own bone marrow harvested before treatment and put back in their body afterwards. If they receive a bone marrow donation, the donor's stem cells will divide and produce cells with foreign DNA - depending on how many of the host's stem cells survived during radiation, the patient may continue to produce foreign DNA throughout their life! If the donor is healthy, it is unlikely that this genetic change will have negative effects on the recipient.

To summarize, transplants and transfusions will only continue to create cells with foreign DNA if they contain stem cells.