If an organ from person A is transplanted to a new human body B, is it possible that we can detect A's DNA in B?
How long until the organ's DNA is replaced by B's DNA so that we are no longer able to detect any signature of A?
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$\begingroup$ The organ from person A will never have it's DNA replaced to match that of its new host B. This is actually a good thing, because many organ transplants are done to treat genetic diseases. If the new organ had its DNA replaced with the host's faulty DNA, the transplant would be ruined. As far as detecting the organ's foreign DNA in its new host, that depends on how the sample was collected. If you look really hard at DNA in blood samples, you might find some evidence of the donor's DNA in the host's blood, but how much probably depends on what organ was transplanted and other factors. $\endgroup$– user137Jan 21 '16 at 2:07
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$\begingroup$ @user137 But cells of the new organ may die and be replaced at least. The new cells have the host's DNA or the new organ's DNA? $\endgroup$– questionhangJan 23 '16 at 8:11
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$\begingroup$ If the transplanted organ's cells die, they probably have to be replaced by other cells in the transplanted organ. These would carry the foreign DNA from the donor. The only way for new cells in the organ to carry the host's DNA would be if host cells colonized the new organ from the outside, which doesn't seem significant. There are cells that can colonize tissues, such as Kupffer cells in the Liver, but these don't make up the bulk of the liver, those are hepatocytes. $\endgroup$– user137Jan 24 '16 at 5:09
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DNA will be never replaced (unless you are speaking about something, where DNA might be only trash, like in the case of blood transplantation or in the case when "organ" would be slowly replaced itself by host regenerative power and "organ" transplantation would be only something temporary, but then we are probably speaking about wider definition of organs).
For further evidence, you may look at cases of chimerism. That is, when young embryos fuse together and create single one with two different cell-lines, which later differentiate to create different organs. https://en.wikipedia.org/wiki/Chimera_%28genetics%29
Furthermore, rather more common but with less drastic effect can be somatic chimeras, that is when (usually) early, when embryo is formed only by small amount of cells, one of cell has a mutation, then later in life, this cell again can give rise to organ or several of them. In that case, those organs will carry this mutation while rest of the body will not. This can be potentially more common as this can happen in any single time during development and even after it (in fact, cancer cells are sort of product of that). More interesting cases here: https://en.wikipedia.org/wiki/Mosaic_%28genetics%29
So, from simple fact that these cases exists and are well-spread, and basically means that several different cell-lines can live in the same body, the answer on your question, if organ DNA will be replaced after transplantation is no.
edit: In the case of whole cell replacement, they can be from both donor and host. However, there are a few problems:
Most of cells that we have are not totipotent, not even pluripotent or multipotent (see: https://en.wikipedia.org/wiki/Cell_potency), most of our cells are plain and stupid. This means that highly specialized cells of some organ would probably be replaced only by other highly-specialized cells of that organ (or their precursor cells that are kept for this solo reason, keep regenerativ ability of particular organ, as quite a lot of highly-specialized cells can't divide any more). However, there are a few documented cases with regnancy, where a few cells (embryogenic, thus with bigger "healing" power) migrated through placenta to mother's body and healed her diabetes. So theoretically this is possible, as well as host getting cancer from donor's organ. But again, reason why we are transplanting organs is because human body is not particularly great in regenerating itself and those organs won't grow. So theoretically possible, but not great concern (except for cancer).
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$\begingroup$ DNA will be replaced as long as cells die. But new cells carry whose DNA? It is possible an organ carry A's and B's DNA simutaneously? $\endgroup$ Jan 23 '16 at 8:14
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$\begingroup$ @questionhang It's not just the DNA that's replaced, it's the cells that are replaced. And they are replaced by cell division. So they get the same DNA as the other cells of that organ have. $\endgroup$– YviDeJan 23 '16 at 11:56
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$\begingroup$ @yvide I know. The cells of the donor's organ die too. The new cells carry the host's DNA or the donor's DNA? $\endgroup$ Jan 23 '16 at 15:39
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$\begingroup$ @questionhang: Did edit. Does that answer your further question? $\endgroup$– ColomboJan 24 '16 at 1:45
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$\begingroup$ @Colombo So it is possible the organ can have host's cells and donor's cells simulatenously? Many years later, the donor's cells will not be purged? $\endgroup$ Jan 24 '16 at 9:19