MadSci Network: Medicine

Re: What happens to one's DNA after an organ or blood transplant?

Date: Fri Mar 17 09:33:51 2000
Posted By: BOTFIELD Nigel, Staff, Haematology, Scunthorpe General Hospital
Area of science: Medicine
ID: 952012178.Me

Hi Mike,
I can see you know a bit about the subject but I will keep the answer 
fairly easy for any newcomers to the topic who come across this.
DNA from transplanted material ( blood, kidney etc ) keeps on working as 
normal until the cell dies. There are two very obvious and very 
unfortunate signs of this.
Consider the following scenario - Jane Doe donates an organ to Joe Public.
Jane's organ is made of cells which carry markers on the surface. These 
markers identify the cells as JANE. Once the organ is transplanted it 
carries on living inside Joe's body - the organ does its job and the cells 
that make up the organ continue to live, divide and die just as though the 
organ was still inside Jane. The problem is that the DNA inside the cells 
instructs the cells to produce the cell marker JANE. Joe's immune system 
can recognise this marker as a foreign object and sets about killing the 
cells in the transplanted organ and eventually destroying the whole organ. 
This is the first sign - organ rejection.
The other sign of transplanted DNA working as normal occurs when the 
transplanted material contains cells from the donor's immune system - this 
occurs if the organ still has blood inside it or if the donated material 
is blood or bone marrow. In this case cells from Jane's immune system find 
themselves surrounded by cells all carrying the cell marker JOE. The 
transplanted cells then function as normal and multiply, produce 
antibodies to the JOE cell marker and try to destroy those cells carrying 
the marker. This is called graft versus host disease.
These problems can be avoided in several ways -
1) Testing the cell markers present on the donor and recipient cells. JANE 
and JOE are quite different markers but LESLEY and LESLIE are quite 
similar and so the chances or organ rejection are lower.
2) Immunosuppressent drugs can stop Joe's immune system attacking the JANE 
cell marker.
3) Removing any residual immune cells in the transplant material - with 
blood this is done by exposing the bag of blood to gamma radiation which 
kills the immune cells but doesn't affect the red cells that transport 
oxygen around the body. Transplant organs can have most but not quite all 
of the blood flushed out of them with saline.
Unfortunately option 3 doesn't work with bone marrow as the marrow 
produces many of the cells that form the immune system and a bone marrow 
transplant is given to patients with irreparably damaged bone marrow who 
would otherwise die of anaemia or infection.
When transplanted cells die ( either normally by apoptosis or by immune or 
infectious attack ) the recipient body treats them like its own - the DNA 
is broken down into its constituent sub-units which can be recycled or 
removed from the body. There seems to be no evidence that DNA from 
transplants can act like a virus and enter other cells in the recipient's 
body and result in unusual gene expression. If such a process was possible 
there would be at least 2 sources of evidence -
1) The large number of transplant recipients over the last 30 years.
2) The human body itself - every day millions of cells die and are 
replaced, if salvaged DNA was capable of entering other cells and being 
expressed then we would see tissues and organs growing in appropriate 
It would take a number of unusual and complicated circumstances to provide 
transplanted material with the opportunity to insert DNA into the 
recipient's genome.
Hope this helps.

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