One of the main problems with gene therapy is that there is a very low possibility that the plasmid with the new piece of DNA will be correctly inserted into the DNA in the human DNA for several reasons: a) The host cell (bacteria, virus or liposome which has been more recently used) has difficulties in travelling successfully to the human cell in the specific organ or tissue. (e.g.: lungs) If the host cell is a virus, the body can easily destroy them because as the virus touches the surface of the membrane, antibodies will attack it as the cell membrane has glycocalyx which are carbohydrates that can recognize molecules or cells that are not common in the body.

b) It is also because the new piece of DNA has to enter the DNA strand in the correct place. Usually, in a part where the bases are not coding for any protein.

Another negative effect might be that when the new piece of DNA enters the human DNA strand, it can have a terrorific effect on it. This happens when it successfully enters the DNA strand but it replaces or simply disrupts the sequence of amino acids which code for an important protein. (This has occured in the 1980s with the X-SCID disease)

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