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I thought that gene therapy, when performed on target cells that regenerate themselves constantly, can be effective for a limited time only. I.e., the effect gradually wears off after a while, depending on how fast the target cells renew themselves. In other words, the patient needs to continue receiving gene therapy every so often to keep getting desired effect.

On the other hand, when targeting cells that do not divide/renew, such as an eye, gene therapy can and actually did cure blindness once and for all, and the patient no longer needs gene therapy injections.

So what about the other diseases that gene therapy allegedly cured? I think they include blood disorders like hemophilia and some serious immune system disorders? I thought they mainly involved cells that do regenerate, like bone marrow and liver?

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Short answer
Both dividing and non-dividing cells can permanently be modified with gene therapy by using vectors that incorporate their payload in the host's chromosomal DNA

Background
Vector-based gene therapy can be applied by using vectors, such as modified retroviruses or adenoviruses, that incorporate their payload in the host's chromosome.

Whether the transformed cells are replicating yes or no, the parent as well as any possible daughter cells will carry the new DNA. For example, immunodeficiency has been treated successfully with gene therapy, but the first trials resulted in blood-bone cancers, because the stem cells started to proliferate uncontrollably, hence dividing cells definitely can be permanently transformed. In fact, when germ line cells are transformed in this way, even the offspring of the host will inherit it.

Sources
- American Medical Association
- Learn Genetics
- Utah University

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  • $\begingroup$ I would also add that "gene therapy" is an increasingly broad term. Viral vectors are one way of altering patient cells, but there are other ways, depending on the cell type. Current gene therapies to treat soft tissue tumors like leukemia include removing patient stem cells, altering them and finally re-inserting them. So far, no cancers have resulted from that cure. Here's a description of the technique: discoverymedicine.com/Runzhe-Chen/2015/10/… $\endgroup$ – Forest Feb 29 '16 at 17:17
  • $\begingroup$ @Forest - the means to obtain the target cells differ, the final method to get the DNA into them is based on vectors afaik $\endgroup$ – AliceD Feb 29 '16 at 18:47
  • $\begingroup$ Ah, I see now. Good point. $\endgroup$ – Forest Feb 29 '16 at 19:05

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