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Home >> Animal Biotechnology and Genomics >>Gene Theraphy>> Ex Vivo VS in Vivi Gene Therapy
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Ex Vivo vs Vivo Gene Therapy
In gene therapy, recombinant vector with the therapeutic gene is used for gene delivery to specified cells and tissues. Two different strategies are used for this gene delivery, i.e. ex vivo and in vivo. In ex vivo approach the cells may be cultured and used for gene transfer, so that these transfected cells are then introduced in a targeted tissue.

Alternatively in the in vivo approach, the gene may be delivered through a vector directly into the target cell or tissue.

Ex vivo gene delivery is common and more certain, but at the same time more problematic, since: it requires (i) a mitotic cell population; (ii) a tissue culture method and (iii) a cell transplantation technology. There are also following advantages of an ex vivo approach, (i) gene transfer efficiency is generally high and retroviral vectors are particularly effective: (ii) the transduced cells can be enriched if the vector has a selectable marker gene and (iii) transduction efficiency can be assessed before re-implantation.

Bone marrow cells, can be multiplied and modified and are the common candidates for ex vivo gene delivery, but for other types of cells, ex vivo modification may be difficult. However, the use of embryonic stem (ES) cells may be really useful. For this purpose, although earlier ES cells were available only from mouse, rat, pig, rabbit, etc. but human ES cells have also become available recently (1998-2002).

Despite some advantage of ex vivo gene delivery, in vivo gene delivery would be preferred, if feasible. However, one major precaution required during in vivo gene delivery is that the gene be delivered only to the targeted cells and no other cells, and in no case to the gene line cells. Retrovirus delivers the gene only to dividing cells and therefore issafe for delivery of gene to cancer celIs. But in other cases receptor mediated endocytosis (RME) may have to be used, so that the vector will have to carry a ligand for the receptor available on the target cells.

Sometimes, instead of targeting specific celI types, selective expression of a transferred gene can also be achieved by the use of tissue specific enhancers/promoters. However, the disadvantages of in vivo gene delivery include the following (i) specificity and low efficiency of stable gene transfer, (ii) for clinicalIy useful therapeutic application, repeated treatments may be needed raising the problem of a host immune response.

Splicesome mediated trans-RNA spllicingIn view of the above advantages and disad­vantages of ex vivo and in vivo approaches, the choice will depend on the relative ease of in vitro culture (ex vivo approach) and the gene transfer efficiency of the target tissue (in vivo approach).
 

 

 
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