Replication-defective retroviral vectors

A number of alternative approaches are being developed that may overcome some of these issues. Replication-defective retroviral vectors are available that will more consistently (a) deliver a chosen gene into cells and (b) ensure chromosomal integration of the gene. A second innovation is the application of nuclear transfer technology. 

Repeat length, of fiber polymers, 11 175 Replication-defective retroviral vectors, 12 457... 

The initial viral-based gene delivery experiments were performed in vitro using replication defective retroviral vectors in an attempt to transduce endothelial cells (Yao et al., 1991). Preliminary viral-based in vivo cardiovascular gene delivery experiments were also performed using retroviral vectors and demonstrated this vector system s ability to successfully transduce vascular endothelial cells (Newman et al., 1991). Although attempts at direct transduction of the carotid artery were not successful, it was established that efficient endothelial transduction could be achieved through the retrovirus-mediated infection of cells ex vivo and their subsequent arterial seeding in vivo (Lynch et al., 1992). 

The envelope glycoproteins of wild-type retroviruses and lentiviruses bind to cell surface receptors to facilitate entry of the vims into the cytoplasm where the viral RNA is reverse transcribed to form a cDNA, the proviras. This provirus is translocated to the nucleus where it integrates into the host cell chromosomes and through the normal process of DNA transcription encodes new viral proteins and new viral RNA, which are assembled at the cell surface into new viral particles. Replication-defective retroviral and lentiviral vectors infect cells by similar mechanisms, but unlike wild-type viruses, the integrated provirus from these vectors encodes the therapeutic gene and viral particles are not produced. 

As early as 1981, several different research groups were successful in developing replication-defective avian and murine retroviral vectors (8-10). With the advent of such tools it was now possible to test an important proof of concept—correcting genetic defects through the transduction of normal genes into affected cells. One of the first important experiments involved the use of a retroviral vector to correct both the enzyme defect and purine metabolic abnormalities in cells taken from a patient with Lesch-Nyhan syndrome (11). 

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