4Bioengineering.com

Gene therapy involves the transfer of genetic material, encoding one or more therapeutic genes and the sequences necessary for their expression, to target cells to alter their genetic makeup for some desired therapeutic effect. Gene therapy was first used to treat adenosine deaminase (ADA) deficiency, a single-gene genetic disorder, but is now being tested in a wide variety of applications, including complex genetic disorders such as cancer, infectious diseases such as human immunodeficiency virus (HIV) infection, and in tissue engineering.

Genetic material has been successfully delivered to a large number of different human cell types, and their phenotypes have been… Continue reading →

Recombinant retroviruses used for human gene therapy are derived from the wild-type Moloney murine leukemia retrovirus. The recombinant viruses are structurally identical to the wild-type virus but carry a genetically engineered genome that encodes the therapeutic gene and sequences which regulate its expression. Recombinant retroviruses cannot self-replicate, but can infect and integrate their genomes into the chromosomal DNA of the target cell.

Recombinant retroviruses consist of a two-part system composed of a retroviral vector and a packaging cell line. The retroviral vector is essentially the wild-type genome with all the viral genes removed. It encodes the therapeutic gene, regulatory sequences… Continue reading →

One approach to improve transduction efficiency is to increase the concentration of infectious virus particles. The concentration of virus particles in virus stocks can be increased by optimizing packaging cell culture conditions, concentrating the virus stocks after they are harvested from the packaging cells, and/or by altering the virus or packaging cell lines.

Significant increases in virus titer have been achieved by optimizing cell culture conditions, such as by reducing the ratio of culture medium to cell number. Packaging cells seeded in the extra capillary space of a hollow fiber bioreactor, and grown to densities (108 cells per milliliter) about… Continue reading →

Transduction efficiencies can also be improved by straightforward environmental or culture medium alterations that maximize the efficiency of extra cellular steps of infection. For example, by reducing the decay rate of recombinant retroviruses, which rapidly lose infectivity with time at 37oC, transduction efficiencies can be improved.

The rapid decay of infectivity (the half-life at 37oC is about 6 to 8 hours) of retroviruses reduces transduction efficiencies because retrovirus binding and infection occurs over a period of several hours, during which time most of the infectivity of the retroviruses is lost. Infection continues for several hours because the virus particles are… Continue reading →

Finally, transduction efficiencies can also be improved by increasing the efficiencies of the steps of infection that occur on or inside the cell. For example, virus binding (and transduction efficiency) can be improved by increasing the concentration of cell surface receptors. The recent cloning of the amphotropic retrovirus receptor, a sodium-dependent phosphate symport, has enabled researchers to measure, and alter, the tissue-specific expression of the receptor.

By culturing CD-4 enriched human peripheral blood lymphocytes in phosphate-free medium for 12 hours, transduction efficiency was increased more than ten-fold, presumably because expression of the amphotropic receptor was unregulated. Transduction efficiencies can also… Continue reading →

The revival of interest in health care among venture capital firms is attracting corporate investors as well.

Medical products companies like Johnson & Johnson Co. and pharmaceutical giants like SmithKline Beecham (now GlaxoSmithKline) have been investing in smaller companies for years. But now they have far more company in the field than ever before.

The newcomers are entering the health care investment arena with at least one of three basic goals:

• To add to their own line of products. Cytyc Corp., for example, the developer of a new means of doing pap smears, has set up a venture unit… Continue reading →

For years, venture capitalists have been seeing opportunity sitting on the shelves of pharmaceutical companies: abandoned drugs, possibly approved by the FDA but, in the eyes of the pharmaceutical executives, capable of generating only a small amount of sales.

To VCs, however, these markets aren’t so small. And many have built successful companies around unwanted compounds they’ve acquired in exchange for milestone and royalty payments.

Now, in a move that could drive up the price for venture investors interested in these compounds, GlaxoSmithKline plc has established a unit through which it would take stakes in companies in return for turning… Continue reading →