Scientists have made a breakthrough by using a single virus instead of four to convert adult cells to embryonic stem cell-like cells, called induced pluripotent stem (iPS) cells.
By simplifying the process to create iPS cells, Whitehead Institute researchers are now hoping that these embryonic stem-cell-like cells could eventually be used to treat such ailments as Parkinson's disease and diabetes.
For a long time, reprogramming efforts were based on four separate viruses to transfer genes into the cells' DNA - one virus for each reprogramming gene (Oct4, Sox2, c-Myc and Klf4). Once activated, these genes convert the cells from their adult, differentiated status to an embryonic-like state.
However, this method poses significant risks for potential use in humans, as the viruses used in reprogramming are associated with cancer because they may insert DNA anywhere in a cell's genome, thus potentially triggering the expression of cancer-causing genes, or oncogenes.
And the latest technique has come as a significant advance in the quest to eliminate the potentially harmful viruses.
Bryce Carey, an MIT graduate student, led the effort and successfully joined the four reprogramming genes in tandem by using bits of DNA that code for polymers known as 2A peptides.
Working with others in the lab, he then manufactured a so-called polycistronic virus capable of expressing all four reprogramming genes once it is inserted into the genomes of mature mouse and human cells.
When the cells' protein-creating machinery reads the tandem genes' DNA, it begins making a protein. However, when it tries to read the 2A peptide DNA that resides between the genes, the machinery momentarily stops, allowing the first gene's protein to be released.
Then the machinery moves on to the second gene, creates that gene's protein, stalls when reaching another piece of 2A peptide DNA, and releases the second gene's protein. The process continues until the machinery has made the proteins for all four genes.
Using the tandem genes, Carey created iPS cells containing just a single copy of the polycistronic vector instead of multiple integrations of the viruses.
And the advancement is quite significant and indicates that the approach can become even safer if combined with technologies such as gene targeting, which allows a single transgene to be inserted at defined locations.
Interestingly, while Carey's single-virus method integrates all four genes into the same location, it has proven to be roughly 100 times less efficient than older approaches to reprogramming. This phenomenon remains under investigation.