New genome editing tool can alter human stem cells

A powerful "genome editing" technology known as CRISPR can precisely and efficiently alter the human stem cells, scientists, including one of Indian-origin, have found.
The findings could streamline and speed efforts to modify and tailor human-induced pluripotent stem cells (iPSCs) for use as treatments or in the development of model systems to study diseases and test drugs.
"Stem cell technology is quickly advancing, and we think that the days when we can use iPSCs for human therapy aren't that far away," said Zhaohui Ye, an instructor of medicine at the Johns Hopkins University School of Medicine.
"This is one of the first studies to detail the use of CRISPR in human iPSCs, showcasing its potential in these cells," said Ye.

CRISPR originated from a microbial immune system that contains DNA segments known as clustered regularly interspaced short palindromic repeats.
The engineered editing system makes use of an enzyme that nicks together DNA with a piece of small RNA that guides the tool to where researchers want to introduce cuts or other changes in the genome.

Ye, Linzhao Cheng, a professor of medicine and oncology in the Johns Hopkins and their colleagues pitted CRISPR against another gene editing technique TALEN in human iPSCs, adult cells reprogrammed to act like embryonic stem cells.
Human iPSCs have already shown enormous promise for treating and studying disease.

The researchers, including Pooja Chaudhari, Doctoral Candidate at Johns Hopkins School of Medicine, compared the ability of both genome editing systems to either cut out pieces of known genes in iPSCs or cut out a piece of these genes and replace it with another.
As model genes, the researchers used JAK2, a gene that when mutated causes a bone marrow disorder known as polycythemia vera; SERPINA1, a gene that when mutated causes alpha1-antitrypsin deficiency, an inherited disorder that may cause lung and liver disease; and AAVS1, a gene that's been recently discovered to be a "safe harbour" in the human genome for inserting foreign genes.

Their comparison found that when simply cutting out portions of genes, the CRISPR system was significantly more efficient than TALEN in all three gene systems, inducing up to 100 times more cuts.
The researchers also found that the CRISPR system has an advantage over TALEN: It can be designed to target only the mutation-containing gene without affecting the healthy gene in patients, where only one copy of a gene is affected.
The findings offer reassurance that CRISPR will be a useful tool for editing the genes of human iPSCs with little risk of off-target effects, said Ye and Cheng.
The study was published in the journal Molecular Therapy.