Electric Shock Allows for CRISPR Gene Editing Without a Viral Vector

Blue purple pink 3d rendering of brain

Engineered cancer cells may be able to home in on tumors in hard-to-reach places like the brain

By harnessing the power of cancer cells' self-homing ability - the process in which cancer cells can track the cells of their kind that have spread within the same organ or other parts of the body - researchers believe they will be able to overcome drug delivery challenges. Still, the study holds promising evidence that genome-edited honing cells could unlock a world of treatment for those with preliminary and reoccurring cancers.

Viral vectors can be extremely efficient at introducing new DNA sequences, Theo Roth, an MD/PhD student at UCSF and an author of the study, told Cancer Therapy Advisor. The other used pre-engineered cells that matched the patient's own genes.

Next, the researchers, in collaboration with colleagues from the Parker Institute for Cancer Immunotherapy at the University of California, Los Angeles, outfitted normal T cells with new receptors crafted to detect melanoma cells. "We think this has many implications and could be applicable across all cancer cell types".

The scientists noted in their study that before the correction of genetic mutations was proposed to do with the use of long DNA sequences in T-cells (human immune cells), which led to the death of these cells due to the toxicity of DNA.

"This is a rapid, flexible method that can be used to alter, enhance, and reprogram T cells so we can give them the specificity we want to destroy cancer, recognize infections, or tamp down the excessive immune response seen in autoimmune disease", said UCSF's Alex Marson, senior author of the new study, in a statement. To capitalize on that ability, researchers engineered these roving tumor cells to secrete a protein that triggers a death switch in resident tumor cells they encounter. The winning candidate, a protein called S-TRAIL, killed off a variety of cancer cells and wasn't particularly toxic to healthy cells.

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With the non-viral CRISPR technique, the UCSF team was able to quickly fix the IL2RA defect in the children's T cells, and to restore cellular signals that had been impaired by the mutations.

To validate these findings, Roth directed CRISPR to label an array of different T cell proteins with green fluorescent protein (GFP), and the outcome was highly specific, with very low levels of "off-target" effects: each subcellular structure Roth's CRISPR templates had been created to tag with GFP - and no others - glowed green under the microscope. The team tested these assassin cells on three types of tumors: primary glioblastoma, the deadliest form of brain cancer; recurrent glioblastoma, where cancer that was treated became immune to chemotherapy; and breast cancer that had metastasized to the brain.

Without using viruses, the researchers were able to generate large numbers of CRISPR-engineered cells reprogrammed to display the new T cell receptor.

"The new twist here is the use of CRISPR-based technology to add resistance or sensitivity features to the parental cells", says Renata Pasqualini, a cancer biologist at Rutgers Cancer Institute of New Jersey in Newark. We show that both approaches allow high expression of targeted ligands that induce tumor cell killing and translate into marked survival benefits in mouse models of multiple cancer types. But the problem is that T-cells which are engineered by the help of a virus is really expensive and painstaking process.

Getting the technique to work took several steps.

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