When T cells are modified to fight cancer more effectively, cellular mechanics don’t pick up a socket wrench. Instead, they take hold of retroviral or lentiviral technology, which is used to install genes for synthetic T-cell receptors. Such technology, however, doesn’t always place genes in just the right place. Enter Mr. GoodCRISPR. This mechanic uses CRISPR gene-editing technology, which is more precise.
CRISPR can be used to install genes, such as chimeric antigen receptor (CAR) genes, into specific parts of the genome. Presumably, when CRISPR is used to build CAR T cells, their genomic engines will run more smoothly—and rack up more trouble-free miles. Such endurance is important for CAR T cells, which are being used in immunotherapy applications. These are long-distance races, and they are particularly grueling when CAR T cells must outpace cancer.
A road test of sorts has been staged by scientists based at Memorial Sloan Kettering Cancer Center (MSK). They decided that CRISPR T-cell engineering might be more effective than conventional T-cell engineering, which, the scientists have observed, can result in clonal expansion, oncogenic transformation, variegated transgene expression, and transcriptional silencing.
The scientists built CRISPR-engineered CAR T cells and evaluated their efficacy in a model of acute lymphoblastic leukemia. The results of this work appeared February 22 in Nature, in an article entitled, “Targeting a CAR to the TRAC Locus with CRISPR/Cas9 Enhances Tumour Rejection.” As the title suggests, the MSK team took advantage of CRISPR’s ability to deliver genes to selected genomic loci.
“Here we show that directing a CD19-specific CAR to the T-cell receptor α constant (TRAC) locus not only results in uniform CAR expression in human peripheral blood T cells, but also enhances T-cell potency, with edited cells vastly outperforming conventionally generated CAR T cells in a mouse model of acute lymphoblastic leukaemia,” wrote the article’s authors. “We further demonstrate that targeting the CAR to the TRAC locus averts tonic CAR signalling and establishes effective internalization and re-expression of the CAR following single or repeated exposure to antigen, delaying effector T-cell differentiation and exhaustion.”
Essentially, the MSK team showed that CRISPR technology can deliver a CAR gene to a very specific location in the genome of the T cell. Moreover, the team demonstrated that this precise approach resulted in CAR T cells that had more stamina.
The CRISPR-modified T cells are able to kill tumor cells for longer because they are less prone to exhaustion. More robust T cells could eventually lead to safer, more effective use of cell-based immunotherapy in patients.
“Cancer cells are relentless in their attempt to evade treatment, so we need CAR T cells that can match and outlast them,” explained Michel Sadelain, M.D., Ph.D., senior author on the Nature paper and director of the Center for Cell Engineering and the Gene Transfer and Gene Expression Laboratory at MSK. “This new discovery shows that we may be able to harness the power of genome editing to give these 'living therapies' a built-in boost. We are eager to continue exploring how genome-editing technology could give us the next generation of CAR T cell therapy.”
Some of the first clinical trials using CRISPR technology are currently in the planning stages. Dr. Sadelain and his team aim to eventually explore the safety and efficacy of these CRISPR-built CAR T cells in a trial.