Sammy Westfall

A new Yale-led study has discovered a novel gene target for cancer immunotherapy.

By using the genome editing system CRISPR to screen for genes, the study determined that the Dhx37 gene modulates the activation of CD8 T cells, which are key players in the immune response against tumors.

“CD8 T cells directly kill tumor cells, which makes them an important target for cancer immunotherapy,” said Matthew Dong MED ’23 GRD ’23, first author of the paper and a graduate student in the lab of genetics and systems biology professor Sidi Chen.

According to the study, modifying the DNA sequences that code for T-cell receptors allows these cells to generate highly specific toxic responses to tumor cells.

“Cancer immunotherapy involves tumor-specific responses elicited by cells of the immune system,” Dong explained. “This is enabled by the highly specific receptors of the adaptive immune cells that are generated through DNA rearrangement.”

Prior to the advent of CRISPR genome editing technology, studies using RNAi, or RNA interference, had been used to identify the genes that regulate CD8 T cells. RNAi is used to deactivate a gene in order to determine its function.

But RNAi studies have shown several limitations, including off-target gene silencing and a dependency on enough RNAi to effectively degrade the protein that the gene codes for.

CRISPR-Cas9, in contrast, does not depend on the quantity of any specific reagent. Unlike RNAi, which interferes with the gene of interest at the RNA level, CRISPR-Cas9 interferes with the gene of interest at the DNA level. This approach ensures that all resulting RNA products are mutated, thus creating a more reliable suppression of the gene.

Critically, the CRISPR screen was conducted in an in vivo setting, or within a living organism. Past CRISPR studies have often been in in vitro settings, where cells isolated from organisms are provided with nutrients in a cell culture and observed under nonphysiological conditions. According to Dong, in vitro cultures often do not accurately model the cellular environment or the complex cell-to-cell interactions present in a living organism.

Nonetheless, Dong emphasized that in vitro and in vivo methods should be used in tandem.

“We looked at cells that were enriched in the tumor to see whether there was a selective pressure, and validated results from this screening in an additional in vitro screen,” he said.

According to Dong, the discovery of Dhx37 as a modulator of CD8 T cell tumor toxicity suggests two potential steps in furthering research in cancer immunotherapy: engineering Dhx37 knockouts in immune cells — in which the Dhx37 gene is deleted from the cells’ genome — for a potential immunotherapy treatment and observing the 3D crystal structure of the Dhx37 to see which part of the gene can be targeted with a drug.

As of February 2019, the FDA has approved 43 oncological immunotherapies.

Viola Lee | kyounga.lee@yale.edu