Researchers from Mass General Brigham and the Broad Institute of MIT and Harvard have identified genetic modifications that can improve the efficacy of chimeric antigen receptor (CAR)-T cell treatment — an immunotherapy that uses modified patient T cells to target cancer. The study used CRISPR screening to pinpoint genes that influenced T cell function and survival in culture and in a preclinical model of multiple myeloma. Their results and technique, published in Nature, could lead to T cell-based immunotherapies for cancer.

“We performed a screen over the entire lifecycle of a T cell, co-culturing them with cancer cells, and then took the work a step further by transferring the cells to an animal model,” said co-senior author Robert Manguso, a researcher at the Krantz Family Center for Cancer Research at Massachusetts General Hospital and director of the Tumor Immunotherapy Discovery Engine at Broad. “We discovered important regulators in vivo that we could not have predicted from the in vitro results.”

“Testing individual genetic modifications to find those that enhance CAR-T function would take a huge amount of time and money. Our approach lets us test hundreds of changes at a time,” added co-senior author Marcela Maus, director of the Cellular Immunotherapy Program at the Mass General Brigham and an associate member in the Broad's Cancer Program.

CAR-T cell therapy has revolutionized the treatment of blood cancers but, thus far, has not been as effective against solid tumors or in patients with relapsed or refractory multiple myeloma. In addition, the number of circulating CAR-T cells decreases over time, limiting their long-term activity. 

In this federally funded study, the research team developed a CRISPR screen that targeted 135 genes in human donor-derived CAR-T cells to identify genes that may improve persistence and function. The investigators cultured the CRISPR-edited cells in vitro, transferred them into a mouse model of multiple myeloma and tracked their survival in vivo for up to 21 days.

Analyses of the modified CAR-T cells revealed that deleting the cell cycle regulator gene CDKN1B increased CAR-T cell proliferation, long-term persistence and anti-tumor activity. The researchers also observed that some genes affected function in vitro but not in vivo, while others boosted early proliferation in the tumor microenvironment but did not provide long-term benefits.

The researchers, including co-first authors Nelson Knudsen, Giulia Escobar, and Felix Korell, propose that targeting CDKN1B in CAR-T cells could enhance treatment outcomes for patients with multiple myeloma and suggest that future studies that harness their screening method could refine therapeutics for other cancers.

Adapted from a press release issued by Mass General Brigham.