Cellular immunotherapies carry seeds of self-destruction but can be rescued with genetic engineering

A team of Memorial Sloan Kettering Cancer Center (MSK) researchers have made an important finding about why genetically engineered immune cells sometimes fail to finish the job when given as a cancer treatment. The new discovery sheds light on the tendency of these modified cells to lose power or even self-destruct before fully destroying a tumor. This is a major problem, for example, in chimeric antigen receptor (CAR) T cell therapy.

The research team, led by cellular therapist and early drug development specialist Christopher A. Klebanoff, MD, had previously found that engineered immune cells lose persistence because of the interaction between a protein called FAS, which sits on their surface, and a molecule that binds to the protein, called FAS ligand (FAS-L). This interaction activates FAS, which causes the immune cell to self-destruct (a process called apoptosis).

Now the researchers have made the surprising finding that FAS-L is produced by the immune cells themselves.

“We go to extraordinary lengths to manufacture genetically engineered cells, and now we find they carry within themselves the seeds of their own destruction,” Dr. Klebanoff says. “They express very high levels of a molecule that functions like a sword they can use to commit suicide with or eliminate their brethren — other immune cells.”

This phenomenon can hamper the effectiveness of many kinds of cell-based therapies, including treatments made for each patient, such as CAR-T cells, as well those made to be “off the shelf,” such as genetically engineered natural killer (CAR-NK) cells.

The findings about FAS-L point the way to reengineering T cells and other immune cells to avoid this fatal pitfall. Preventing the interactive signaling between FAS and FAS-L could enable cell therapies to work more consistently for patients.

The discovery is reported on July 22 in Nature Cancer: “CAR-engineered lymphocyte persistence is governed by a FAS ligand–FAS autoregulatory circuit”

Locating FAS-Ligand’s Production Site and Impact on Cell Therapies

Researchers previously believed that FAS-L is produced by tumor cells — or the cells that surround and support them — as part of a defense against immune attack. But they lacked solid evidence supporting this assumption.

To detect the source of FAS-L, a team of MSK experts from different disciplines created a single-cell expression “atlas” using cells from more than 50 patients with diverse cancer types. Included in the analysis was a collection of samples from patients receiving CAR-T cell therapy.

The analysis revealed a few key findings about FAS-L:

1) T cells and NK cells themselves are the major source of FAS-L. (This is true even after they have been engineered.)

2) The presence of FAS-L was often enough to cause CAR-T cells and engineered NK cells to eliminate themselves.

3) Significantly, the CAR-T and NK cells do not require FAS-L to destroy cancer cells.

“For the cancers we studied, FAS-ligand’s effect on therapy appears to be strictly negative — as a brake that restrains the engineered cells’ longevity,” Dr. Klebanoff explains. “We wanted to figure out how to disable FAS-L to increase the power of cellular immunotherapies.”

Seeking To Block the Signal Between FAS-Ligand and FAS Receptors

Based on these surprising findings, the researchers developed a genetic engineering technology to block the signal between FAS-L and FAS. They created a decoy receptor called FAS-DNR, which binds to FAS-L but does not trigger the self-destruction process. When this decoy receptor was added to human CAR-T and CAR-NK cells, the cells lasted longer and had more potency against tumors.

“When we armor the CAR-T and CAR-NK cells with these decoy receptors, they are protected from apoptosis even when there is a large amount of FAS-ligand engagement,” says Fei Yi, PhD, a research fellow in the Klebanoff Lab and the study’s first author.

Dr. Klebanoff says using the decoy FAS-DNR receptors could be broadly applicable, improving cell therapies for many types of cancer. The strategy of blocking FAS activation is already being incorporated into clinical trials. But knowing FAS-L is on the immune cells themselves makes it easier to negate its effects.

“This allows us to fix the challenge of persistence with engineered cells before they are put back into the patient,” Dr. Klebanoff says.

Only at MSK

Dr. Klebanoff credits the team of MSK researchers that produced the finding, including fellow experts in cell immunobiology and cell therapy, including Katharine Hsu, MD, PhD, Jae Park, MD, and Anthony Daniyan, MD, and computational biology experts including Caleb Lareau, PhD.

“It’s been an extraordinary collaboration led by Fei and enabled by the unique environment at MSK across many departments,” Dr. Klebanoff says.