Inside-out engineering yields better cancer-fighting cells

On a recent Saturday morning, my coffee grinder fell apart in my hands. Usually, it’s a quick bean-cap-grind process where I wait until the grunting, harsh sound reaches the right timbre. This time, when I removed the cover, the plastic casing of the car came off.

I could see how it works from inside the grinder. The shutter button depresses a (usually hidden) plastic pin that activates a motor activation switch that causes the blades to rotate. To get it working again, I had to put everything back together exactly as before. I smashed it with pin alignment and then gingerly put the shell in place. The gadget has been restored.

I bring this up to explain why I was disappointed by a scientific article that recently crossed my desk. Stanford Medicine cancer researchers Robbie Meisner, Dr. Aidan Tusley, and their colleagues reengineered cancer-fighting immune cells called CAR-T cells by moving an important widget from the inside of the cells to the outside. It’s a weird move, so weird it looks like they took a piece of a coffee grinder and stuck it on the outside of the lid.

But their unusual strategy succeeded. As explained in a new study published recently NatureThe team’s inside-out innovation produced cancer-killing cells that were more likely to destroy tumors and spare healthy tissue, a much-needed development in cancer immunotherapy.

“We didn’t expect this to work at all,” said Meisner, an assistant professor of pediatrics. “We assumed you had to use something that’s on the cell surface to make a surface receptor.”

CAR-T cells, called chimeric antigen receptor T-cells, are immune cells that have been engineered to fight cancer. To make them, doctors take immune cells from a patient’s body and modify them in the lab by adding a synthetic receptor to their surface that recognizes a specific marker on the outside of tumor cells. Then they put the CAR-T cells back into the patient. The engineered cells travel through the bloodstream, bind to cancer cells, and attack and destroy the cancer.

Targeting cancer while avoiding healthy tissue

CAR-T cells are used in several FDA-approved cancer treatments that target specific forms of blood cancer that arise from white blood cells known as B cells. While effective, this treatment attracts: and: cancerous B cells. The therapies get rid of the cancer, but also kill the patient’s healthy B cells.

“You can live without B cells,” Meisner said. “That’s why it worked.”

But because you can’t safely give cells that attack, say, a patient’s healthy liver or lung tissue, engineering CAR-T cells to attack solid tumors in a patient’s organs has been tricky.

“Researchers have struggled to find something that works well in solid tumors,” said life sciences researcher Tusley, noting that solid tumor markers are shared with healthy tissues. “They don’t have one clear target that’s really easy to go after.”

A possible solution is to create CAR-T cells that attack only when they bind to a specific combination of two types of cell surface markers, since the surfaces of tumor cells can carry different combinations of molecules on their surface than healthy cells. Until now, scientists have been limited in that they could barely modify the molecular widgets used to assemble CAR-T cells, limiting their options for creating cells that switch on in response to combinations of signals. To get around this problem, Meisner and Tousley set out to tweak the inner workings of CAR-T cells.

“Domino chain” of protein signals.

Cells have many moving parts, including many proteins that transmit signals from the surface of the cell to the interior. These proteins work like a chain of falling dominoes. A receptor on the surface of the cell detects the beginning of the message and then transmits it by causing small molecular changes inside the cell. These changes cascade down a long sequence of different proteins, each of which causes a molecular change for the next member of the series.

When looking for new ways to activate CAR-T cells, scientists decided to insert some of the intermediate proteins into the cell membrane, attaching them to chimeric antigen receptors that bind markers on other cells, including cancer. Does this turn on the ability of CAR-T cells to kill? Strangely enough, said Tusli, it happened.

The scientists then studied the mechanism of how the signal is activated. They figured out (through a lot of trial and error) how to make two types of engineered receptors, each latching on to a different molecule on the cancer cell, then bind to each other. Together (and only together) the complex activates a signaling cascade to initiate the cells’ cancer-killing activity.

The feat required multiple returns to discoveries in the 1990s detailing cell signaling cascades.

“Aidan spent his COVID shutdown reading old papers that defined the basic biology of these molecules,” Meisner said, noting that the early studies were done decades ago just out of curiosity, not with any eye toward future treatments. “Ultimately, we have opened up a new form of cell engineering that allows us to use the internal mechanisms of cells in unexpected ways.”

From curiosity to cancer therapy

Many of the team’s early CAR-T cells had “leakage” activation, meaning the cells were activated by only one of two molecules on the surface of cancer cells, molecules that are also found on healthy cells. In other words, the CAR-T cells’ defenses against combinations of cancer-specific surface molecules weren’t very effective, and they could accidentally attack healthy cells.

The team had to create more than 100 variants of the synthetic receptors to finally solve this problem, Tusli said.

“Getting to the point where the cells were wired and consistently killed only cancer cells with both markers took a year of engineering and creating different versions of the CAR-T cells,” he said.

Early tests in mice show that CAR-T cells can indeed target solid tumors without harming healthy tissue, although more research is needed to identify the best cell pairs for human cancer therapy.

“Anyone who has been through cancer knows that many current treatments are devastating to the entire body,” Tusley says. “We’re trying to figure out ways to attack just the cancer and leave the rest of the body unharmed.”

He’s glad he stuck with the unconventional project.

“I liked this idea. “Can we do it in a different way than it’s traditionally been done?” Tusley said. “This is an unexplored area of ​​chimeric antigen receptor design. The novelty was really fun and kept me hooked even when there were a lot of setbacks.”

Photo by Design Cells