A team led by researchers from the Penn State College of Medicine has re-engineered immune cells so that they can penetrate and kill solid tumors grown in the lab. They created a light-activated switch that controls protein function associated with cell structure and shape and incorporated it into natural killer cells, a type of immune cell that fights infections and tumors. When these cells are exposed to blue light, they morph and can then migrate into tumor spheroids — 3D tumors grown in the lab from either mouse or human cell lines — and kill tumor cells. This novel approach could improve cell-based immunotherapies, the researchers said.

The findings will publish this week on October 25 in the Proceedings of the National Academy of Sciences. The researchers also filed a provisional application to patent the technology described in the paper.

“This technology is totally out of the box. It’s akin to CAR T-cell therapy, but here, the guiding principle is the ability of cells to infiltrate the tumor,” said senior author Nikolay Dokholyan, G. Thomas Passananti Professor at the Penn State College of Medicine and professor of biochemistry and molecular biology. “I don’t know of another approach that is anything close to this.”

CAR T-cell therapy was first approved by the Food and Drug Administration in 2017, and since then, it has demonstrated encouraging results for some cancers, particularly blood cancers. T-cells, a white blood cell in the immune system, are removed from a patient and re-engineered to produce a protein on their surface that binds to a specific target protein on cancer cells. When the CAR T-cells are infused back into the patient, they kill cancer cells with that target protein.

However, CAR T-cell therapy is less successful for treating solid tumors, which make up approximately 90% of adult human cancers and 40% of childhood cancers, Dokholyan said. Immune cells can’t infiltrate the dense network of proteins and other cells surrounding the tumor, and the hostile environment inhibits their tumor-fighting abilities. Plus, tremendous diversity among solid tumors makes it difficult to home in on a specific target protein to attack. To improve cell-based immunotherapies for solid tumors, Dokholyan said immune cells need to be able to bypass the solid tumor’s defenses.

Using computation modeling, the team designed and tested a light-controlled version of septin-7, an internal protein essential for maintaining a cell’s cytoskeleton — the structure that maintains cellular shape and organization. They inserted a light-sensitive domain into septin-7 to create what Dokholyan called “an allosteric regulator.” The light-sensitive portion of the protein is located far from the protein’s active site and doesn’t interfere with the structure and function of the protein until it’s triggered. The domain is activated by blue light, which switches the protein function on and off.

They then re-engineered human natural killer immune cells with the light-sensitive septin-7 protein. In the presence of blue light, the researchers observed that septin-7’s normal function was disrupted. The cells also exhibited a more elongated, spindle-like shape and greater protrusions extending outward, which help the cell interact with their environment and move from one location to another.

“Even though natural killer cells are small, around 10 micrometers, upon activation of this protein with blue light, the immune cells changed shape and can squeeze into tiny holes around three micrometers in size. That’s enough to infiltrate tumor spheroids and kill them from the inside,” Dokholyan said.

The researchers tested the re-engineered natural killer immune cells with two types of solid tumor spheroids, one created using human breast cancer cells and the other with human cervical cancer cells. Within seven days, they killed the tumor cells. In contrast, natural killer cells that hadn’t been re-engineered attacked the tumor spheroid from the outside but were unable to breach the tumor. Eventually, the tumor continued to grow. They also re-engineered immune cells from mice and tested them with tumor spheroids made from mouse melanoma cells.

While the results were robust, Dokholyan emphasized that this work is still in its preliminary stages and more research is needed to evaluate this technology for potential therapeutic use. He said he also hopes to explore other activation cues that could modulate protein function and cellular behavior.

Other Penn State authors on the paper include Todd Schell, professor of microbiology and immunology at the Penn State College of Medicine; Brianna Hnath, doctoral candidate in biomedical engineering; Congzhou Mike Sha, joint degree student in the MD/PhD Medical Scientist Training Program; and Lynne Beidler, research technologist. First author Jiaxing Chen was a doctoral candidate when the research was conducted and is currently a postdoctoral researcher at the University of Pennsylvania.

Funding from the National Institutes of Health and the Passan Foundation supported this work.