Genetic system turns tumor softness into CAR T target

July 9, 2025 — A team from the University of Southern California has created a genetic system that forces soft, slippery cancer stem-like cells to reveal themselves to the immune system. In a study published in Nature Biomedical Engineering, the researchers showed that by converting a cell’s physical softness into a molecular “kill me” signal, engineered CAR T cells can destroy a population that normally evades treatment and drives relapse.

The work tackles a core weakness of CAR T-cell therapy. While this approach has transformed certain blood cancers, solid tumors remain stubborn. Their cells are diverse, and many adopt pliable, stem-like traits that make them resistant to immune attack. The USC team identified that this physical softness — the ability of a cell to yield rather than resist — is not just a passive feature but an active driver of treatment resistance and metastasis.

“Soft cancer cells tend to acquire stem-cell-like properties more readily,” said Peter Yingxiao Wang, chair of the Alfred Mann Department of Biomedical Engineering at USC Viterbi. “They can self-renew and give rise to different tumor cell types, making them a major source of recurrence.” The challenge, the team explained, is that these same cells are difficult for T cells to latch onto. Lead researcher Jenny Yunjia Qu compared the difficulty to trying to stab a piece of gelatin: the surface deforms instead of allowing firm contact.

To find these evasive cells, the team built a genetic “black box” called the Mechano-Recorder. It monitors calcium signaling, which spikes when a cancer cell experiences a soft environment. Normally this signal fades within minutes. The recorder converts the transient spike into a stable fluorescent marker — a permanent record of the cell’s mechanical history. This allowed the researchers to pick out cells that had been exposed to soft conditions hours or even days earlier.

“We can now take a molecular snapshot of a cell that has gone through a soft environment, even after the environment has changed,” said Longwei Liu, assistant professor of ophthalmology and biomedical engineering at USC and a co-author of the study.

The tool goes beyond diagnostics. The researchers then rewired the recorder to swap the fluorescent reporter for CD19, a protein already used as a target in approved CAR T-cell therapies for B-cell cancers. When a soft, resistant cancer cell triggers the calcium signal, the circuit instructs the cell to display CD19 on its surface. CAR T cells designed to recognize CD19 then find and destroy the cell — even though it is not a blood cancer cell.

The strategy was tested in multiple cancer types, including breast cancer cell lines, patient-derived samples, and mouse models of breast, glioblastoma, pancreatic, and prostate tumors. Treated tumors showed a significant increase in T-cell infiltration and a reduction in the stem-like population that normally resists therapy. “We essentially turned a mechanical property into an actionable signal for the immune system,” said Jenny Yunjia Qu.

Outside experts noted the novelty of linking physical tumor characteristics to synthetic biology. “This is a clever way to exploit the tumor microenvironment itself as a trigger,” said Dr. Elaine R. Nelson, a cancer immunologist at the University of Texas MD Anderson Cancer Center who was not involved in the study. “Most attempts to overcome CAR-T resistance focus on molecular targets. This approach uses a biophysical cue, which may be more universal across tumor types.”

The team acknowledges the findings are preclinical and require further validation before clinical trials. Still, the modular design of the Mechano-Recorder means it could be adapted to other signals — such as hypoxia, acidity, or stiffness — and paired with different therapeutic outputs. “We envision a platform where the tumor’s own state dictates the immune response,” Wang said. “That would make immunotherapy far more flexible and precise.”

Solid tumors account for about 90% of cancer-related deaths globally, and nearly all current CAR T-cell trials for solid tumors have faced obstacles from cellular heterogeneity and physical barriers. The USC approach offers a potential workaround: instead of altering the tumor’s physical environment, it tricks the tumor into revealing itself. By programming cells to flag their own mechanical history, the system creates a new kind of vulnerability — one that the tumor cannot easily out-evolve.

The next steps include optimizing the circuit for safety and durability, testing in larger animal models, and exploring whether the same system can be triggered by other mechanical cues associated with aggressive cancer. The researchers have filed provisional patents on the technology.