Scientists develop genetic tool to make soft tumors vulnerable to CAR-T cell therapy

Researchers at USC have developed innovative genetic tools, including the Mechano-Recorder and SHIFTERS, to overcome the physical and biological barriers that protect solid tumors from CAR-T cell therapy. By exploiting tumor hypoxia, focused ultrasound, and mechanical softness, these systems force evasive, soft cancer stem-like cells to express the CD19 antigen. This genetic rewiring successfully flags previously stealthy solid tumors for targeted destruction by engineered T-cells in laboratory and animal models.

Mechano-Recorder genetic tool development

• ▪The Mechano-Recorder converts transient calcium signaling, which is elevated in softer cancer cells, into a stable, long-lasting fluorescent signal to barcode the cells based on their mechanical experience.
• ▪Researchers at the USC Viterbi School of Engineering and the Keck School of Medicine of USC developed a genetic tool called the Mechano-Recorder to identify and track soft cancer cells.
• ▪The Mechano-Recorder was successfully tested in laboratory models of breast cancer, glioblastoma, pancreatic cancer, and prostate cancer.

Soft tumor microenvironment resistance

• ▪CAR-T cells struggle to physically grab and penetrate softer, gelatinous cancer cells compared to stiffer cancer cells, reducing their therapeutic efficacy.
• ▪The physically soft microenvironment of solid tumors causes cancer cells to become resistant to being killed by CAR-T cell therapy and other treatments.

CD19 marker engineering

• ▪USC researchers genetically reprogrammed the Mechano-Recorder to replace its fluorescent reporter with CD19, a clinically validated antigen, to broadcast a targetable marker on soft cancer cells.
• ▪In laboratory models of breast cancer, expressing the CD19 antigen on soft cancer cells successfully enhanced T-cell infiltration and overcame CAR-T cell resistance.

SHIFTERS ultrasound-activated therapy

• ▪In animal models carrying human brain and liver tumors, SHIFTERS-activated tumors shrank dramatically following CAR-T cell attack, while untreated tumors continued to grow.
• ▪USC Viterbi School of Engineering researchers developed SHIFTERS, an experimental system that uses focused ultrasound and tumor hypoxia to prompt solid tumor cells to temporarily display the CD19 marker.
• ▪The SHIFTERS system requires two keys for activation: the biological key of low oxygen (hypoxia) within the tumor and the physical key of focused ultrasound applied by a physician.
• ▪USC researchers discovered that having only 10% to 25% of tumor cells display the CD19 marker was sufficient to activate CAR-T cells to destroy neighboring non-engineered cancer cells.

Cancer stem-like cell evasion

• ▪Soft tumor environments promote the development of cancer stem-like cells, which possess self-renewal abilities that drive tumor growth, drug resistance, and metastasis.
• ▪Cancer stem-like cells utilize their mechanical softness to evade immune detection, acting as key drivers of cancer recurrence and treatment resistance.

CAR-T solid tumor challenges

• ▪Solid tumors are highly difficult for CAR-T cells to target because they arise from normal tissue and often lack a distinct, naturally occurring surface marker that distinguishes them from healthy cells.
• ▪While CAR-T cell therapy has produced remarkable results against blood cancers, its success has largely stopped at solid tumors of the brain, liver, lung, breast, and pancreas.