Identifying and reprogramming softness-driven cancer stem-like cells overcomes CAR-T cell resistance in solid tumours

Solid tumors are mechanically heterogeneous, containing both stiff and soft regions. While it is known that mechanical cues influence cancer cell behavior, the specific impact of a soft extracellular matrix (ECM) on the efficacy of CAR-T cell immunotherapy remained poorly understood. This study investigates how mechanical softness drives immune evasion and whether these resistant cells can be therapeutically targeted.

The researchers utilized polyacrylamide hydrogels of varying stiffness to mimic the mechanical environment of breast tumors. They observed that cells on soft ECMs were more resistant to CAR-T cell killing. To study this, they engineered a genetic 'mechano-recorder' that uses an AND-gate system (integrating calcium-dependent NFAT translocation and doxycycline-gated transcription) to convert past mechanical experience into a stable fluorescent mark. They later rewired this system into a 'mechano-reprogrammer' by replacing the fluorescent reporter with the CD19 antigen, effectively forcing softness-responsive, stem-like cells to express a targetable marker for CD19-CAR-T cells.

Cells cultured on soft ECMs exhibited elevated extracellular ATP and sustained calcium signaling, which correlated with a transition to a cancer stem-like cell (CSLC) state. These 'mechano-stemness' cells were inherently resistant to standard CAR-T therapies. By using the mechano-reprogrammer, the researchers successfully converted this mechanical resistance into a therapeutic vulnerability. In both in vitro and in vivo models, the rewired cells expressed CD19 in response to soft environments, allowing CD19-CAR-T cells to effectively eliminate the previously resistant CSLC population and improve overall tumor control.

This study provides a novel strategy to overcome the physical barriers to immunotherapy in solid tumors. By identifying and reprogramming the specific subpopulation of cells that evade treatment due to their mechanical niche, this approach offers a way to target the most aggressive, stem-like cells that often drive tumor recurrence. This synthetic biology approach could be adapted to improve the efficacy of CAR-T therapies across various solid tumor types.