A Critical Role for Fas-Mediated Off-Target Tumor Killing in T-cell Immunotherapy

Area of Science:

• Immunology
• Oncology
• Molecular Biology

Background:

• T cell-based therapies show promise but face tumor resistance, including antigen escape.
• Understanding T cell-mediated tumor elimination is crucial for overcoming resistance mechanisms.

Purpose of the Study:

• To investigate the role of Fas-FasL in T cell-mediated tumor killing and identify mechanisms to overcome tumor heterogeneity and immune escape.

Main Methods:

• Utilized CRISPR/Cas9 screening to identify key factors in T cell killing.
• Investigated Fas-FasL mediated on-target and bystander killing in various T cell models (CAR-T, bispecific antibodies).
• Analyzed tumoral FAS expression as a predictor of patient survival in a clinical trial (NCT02348216).

Main Results:

• Identified a critical role for Fas-FasL in antigen-specific T cell killing.
• Demonstrated Fas-FasL-mediated bystander killing of antigen-negative tumor cells.
• Showed enhanced clearance of antigen-heterogeneous tumors in vivo through localized bystander cytotoxicity.
• Confirmed Fas-mediated killing in CAR-T and bispecific antibody models, augmented by inhibiting Fas signaling regulators.
• Found tumoral FAS expression predicted survival in CAR-T treated patients.

Conclusions:

• Fas-dependent bystander killing of antigen-negative tumors by T cells is reported in vivo for the first time.
• This mechanism may contribute to high response rates in immunotherapies despite tumor heterogeneity.
• Targeting the Fas pathway could enhance T cell-mediated killing and prevent cancer relapse.