Direct and abscopal anti-tumor responses elicited by peripheral nerve schwannoma irradiation synergize with anti-PD1 treatment in vestibular schwannoma models

NF2-related schwannomatosis (NF2-SWN) is a progressive and disabling disease requiring effective treatments. The hallmark of NF2-SWN is bilateral vestibular schwannomas (VSs), which progressively enlarge, leading to permanent sensorineural hearing loss and severely impacting patients quality of life. Currently, there are no FDA-approved drugs for VS or the associated hearing loss. Immune checkpoint inhibitors (ICIs) have revolutionized cancer treatment, but have not yet been systematically investigated in non-malignant tumors such as VS. In our studies, we demonstrated that combining anti-PD1 (PD1) treatment with radiation therapy (RT) provides three significant therapeutic benefits: i) Enhanced PD1 efficacy and immune memory: RT induces immunogenic cell death and activates the STING pathway, enhancing PD1 efficacy and generating long-term immune memory, ii) Reduced RT dose and associated tissue injury: The combination strategy reduces the required RT dose necessary for effective tumor control, potentially minimizing RT injury to surrounding normal tissues, and iii) Elicited abscopal effects on cerebellopontine angle (CPA) schwannomas: RT to peripheral nerve tumor induces a systemic abscopal effect, which synergizes with PD-1 to effectively control intracranial schwannomas without direct irradiation, sparing the cochlea from radiation exposure and avoiding auditory radiation injury. Together, our findings provide a compelling rationale for deploying ICIs in combination with radiotherapy as a novel treatment approach for patients with VS and NF2-SWN.