Annotation of CD8 T-cell function via ICAM-1 imaging identifies FAK inhibition as an adjuvant to augment the antitumor immunity of radiotherapy.

Radiotherapy (RT) may trigger systemic antitumor immunity, manifesting as regression of non-irradiated lesions (abscopal effect). Intracellular adhesion molecule-1 (ICAM-1) is a key molecule involved in the abscopal effect of RT. However, the specific function of ICAM-1 in CD8 T cells during antitumor immune responses remains unclear. Herein, we investigated whether noninvasive imaging of ICAM-1 can be used to annotate CD8 T-cell function, thereby better selecting combinational therapy to enhance the antitumor immunity induced by RT. Using knockout mouse models, we investigated the role of ICAM-1 expressed on CD8 T cells in the antitumor immunity of RT and conducted drug screening guided by ICAM-1-targeted noninvasive imaging. The systemic antitumor effect of RT relies on the expression of ICAM-1 on CD8 T cells. ICAM-1 expression is essential for CD8 T-cell activation, proliferation, and effector function. Noninvasive annotation of the proliferation and effector function of CD8 T cells by ICAM-1-targeted imaging identified VS-6063, a focal adhesion kinase inhibitor, as a new adjuvant to augment systemic antitumor immunity of RT in an immunologically "cold" tumor model. Mechanistically, VS-6063 overcomes the physical barriers in tumors and promotes the migration and infiltration of CD8 T cells primed by RT into distant tumors. Our findings highlight that molecular imaging of ICAM-1 levels provides a dynamic readout of the proliferation and effector function of tumor-infiltrating CD8 T cells, which facilitates the high-throughput exploitation of new combinational drugs to maximize the systemic antitumor effect of RT.