Preclinical Evaluation and Pilot Clinical Study of CD137 PET Radiotracer for Noninvasive Monitoring Early Responses of Immunotherapy

Given the variability in the effectiveness of immune checkpoint blocking therapy among patients and tumor types, development of noninvasive methods for longitudinal assessment of immune cell function and early tumor response is crucial for precision immunotherapy. CD137 (4-1BB), a marker of activated T cells, plays a significant role in immunotherapy. However, its potential as an imaging biomarker for activated T cells in the tumor microenvironment has not been explored. This study introduces a bicyclic peptide-based probe that targets CD137 for noninvasive PET imaging of tumor-infiltrating activated T cells.