A radiolabeled dendrimer non-invasively identifies and tracks innate immune cell activation in a mouse model of experimental autoimmune encephalomyelitis.

Multiple sclerosis (MS) is a chronic neurodegenerative disease driven by infiltration of activated innate immune cells into the central nervous system (CNS). Current imaging approaches for diagnosing and monitoring disease progression rely on structural lesions and cannot directly assess innate immune activity. Here, we describe a dendrimer positron emission tomography (PET) tracer, 18F-flurimedrimer (18F-FMD), for non-invasive, longitudinal tracking of activated myeloid cells. In an experimental autoimmune encephalomyelitis (EAE) murine model, 18F-FMD specifically detects myeloid activation at presymptomatic and symptomatic stages, with PET signal correlating with disease severity. Moreover, 18F-FMD sensitively captures therapeutic response to fingolimod (FTY720) and a CSF1R dendranib (H74DS3M8), both of which suppress immune cell activation and attenuate disease severity. These findings highlight the potential of 18F-FMD PET for specific, real-time monitoring of innate immune responses, and the applicability of the dendrimer in clinical settings for monitoring therapeutic efficacy, advancing the development of personalized, myeloid-targeted strategies for MS.