Photoacoustic Nanotagging for In Vivo Tracking and Optimization of Macrophage Immunotherapy in Solid Tumors.

Macrophage-based immunotherapy holds promise for solid tumors, yet critical limitations remain such as narrow insight into their in vivo localization and persistence of therapeutic macrophages for assessing their treatment efficacy. We report an immunostimulatory macrophage nanotagging strategy for image-guided optimization of macrophage-based solid tumor immunotherapy. Nanotags employ the branched gold nanostructure for efficient absorption in the near-infrared range for photoacoustic contrast. Subsequent conjugation with interferon gamma (IFNγ) confers macrophage polarization capability into an antitumor phenotype that is superior to free IFNγ without sacrificing the viability. Following systemic administration, nanotagged macrophages are non-invasively monitored using ultrasound-guided photoacoustic (US/PA) imaging enabling localization of the infused macrophages and their persistence in the solid tumor mass in real-time. Based on the observed limited persistence of systemically administered macrophages, lipopolysaccharide is introduced as a local supportive agent. The combination approach enhances macrophage retention and therapeutic efficacy. Rechallenged mice remain tumor-free, indicating adaptive immune memory. Together, this approach offers a platform for longitudinal monitoring of therapeutic macrophages and imaging-guided optimization of macrophage-based solid tumor immunotherapy.