Cold to Hot: Binary Cooperative Microneedle Array-Amplified Photoimmunotherapy for Eliciting Antitumor Immunity and the Abscopal Effect

In this study, an ingenious core–shell structure microneedle (CSMN) array was designed to synergistically boost robust immune response by the intralesional codelivery of photosensitizer and indoleamine 2,3-dioxygenase (IDO) blockade. Photosensitizer indocyanine green was encapsulated into chitosan nanoparticles (ICG-NPs), followed by concentrating on the tip shell of microneedles. 1-Methyl-tryptophan was loaded into the cross-linked poly(vinyl pyrrolidone) and poly(vinyl alcohol) gel as the microneedle core. Through the direct deposition of the ICG-NP-loaded tips into the tumor site with uniform spatial distribution, the CSMNs effectively converted the near-infrared laser into heat to ablate primary tumors, generated tumor-associated antigens and damage-associated molecular patterns, and promoted the maturation of dendritic cells and the secretion of immunostimulatory cytokines. The IDO blockade further reversed the IDO-mediated immunosuppression, ultimately arousing an effective systematic immune response. The in vivo results showed that 80% of the melanoma tumor was eradicated, followed by a relapse-free survival in more than 120 days. Of note, this synergistic strategy significantly inhibited lung metastasis and controlled the development of already metastasized tumors. Our work provides a new, generalizable framework for using the microneedle-based photothermal therapy to initiate antitumor immunity and sensitize tumors to IDO blockade.