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 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.