Fluorescent nanodiamonds engage innate immune effector cells: A potential vehicle for targeted anti-tumor immunotherapy

Fluorescent nanodiamonds (FNDs) are nontoxic, infinitely photostable, and emit fluorescence in the near infrared region. Natural killer (NK) cells and monocytes are part of the innate immune system and are crucial to the control of carcinogenesis. FND-mediated stimulation of these cells may serve as a strategy to enhance anti-tumor activity. FNDs were fabricated with a diameter of 70 ± 28 nm. Innate immune cell FND uptake, viability, surface marker expression, and cytokine production were evaluated in vitro. Evaluation of fluorescence emission from the FNDs was conducted in an animal model. In vitro results demonstrated that treatment of immune cells with FNDs resulted in significant dose-dependent FND uptake, no compromise in cell viability, and immune cell activation. FNDs were visualized in an animal model. Hence, FNDs may serve as novel agents with “track and trace” capabilities to stimulate innate immune cell anti-tumor responses, especially as FNDs are amenable to surface-conjugation with immunomodulatory molecules.

Graphical AbstractFluorescent nanodiamonds (FNDs) are a unique tool that may be employed in the treatment of cancer. High-energy electron beams are employed to introduce nitrogen vacancy centers within the diamond lattice to yield infinitely photostable near-infrared fluorescence. Upon treatment of immune cells with biocompatible FNDs, FNDs are taken up and may be visualized within the cytoplasm by flow cytometry and confocal microscopy. FNDs present an extensive, modifiable surface area and may serve as a vector for targeted delivery of immunomodulatory agents to promote immune cell effector functions in the fight against cancer.174