Engineered fluorescent carbon dots as promising immune adjuvants to efficiently enhance cancer immunotherapy

Currently, cancer immunotherapy appears to be an effective strategy for cancer therapy, but the state of unresponsiveness to tumor antigenic stimulation in immune systems is one of the stumbling blocks to the clinical applications of cancer immunotherapy. Nanomaterials have been increasingly applied in cancer immunotherapy by virtue of their irreplaceable superiority to carry antigens to specific sites and stimulate immune responses. Among the many excellent fluorescent nanomaterials, carbon dots (CDs) stand out from the others as a result of their extraordinary performance. Therefore, photoluminescent CDs were used as vaccine adjuvants to be combined with tumor protein antigen model ovalbumin (OVA), with red, yellow and green colored luminescence under different excitation wavelengths. These CDs could positively contribute to antigen uptake and efficiently accelerate the maturation of dendritic cells (DCs). The obtained nanocomposite of CDs and OVA (CDs-OVA) could efficiently enhance the expression of costimulatory molecules CD80 and CD86, and the production of tumor necrosis factor α (TNF-α) from DCs. In addition, CDs-OVA could also strongly stimulate splenocyte proliferation and the production of interferon gamma (IFN-γ). In addition, this CDs-OVA vaccine could effectively be endocytosed and processed by immune cells in vivo, then it could induce strong antigen-specific cellular immune responses to inhibit the growth of B16-OVA melanoma cancer in C57BL/6 mice. This work represents not only the first report of CDs as vaccine adjuvants for tumor inhibition, but also opens up many possibilities for more biomedical applications of CDs in cancer immunotherapy and in other potential clinical applications.