Chromium Nanoparticles Improve Macrophage and T Cell Infiltration for Cancer Immunotherapy

Immune checkpoint blockade has been regarded as a highly promising cancer immunotherapy approach. However, inefficient immune cell infiltration and the immunosuppressive tumor microenvironment (TME) remain significant causes of low clinical response rates. Here, we identified that trivalent chromium irons (Cr3+) could enhance tumor infiltration of immune cells including M1-type tumor-associated macrophages and CD8+ T cells. Mechanistically, this effect is dependent on the expression of macrophage inflammatory protein-1α (MIP-1α) and the PI3K/Akt/mTOR pathway. Moreover, the Cr-based nanoparticles (Cr NPs) exhibited superior photothermal properties under near-infrared laser irradiation, showing great potential in transforming "cold" tumors into "hot" ones. In combination with the PD-1/PD-L1 pathway inhibitor, we demonstrated that the Cr NPs significantly improved anticancer efficacy in mouse models of hepatoma and melanoma by increasing antitumor immune cell infiltration and relieving immunosuppressive TME. Overall, the Cr NPs offer a new dual-functional platform for local and systemic cancer treatments, paving the way toward cancer photometalloimmunotherapy.