Biomimetic Anti‐PD‐1 Peptide‐Loaded 2D FePSe(3) Nanosheets for Efficient Photothermal and Enhanced Immune Therapy with Multimodal MR/PA/Thermal Imaging

Metal phosphorous trichalcogenides (MPX(3)) are novel 2D nanomaterials that have recently been exploited as efficient photothermal–chemodynamic agents for cancer therapy. As a representative MPX(3), FePSe(3) has the potential to be developed as magnetic resonance imaging (MRI) and photoacoustic imaging (PAI) agents due to the composition of Fe and the previously revealed PA signal. Here, a FePSe(3)‐based theranostic agent, FePSe(3)@APP@CCM, loaded with anti‐PD‐1 peptide (APP) as the inner component and CT26 cancer cell membrane (CCM) as the outer shell is reported, which acts as a multifunctional agent for MR and PA imaging and photothermal and immunotherapy against cancer. FePSe(3)@APP@CCM induces highly efficient tumor ablation and suppresses tumor growth by photothermal therapy under near‐infrared laser excitation, which further activates immune responses. Moreover, APP blocks the PD‐1/PD‐L1 pathway to activate cytotoxic T cells, causing strong anticancer immunity. The combined therapy significantly prolongs the lifespan of experimental mice. The multimodal imaging and synergistic therapeutic effects of PTT and its triggered immune responses and APP‐related immunotherapy are clearly demonstrated by in vitro and in vivo experiments. This work demonstrates the potential of MPX(3)‐based biomaterials as novel theranostic agents.