Self-Assembled PD-L1 Downregulator to Boost Photodynamic Activated Tumor Immunotherapy Through CDK5 Inhibition

The immunosuppressive characteristics and acquired immune resistance can restrain the therapy-initiated anti-tumor immunity. In this work, an antibody free programmed death receptor ligand 1 (PD-L1) downregulator (designated as CeSe) is fabricated to boost photodynamic activated immunotherapy through cyclin-dependent kinase 5 (CDK5) inhibition. Among which, FDA approved photosensitizer of chlorin e6 (Ce6) and preclinical available CDK5 inhibitor of seliciclib (Se) are utilized to prepare the nanomedicine of CeSe through self-assembly technique without drug excipient. Nanoscale CeSe exhibits an increased stability and drug delivery efficiency, contributing to intracellular production of reactive oxygen species (ROS) for robust photodynamic therapy (PDT). The PDT of CeSe can not only suppress the primary tumor growth, but also induce the immunogenic cell death (ICD) to release tumor associated antigens. More importantly, the CDK5 inhibition by CeSe can downregulate PD-L1 to re-activate the systemic anti-tumor immunity by decreasing the tumor immune escape and therapy-induced acquired immune resistance. This work provides an antibody free strategy to activate systemic immune response for metastatic tumor treatment, which may accelerate the development of translational nanomedicine with sophisticated mechanism.