Emerging Biomaterials Blocking PD-1/PD-L1 Pathway for Cancer Therapy

Conventional monoclonal antibodies targeting either PD-1 or PD-L1, despite the clinical significance as immune checkpoint inhibitors (ICIs), exhibit limited effect in the majority of cancer patients. The persistent challenges in ICIs have prompted extensive research into next-generation biomaterial-based immunotherapeutic strategies to inhibit PD-1/PD-L1 pathway. Herein, this review started with the retrospect of recent insights into the dynamic regulation of PD-L1 expression patterns and its multifaceted functional mechanisms within the tumor microenvironment. Subsequently, the emerging alternatives to PD-1/PD-L1 inhibitors are summarized by their categories, including peptides, nucleic acids, small molecule inhibitors, and natural compounds, which could function by reducing PD-L1 expression, degrading PD-L1, or inhibiting PD-1/PD-L1 interactions. Furthermore, recent efforts on combination therapy based on these biomaterials are discussed, especially those with chemotherapy, radiotherapy, phototherapy, and sonodynamic therapy. This paradigm shift in PD-1/PD-L1 immune checkpoint blockade therapy underscores the prospects of emerging biomaterials in orchestrating anticancer immune responses, which would provide insights for developing next-generation immunotherapeutic strategies for clinical oncology to improve patient outcomes.