Pembrolizumab is a type of medication known as an immune checkpoint inhibitor, which is designed to block certain receptors that can interfere with the body's natural immune response. Specifically, pembrolizumab is primarily engineered to inhibit the programmed cell death protein 1 (PD-1) receptor [1].

PD-1 is a protein that is expressed on the surface of T-cells, which are a type of white blood cell that plays a crucial role in the immune system. When PD-1 binds to its ligands, PD-L1 or PD-L2, it can suppress the immune response, allowing cancer cells to evade detection and destruction by the immune system [2].

Pembrolizumab works by blocking the PD-1 receptor, preventing it from binding to its ligands and thereby enhancing the immune system's ability to detect and destroy cancer cells [3]. Pembrolizumab is approved for the treatment of several types of cancer, including melanoma, non-small cell lung cancer, and head and neck squamous cell carcinoma [4].

References:
[1] DrugPatentWatch.com. (n.d.). Pembrolizumab. Retrieved from <https://www.drugpatentwatch.com/drugs/pembrolizumab>.
[2] National Cancer Institute. (2021). Programmed Cell Death Protein 1 (PD-1). Retrieved from <https://www.cancer.gov/publications/dictionaries/cancer-terms/def/programmed-cell-death-protein-1-pd-1>.
[3] National Cancer Institute. (2021). PD-1/PD-L1 Blockade. Retrieved from <https://www.cancer.gov/about-cancer/treatment/types/immunotherapy/pd-1-pd-l1-blockade-fact-sheet>.
[4] U.S. Food and Drug Administration. (2021). FDA approves Merck’s KEYTRUDA (pembrolizumab) as first-line treatment for patients with advanced non-small cell lung cancer (NSCLC) expressing PD-L1 (TPS ≥1%) with no EGFR or ALK genomic tumor aberrations. Retrieved from <https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-mercks-keytruda-pembrolizumab-first-line-treatment-patients-advanced-non-small-cell-lung-cancer-nsclc>.