Medicinal Plants in the Regulation of PD-L1/PD-1 Immune Checkpoint of Various Human Cancer Cells: A Narrative Review

Background: Immunotherapy has garnered attention in cancer treatment following the success of recent trials in solid tumors adopting PD-L1/PD-1 checkpoint inhibition. PD-1 is a T-cell checkpoint molecule that limits autoimmune and auto-inflammatory reactivity in the normal host by suppressing adaptive immune responses. Although PD-L1 expression in the tumor is generally considered a poor prognostic marker, it has been used to screen patients for cancer therapy since it is associated with a positive response to PD-L1/PD-1 blocking antibodies. Outline: This review focuses on the complex interconnections between cancer-reactive and selfreactive immune cells, as well as the potential contribution of a wide range of leading immunomodulatory chemical products from plant-based origins as cancer therapeutics or to foreseeably ameliorate autoimmune diseases. The natural compounds derived from plants should be used as a PD-L1/PD-1 checkpoint modulator to combat cancer cells and other chronic diseases. Conclusion: The significance of herbal plant extracts in the regulation of the PD-L1/PD-1 checkpoint is presented in this review together with the expression of PD-L1 and PD-1 in cancer cells and diseases in human bodies.