PD-1 or PDCD1 (Programmed cell death 1), also known as CD279, is a cell surface receptor expressed on T cells and pro-B cells, which was firstly isolated from a murine T cell hybridoma and a hematopoietic progenitor cell line in 1992. It is an inducible immune modulatory receptor and belongs to a member of the CD28 receptor family. The expression of PD-1 is significantly involved in programmed cell death of lymphocytes. PD-1 has two ligands that are PD-L1 (B7-H1 or CD274) and PD-L2 (B7-DC or CD273). Upon their interactions, PD-1 plays an active role in negative regulation of T cell responses to antigen stimulation and maintaining peripheral tolerance. Thus, it is regarded as an important immune checkpoint for therapeutic antibodies against cancers.
VEGFA (Vascular endothelial growth factor A), also known as VPF, VEGF or MVCD1, is the most potent growth factor for endothelial cells and belongs to the PDGF/VEGF growth factor family. In humans, it is encoded by the VEGFA gene localizing at the chromosome 6p21.1. VEGF-A, as well as VEGF-C, and -D are found in the lung. During the embryonic and pseudoglandular stages, it is expressed in epithelial and mesenchymal compartments, then becoming more restricted to the epithelium as development process. VEGFA encodes a heparin-binding protein existing as a disulfide-linked homodimer. This growth factor is involved in inducing proliferation and migration of vascular endothelial cells. It is essential for physiological and pathological angiogenesis and considered as a powerful vascular permeability-enhancing agent.