TAPBPL (mouse):Fc (human) (rec.)

T cells play critical roles in the adaptive immune system, protecting the human body against cancer, bacterial, viral, fungal, and parasitic infections. T cell immune response is tightly controlled by immune checkpoint proteins that negatively or positively regulate T cell response. Among the immune checkpoint proteins, the B7 family plays a key role in controlling immune responses and belongs to the immunoglobulin (Ig) superfamily. A number of B7 family ligands have been identified, such as B7-1 (CD80), B7-2 (CD86), PD-L1 (B7-H1), PD-L2 (B7-DC), B7-H2 [inducible T cell co-stimulator ligand (ICOS)], B7-H3, B7-H4 (B7x, B7S1), B7-H5 (VISTA) and B7- H6.

Because of the potential clinical applications of immune checkpoint proteins, there has been intense interest in identifying additional T-cell regulators. Recently, new antigen processing (TAP) binding protein-like (TAPBPL)/TAP binding protein-related (TAPBPR) molecule has been shown to share significant sequence similarity with some known B7 family members. TAPBPL protein is expressed on the surface of T cells, on antigen-presenting cells (APCs) including resting B cells, monocytes, macrophages, and DCs, as well as on some cancer cells including leukemia cells. TAPBPL behaves like other immune checkpoint proteins such as B7-H5 / VISTA or PD-L1 with a soluble recombinant version TAPBPL-Fc fusion protein that inhibits the proliferation and activation of CD4 and CD8 T cells in vitro and ameliorates autoimmune disease EAE in vivo. In contrast, treatment with anti-TAPBPL blocking antibody enhances antitumor immunity and inhibits tumor growth in vivo. Therefore, TAPBPL contains typical features of B7 family members, suggesting that it is a B7 family member or a B7 family-related molecule.