B7 Homolog 4 (B7-H4) is glycosylated member of the B7 family of immune costimulatory proteins.It is widely expressed, including in kidney, liver, lung, pancreas, placenta, prostate, spleen, testis and thymus. B7-H4 negatively regulates T-cell-mediated immune response by inhibiting T-cell activation, proliferation, cytokine production and development of cytotoxicity. When expressed on the cell surface of tumor macrophages, plays an important role, together with regulatory T-cells (Treg), in the suppression of tumor-associated antigen-specific T-cell immunity. It also involved in promoting epithelial cell transformation.

B7 Homolog 4 (B7-H4) is glycosylated member of the B7 family of immune costimulatory proteins. Mature human B7-H4 consists of a 235 amino acid (aa) extracellular domain (ECD) with two Ig-like V-type domains, a 21 aa transmembrane segment, and a 2 aa cytoplasmic tail. It is widely expressed, including in kidney, liver, lung, pancreas, placenta, prostate, spleen, testis and thymus. B7-H4 negatively regulates T-cell-mediated immune response by inhibiting T-cell activation, proliferation, cytokine production and development of cytotoxicity. When expressed on the cell surface of tumor macrophages, plays an important role, together with regulatory T-cells (Treg), in the suppression of tumor-associated antigen-specific T-cell immunity. It also involved in promoting epithelial cell transformation.

B7-H4, also known as B7x and B7S1, is a 50-80 kDa glycosylated member of the B7 family of immunomodulatory proteins.B7-H4 is up-regulated in several carcinomas in correlation with tumor progression and metastasis. A soluble form of B7-H4 is elevated in the serum of ovarian cancer, renal cell carcinoma, and rheumatoid arthritis patients, also in correlation with advanced disease status .