B7-H3 (CD276) is a type I transmembrane protein with high sequence and structural homology to other B7 family molecules. Expression of B7-H3 on immune cells is believed to serve a costimulatory role, but the function of B7-H3 on tumor cells is less clear. While some reports indicate that B7-H3 expression on tumor cell lines increases their immunogenicity and facilitates tumor rejection, in situ B7-H3 expression in many human tumors has been associated with poor outcome. In the setting of human brain tumors, B7-H3 expression levels in gliomas was found to be correlated with tumor grade and was associated with increased immunoreactivity of diffuse intrinsic pontine gliomas.