Anti-CD28 molecule antibodies are directed against the protein encoded by the gene CD28 in humans. The gene may also be known as Tp44, T-cell-specific surface glycoprotein CD28, and CD28 antigen. Structurally, the protein is reported to be 25.1 kilodaltons in mass. Based on gene name, canine, porcine, monkey, mouse and rat orthologs may also be found.