CD28 homolog (CD28H), also called transmembrane and immunoglobulin domain containing 2 (TMIGD2) and IGPR-1,is encoded by the TMIGD2 gene. CD28H is constitutively expressed on naive T and NK cells. After interaction of CD28 homolog with B7 homologue,the peripheral effector and memory T cells can be activated and proliferated by Akt-dependent signalling cascade. Plays a role in cell-cell interaction, cell migration, and angiogenesis. Through interaction with HHLA2, costimulates T-cells in the context of TCR-mediated activation. Enhances T-cell proliferation and cytokine production via an AKT-dependent signaling cascade.