HHLA2 and cancer: According to the report, HHLA2 has a costimulatory receptor TMIGD2 (transmembrane and immunoglobulin domain containing 2) and a coinhibitory receptor KIR3DL3 (killer cell Ig-like receptor, three Ig domains, and long cytoplasmic tail), which endows it with both immunostimulant and immunosuppression functions in cancer development [41].