HHLA2 and neoplasm: Thus, to elucidate the molecular mechanism of immune regulation by HHLA2, we should study the HHLA2/FAP receptors in the tumor region and stromal tissues through colocalization experiments and the use of multiple immunostaining analyses using a panel of proteins, such as CAFs and immune-regulated proteins, including HHLA2, TMIGD2, and KIR3DL3, in the TME.