Studies have shown that low dose decitabine (DAC) can not only significantly induce and increase the expression of tumor antigens, such as NY-ESO-1, MAGE-A3/6, but also multiply the expression of immune markers such as CD80, MHC-I molecules, and then improve the infiltration of immune cells into tumor sites, providing a more appropriate immune microenvironment for immune checkpoint inhibitors, therapeutic vaccines, adoptive cell therapy, and other immunotherapies (15–21). The gene discussed is CD80; the disease is neoplasm.