Besides, a recent study has reported that the inhibition of IDO1 activity not only decreased Treg cell populations and restored cytotoxic T lymphocyte function but also synergistically alleviated tumor microenvironment immune suppression combined with anti-PD-1 antibody treatment, providing a new strategy for the clinical treatment of breast cancer with bone metastasis [239]. The gene discussed is IDO1; the disease is breast carcinoma.