In murine sarcoma models, tumor-derived retinoic acid (RA) blocked monocyte differentiation into dendritic cells (DCs) within the TME to promote immune suppression, whilst blocking RA production in tumor cells or inhibiting RA signaling within the TME increased the percentage of immunostimulatory antigen-presenting cells (APCs), engendered T cell-dependent anti-tumor immunity, and showed strong synergy with anti-PD-1 therapy [68]. The gene discussed is PDCD1; the disease is neoplasm.