Receptor tyrosine kinases, such as TYRO3 (a type of protein tyrosine kinase), AXL (a type of receptor tyrosine kinase), and C-Mer proto-oncogene tyrosine kinase (MERTK) and their ligands, Gas 6 and Protein S, can reverse the tumorigenic properties of MDSCs, increase the numbers of tumor infiltrating CD8+ T cells, and strengthen anti-PD-1 immune checkpoint therapy. The gene discussed is PDCD1; the disease is neoplasm.