The Saban Research Institute of Children's Hospital 1 article published in JoVE Cancer Research Conditional Knockdown of Gene Expression in Cancer Cell Lines to Study the Recruitment of Monocytes/Macrophages to the Tumor Microenvironment Marta H. Kubala1,2, Yves A. DeClerck1,2,3 1Division of Hematology, Oncology and Blood and Marrow Transplantation, Department of Pediatrics, University of Southern California, 2 This protocol serves as a scheme for setting up a functional Tet-ON system in cancer cell lines and its subsequent use, in particular for studying the role of tumor cell-derived proteins in recruitment of monocytes/macrophages to the tumor microenvironment.