Which therapeutic approach uses the body’s own immune system to fight cancer?

The correct choice highlights the use of monoclonal antibodies as a therapeutic approach that harnesses the body's immune system to combat cancer. Monoclonal antibodies are engineered immune proteins that can specifically target cancer cells. By binding to antigens present on the surface of these cells, they can block growth signals, recruit immune cells to attack the cancer, or deliver cytotoxic agents directly to the tumor.

This method takes advantage of the immune system's natural ability to recognize and destroy foreign invaders, including cancer cells, thus enhancing the body’s ability to fight the disease. Monoclonal antibodies have become a cornerstone in cancer treatment, demonstrating effectiveness in a wide array of cancers.

The other approaches listed do not primarily function by utilizing the immune system in the same specific and targeted way as monoclonal antibodies. Attenuated leukocytes are not a standard method for cancer treatment, and while irradiated erythrocytes and enhanced thrombocytes may play roles in different therapeutic or supportive settings, they do not directly engage the immune system in the fight against cancer like monoclonal antibodies do.