The functions of NK cells in killing virus-infected cells and tumor cells need to be completed step by step: First, NK cells complete the binding to target cells under the mediation of cell adhesion molecules; Next, NK cells undergo polarization to complete the migration of cytotoxic particles to target cells; Finally, the cell loner releases perforin and granzyme to the target cells (Figure 3A). The gene discussed is PRF1; the disease is neoplasm.