<prompt> Which of the following does not describe a documented mechanism of tumor-mediated immune evasion?Down regulation of class I MHCSecretion of TGF-bSecretion of decoy moleculesAntigenic variation  <response>: Tumor cells have evolved mechanisms to escape and evade immune recognition. These mechanisms include various molecular genetic processes of eliminating MHC I from the tumor cell surface. Mutations inhibit efficient antigen processing and presentation. Tumor cells also block immune cells by secretion of suppressor proteins, most commonly TGF-b1, and other cytokine like decoy molecules to confuse the immune system. Antigenic variation is an immune escape mechanism ascribed to pathogenic microbes such as viruses for example. 