Yet when researchers removed a key part of that system from acute myeloid leukemia (AML) cells, the immune cells continued killing them. The researchers therefore expected that removing MHC from AML cells would make them invisible to T cells. Disabling several known NK cell mechanisms did not stop the T cells from killing the leukemia cells. Yet when the researchers removed TCRs from the T cells, their ability to eliminate AML cells disappeared. They genetically modified AML cells, repeatedly exposed them to T cells, and identified changes that allowed some leukemia cells to survive.