Infiltration of functionally competent cytotoxic (CD8⁺) T lymphocytes is necessary for effective immune surveillance in cancer. Kv1.3 potassium channels regulate the activation and function of T cells. This image depicts a section from a head and neck cancer stained for cytokeratin (tumor cell marker, yellow), CD8 (green), Ki-67 (cell proliferation marker, magenta), and Kv1.3 channels (red). The CD8⁺ lymphocytes that showed low Kv1.3 expression also showed decreased cell proliferation, indicating that Kv1.3 channels could be potential markers of the function of tumor-infiltrating T cells in head and neck cancer. For details, see article by Chimote and colleagues on page 53.