These HTLV-1–infected T cells express viral proteins that lead to the activation and expansion of HTLV-1–specific CD8+ T lymphocytes (CTLs) (9, 10), which subsequently produce proinflammatory cytokines and chemokines and may cause bystander damage to neurons and glial cells in patients with HAM/TSP. Here, CD8A is linked to tropical spastic paraparesis.