In this model, HTLV-1-negative healthy human peripheral blood mononuclear cells (PBMCs) (2 × 106/mouse) were transplanted directly into the spleens of severely immunodeficient NOD-SCID/γcnull (NOG) mice, together with cells from the mitomycin C (MMC)-treated HTLV-1-infected cell line ILT-M1 (1 × 106/mouse), which is an IL-2-dependent CD8+ T cell line derived from a HAM/TSP patient (kindly provided by Prof. Kannagi of Tokyo Medical and Dental University). This evidence concerns the gene IL2 and tropical spastic paraparesis.