Later on, they also discovered that large quantities of HTLV-1-specific antibodies are present in the cerebrospinal fluid of patients with certain HAM/TSP-related HLA haplotypes (Kitze et al., 1996) and identified an HLA-DRB1∗0101-restricted dominant epitope on HTLV-1 envelope (Env) glycoprotein gp21 (Kitze et al., 1998). Here, ERVW-1 is linked to tropical spastic paraparesis.