CD4 and tropical spastic paraparesis: Following permanent host cell genome integration, predominantly in CD4 + T-lymphocytes, HTLV-1 most frequently causes adult T-cell leukaemia/lymphoma (ATL) (Hinuma et al. 1981) or HTLV-1-associated myelopathy (HAM), formerly tropical spastic paraparesis (Gessain et al. 1985; Osame et al. 1986).