HTLV-1 is the etiological agent of two main very severe diseases: a lympho-proliferative disorder, of mainly CD4 T-cells, named adult T-cell leukemia/lymphoma (ATL) [2], and a chronic neuromyelopathy named tropical spastic paraparesis/HTLV-1 associated myelopathy (TSP/HAM) [3, 4]. Here, CD4 is linked to tropical spastic paraparesis.