Human T-cell leukemia virus type 1 (HTLV-1) is a highly oncogenic delta-retrovirus predominantly infecting CD4+ T cells and causing an aggressive type of cancer called adult T-cell leukemia/lymphoma (ATL) or an inflammatory neurological disease leading to damage of the spinal cord, known as HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) [1,2,3,4]. Here, CD4 is linked to tropical spastic paraparesis.