CD4 and adult T-cell leukemia/lymphoma: However, after a long latency period, approximately 5% of HTLV-1 carriers develop adult T-cell leukemia/lymphoma (ATLL), a CD4+ T-cell malignancy, and 1–4% develop HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP), a chronic inflammatory disease [14].