CD4 and adult T-cell leukemia/lymphoma: In vivo and irrespective of the clinical status (i.e., in asymptomatic carriers (ACs), ATLL or HAM/TSP patients) the HTLV-1 provirus is predominantly detected in CD4+ T lymphocytes [38], even if infection of CD8+ T lymphocytes [39–41], and to a lesser extent of B lymphocytes has also been documented [42].