How does HTLV-1 cause adult T-cell leukaemia/lymphoma (ATL)?

• Molecular mechanisms of HTLV-1 oncogenesis.
• Innate and acquired immune response to HTLV-1.
• Clonality of HTLV-1 in vivo.
• We bring together the host and viral factors that result in ATL.

A typical person infected with the retrovirus human T-lymphotropic virus type 1 (HTLV-1) carries tens of thousands of clones of HTLV-1-infected T lymphocytes, each clone distinguished by a unique integration site of the provirus in the host genome. However, only 5% of infected people develop the malignant disease adult T cell leukaemia/lymphoma, usually more than 50 years after becoming infected. We review the host and viral factors that cause this aggressive disease.