In the present study, the host-virus interactions in the manifestation of ATLL and HAM/TSP were investigated by assessment of HTLV-1-PVL and HBZ as viral elements, AKT1 as a regulator of the cell cycle progression and cell survival, BAD as proapoptetic agent and finally RORγt, FOXP3 genes as the main transcription factor in Th17 and Treg cells, and IFN-λ3 as an antiviral agent in the innate immune responses. The gene discussed is IFNL3; the disease is adult T-cell leukemia/lymphoma.