Immunomodulatory drugs (IMiDs) including lenalidomide, a single compound shows various pharmacological action such as the stimulation of T cells and natural killer (NK) cells, the suppression hematopoietic tumor proliferation, suppression of neo-vascularisation, and anti-inflammatory action. It has been thought that IMiDs stimulates CD8+ cytotoxic T cells primarily, it is recently shown that they also stimulate CD4+ helper-T cells similarly. Lenalidomide stimulates T cells and NK-cell through production of Th1 type cytokines IL-2 and IFN-γ from CD4+ helper-T cells. Lenalidomide also activate T cells indirectly by inhibiting regulatory T cells and myeloid derived suppressor cells (MDSC) which inhibit the activation of T cells, but controversy still exist about effects on regulatory T cells.