IL-27 is a heterodimeric cytokine which belongs to the IL-6/IL-12 family of long type I cytokines. It is expressed onmonocytes, endothelial cells and dendritic cells. IL-27 is an early product of activated antigen-presenting cells and drivesrapid clonal expansion of naive CD4(+) T cells and plays a role in the early regulation of Th1 cells initiation which drivesefficient adaptive immune response. IL-27 has an antiproliferative activity on melanomas through WSX-1/STAT1 signaling.Thus, IL-27 protein may be an attractive candidate as an antitumor agent applicable to cancer immunotherapy. IL-27reveals to be a potent inhibitor of TH17 cell development and of IL-17 production. Indeed IL27 alone is also able to inhibitthe production of IL17 by CD4 and CD8 T-cells. IL-27 has also an effect on cytokine production. It suppressesproinflammatory cytokine production such as IL2, IL4, IL5 and IL6 and activates suppressors of cytokine signaling such asSOCS1 and SOCS3. Apart from suppression of cytokine production, IL-27 also antagonizes the effects of some cytokinessuch as IL6 through direct effects on T-cells. Another important role of IL-27 is its antitumor activity as well as itsantiangiogenic activity with activation of production of antiangiogenic chemokines such as IP-10 and MIG.