Myeloid-derived suppressor cell impact on endogenous and adoptively transferred T cells

Novel models of autochthonous tumorigenesis and adoptive T cell therapy (ATT) are providing new clues regarding the pro-tumorigenic and immunosuppressive effects of myeloidderived suppressor cells (MDSC), and their interaction with T cells. New findings are shifting the perception of the main level at which MDSC act, from direct cell-to-cell suppression to others, such as limiting T cell infiltration. Adoptively transferred, high-avidity T cells recognizing peptides with high-affinity for MHC-I eliminated large tumors. However, low-avidity T cells or low-affinity peptides resulted in failure to eradicate tumors. Manipulation of intratumoral myeloid cells improved the outcome of otherwise unsuccessful ATT. Therefore, therapeutic intervention directed at the tumor stroma might be required when using suboptimal T cells for ATT.