Mo-MDSCs are pivotal players in colorectal cancer and may be associated with tumor recurrence after surgery.

Colorectal cancer (CRC) is the third most common malignancy. Its development and progression is associated with natural immunosuppression related, among others, to myeloid derived suppressor cells (MDSCs). Overall, 54 patients in different stage of CRC, before any treatment were recruited into the study. The analysis included flow cytometry evaluation of blood MDSCs subsets, correlation their level with the tumor stage and T cell subsets. In the case of 11 patients, MDSCs level was evaluated before and 3 days after surgery, and these patients were monitored for cancer recurrence over 5 years. The results showed that frequency of circulating MDSCs subsets is increased significantly in CRC patients, with highest level detected in most advanced tumor stages. Moreover, only monocytic MDSCs (Mo-MDSCs) positively correlate with regulatory Treg, and negatively with tumor Her2/neu specific CD8+ T cells. Circulating MDSCs, in contrast to tumor resident (mostly Mo-MDSCs), are negative for PD-L1 expression. Additionally, after surgery the blood level of Mo-MDSCs increases significantly, and this is associated with tumor recurrence during a 5-year follow-up. In conclusion, Mo-MDSCs are pivotal players in CRC-related immunosuppression and may be associated with the risk of tumor recurrence after surgery.