Comparatıve Analysıs of Myeloıd-Derıved Suppressor Cells From Blood and Spleen in Gastrıc and Pancreatıc Cancer

Abstract

Under physiological conditions, development and maturation of the myeloid cells take place in the bone marrow. In case of chronic inflammatory disorders such as cancer, production of chemokines, growth factors, and cytokines are augmented, and myelopoiesis is boosted. However, the myeloid cells enter circulation without full maturation and may interfere with immune responses. These immature immunosuppressive cells are called “myeloid-derived suppressor cells (MDSCs)”. MDSCs employ different mechanisms such as reactive oxygen species, nitric oxide, arginase 1, indoleamine 2,3-dioxygenase to suppress immune responses. MDSCs are accumulated in the peripheral blood, bone marrow, liver, and especially in the spleen and support tumor formation and metastasis in tumor-bearing mice. On the other hand, since obtaining spleen samples is very challenging, peripheral blood is generally used in human studies. Increased amounts of MDSCs were found in the peripheral blood of cancer patients and were associated with bad prognosis. However, there is more room for research about MDSCs in the human spleen. In this study, from peripheral blood and spleen samples of gastric and pancreatic cancer patients who underwent splenectomy, the subtypes of MDSCs were determined. Particularly, polymorphonuclear MDSCs (PMN-MDSCs) were accumulated in the spleen, and they were in close proximity with T cells. Increased percentages of PMN- MDSCs both in peripheral blood and spleen were associated with bad prognosis regardless of clinical stage. Furthermore, the spleen specimens which were obtained from the patients with traumatic injury served as non-malignant controls. PMN- MDSCs were accumulated in injured spleen similar to that of observed in the cancer patients. Increased percentages of PMN-MDSCs in the spleen were positively correlated with injury severity scores. Furthermore, the splenic PMN-MDSCs as well as the circulating PMN-MDSCs, displayed similar distribution, morphological properties, capacities to produce reactive oxygen species, nitric oxide, and suppressed T cells. Both in cancer and traumatic injury the expression of human MDSC-associated immune regulatory molecules were increased. In conclusion, our results demonstrated the immune modulatory function of the human spleen through MDSCs in inflammatory disorders such as cancer and trauma.