Myeloid-derived suppressor cells utilize different mechanisms to block both innate and adaptive arms of anti-tumour immunity, mostly through inhibition of T cell activation and expansion . Human monocytic myeloid derived suppressor cells are mostly identified as CD14+ cells with negative or low expression of HLADR. And also express high levels of CD11b and CD33 antigen . Human granulocytic myeloid derived suppressor cells are usually defined as CD66b+ CD11b+ CD15+ HLADR- cells and display an intermediate expression of CD33 and a variable expression of CD11b, depending on their maturation stage .