CD33(+) /HLA-DR(neg) and CD33(+) /HLA-DR(+/-) Cells: Rare Populations in the Human Decidua with Characteristics of MDSC.

Human pregnancy needs a remarkable local immune tolerance toward the conceptus. Myeloid-derived suppressor cells (MDSC) are important players promoting cancer initiation and progression by suppressing T-cell functions and thus inducing immune tolerance. Therefore, MDSC were expected within decidua. Subpopulations of CD33(+) immune cells were isolated from human early pregnancy decidua and characterized phenotypically and functionally by microscopy, FACS analysis, RT-PCR, Western blotting and in the coculture with T cells. Decidua harbors CD33(+) /HLA-DR(neg) and CD33(+) /HLA-DR(+/-) cells which both express arginase, iNOS and IDO and a typical cytokine profile. Both subtypes potently suppress T-cell proliferation and therefore fulfill the criteria of MDSC. We characterized a new population of CD33(+) /HLA-DR(neg) and CD33(+) /HLA-DR(+/-) cells in human early pregnancy decidua with properties of classical MDSC and thus potentially being an important player in immune tolerance in pregnancy.