ITGAM and plasma cell myeloma: In addition to the increased number, CD11b+Gr-1+ cells from the BM of multiple myeloma–bearing mice produced higher amounts of S100A9 protein (Fig. 1D), which is consistent with the accumulation of MDSC in tumor-bearing mice because MDSC are known to express more S100A9 protein than neutrophils and monocytes (36).