MS4A1 and neoplasm: In particular, based on high level of SDC1, TNFRSF17, MZB1, CD38 and low level of CD19 and MS4A1, Cluster 0, Cluster 1 and Cluster 12 were defined as SDC1+ cells, namely plasma cell in HD controls and tumor cells in MM patient (Figure 1E and Supplementary Figure 1B).