CD38 and cancer: In conclusion, using integrative analysis of synovial tissue biopsies and PBMC, we have shown that (1) CD38 and plasma cell/plasmablast-related genes are up-regulated in ACPA+RF+ arthralgia and UA disease stages before the onset of RA; (2) CD38 is expressed at the highest level on plasma cells in the peripheral blood compared to other immune cell populations in donors with RA or SLE and healthy donors; (3) daratumumab, an approved cancer drug, effectively depletes plasma cells/plasmablasts in SLE and RA PBMC ex vivo.