CD19 and neoplasm: We have previously reported on development and establishment of the RPCI-WM1 human WM cell line, which is CD19- and CD20- and was developed from a WM patient with terminal disease.[10] RPCI-WM1 constitutes a unique model amongst the other WM cell lines (BCWM.1 and MWCL-1) due to loss of CD19/20[10, 11] and as such may derive its origins from a tumor population that was predominately comprised of plasma or plasmacytoid cells.