Clonogenic growth of MM cells from clinical specimens. (A) MM colony formation of CD138⁺ and CD138^- cells from 3 clinical samples plated at various densities. (B) Flow cytometric evaluation of colonies derived from CD138^-/CD34^- cells. The top 2 panels show the initial clinical marrow specimen; the middle panels, the CD138-depleted cells prior to plating; and the bottom panels, the pooled colonies after 21 days from a representative MM patient. (C) Flow cytometric evaluation of pooled colonies from 3 additional patients. (D) Colony formation of CD138^- clinical MM samples during serial replating.