Effect of rituximab on clonogenic MM progenitors in vitro. MM colony formation following treatment of bone marrow mononuclear cells depleted of CD34⁺ and CD138⁺ cells with rituximab or 10% human serum (compl.). Results are presented as a percentage of the untreated control group. P < .01 for the rituximab and rituximab plus complement groups compared to the untreated (control) group by Student t test (n = 3).