“…Another possibility is that the unconjugated anti-CD20 Ab induced a higher level of expression of the CD22 antigen, as was suggested by previous in vitro studies (5), but our Ab localization studies did not support this possibility. The specificity of epratuzumab (hLL2) uptake in Ramos tumors was established previously (29). The mechanism of action of unconjugated anti-CD20 IgG alone has been investigated in many experimental models (1,2,13,33,34), and seems to require one or more accessory factors, such as various effector cells (acting via Ab-dependent cellular cytotoxicity), complement, and/or the production of chemokines by the Ab-treated tumor (13).…”