Host effector cells are required for in vivo antitumor activity of c1F6. Raji-bearing mice were depleted of (A) NK cells, (B) macrophages (Mφ), (C) neutrophils (Neut), or (D) NK, Mφ, and Neut subsets as described in “Materials and methods.” After that, mice were either left untreated or treated with 4 mg/kg c1F6 one day following Raji challenge (n = 10 per group). (A) Untreated versus c1F6 (P < .001), untreated versus c1F6 − NK (P = .002), and c1F6 versus c1F6 − NK (P = .021). (B) Untreated versus c1F6 (P < .001), untreated versus c1F6 − Mφ (P < .001), and c1F6 versus c1F6 − Mφ (P < .001). (C) Untreated versus c1F6 (P < .001), untreated versus c1F6 − Neut (P = .058), and c1F6 versus c1F6 − Neut (P = .002). (D) Untreated versus c1F6 (P < .001), untreated versus all depleted + c1F6 (P = .177), and c1F6 versus all depleted + c1F6 (P < .001).