In vivo imaging of differentiation therapy with multiplexed mAbs. (A) Differentiation of NB4 cells treated for 48 hours with a combination of ATRA (1 μM) and VPA (1 mM) as evaluated with CD11b, CD11c or multiplex of both by flow cytometry. Multiplexing of both mAbs provides significant increases in mean fluorescence intensity. **P < .01; ***P < .001. (B) Subcutaneous tumors (n = 4) treated with ATRA (60 mg/kg) and VPA (350 mg/kg) for 3 days show significant increases in fluorescence intensity (C; *P < .05) and reduced tumor growth (D; *P < .05) compared with controls (means ± SEM, n = 3) and confirmed ex vivo by immunohistochemistry of tumors with CD11b (E). Scale bars: yellow indicates 20×, 0.1 mm; white, 40×, 0.05 mm.