The therapeutic potential of the CD64-targeting ADC, H22 (scFv)-SNAP-AURIF was investigated using XTT cell viability assays (Sigma-Aldrich, USA). Briefly, 5 × 103 IFN-Gamma stimulated CD64+ U937 cells, CD64- MDA-MB-468 cells or ex vivo differentiated hMDMs were seeded overnight in 96-well plates before treatment with decreasing concentration of H22 (scFv)-SNAP-AURIF or H22 (scFv)-ETA' for 72 h. Thereafter, the treated cells were incubated with freshly prepared XTT labelling reagent (sodium 2,3,-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-[ (phenylamino)-carbonyl]-2H-tetrazolium) and electron coupling reagent mixture, phenanzine methosulfate (50:1) for 4 h. The readout was conducted by measuring absorbance of the reduced XTT reagent at 450 nm with a reference of 655 nm on a Spectrophotometer (Bio-Rad, USA), and the data were analyzed using GraphPad Prism v10.0 software (Graphpad softwares, USA). Data were expressed as mean ± standard error of mean (SEM) unless otherwise indicated.