Dose- and DAR-dependent in vitro cytotoxicity of SPDP-based ADCs. CD22-positive Daudi (a), Nalm6 (b), and CD22-negative Jurkat (c) cells were incubated with varying concentrations of SPDP-based ADCs with distinct OARs. ONC and huRFB4 IgG were used as positive and negative control, respectively. Cell viability was determined after 72 h and is expressed relative to buffer-treated control cells. (d) Cytotoxic activities towards Daudi cells of immunoconjugates with low OAR were compared to antibody-ONC populations with higher ONC loading (OARs 8–12) at equal molar doses of 10 nM each. As immunoconjugate species with eight to twelve ONC payloads could not be further separated, molar calculations for the 250–290 kDa ADC were averaged for a payload of 10 RNases. Data depict the mean value ± SE from one representative experiment performed in triplicate.