Cytotoxic effects of aIgM ADCs were evaluated by exposing IgM+ lymphoma B cells or off-target (IgM-) cells to different ADC concentrations. Cell viability was analyzed 72 h post ADC addition by a colorimetric method using CellTiter 96® AQueous One Solution Cell Proliferation Assay (Promega). Briefly, cells were seeded (1x104 cells/well) in a 96-well plate with the desired antibody concentrations ranging from 0.014-90 nM in a serial dilution. After 72 h, MTS solution was added to the cells and plate was incubated for 2 h. Absorption was measured at 490 nm using CLARIOstar plus microplate reader (BMG LABTECH). Cell proliferation was normalized to untreated control cell absorption values. The resulting curves were fitted with a variable slope four-parameter fit and EC50s were calculated using GraphPad Prism.