p-Benzyl-isothiocyanate-desferrioxamine (DFO-Bz-SCN, Macrocylics, Inc.) was conjugated to MEHD7945A and a non-specific human IgG isotype (Sigma) according to published protocols53,54. The synthesis was performed using 7:1 and 5:1 mole equivalence of DFO-Bz-SCN to MEHD7945A or IgG, respectively in a 0.9% saline, pH ~9 at 37 °C for 1 h. The pure mAb DFO-conjugates were obtained through by purification with a spin column filter with a molecular weight cut-off of 30 kDa (GE Vivaspin 500) to remove unbound chelate.