Functionalized thiol-reactive sCT analogue was added intermittently with constant stirring to thiol-mAb solution at 10:1 molar ratio, and the reaction between the thiolreactive MAL groups in functionalized sCT and SH group of thiol-mAb was allowed to proceed at room temperature in the dark with constant stirring for 2 h. Unreacted sCT-PEG was removed by dialysis at 4°C (Fig. 1c) .