STEM uses pre-selected, functional CDR libraries to cover more practical diversity which can be missed when using alternative methods such as CDR walking.
The typical steps in CDR walking:
Mutate a single CDR
Identify the best clone
Use this sequence and mutate the next CDR
With CDR walking, only a single CDR sequence is selected per library, keeping paired mutations that work across multiple CDRs from being selected, which ultimately limits affinity improvement.
STEM is a 3 stage approach that allows us to simultaneously mutate CDRs and involves three separate library construction and selection/screening steps. This generates more diverse libraries that capture mAbs with the rarest characteristics—delivering more options for you to choose from.