Comment by pazimzadeh

it is a rate-limiting step.

previously you'd inject a rabbit or other small mammal with what wanted antibodies to bind against, plus an adjuvant compound

then you'd need to screen the antibodies and figure out what they do. some antibodies will bind to your target but not neutralize it, so have to rule those out.

then I think you'd have to do amino acid sequencing on it I think and then clone the sequence in some B-cells to produce it.

there's probably a way better approach than what I just said but it's usually still going to start with stabbing an animal with your target.