[gizmo686]

2 problems:

Scientists don't have that precise knowledge of what the human body is made of. There is a whole microbriome of non human organisms that are vital to our health.

2) Even if we did, it would still be a major accomplishment to find something that kills everything else but not us. We are happy when we find a treatment that kills 1 bad thing without killing us.

3) The only mechanism we have for artificial immunity is vaccines. These do not kill anything; they just train our immune system. Given how our immune system works, this limits us to a blacklist approach, of training it to attack specific proteins.