(disclaimer: layperson remembering how the immune system works.)

the adaptive immune system effectively does KYC by checking the antigens presented on the surfaces of cells. the thymus selects for B-cells (iirc?) which don't react to a corpus of the body's own antigens, but cover a wide library of everything else. when it sees something it doesn't recognize, it reproduces, warns the rest of the immune system and marks targets. that's why our immune systems can eventually conquer almost every pathogen we encounter, if we can survive long enough for it to do its work.

but the KYC I was referring to was KYC that vendors of oligonucleotides (should) be doing, to keep people from ordering nefarious sequences.