Plot Nitpick:

This is slightly more involved biology and the writers probably wouldn't have known, but there is no reason Megan would need to continuously collect DNA from Adam: PCR and cloning (cloning refers to copying stretches of DNA, not specifically an organism. Ex; me taking a stretch of DNA and putting it into a plasmid is "cloning" that stretch) mean that once you have your sequence, you're all set. Forever. Make as many copies as you want, and you can always double check it by sequencing your constructs again. It is incredibly easy to work with DNA.

What are not easy to work with are human cells.

Cells, unlike DNA, need cultured and have lifetimes. You can freeze some bad boys down and thaw them again and get them to divide a couple times, but beyond a few of these 'passages', even immortalized cell lines, lines designed and altered explicitly for lab use, go wonky.

Wild cells? People don't usually passage wild cells very many times, to my knowledge. They age, like their host. It changes things about them.

I think it makes more sense that what Megan needed from Adam was living cellular tissue, not DNA. Plus, for science I won't go into unless ya ask (feel free, I'm incapable of shutting up), it's entirely possible that she could not engineer Adam's mutation into lab lines. Ergo, you need him, quite literally pieces of him. Now, how one would go about collecting nerve cells, some of the most finicky types of cells I've ever heard of and that don't divide regularly like everybody else, is. Let's not go there. We can assume that maybe the glial buildup is mediated by autoimmune responses instead, or something. Like adding Adam's immune cells to anyone else's nerve/PEDOT interfaces alleviated the issue for the lifetime of the cells. For collecting immune cells, blood or bone marrow works.

Personal headcanon to make it all fit together is the following:

-Adam, already having grown up middle class and having to help his parents with bills, has a history of plasma donation bc that's paid

-Adam knows he is O-, and willingly donates blood

-Megan arranged for people to impersonate blood donation crew members to steal whole blood from him.

This would necessitate knowing when he planned on going and being close enough emotionally to him to influence his schedule.

End rant,