Adam Jensen's DNA/gene sequence (mentioned in the intro cutscene during Page's IM session) was secretly used by Dr. Megan Reed (presumably while she was dating Adam). She found out, through experiments, that his DNA does not reject augmentation technology and therefore does not need Neuropozyne. Not only this, but she also found out how to make everyone's DNA accept augmentations. [This is revealed in the cutscene in which Adam returns to his apartment to talk to Sarif. Sarif exclaims "So everyone can become like you...More than human" (or something to that effect)]. Without this technological breakthrough, the Dentons (as well as all augmented characters in the original Deus Ex) could not exist. I am not aware of any reference to augmentation rejection or Neuropozyne-like drugs in DX.