The Argeneau’s are essentially humans that are from Atlantis. They had advanced technology and created a vaccine of nanos that was intended to heal major wounds and illnesses and then die after completing their task. The first test run was not a total success because one of the side effects was insanity which is where the “No Fangers” came from. They edited the vaccine and fixed that side effect however the nanos did not die off after fixing the initial injury because the human body is always receiving damage daily from the sun, weather, food choices, and more. Since the nanos use red blood cells as fuel the people who received the vaccines had to receive blood transfusion in their hospitals. Once Atlantis fell they were thrust into the world with all the other humans that were no where close to their technology level. The nanos altered their bodies to make them more efficient at getting the red blood cells the nanos need for fuel. All of these adaptations make them more like a vampire, however they prefer to call themselves immortals as appose to vampires.