Replicants are bioengineered humanoids possessing a digital software program as consciousness via an organic computer system as a brain.
An innovative feat of synthetic biology, their human-derived neurons possess many internal components that do not exist anywhere in nature. The unique properties of these components causes the neurons to generate electrical signals that are digital in nature. This has the effect of making the consciousness that emerges from a replicant brain based entirely upon electronic digital information transfer rather than electrochemical interactions like the human brain. This means that replicant consciousness is fundamentally a highly advanced artificial intelligence software program contained in what is essentially an organic computer system.
The digital consciousness software program of replicants enables their minds to be as easily programmed as a conventional computer program - because it is still fundamentally a computer program; a computer program via biological hardware. Yet, it still mimics the functions of a human brain processing the 'software' of human thought—which appears to have linear sequential aspects, parallel processing aspects, and also neural cooperative hierarchical caching and even quantum processing aspects.
Outwardly indistinguishable from humans on a physical level, replicants possess all the same anatomical systems of humans - blood, internal organs, immune system, lymphatic system, etc. Despite this, the law does not consider replicants human and therefore accords them no rights nor protection. Although composed entirely of organic substance, they are legally regarded as androids due to their computational machine-like sentience.
A key aspect of replicant psychology is that they are lacking in empathy. Because of that, measuring the degree of empathic response via a Voight-Kampff machine is the most used method of detecting replicants. NEXUS 6 replicants also have an in-built fail-safe mechanism, namely a four year lifespan, to prevent them from developing empathic cognition and therefore immunity to a Voight-Kampff machine. This is especially necessary for Mental-A models whose intellectual capacity at least matches their designers.
Replicants are illegal on Earth after a bloody mutiny against an off-world colony staged by a Nexus-6 combat. Special police units (Blade Runners) are sent to investigate, test and ultimately "retire" (kill) replicants found on Earth.