In the Blade Runner game from 1997 (which take time at the similar time as the movie), the player character can visit JF Sebastian's house. If my memory is right, upon pointing at the walking "toys", the protagonists comments
They are obviously replicants, but no one would pay me for retiring them.
Since you are the Police officer and the toys ...
You can't use the book as reference for anything in the movie(s). They're very dissimilar. JF Sebastian isn't even in the book.
There is no reference anywhere to precisely how the toys were made.
They are replicants, or of the same manufacturing type as replicants, but were made my J F Sebastian for his own amusement or as company. They are clearly shown to ...
The answer to this really is that "nobody knows", not for certain. Their composition changed with each telling.
Ridley Scott insists that they were biological, but their behaviour isn't that of a purely biological entity. There's a lot of grey area.
From Wikipedia - Replicant
In his novel Do Androids Dream of Electric Sheep? (the inspiration for ...