Yeah, right - Tyrell, he's reliable (not).
Some have suggested that Tyrell used JF's DNA to extract the genetic code for 'accelerated decrepitude' to go into the Nexus 6 reps - what a nice guy.
In the book he and Rachel tried to trick Deck into wrongly identifying a human as a Rep. You can't believe a word he says...
...after all, if you like the Deck-is-a-Rep idea then Tyrell would almost certainly have been in on it.
Also, I don't remember Tyrell specifically saying Rachael was the only replicant experiment currently being tested...
...perhaps he thought better of it than to mention the new 'Rep-hunter' model.
Ever heard of a hunter-killer virus? Send a virus to kill a virus. Why not send a Rep to kill a Rep? No emotional barriers. Keeps going until the job is done.