What's the translation for Mammalian Two-Hybrid System to Chinese?
According after reading your reference :


  Mammalian Two-Hybrid System


Original record is talking about "protein-protein interactions in mammalian cells". The protein is not living thing so it can't 雜交, 交合, 雜交 (these terms mean cross mating). 

It seems below is better.

哺乳動物細胞雙混合系統