"producer cell line" vs. "host cell line" in biopharmacology
I would lean towards staying with "producer cell line". In my mind, a host cell line is hosting something, like a virus, while a producer produces something. The non-transformed cell line would be the parent cell line.

On the other hand, "host cell line" also implies hosting the recombinant protein product that is later purified, so there's an argument to be made for either phrase. I still prefer producer, though, as I think it's more directly descriptive of what the cells are actually doing - producing the protein of interest.