How about an antibiotic or vaccine developed using humice, mice with human immune systems? Dicey. Although nothing from the animal is in the final product, and the human immune system is used to add an immune system to an immunodeficient mouse without cross breeding the species, per se it's the animal equivalent of flax and cotton fabric.
There are literally thousands of pages written on that by people smarter than me. All well reasoned.
I just stick to the basics: I don’t do it.
If I happen to have a donkey and horse get busy, then I’ll worry about it.
And I know we shouldn’t mix fish and alligators. Heck, anyone who watched a sci-fi show.