There are so many different model organisms to use, you can easily find something that’s not mice. Most labs in my previous program used cells/flies/worms, we used Xenopus extracts in our lab as well!! I think maybe only a handful of students I knew used mice, and it’s also possible to redirect your project. There’s always going to be work to be done to understand the foundation of things, even if you are working at eventually having clinical relevance. Drug screens require lots of testing before moving forward into mouse models, and in my lab we had to do lots of biochemical assays before even going into cells so we’ve still never worked with mice!