Pfizer used the HEK 293 line didn't they?

It's not known whether is was from an abortion or a spontaneous miscarriage. It's only known that the line derives from cells isolated in the Netherlands in the early 1970s. (And that they're embryonic kidney cells).

Traditional vaccines grow the virus in chicken eggs, before the protein that the immune system is to be trained to recognize is separated off the viruses. But you still test what happens in a human cell as part of the development, generally speaking. Oxford/AstraZeneca vaccine is like that. And they used the HEK 293 cell line as part of the development.

But it's much more obvious in the case of the mRNA vaccines, because they don't do the chicken egg bit. The vaccine doesn't do anything until it is in a human cell, and then it generates the spike protein. You'd need to stick it in a human cell to see if it does what you hope, and makes the spike protein.