I've got a pet house cat. She stays indoors
My daughter has a cat.  We just had to take her for the feline leukemia shot.
I'm vaguely familiar with feline leukemia virus. I know it was called  FeLV when I worked at a vet clinic. 
It's terrible.  I had an outside cat when I was younger that got it.  I had to have him put to sleep.  He couldn't breathe and his lungs filled with fluid.
That's too bad..I'm sorry for your loss! I didn't know it had such an impact on their immune system. 
I don't really know what it does, but I do know it's fatal.  So if we are going to have a cat, it has to have that vaccine.
That's a good idea, I didn't know there was a vaccine, but that would definitely help boost immunity. I bet keeping the cat indoors would help, too, since FeLV can be transmitted from unvaccinated stray cats. 
Yes, we've always had indoor cats, but every now in then they will escape to our back yard - I just didn't want to take the chance ya know?