Cancer and lukemia in kittens.

So as of Monday I had to get my cat if four years put down due to her being positive for feline lukemia and growing a tumor in her stomach. I already had a kitten from a friend of mines litter picked out. With this happening with my cat I've decided to take a second kitten aswell. What kind of prevention and pre problem solutions can I take to make sure this doesn't happen again? I've read online that most lukemia in cats is transmitted from the mother either in womb or by milk. The mother cat is an indoor/outdoor seems to be very healthy, never had any medical issues was a farm cat even with the litter of kittens kept her size and nutrition. Also what I've read says that most kittens will test positive for the virus regardless of wether they will have it for life or their immune systems will take care of it before it's a problem. I've also read that kittens infected shouldn't be vaccinated because it will only further activate the virus. Any input is appreciated, and thanks in advance for any help.

I would test the new kittens and the mom and if they are negative, then keeping them indoors and away from other cats will be all you need to keep them from getting it.