Since my immortality theory didn't get a response I was looking for I have one of my other theories. I'm not really sure about anything I say in this post but I think that White blood cells adapt to viruses and bacteria when they encounter them. So what I think is, we can take WBCs and expose them to viruses outside of the body.If the WBCs die we clone it from its remains and expose it to the virus again with the expectation that it started to adapt to the virus. We repeat that process until the WBC can defeat the virus and then we can use it to cure people. I suppose the difficulty would be that it can only be used for the donor of the WBC but we can perhaps work around that. I suppose nanites could be easier, cheaper, and more effective but you know once its done the cell can reproduce itself.