Was just reading that bone marrow transplants were also noticed to have taken out Epstein-Barr virus antibodies in bone marrow recipients. EBV is also associated with some cancers and MS, same virus that causes simple cold-like stuff in kids or mono in teens and young adults can be much more serious in some. The subjects got the transplants also due to other cancers. Of course - that's a straight-up virus rather than retrovirus. I've seen no further report on whether the results held up over time, though. I assume the only reason they noticed at all was due to more general immunologcal testing before and after.
I know transplant has been considered and apparently tested as a treatment for MS as well (a friend was considering it), but I've heard no further data on that one, either. Problem there is, the dx takes so long to get avg. 7 years) and the course of MS is so uncertain.
Problem is, darn bone marrow transplants are just so risky! That same friend was given a death sentence, and then rebounded hugely not 30 days later...only change was removal from a particular work environment. So how to know when the risk is worth it? Gyah! We know so little!