That's a very good question, @sarahcall17 . And, it's a question beyond my knowledge. I'm well past my sell-by date to be considered for Lemtrada! Hopefully, @orlando27, @tracyd and/or @us-emma may have a view.

@sarahcall17 - I asked my neuro and MS nurse just this last week before being put on the wait list for the treatment at Kings (I'm now scheduled to start treatment on 14 August). Their response was that it was highly unlikely that Lemtrada would not work (I.e. significantly reduce the number of relapses after multiple courses) and that they didn't really have any experience of this - but that we would cross that bridge it we ever came to it to find a suitable alternative treatment. The nurse did raise a concern that it was unknown what impact the permanent change in your immune system would have on the PML risk if you reverted to Tysabri - and whether Lemtrada could put you at higher risk- but I imagine this is just something that would be monitored for if you were to go down this route. In addition, failure on either Tysabri or Lemtrada is a requirement to be considered for the "compassionate" HSCT programme run at Kings - so that could potentially be a further, aggressive, option. One further point - the nurse explained to me that stopping treatment midway through (I.e even just after one infusion from the first round) carries the same SE risk as the full course - so I think you would need a very strong medical reason to change treatment once started (I.e as you say, because your body simply can't tolerate the infusions). I'd be very interested to hear other peoples' responses to this question. K