For patients with MS on natalizumab, at what JC virus antibody titer do you consider switching DMTs?  

I am comfortable continuing Tysabri as long as the JCV index remains below 0.9. I would discuss switching therapies or would consider extending-interval dosing (treating every 6 to 8 weeks, instead of every 4 weeks), if the index is between 0.9 and 1.5. I would not continue Tysabri if the index is a...

If a patient has been on therapy >1 year and particularly close to 2 years, I switch for any positive result. If the index is 0.3-0.9 and the patient is on therapy <1 year, I discuss change in monitoring strategy and options to switch if the patient is willing to do that. If index is >1.0, ...

At any level. With so many effective disease-modifying treatment options these days, there's no reason to expose the patient.