Is tysabri (natalizumab) a treatment for ms?

Yes. This is a monoclonal antibody, infused once monthly, and is the currently most potent medication on the market for MS. In several cases, a deadly infection called PML has occurred with pts taking this medication, but blood tests can predict risk, and if positive can prompt the discontinuation of Tysabri (natalizumab).. Drug can be used early or late, but is approved for first line.
Yes. As far as i know, this is the only use for it.