Not sure why you would expect this but it was always an issue with T, VLA-4 KO is supposed to be embryo lethal,
Neurodevelopmental retardation in a baby born to a multiple sclerosis patient being treated with fingolimod.
and T seems to work pretty good,
The real-world effectiveness of natalizumab and fingolimod in relapsing-remitting multiple sclerosis. An Italian multicentre study.