https://www.nature.com/articles/d41586-024-00470-5
It's for "re-setting the immune system" -
Researchers have therefore turned to CAR T cells, and specifically to those that kill B cells carrying a protein called CD19. CAR T cells are better cell killers than are the antibodies, and seem to penetrate into tissues including the brain that antibodies can’t reach. More thorough depletion of these B cells, the theory goes, should reset the malfunctioning immune system — halting the brain damage that defines the disease
Doesn't sound as though it will repair myelin or reverse the nerve damage that has already occurred.
However, if this works, it would likely be a one-and-done, unlike current DMT drugs that require repeated and multi-year use.