Haha, well, you’ve done more biology than me, as I dropped it from a great height before I had to do anything silly like take an ‘O’ Level in the subject.
In more recent times, I did a postgrad diploma in medical law, but that pretty much only deals with medical issues that were caused by someone, as you can’t sue anybody for naturally occurring conditions like MS!
Dunno much about leukocytes, but yes, in general I would assume any drug that has the potential to repair myelin without compromising the immune system has to be a positive thing, because if you use immunosuppression, you’re always going to have this trade-off that the price is infections - and I don’t just mean the odd cold, but life-threatening ones such as we see with untreated AIDS.
That’s why many of the existing DMDs are classed as immune system modifiers, but not immunosuppressants, otherwise you’d have the unwanted side-effect of constant infections. Not much point being able to halt MS, but then die of a common infection because your immune system was wiped out. 
I’m always interested in research, but I don’t get too excited, because, as others have pointed out it’s always mice! For a start, mice don’t actually get MS, but a lab-induced condition used to model MS. So although the pathology appears similar, we don’t know for sure that what works on one would work on the other, as they’re not the same disease. Secondly, and rather obviously, mice aren’t people, so showing it worked on mice (which didn’t really have MS) is a long way from proving it’s safe and effective for humans.
The mouse model may pave the way for some important revelations that can be adapted for humans though!
Tina