I don't know the history on Campath other than the time that Genzyme has had it. I really don't see the value here for Sanofi either. Genzyme had so many persistent problems in their Allston facility that the FDA actually issues a consent decree. Still, they have never fully recovered from that mess.
I have been considering buying puts on the prospect that Sanofi does indead walk away from this deal now that they are looking at the books. The current portfolio is not worth $18 billion and Campath if (and that is if) approved for MS is likely not a multi-billion dollar market as GENZ would have everyone believe.
Anyway, interested to hear more on the Campath history.