Hi there and welcome. There are a handful of use who have/are using Tysabri for Crohn's. I was on it for 6 months but discontinued because the benefit was so little that it nowhere near made the risk worthwhile.
The others on here seem to have had great luck with Tysabri. I'd imaging that they'll check in sooner or later and reply to your post.
--female dx as UC in '04 (1st symptoms in '03), switched to Crohn's in '05, 1 fistula, crohn's colitis, limited to large intestine --rejected (reaction/didn't work): Asacol, AZA, 6-MP, MTX, Remicade, Humira, prednisone, Tysabri
--Prochymal in Phase III study (can't wait til it's approved!)
--Compounded budesonide 3mg/daily, Started Cimzia first dose 2/10/09. Dx Osteoporosis 10/08 started Forteo 1/27/09