Stem cell therapy for what, exactly? Did he/she mention anything specifically? When I first got sick, a doctor mentioned stem cell therapy as well, but didn't go into specifics. He just mentioned it, as though it was a specific therapy for this condition (it's not). I don't think the average physician has much of a clue about capillary leak syndrome and when they don't understand something they often just toss random ideas at you without any real understanding of what they're talking about. At least that's been my experience. I notice in your bio that you also suffer from carcinoid syndrome. Have your doctors ever linked it to your capillary leak condtion?
If anything, stell cell therapy has been reported to cause SCLS. See here: http://www.bloodjournal.org/content/115/13/2723?sso-checked=true