Carl Zimmer's very interesting book Parasite Rex (though now over a decade and a half old) cites some studies on using worms to treat Crohn's disease and googling around yields this a more recent paper published in Science about studies done on mice [1].
[1] Layperson Summary - http://www.sciencemag.org/news/2016/04/parasitic-worms-may-p...
[2] Actual Article - http://science.sciencemag.org/content/352/6285/608