Abstract: T cells are programmed to target the gastrointestinal tract by activation with dendritic cells capable of producing and/or transporting retinoic acid. Methods for using the programmed dendritic cells and/or T and/or B cells to treat a variety of pathogens and infectious agents residing in the intestine are also disclosed. Similarly, inhibitors of retinoic acid synthesis by dendritic cells or other cells in the gut, and inhibitors of retinoic acid receptors in T and/or B cells or other cells in the intestinal mucosa, are disclosed for treating a variety of gastrointestinal autoimmune diseases such as inflammatory bowel disease and celiac disease.