CD4 and obesity due to melanocortin 4 receptor deficiency: To test the generalizability of our finding that host recipient background shapes microbiota re-assembly with human-to-mouse FMT, further studies are required in other colitis models, such as naïve CD4+ T cell transfer to Rag-1−/− mice, and disease models, such as the Leptin-deficient (Ob/Ob) obesity mouse model.