RAG1 and Chronic colitis: Wurbel et al. showed that the CCL25/CCR9 interaction is dispensable for the function of tTregs and the induction of pTregs in the colonic lamina propria (cLP) during chronic colitis induced by the transfer of CD45RB CD4+ T cells into either Rag1−/− or Rag1−/− CCL25−/− recipient mice [51].