Mycobacterium bovis Bacillus Calmette-Guérin killed by extended freeze-drying reduces colitis in mice

Background & Aims: Mycobacterium bovis Bacillus Calmette-Guérin (BCG), killed by extended freeze-drying (EFD), induces secretion of interleukin-10 and reduces lung inflammation in a mouse model of asthma. We investigated the effects of EFD BCG in mouse models of inflammatory bowel disease. Methods: EFD BCG was administered subcutaneously to mice with colitis induced by dextran sodium sulfate (DSS), oxazolone, or adoptive transfer of CD4⁺CD45RB^highFoxp3^- T cells from C57Bl/6 Foxp3GFP mice to RAG2^-/- mice. Results: EFD BCG, administered either before induction of DSS and oxazolone colitis or after development of acute or chronic DSS-induced colitis, reduced symptom scores, loss of body weight, and inflammation. Although transfer of CD4⁺CD45RB ^highFoxp3^- cells induced colitis in RAG2^-/- mice, administration of EFD BCG at the time of the transfer converted Foxp3 ^- T cells to Foxp3⁺ T cells and the mice did not develop colitis. EFD BCG protected mice from colitis via a mechanism that required expansion of T regulatory cells and production of interleukin-10 and transforming growth factor β. EFD BCG activated the retinoid X receptor (RXR)-αperoxisome proliferator-activated receptor (PPAR)-γ heterodimer, blocked translocation of nuclear factor κB to the nucleus, and reduced colonic inflammation; it did not increase the number of colon tumors that formed in mice with chronic DSS-induced colitis. Conclusions: EFD BCG controls severe colitis in mice by expanding T regulatory cell populations and PPAR-γ and might be developed to treat patients with inflammatory bowel disease.