Clearly, the epigenetic switch postulated to govern TB emergence and to control ELF5-driven expression of CDX2 and EOMES may be more complicated in the BMP4/hESC system than envisaged in the model proposed by Hemberger et al. (Ng et al. 2008; Roper and Hemberger 2009). The gene discussed is ELF5; the disease is tuberculosis.