The experimental system first described by Thomson’s group (Xu et al. 2002; Xu 2006) and later by us (Das et al. 2007; Schulz et al. 2008) and others (Besser 2004; Gerami-Naini et al. 2004; Golos et al. 2006; Zhang et al. 2007; Wu et al. 2008; Douglas et al. 2009; Erb et al. 2011; Marchand et al. 2011), in which hESC are driven towards TB in response to the growth factor BMP4, is particularly attractive in that it allows the “birth” of TB to be followed from pluripotent progenitors and the subsequent differentiation of these early TB to be followed along specific sub-lineages. Here, BMP4 is linked to tuberculosis.