Other attenuated Mtb strain, presently in preclinical development with promising results in murine infection models, is the MtbΔppe25-pe19 strain, in which selected PE and PPE proteins of the ESX-5 secretion system have been deleted, but which retains an intact ESX-1 secretion system (Bottai et al., 2012; Sayes et al., 2012, 2016). The gene discussed is ESX1; the disease is infection.