The study of the early Universe relies on our ability to check our models by analyzing the behaviour of astrophysical objects at conditions close to those of the first epochs. Low-metallicity nearby galaxies with young massive stars may be used as laboratories to study these objects that have been proposed as active agents of the reionization of the Universe and dominate the energy budget of galaxies.We present observations and analyses of individual OB stars in the sub-SMC metallicity galaxy Sextans A (which the lowest confirmed Fe abundance in the Local Group, kaufer et al. 2004 & Hosek et al. 2014), obtained with OSIRIS@GTC. This work extends the limits of this kind of studies to unprecedented low metallicities.