CD4 and infection: Given that this latter setting is one where haematopoietic cells from B6.Bach2ΔT and B6.Bach2fl/fl donors compete to fill various tissue niches and expand following infection, our results indicate an important role for BACH2 in T cell development, tissue recruitment and/or retention, independent of T cell activation, as well as a distinct role in CD4+ T cell differentiation following infection.