These are, respectively, the analysis of the rat lymphopenia mutation present in the type I diabetic BB rat, which has been shown to be due to a premature stop in the GIMAP5 open reading frame [22,23], the development of a mouse strain bearing a targeted deletion of the mouse GIMAP5 gene [11] and the use of mouse reaggregate foetal thymic organ culture to examine GIMAP gene function by shRNA knockdown [4]. Here, GIMAP5 is linked to lymphopenia.