CD274 and lymphopenia: Indeed, during infection innate immune cells such as neutrophils, dendritic cells and monocytes have been shown to engage with T cells through PD-L1/PD-1 interactions, leading to T-cell apoptosis and lymphopenia (de Kleijn et al, 2013; Francisco et al, 2010; Garcia-Diaz et al, 2017; Jiang et al, 2019; Sun et al, 2018).