CD4 and neoplasm: LAG3 is expressed on activated CD4+ and CD8+ T cells and Tregs, and its surface expression is associated with downmodulation of T cell responses.8 While LAG3 expression on Tregs is necessary for their suppressive function9 and an infiltration of LAG3+ T cells is associated with poor prognosis for a range of human tumours, studies to date have shown that LAG3-blockade or genetic ablation in mice confers negligible effects on tumour growth.10 However, anti-LAG3 therapy in combination with a second immune checkpoint blockade, particularly anti-PD1, can significantly reduce tumour growth.