Indeed, anti–PD-1 therapy increased the levels of IL-21 in BALF of tumor-bearing aged mice, which was disrupted by ICOSL blockade (Figure 5B), and lung-infiltrating ICOS+CD4+ T cells in anti–PD-1 Ab–treated aged mice had an ability to produce IL-21 (Supplemental Figure 8C). The gene discussed is IL21; the disease is neoplasm.