NFKB1 and neuroblastoma: The PD‐1 T‐cell checkpoint protein was detected on the surface 43% of CD4+ T cells and 77% of CD8+ T cells isolated from 9464D Nb tumors growing in p50(f/f);Lys‐Cre hosts and to a similar extent in tumor from p50(f/f) mice (Fig. S5A).