PDCD1 and cancer: We confirmed that the expression profile of IC ligands in primary cultures of epithelial and mesenchymal cancer cells was comparable to that observed in cancer cells growing in vivo (Fig. 3b), and that PD-1, CTLA-4, and TIGIT receptors were expressed by CD8+ T cells after 2 and 4 days of in vitro CD3/CD28 activation (Fig. 3c–e).