This is consistent with previous findings that tumor cells may hijack the immune checkpoints to inhibit or exhaust T-cell activities through the PD-1/PD-L1 pathway.29 Indeed, CL1-5 and CL141 cells pretreated with pemetrexed or 5-FU displayed greater abilities to inhibit Jurkat T-cell or CTL-mediated cytokine secretion (figure 2A–D), supporting the idea that these antimetabolic chemotherapeutics are capable of inducing PD-L1 expression in tumor cells and the following T-cell suppression. Here, PDCD1 is linked to neoplasm.