IL21 and neoplasm: Our results showed that compared with either treatment alone, IL-21 neutralization combined with an anti-PD-1 neutralizing antibody could effectively inhibit IL-21high/PD-L1high tumor explant-induced Treg generation, whereas this effect was not observed with IL-21low/PD-L1low tumor explant-induced Treg generation, indicating that other mechanisms might be involved in Treg generation in tumor microenvironments with low expression of IL-21 and PD-L1.