Vaccinia virus rTTV∆TK-mIL21 with the IL-21 insertion and expressing the corresponding protein IL-21 has been shown to have an antitumor activity against murine glioma GL261 and has also been demonstrated to provide a benefit through modulating the TME by raising the abundance of NK cells and CD4+ and CD8+ T cells while reducing inhibitory Treg cells [105]. Here, IL21 is linked to central nervous system cancer.