Oncolytic Newcastle disease virus expressing the co-stimulator OX40L as immunopotentiator for colorectal cancer therapy.

NDV as an attractive candidate for oncolytic immunotherapy selectively lyses tumor cells but shows limited anti-tumor immunity. Immune co-stimulator OX40 ligand (OX40L) boosts anti-tumor immunity response by delivering a potent costimulatory signal to CD4 and CD8 T cells. To improve the anti-tumor immunity of NDV, the recombinant NDV expressing the murine OX40L (rNDV-mOX40L) was engineered. The viral growth kinetics was examined in CT26 cell lines. The ability of rNDV-mOX40L to express mOX40L was detected in the infected tumor cells and tumor tissues. The anti-tumor activity of rNDV-mOX40L was studied in the CT26 animal model. Tumor-specific CD4, CD8 and OX40 T cells were examined by immunohistochemistry staining. The virus growth curve showed that the insertion of the mOX40L gene did not affect the growth kinetics of NDV. rNDV-mOX40L expresses mOX40L and effectively inhibits the growth of CT26 colorectal cancer in vivo. The tumor inhibition rate of the rNDV-mOX40L-treated group was increased by 15.8% compared to that of  NDV-treated group in the CT26 model. Furthermore, immunohistochemistry staining of tumor tissues removed from the CT26 model revealed that intense infiltration of tumor-specific CD4, CD8 T cells, especially OX40 T cells were found in the rNDV-mOX40L-treated group. FACS showed that rNDV-mOX40L significantly enhanced the number of CD4 and CD8T cells in spleen. Moreover, compared to the NDV-treated group, the level of mouse IFN-γ protein in the tumor site increased significantly in the rNDV-mOX40L-treated group. Taken together, rNDV-mOX40L exhibited superior anti-tumor immunity by stimulating tumor-specific T cells and may be a promising agent for cancer immunotherapy.