Oncolytic viruses expressing MATEs facilitate target-independent T-cell activation in tumors.

Oncolytic viruses (OV) expressing bispecific T-cell engagers (BiTEs) are promising tools for tumor immunotherapy but the range of target tumors is limited. To facilitate effective T-cell stimulation with broad-range applicability, we established membrane-associated T-cell engagers (MATEs) harboring the protein transduction domain of the HIV-Tat protein to achieve non-selective binding to target cells. In vitro, MATEs effectively activated murine T cells and improved killing of MC38 colon carcinoma cells. Similarly, humanized MATEs activated T cells in PBMCs from human donors. In MC38-tumors in mice, MATE-expression by the oncolytic adenovirus Ad5/11 facilitated intratumoral T-cell activation, reduced tumor growth and prolonged survival accompanied by infiltration of tumor-directed CD8⁺ T cells and improved CD8/CD4 T-cell ratio. Absence of early T-cell activation in tumor draining lymph nodes suggests the safe applicability of this strategy. Furthermore, MATE-expression by Ad5/11 was capable of breaking resistance to αPD-1 checkpoint therapy thereby promoting T-cell/tumor cell proximity and clustering of CD8⁺ and CD4⁺ T cells. In summary, we demonstrated that MATE expressing OVs are powerful T-cell activating tools suitable for local immunotherapy of a broad range of tumors.