TNF-superfamily arming and leukocyte based delivery of oncolytic myxoma virus in a syngeneic murine lung metastasis model

Lung metastatic cancers represent a major challenge in both basic and clinical cancer research. The ability to treat lung metastases to date has been challenging, current treatment paradigms are a mix of classic radiotherapy, chemotherapies and tumor-targeted therapies, with no one treatment that is effective for all tumors. Oncolytic viruses (OVs) represent a new therapeutic modality for hard-to-treat tumors. However, major questions still exist in the field, especially around how to therapeutically arm and deliver OVs to sites of disseminated tumors. To address this need, oncolytic myxoma viruses (MYXV) that expresses TNF superfamily member transgenes (vMYX-hTNF or vMyx-mLIGHT) were tested in an immunocompetent syngeneic lung metastatic murine osteosarcoma model. Three versions of this model were used; 1-an early intervention model, 2-an established tumor model, defined by both average tumor burden and failure of anti-PD-L1 and vMyx-TNF monotherapies, and 3-a late-stage disease model, defined by the failure the combination of vMyx-hTNF/PBMCs and anti-PD-L1 therapy. These three models were designed to test different questions about therapeutic efficacy of armed MYXV and delivery of MYXV to lung metastases. In the early intervention model, vMyx-hTNF was found to be an effective therapy, especially when delivered by leukocyte carrier cells (either bone marrow or PBMCs). Next, the combination of immune checkpoint inhibitors, including anti-PD-L1, anti-PD-1 and anti-CTLA-4, with vMyx-TNF/PBMCs were found to increase efficacy in treated mice compared to monotherapies. The established model was used to test potential synergy of vMyx-hTNF with anti-PD-L1 therapy. This model was defined by the failure of the monotherapies, however, in combination, treated mice survived significantly longer, and had lower average tumor burden throughout. This model was also used to test tumor specific delivery using ex vivo loaded PBMCs as carrier cells. Using MYXV expressing Tdtomato, PBMCs were found to deliver MYXV to tumors more effectively than free virus. In the most stringent late-stage disease model, vMyx-mLIGHT/PBMCs and vMyx-mLIGHT/PBMCs plus anti-PD-1 were tested and found to be efficacious where combination vMyx-TNF/PBMCs plus PD-1 failed. These results taken together show that TNFSF arming of MYXV, especially when delivered by autologous PBMCs, represents a new potential treatment strategy for lung metastatic tumors.