We report here the successful vectorization of a hamster monoclonal IgG (namely J43) recognizing the murine Programmed cell death-1 (mPD-1) in Western Reserve (WR) oncolytic vaccinia virus. Three forms of mPD-1 binders have been inserted into the virus: whole antibody (mAb), Fragment antigen-binding (Fab) or single-chain variable fragment (scFv). MAb, Fab and scFv were produced and assembled with the expected patterns in supernatants of cells infected by the recombinant viruses. The three purified mPD-1 binders were able to block the binding of mPD-1 ligand to mPD-1 in vitro. Moreover, mAb was detected in tumor and in serum of C57BL/6 mice when the recombinant WR-mAb was injected intratumorally (IT) in B16F10 and MCA 205 tumors. The concentration of circulating mAb detected after IT injection was up to 1,900-fold higher than the level obtained after a subcutaneous (SC) injection (i.e., without tumor) confirming the virus tropism for tumoral cells and/or microenvironment. Moreover, the overall tumoral accumulation of the mAb was higher and lasted longer after IT injection of WR-mAb1, than after IT administration of 10 µg of J43. The IT injection of viruses induced a massive infiltration of immune cells including activated lymphocytes (CD8+ and CD4+). Interestingly, in the MCA 205 tumor model, WR-mAb1 and WR-scFv induced a therapeutic control of tumor growth similar to unarmed WR combined to systemically administered J43 and superior to that obtained with an unarmed WR. These results pave the way for next generation of oncolytic vaccinia armed with immunomodulatory therapeutic proteins such as mAbs.

Oncolytic virotherapy is an emergent promising therapeutic approach for the treatment of cancer. We have constructed a vaccinia virus (WR strain) deleted for thymidine kinase (TK) and ribonucleotide reductase (RR) genes that expressed the fusion suicide gene FCU1 derived from the yeast cytosine deaminase and uracil phosphoribosyltransferase genes. We evaluated this construct (VV-FCU1) in the orthotopic model of renal carcinoma (RenCa). Systemic administration of VV-FCU1 resulted in orthotopic tumor growth inhibition, despite temporary expression of viral proteins. VV-FCU1 treatment was associated with an infiltration of tumors by CD8+ T lymphocytes and a decrease in the proportion of infiltrating Tregs, thus modifying the ratio of CD8+/CD4+ Treg in favor of CD8+cytotoxic T cells. We demonstrated that VV-FCU1 treatment prolonged survival of animals implanted with RenCa cells in kidney. Depletion of CD8+ T cells abolished the therapeutic effect of VV-FCU1 while depletion of CD4+ T cells enhanced its protective activity. Administration of the prodrug 5-fluorocytosine (5-FC) resulted in a sustained control of tumor growth but did not extend survival. This study shows the importance of CD4+ and CD8+ T cells in vaccinia virus-mediated oncolytic virotherapy and suggests that this approach may be evaluated for the treatment of human renal cell carcinoma.

TG4010, a Modified Vaccinia virus Ankara (MVA) expressing human mucin1 (MUC1) has demonstrated clinical benefit for patients suffering from advanced non-small cell lung cancer (NSCLC) in combination with chemotherapy. To support its development, preclinical experiments were performed with either TG4010 or β-galactosidase-encoding MVA vector (MVA-βgal) in mice presenting tumors in the lung. Tumor growth was obtained after intravenous injection of CT26 murine colon cancer cells, engineered to express either MUC1 or βgal. Mice showed increased survival rates after repeated intravenous injections of TG4010 or MVA-βgal, compared to an empty MVA control vector. Treatment with MVA vectors led to the accumulation of CD3dimCD8dim T cells, with two subpopulations characterized as KLRG1+CD127− short-lived effector cells (SLECs), and KLRG1−CD127− early effector cells (EECs) comprising cells releasing IFNγ, Granzyme B and CD107a upon antigen-specific peptide stimulation. EECs were characterized by an up-regulation of PD-1. Tumor growth in the diseased lung correlated with the appearance of PD1+ Treg cells that partially disappeared after TG4010 treatment. At late stage of tumor development in the lung, PD-L1 was detected on CD45− tumor cells, on CD4+ cells, including Treg cells, on CD3+CD8+ and CD3dimCD8dim T lymphocytes, on NK cells, on MDSCs and on alveolar macrophages. We demonstrated that targeting the PD-1/PD-L1 pathway with blocking monoclonal antibodies several days after TG4010 treatment, at late stage of tumor development, enhanced the therapeutic protection induced by the vaccine, supporting the ongoing clinical evaluation of TG4010 immunotherapy in combination with Nivolumab.