Generation of interleukin-13 receptor alpha2 antigen expressing modified vaccinia ankara recombinant virus for potential cancer immunotherapy

Abstract

Genetically modified recombinant poxviruses have shown promise in preclinical models of cancer immunotherapy due to their ability to induce effective cell-mediated immunity against target tumor-associated antigens (TAA). One such vector, recombinant Modified Vaccinia Ankara (MVA), is capable of expressing foreign genes in infected host cells. MVA is replication restricted in most mammalian cells exemplifying a unique safety profile. We have demonstrated that the interleukin-13 receptor α2 (IL-13Rα2) is selectively expressed in various solid tumors but not in normal tissues making it a promising TAA. Prophylactic and therapeutic vaccination with a plasmid vector expressing IL-13Rα2 caused only partial regression of established tumors [1], suggesting that host immune responses against IL-13Rα2 needed further enhancement. Thus, we constructed a recombinant MVA (rMVA-IL13Rα2) expressing both IL-13Rα2 and a green fluorescent protein (GFP) reporter gene. Purified virus titration by immunostaining using anti-vaccinia antibody and anti-IL-13Rα2 antibody confirmed the identity and purity of the recombinant MVA. Western Blot analysis showed the presence of IL-13Rα2 protein (65 kDa). Flow cytometric analysis of IL-13Rα2 negative T98G glioma cells infected with rMVA-IL13Rα2 virus (T98G-IL13Rα2) demonstrated surface expression of IL-13Rα2, indicating the infectivity potential of the recombinant virus. Incubation of T98G-IL13Rα2 cells with varying concentrations (0-100 ng/ml) of IL13-PE (interleukin-13 fused to truncated Pseudomonas exotoxin [2] resulted in depletion of GFP+ T98G-IL13Rα2 cells in a concentration-dependent manner. Higher concentrations of IL13-PE (10-1000 ng/ml) also inhibited the protein synthesis in T98G-IL13Rα2 compared to cells infected with control pLW44-MVA. We further observed that IL13-PE treatment of rMVA-IL13Rα2 infected chicken fibroblast, DF-1 cells led to a reduction in virus titer compared to untreated cells. These results indicate that rMVA-IL13Rα2 virus can successfully infect mammalian cells and express IL-13Rα2 in a biologically active form on the cell surface. The immunization studies of rMVA-IL13Rα2 are ongoing in a syngeneic mouse model of metastatic breast carcinoma. Based on in vitro results, we expect the rMVA-IL13Rα2 to be a useful agent in tumor immunotherapy as a vaccine alone and in combination with other therapeutic agents to eradicate metastatic tumors.