Myxoma Virus Expressing a Fusion Protein of Interleukin-15

• Published in: PloS one 2014-10, Vol.9 (10)
• Main Authors: Tosic, Vesna, Thomas, Diana L, Kranz, David M, Liu, Jia, McFadden, Grant, Shisler, Joanna L, MacNeill, Amy L, Roy, Edward J
• Format: Article
• Language: English
• Subjects: Analysis; Genetic vectors; Health aspects; House mouse; Interleukins; Melanoma; Myxoma; T cells
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0109801

Myxoma virus, a rabbit poxvirus, can efficiently infect various types of mouse and human cancer cells. It is a strict rabbit-specific pathogen, and is thought to be safe as a therapeutic agent in all non-rabbit hosts tested including mice and humans. Interleukin-15 (IL15) is an immuno-modulatory cytokine with significant potential for stimulating anti-tumor T lymphocytes and NK cells. Co-expression of IL15 with the [alpha] subunit of IL15 receptor (IL15R[alpha]) greatly enhances IL15 stability and bioavailability. Therefore, we engineered a new recombinant myxoma virus (vMyx-IL15R[alpha]-tdTr), which expresses an IL15R[alpha]-IL15 fusion protein plus tdTomato red fluorescent reporter protein. Permissive rabbit kidney epithelial (RK-13) cells infected with vMyx-IL15R[alpha]-tdTr expressed and secreted the IL15R[alpha]-IL15 fusion protein. Functional activity was confirmed by demonstrating that the secreted fusion protein stimulated proliferation of cytokine-dependent CTLL-2 cells. Multi-step growth curves showed that murine melanoma (B16-F10 and B16.SIY) cell lines were permissive to vMyx-IL15R[alpha]-tdTr infection. In vivo experiments in RAG1.sup.-/- mice showed that subcutaneous B16-F10 tumors treated with vMyx-IL15R[alpha]-tdTr exhibited attenuated tumor growth and a significant survival benefit for the treated group compared to the PBS control and the control viruses (vMyx-IL15-tdTr and vMyx-tdTr). Immunohistological analysis of the subcutaneous tumors showed dramatically increased infiltration of NK cells in vMyx-IL15R[alpha]-tdTr treated tumors compared to the controls. In vivo experiments with immunocompetent C57BL/6 mice revealed a strong infiltrate of both NK cells and CD8.sup.+ T cells in response to vMyx-IL15R[alpha]-tdTr, and prolonged survival. We conclude that delivery of IL15R[alpha]-IL15 in a myxoma virus vector stimulates both innate and adaptive components of the immune system.