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Histological evaluation of intratumoral myxoma virus treatment in an immunocompetent mouse model of melanoma

Authors Doty R, Liu J, McFadden G, Roy E, MacNeill AL

Received 11 September 2012

Accepted for publication 1 November 2012

Published 14 January 2013 Volume 2013:2 Pages 1—17


Checked for plagiarism Yes

Review by Single-blind

Peer reviewer comments 6

Rosalinda A Doty,1 Jia Liu,2 Grant McFadden,2 Edward J Roy,3 Amy L MacNeill1

1Department of Pathobiology, University of Illinois, Urbana, IL, 2Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, FL, 3Department of Molecular and Integrative Physiology, University of Illinois, Urbana, IL, USA

Abstract: Two recombinant myxoma viruses (MYXV expressing a fluorescent protein [MYXV-Tred] and MYXV-Tred encoding murine interleukin-15 [MYXV-IL15]) were evaluated for therapeutic effects in an aggressive B16F10 melanoma model in immunocompetent mice. It was hypothesized that continuous expression of IL-15 within a tumor would recruit cytotoxic effector cells to induce an antitumor immune response and improve treatment efficacy. Weekly intratumoral injections were given to evaluate the effect of treatment on the median survival time of C57BL/6 mice bearing established B16F10 melanomas. Mice that received MYXV-Tred or MYXV-IL15 lived significantly longer than mice given treatment controls. Unexpectedly, the median survival time of MYXV-IL15-treated mice was similar to that of MYXV-treated mice. At 1, 2, and 4 days postinoculation, viral plaque assays detected replicating MYXV-Tred and MYXV-IL15 within treated tumors. At these time points in MYXV-IL15-treated tumors, IL-15 concentration, lymphocyte grades, and cluster of differentiation-3+ cell counts were significantly increased when compared to other treatment groups. However, viral titers, recombinant protein expression, and lymphocyte numbers within the tumors diminished rapidly at 7 days postinoculation. These data indicate that treatment with recombinant MYXV should be repeated at least every 4 days to maintain recombinant protein expression within a murine tumor. Additionally, neutrophilic inflammation was significantly increased in MYXV-Tred- and MYXV-IL15-treated tumors at early time points. It is speculated that neutrophilic inflammation induced by intratumoral replication of recombinant MXYV contributes to the antitumoral effect of MYXV treatment in this melanoma model. These findings support the inclusion of neutrophil chemotaxins in recombinant poxvirus oncolytic virotherapy.

Keywords: cancer, interleukin-15, melanoma, myxoma virus, neutrophils, oncolytic virus

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