Abstract 2559: Molecular and immunological correlates of latent versus productive reoviral infection in cancers
Authors: Mansfield James , Stuff Andrew , Coffey Matt , Nuovo Gerard , Picchiori Flavia , Hofmeister Craig C. 
Published: May 2015

An oncolytic virus, due to its ability to replicate and lyse cancer cells while leaving normal cells intact, is an example of targeted cancer therapy. Reovirus is intrinsically oncolytic without the need for any genetic manipulation. While reovirus can be detected inside hematopoietic cancer cells after exposure, the key question is whether a reoviral infection is productive or latent?. We show that productive infection is associated with tumor cell killing by both direct apoptosis and increased T cell and NK cell response to the tumor.

We analyzed several human multiple myeloma cell lines either resistant or sensitive to reovirus infection and a metastatic melanoma model in mice after reoviral infection. Latent reoviral infection was defined by reoviral RNA proliferation with no detectable reoviral capsid protein; productive infection was defined by ample reoviral RNA proliferation and capsid production. C57BL/6 mice were injected subcutaneously with B16 or B16-VEGF cells. Immune cell depletions involved intraperitoneal injections of anti-CD8, anti-CD4 and immunoglobulin G control. For NK depletion, anti-asialo-GM1 or rabbit IgG isotype control was injected intraperitoneally. Fluorescence-activated cell sorting of spleens and/or lymph nodes confirmed subset-specific depletions. Paclitaxel was injected intraperitoneally at 10 mg/kg per injection.

Myeloma cell lines resistant to reoviral infection showed that the majority of the cancer cells had latent reoviral infection with very weak productive infection (productive/latent reoviral infection 6%). Myeloma cells sensitive to reoviral infection showed many cells with a productive viral infection (productive/latent reoviral infection was 50%. P38 expression was identical in the resistant and sensitive myeloma cell lines; two molecular markers that marked the reoviral sensitive myeloma cell lines were high CUG2 expression and low ammonia production. In the metastatic melanoma model, latent infection was dominant in mice treated with reovirus alone; productive infection was dominant in mice treated with reovirus and chemotherapy. In both the cell lines and metastatic melanoma model, productive infection was associated with elevated caspase-3 expression. In the metastatic melanoma model, productive infection was associated with increased T cell and NK cell infiltration of the tumor. Immune cell infiltrates in the tumor were investigated using a combination of multimarker IHC and multispectral imaging.

Most cancers (resistant and sensitive) show ample reoviral RNA proliferation. Cancers sensitive to reoviral oncolysis allow reoviral productive infection that may reflect high CUG2 expression or low NH3 production. Productive reoviral infection kills cancer cells both by direct caspase-3-induced apoptosis and by enhancing the T cell and NK cell response against the cancer.

Citation Format: James Mansfield, Andrew Stuff, Matt Coffey, Gerard Nuovo, Flavia Picchiori, Craig C. Hofmeister. Molecular and immunological correlates of latent versus productive reoviral infection in cancers. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2559. doi:10.1158/1538-7445.AM2014-2559