Immune-mediated antitumor activity of reovirus is required for therapy and is independent of direct viral oncolysis and replication.
OBJECTIVE
Reovirus is a naturally occurring oncolytic virus in clinical trials. Although tumor infection by reovirus can generate adaptive antitumor immunity, its therapeutic importance versus direct viral oncolysis is undefined. This study addresses the requirement for viral oncolysis and replication, and the relative importance of antitumor immunity and direct oncolysis in therapy.


METHODS
Nonantigen specific T cells loaded with reovirus were delivered i.v. to C57BL/6 and severe combined immunodeficient mice bearing lymph node and splenic metastases from the murine melanoma, B16ova, with assessment of viral replication, metastatic clearance by tumor colony outgrowth, and immune priming. Human cytotoxic lymphocyte priming assays were done with dendritic cells loaded with Mel888 cells before the addition of reovirus.


RESULTS
B16ova was resistant to direct oncolysis in vitro, and failed to support reovirus replication in vitro or in vivo. Nevertheless, reovirus purged lymph node and splenic metastases in C57BL/6 mice and generated antitumor immunity. In contrast, reovirus failed to reduce tumor burden in severe combined immunodeficient mice bearing either B16ova or reovirus-sensitive B16tk metastases. In the human system, reovirus acted solely as an adjuvant when added to dendritic cells already loaded with Mel888, supporting priming of specific antitumor cytotoxic lymphocyte, in the absence of significant direct tumor oncolysis; UV-treated nonreplicating reovirus was similarly immunogenic.


CONCLUSIONS
The immune response is critical in mediating the efficacy of reovirus, and does not depend upon direct viral oncolysis or replication. The findings are of direct relevance to fulfilling the potential of this novel anticancer agent.
Prestwich
Robin J
RJ
Leeds Institute of Molecular Medicine, University of Leeds, Leeds, United Kingdom.
Ilett
Elizabeth J
EJ
Leeds Institute of Molecular Medicine, University of Leeds, Leeds, United Kingdom.
Errington
Fiona
F
Leeds Institute of Molecular Medicine, University of Leeds, Leeds, United Kingdom.
Diaz
Rosa M
RM
Molecular Medicine Program, Mayo Clinic, Rochester, Minnesota.
Steele
Lynette P
LP
Leeds Institute of Molecular Medicine, University of Leeds, Leeds, United Kingdom.
Kottke
Tim
T
Molecular Medicine Program, Mayo Clinic, Rochester, Minnesota.
Thompson
Jill
J
Molecular Medicine Program, Mayo Clinic, Rochester, Minnesota.
Galivo
Feorillo
F
Molecular Medicine Program, Mayo Clinic, Rochester, Minnesota.
Harrington
Kevin J
KJ
Targeted Therapy Laboratory, Institute of Cancer Research, Cancer Research UK, Chester Beatty Laboratories, London, United Kingdom.
Pandha
Hardev S
HS
Postgraduate Medical School, University of Surrey, Guildford, United Kingdom.
Selby
Peter J
PJ
Leeds Institute of Molecular Medicine, University of Leeds, Leeds, United Kingdom.
Vile
Richard G
RG
Leeds Institute of Molecular Medicine, University of Leeds, Leeds, United Kingdom.|Molecular Medicine Program, Mayo Clinic, Rochester, Minnesota.|Department of Immunology, Mayo Clinic, Rochester, Minnesota.
Melcher
Alan A
AA
Leeds Institute of Molecular Medicine, University of Leeds, Leeds, United Kingdom.
D000818:Animals; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D003602:Cytotoxicity, Immunologic / Q000502:physiology*; D006801:Humans; D016219:Immunotherapy, Adoptive / Q000379:methods; D012089:Mammalian orthoreovirus 3 / Q000276:immunology / Q000502:physiology*; D008546:Melanoma, Experimental / Q000276:immunology / Q000473:pathology / Q000628:therapy* / Q000821:virology; D051379:Mice; D008810:Mice, Inbred C57BL; D009362:Neoplasm Metastasis; D050130:Oncolytic Virotherapy; D050504:Oncolytic Viruses / Q000276:immunology / Q000502:physiology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology / Q000637:transplantation / Q000821:virology; D016896:Treatment Outcome; D014779:Virus Replication / Q000276:immunology / Q000502:physiology*