R. V. Dave1,2, F. Errington-Mais1, E. West1, P. Selby1, G. J. Toogood2, A. Melcher1 1Targeted And Biological Therapies Group,Leeds Institute Of Cancer And Pathology,Leeds, YORKSHIRE, United Kingdom 2Department Of Hepatobiliary And Transplant Surgery,St James University Hospital,Leeds, YORKSHIRE, United Kingdom
Introduction: There is still a need for a novel treatment modality for colorectal cancer (CRC) liver metastases (CRLM). We examined the ability of JX-594-based vaccinia viruses (JXVV) to preferentially replicate in and kill CRLM, and induce immune-mediated tumour cytotoxicity by activation of natural killer (NK) cells.
Methods: The vaccinia virus was genetically manipulated to encode for granulocyte macrophage colony stimulating factor (JXVV-GM-CSF-fLuc) and green fluorescent protein (JXVV-GM-CSF-GFP). Viability assays and Enzyme Linked Immunoabsorbent Assay were used to confirm tumour cell killing and production of inflammatory cytokines when CRC cell lines were infected with JXVV. Viral replication was investigated by plaque assay and using a novel ex-vivo ‘tissue core’ method from freshly resected liver tissue. Induction of the innate immune response was measured by flow-cytometric analysis of JXVV-treated NK cells from blood, liver and lymph nodes, and anti-tumour cytotoxicity investigated by chromium release.
Results: We demonstrated direct lysis of CRC cell lines by treatment with JXVV, with greater lysis and replication (up to 250-fold) in cells with upregulated surface EGFR. JXVV treatment resulted in substantial expression of GMCSF and induction of inflammatory cytokines within the tumour microenvironment, and inhibition of anti-inflammatory and pro-angiogenic cytokines. Ex vivo infection of CRLM with JX-594-GFP-GMCSF resulted in tumour-specific GFP and GMCSF expression, which was not seen in normal liver tissue resected around the tumour. Treatment of NK cells with JX-594-GMCSF led to activation, degranulation and increased cytotoxicity against CRC cell targets. This was dependant on Interferon alpha production and the presence of CD14+ve monocytes, which acquired an antigen-presenting phenotype (CD86+veCD11c+veClassIIDR+ve). It was also observed that JX-594-GFP-GMCSF expressed GFP within monocytes, but did not replicate or express transgenes within lymphocytes, further implicating monocytes in JXVV-mediated NK cell activation.
Conclusion: Oncolytic Virotherapy holds promise as a novel treatment modality. Direct tumour-specific lysis and transgene expression and the induction of tumour-specific innate immunity means that it may provide a two-pronged attack against tumour cells whilst sparing normal tissue.