Oncolytic Rhabdoviruses Expressing Immunomodulatory miRNA Enhance Anti-Tumour Efficacy

Background:Tumour-induced immunosuppressive mechanisms in the tumour microenvironment (TME) is a major reason for the limited current success of therapeutic cancer vaccines. Reversing this immunosuppressive milieu will be critical to generate effective anti-tumour immunity. Oncolytic viruses (OV) specifically replicate in and lyse tumour cells. In addition, OV stimulate the immune system and facilitate the generation of anti-tumour immune responses.

MiRNAs are small endogenous non-coding RNAs implicated in the post-transcriptional control of gene expression. Modulating the activity of miRNAs provides opportunities for novel cancer interventions. However, low bioavailability and poor cellular uptake are major challenges for delivering miRNA mimetics specifically to cells within theTME.

We hypothesise that expressing immunomodulatory miRNAs from OVs will lead to enhanced anti-tumour immune response by targeting immunosuppressive elements within the TME.

Results: Specific 22nt mature miRNA sequences targeting key immunosuppressive molecules, or a control miRNA sequence targeting GFP were constructed into the pre-miR30 cassette and cloned into oncolytic Rhabdoviruses, VSVΔ51 and MG-1. Here, we show that the mature 22nt sequences are efficiently processed from the pre-miR30 cassette following VSVΔ51/MG-1 infection of melanoma and ovarian cancer cells, without impairing cytotoxicity or replication. Moreover, in vitro knockdown of immunosuppressive molecules in tumour cells and M2 macrophages are observed following infection. Intravenous delivery to B16-F10 tumour-bearing mice resulted in knockdown of predicted targets, in both the TME and within the spleen. This led to reduced tumour burden and an increased anti-tumour T cell response compared to control treated mice.

Conclusion: Expression of immunomodulatory miRNA from oncolytic Rhabdoviruses results in knockdown of immunosuppressive targets in both the TME and spleen leading to enhanced anti-tumour immunity and reduced tumour burden of B16-F10 bearing mice.