An effective oncolytic adenovirus 11 armed with the immunostimulatory B7-DC gene

We aim to understand and develop a safe and effective virus for the treatment of cancer. Cancer is a leading cause of death but standard treatments such as radio- and chemo-therapy are often not curative and have significant side effects. Using viruses to kill cancer cells is one of the newer treatments being studied, some of which are already being delivered to humans.
The use of virus alone however is not strong enough to completely destroy a tumour. We will make it more powerful by genetic modification so that it could stimulate the immune system. The tumour would then be attacked by the virus as well as immune cells. This is based on the fact that the immune system can kill cancer cells although it needs a strong trigger to do so.
A virus has to enter before it could multiply in and destroy a cell. We will use a virus that enters cells more efficiently so that it could perform its function better. We will also make it more destructive to cancer cells but not the surrounding normal cells. This virus will be tested on mice to confirm its safety and effectiveness before any consideration for human trials.

Background: Oncolytic adenoviral therapy aims to exploit the ability of virus to destroy its host cells. To improve its potency, various genes can be inserted into the virus & delivered to the tumour environment. The use of adenovirus 5 (Ad5) however is limited by its inability to transduce certain cells & a high prevalence of neutralising antibodies to its hexon proteins. This is in contrast to Ad11 which binds to a different receptor (CD46), has a low prevalence of antibodies & is a promising gene transfer vector. B7-DC is a costimulatory molecule that can significantly enhance antitumour immunity when expressed on cancer cells. A mutant form of B7-DC, K113S, which does not bind to the negative regulator Programmed Death-1, could be a more powerful immune stimulator.

Aims & objectives: Assessment of Ad11 as a potential oncolytic virus; validation of the therapeutic effect of B7-DC by constructing & infecting tumour with a replication-defective Ad5 armed with this gene; validation of the immune mechanisms of B7-DC-induced immunity; construction & assessment of B7-DC-armed Ad11; improvement of Ad11‘s potency & selectivity.

Preliminary data: On FACS, human pancreatic cancer cell lines showed significantly higher expression of CD46 compared to the Ad5 receptor CAR. Using the MTS & TCID50 dilution assays, Ad11 was shown to be more effective in lysing & replicating in tumours that are relatively insensitive to Ad5. Non-replicative Ad5 armed with B7-DC or K113S have been constructed. After infecting the murine rectal adenocarcinoma CMT-93 cells, B7-DC & K113S expression was confirmed by FACS, immunohistochemistry & Western blot.

Methodology: To test the therapeutic potential of B7-DC & K113S, the recombinant Ad5-B7-DC/K113S will be tested on C57/BL6 mice bearing the CMT-93 tumour. Validation of the immune mechanisms will be performed using the chromium-release assay, the JAM test, ELISPOT & the T-cell subset depletion assays. B7-DC & K113S-armed Ad11 will be constructed as with Ad5 & tested in vivo. Improvement of Ad11‘s oncolytic potency & selectivity will be achieved by insertion of the adenovirus death protein & deletions of E1A 231R & E1B-19k.

Scientific opportunities: Understanding the role of Ad11 in oncolytic viral gene therapy. Exploration of B7-DC & antitumour immunity.

Medical opportunities: Development of a potent & selective oncolytic virus that can destroy many cancer cell types whilst having minimal toxicity.