CANCER THERAPY USING ANTIBODY-MEDIATED DELIVERY OF ONCOLYTIC VIRUSES

Some viruses that infect humans are currently under investigation for the treatment of cancer; these are referred to as oncolytic viruses. Some of these oncolytic viruses rarely produce serious symptoms in humans while others have been modified so that they no longer cause disease. They act both by directly killing cancer cells and also by stimulating the body's own immune system to attack the cancer. However, with regard to oncolytic viruses, the immune system represents a double-edged sword, because as well as stimulating anti-cancer immune responses, oncolytic viruses also stimulate anti-viral immune responses, including the production of anti-viral neutralizing antibodies. The current perception is that these anti-viral neutralizing antibodies are a barrier to intravenous delivery of oncolytic viruses, because they will neutralize the virus and prevent it reaching the tumour. Thus repeated intravenous injections would be ineffective because of the anti-viral immune response that is generated after the first dose is given to a patient. However, our research has unexpectedly found that neutralizing antibodies may play a role in cancer treatment.

We have found that some immune cells in the blood called monocytes can be loaded with pre-formed virus-antibody complexes (so the virus is fully neutralized) and then, by mechanisms not currently known, reactivate the virus so that it can be transferred to tumour cells which it infects and kills. This is very unexpected, as monocytes are thought to destroy all antibody-coated virus they encounter. Our research therefore has significant implications for the future of oncolytic virotherapy and for the design of clinical oncolytic virotherapy treatment strategies.

We propose to investigate this further to determine how many of the oncolytic viruses currently under investigation in the clinic, can be reactivated by monocytes in this way. We will also find out whether other cells in the blood can also reactivate antibody-neutralized viruses in the same way as monocytes and investigate the mechanisms involved in the process. This work will increase our understanding of the role of neutralizing antibodies in oncolytic virotherapy and enable improvements in the use of oncolytic viruses for treating cancer.

Antibody-neutralization of viruses is thought to be irreversible. Hence the current perception that anti-viral neutralizing antibodies in patients are a barrier to systemic oncolytic viral therapy. However, our research has discovered that monocytes are able to internalize, process and reactivate antibody-neutralized viruses such that they can then be transmitted to tumour target cells resulting in infection and lysis.

We generated reovirus-NAb (reoNAb) complexes by incubating reovirus with a neutralizing volume of human serum. These were loaded onto isolated human monocytes and co-cultured with reovirus-susceptible tumour cells. When loaded onto monocytes, reoNAb complexes induced tumour cell death, whereas free reoNAb complexes were ineffective. Thus the virus was fully neutralized by the serum-derived NAb and unable to infect the target cells directly but when loaded onto monocytes it became effective for target cell killing. We have identified a role for antibody receptor FcgammaRIII in reoNAb uptake by monocytes, but our data suggests other receptors are also involved.

This project will use complementary human in vitro and murine in vivo models to investigate the reactivation of antibody-neutralized viruses by monocytes. We will discover whether other oncolytic viruses currently being tested in the clinic are also reactivated by monocytes following antibody neutralization. This will identify those viruses that are applicable for repeat systemic delivery in patients and may also indicate any common viral physiology that would enable prediction of which viruses can be reactivated in this manner. We will also identify other immune cell subsets that are capable of reactivating antibody-neutralized oncolytic viruses and identify the receptors required and we will compare the effect of different antibody isotypes. These investigations will define strategies to improve oncolytic virotherapy in the clinic.

The preliminary data we present here have indicated an unexpected function of monocytes in reactivating oncolytic virus (OV) that has been fully neutralized by antibodies. The proposed work outlined in this application will identify: other oncolytic viruses that can be similarly reactivated by monocytes; other immune cells capable of mediating OV reactivation; and define the mechanisms involved in this novel aspect of monocyte function. Our work will be of direct relevance to the design of oncolytic virotherapy regimens, enabling more rapid potentiation of oncolytic virotherapy in the clinic. In addition, by providing a new level of understanding of monocyte-mediated viral dissemination, it will have a direct scientific impact in the fields of microbiology and immunology, with particular relevance to chronic viral infections. Thus, it has the potential to impact on UK health, society and the economy.

Industrial Impact: the current perception within the OV Biotech Industry, is that neutralizing antibodies are a barrier to systemic OV administration in patients and research is currently focused on how to overcome this. Our discovery that monocytes can reactivate antibody-neutralized virus may highlight new opportunities for increasing viral delivery to tumours (especially in patients with previous exposure to the virus) leading to the design of novel therapeutics to enhance oncolytic virotherapy. In addition, dissemination of antibody-neutralized virus by monocytes may contribute to chronic viral infections. Therefore, an understanding of the mechanisms involved raises the possibility of identifying novel anti-viral drug targets and will provide the pharmaceutical industry with new leads in optimising the development of anti-viral drugs.

Public Sector, Society and Economic Impact: Cancer is a major cause of mortality worldwide with incidence rates projected to rise as the population ages. Cancer treatment places a huge burden on public resources and improved therapies are urgently required. Our work will inform the rapidly growing area of cancer immunotherapy by establishing and disseminating evidence to inform clinicians in the design of OV clinical trials, potentially giving huge savings in time and money before the full potential of OV therapy is available. Furthermore, viral infections themselves are a major threat to human health. Many infections require hospitalization and treatment costs are high. Even when hospitalization is not required there is a significant economic impact through work hours lost as a result of illness. Viral infections in animals can have a significant impact on the farming community, sometimes resulting in drastic loss of livestock; ensuing price increases then impacting on society generally. Our research has the potential to deliver impact by improving the understanding of viral dissemination routes in both humans and animals.
The findings from our work will be publicized via the University of Leeds press office and by public engagement activities, to raise awareness in the general public.

Training of skilled researchers: One postdoctoral researcher will be recruited as part of this project. He/she will gain experience in molecular biology techniques, fluorescence microscopy, tissue culture, virology methods and animal experimentation. Conference attendance will broaden their experience and allow them the opportunity to establish their own contact networks. Upon completion of this position he/she should therefore be well equipped for moving forward to the next stage of their career.