Hepatitis C virus (HCV) infects 1-2% of the population world-wide, forming a chronic infection of the liver (Gower E, et al., 2014, J Hepatol. pii: S0168-8278(14)00526-1). Though largely asymptomatic for much of the infection, HCV-infected persons can develop cirrhosis and liver cancer during the later stages of the infection. The lack of symptoms associated with HCV infections contributes to the fact that the majority of infected persons go undiagnosed. A recent estimate in Canada has predicted that while infection rates will slowly drop over the next 20 years due to HCV screening and the use of anti-viral medications, the number of persons affected by cirrhosis and liver cancer will greatly increase, due largely to the aging of the currently infected population (Myers R P, et al., 2014, Can J Gastroenterol Hepatol. 28(5):243-250). New direct-acting anti-virals (DAAs) will aid in the treatment of HCV, though treatment rates will likely remain low (currently approximately 1.4% of infected persons in Canada, and approximately 5% in Britain and France), treatments are not entirely effective, and DAAs are prone to the development of resistance. The development of a therapeutic vaccine which could be used to treat large at-risk populations would help immensely to stem the oncoming tide of HCV-related disease.
Studies of HCV-infected chimpanzees and intravenous drug users have indicated that the production of a broad anti-HCV T cell response, potentially in combination with HCV neutralizing antibodies, will eliminate an HCV infection (Ghany M G, & Liang T J, 2013, N Engl J Med. 369(7):679-80). An estimated 20-25% of persons infected with HCV will spontaneously clear the virus, dependent on the production of a suitable immune response. Therefore, there is good reason to believe that a successful therapeutic HCV vaccine can be developed.
The largest current hurdle in the development of a successful therapeutic vaccine for HCV is the lack of animal models suitable for testing vaccine efficacy. This stems from the host-restricted nature of HCV infections, being largely restricted to infection in humans and, more specifically, human hepatocytes. Chimpanzees, though infectable, are unlikely to be used to any great extent in coming years, with the United States government no longer supporting chimpanzee use in research, and biopharmaceutical companies discontinuing their use. Vaccine efficacy testing in small animal models, generally mice, has involved the use of HCV recombinant viruses (such as vaccinia virus) (Singh S, et al., 2014, Vaccine. 32(23):2712-21), HCV recombinant lymphoma tumours (Ip P P, et al., 2014, Mol Ther. 22(4):881-90), recombinant expression of HCV antigens in the liver through transgenic modification (Satoi J, et al., 2001, J Virol. 75(24):12121-7), or transient expression construct delivery (Yu W, et al., 2014, Vaccine. 32(27):3409-16). Each of these methodologies has unique advantages and disadvantages; none mimic a chronic HCV infection very well. Recent efforts to generate a transgenic mouse that can be infected with HCV have demonstrated that HCV will only infect and persist in the livers of innate immune-incompetent mice; and even then only at very low levels (Domer M, et al., 2013, Nature. 501(7466):237-41). The use of immune-incompetent animals greatly limits the use of these models in vaccine efficacy testing.
It has recently been reported that mouse cells cultured in vitro can be made to be more permissive of HCV replication (Frentzen A, et al., 2014, Hepatology. 59(1):78-88). This was accomplished by over-expressing the liver microRNA, miR-122, in in vitro cultured hepatoma cells that were also deficient for the anti-viral protein, MAVS. The authors suggest that such cells could potentially be used to generate clones that stably replicate HCV, and that ultimately this approach may help to develop an immune-competent small animal model for HCV.
U.S. Pat. No. 7,416,840 describes cells and cell lines which replicate HCV of non-hepatic human and non-human hepatic origin, and the use of these cells and cell lines to identify anti-HCV agents. The ability of these cells to be used to screen for anti-HCV agents is dependent on the ability of the transfected HCV sequences to self-replicate, as such, the HCV RNA used for transfection of the non-human hepatic cells had already been passaged through human non-hepatic cells and had accumulated permissive mutations allowing it to replicate in these cells.
U.S. Pat. No. 6,127,116 describes a genetically engineered HCV nucleic acid clone that is capable of replication, expression of functional HCV proteins and infection in vivo and in vitro. The nucleic acid clone includes specifically defined 3′ and 5′ non-translated regions (NTRs) to permit replication of the polyprotein encoding sequences within a host cell.
International Patent Application Publication No. WO 2009/005615 describes a use of the NS4B protein nucleotide binding motif (NBM) of HCV for identifying agents that inhibit a neoplastic cellular phenotype. Expression of NS4B NBM polypeptide in mammalian cells were shown to promote a neoplastic cellular phenotype, thus cells expressing NS4B NBM are described as being useful for in vitro and in vivo methods of screening for anti-cancer agents.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.