Although very different at a molecular level, hepatitis viruses B and C (HBV and HCV) both infect only humans and chimpanzees which means that there is a lack of suitable small animal models for studying viral lifecycles and for testing new drugs. One alternative would be to study the viruses and test new compounds in liver cells grown in vitro, but human hepatocytes are very difficult to grow and maintain in culture.

A team of researchers led by scientists at the Salk Institute has now provided a solution to the problem by generating a mouse with a liver that is almost completely ‘humanised’. The team had previously generated a mouse with a partially humanised liver but wanted to achieve more complete transformation. Around 95% of the liver cells of the new mice are human in origin and the animals are susceptible to infection by both HBV and HCV. Mice infected with HCV were shown to respond to drugs such as pegylated interferon α2a and ribavirin that are used to treat human patients. Adefovir dipivoxil, used to treat HBV patients, was found to lower viral titres in mice infected with HBV.

The mice were generated by using genetic and pharmacological pressures to lead to a growth disadvantage for mouse hepatocytes and positive selection for transplanted human hepatocytes. The mice provide a new way to study pathogens that target the human liver and to test drugs to treat human hepatitis. In the future, the mice could also be used to study other hepatotrophic pathogens such as malaria, as well as cirrhosis and liver cancer.

The study is published in the Journal of Clinical Investigation.

Some 200 million people worldwide are estimated to be infected with the hepatitis C virus (HCV) which can eventually lead to cirrhosis, liver cancer, and in some cases, death. The current standard-of-care treatment for persistent infection – a combination of pegylated interferon-α and ribavirin – is able to clear the infection in around 50% of patients. In some patients, however, treatment is associated with haemolytic anaemia which may be severe enough to need dosage reduction or even discontinuation of treatment.

A team led by scientists at Duke University’s Institute for Genome Sciences & Policy (IGSP) have now discovered that loss of function mutations in the gene ITPA, which encodes the enzyme inosine triphosphatase, protect against the development of anaemia. Previous studies had identified the genetic variants with enzyme deficiency and, through a genome-wide association study, the Duke team were able to show that they were also protective against anaemia caused by ribavirin. The finding may offer new treatment opportunities for HCV patients with coronary artery disease or kidney disease who are often not treated with ribavirin because of fears that anaemia could exacerbate their condition.

Inosine triphosphatase deficiency was first recognised over 30 years ago and is not thought to be clinically important. A diagnostic test that could predict deficiency, and hence reduced susceptibility to ribavirin-associated anaemia, would allow broader treatment options for HCV patients.

The study is published in the journal Nature.

Chikungunya is a viral disease spread by mosquitoes which causes fever and severe joint pain – the name derives from a verb meaning ‘to become contorted’ and describes the appearance of sufferers bent with pain. Chikungunya is an alphavirus of the family Togaviridae and is usually spread by Aedes aegypti mosquitoes. In 2005-2006, however, a point mutation in one of the viral envelope genes facilitated transmission by Aedes albopictus (tiger mosquito), increasing the risk of outbreaks in areas where the Asian tiger mosquito is present. In the coming years, expansion of the ranges of mosquitoes and changes in insect vectors could increase the spread of Chikungunya virus and other arboviruses.

There is no cure for Chikungunya and treatment is focussed on relieving symptoms. There is also no commercially available vaccine but researchers in the US have now developed an experimental vaccine using non-infectious virus-like particles (VLPs). Selective expression of viral structural proteins produced VLPs that resemble replication-competent alphaviruses and immunization with these VLPs led to neutralizing antibodies against envelope proteins from alternative Chikungunya strains. Rhesus macaques produced high-titre neutralizing antibodies that protected against viremia after high-dose challenge. When the monkey antibodies were transferred into immunodeficient mice, they protected against subsequent lethal viral challenge, indicating a humoral mechanism of protection. VLPs could potentially be developed to offer protection from other alphaviruses such as O’nyong’nyong virus, Ross River virus and Barmah Forest virus. Virus-like particle based-vaccines against human papillomavirus and hepatitis B virus have already been approved by the Food and Drug Administration.

The study is published in the journal Nature Medicine.

For more than 50 years, it has been supposed that the rate of spread of viruses is limited by replication kinetics in an iterative process of infection, replication and release, but scientists at Imperial College London have now challenged this view. Using live video microscopy, vaccinia virus was found to spread four times more quickly than should have been possible, based on the rate at which it can replicate. The videos showed that the virus spreads by surfing from cell to cell, using a mechanism that allows it to bounce past cells that are already infected and reach uninfected cells as quickly as possible. Soon after vaccinia infects a cell, two viral proteins, A33 and A36, are expressed at the cell surface, marking the cell as infected. When new viruses approach the infected cell, these proteins trigger the host cell to project actin ‘tails’ which physically repel approaching viruses. In this way, the viruses are propelled from cell to cell until they find one that is not already infected.

HSV-1 also spreads at a faster rate than should be possible given its replication rate and may use a similar spreading mechanism. If the ability to signal that a cell is already infected proves to be a common feature of pathogenic viruses, the discovery could eventually lead to new antiviral drugs that exploit this mechanism.

The study is published in the journal Science.

The concept of ‘lethal mutagenesis’ has been developed as a means of curing viral infections and has also been used to explain the action of some antiviral drugs. Although mutation is the basis for adaptation and survival, especially in the presence of antiviral drugs, most mutations are detrimental and the theory of lethal mutagenesis holds that an infecting population can be pushed to extinction by an overwhelmingly high mutation rate. Chemical mutagens have been used to increase error rates in a number of RNA viruses including HIV-1 and HCV and have been found to significantly reduce viral titres and, in some cases, achieve extinction. For example, the antiviral activity of the ribonucleoside analogue 5-azacytidine (5-AZC) against HIV-1 has been attributed primarily to an increase in mutant frequency consistent with lethal mutagenesis caused by incorporation of 5-AZC into viral DNA.

A team of researchers from the University of Texas at Austin have now raised serious concerns about the strategy of inducing lethal mutations, suggesting that it could cause viruses to become more virulent. The team predicted that growing the DNA bacteriophage T7 in the presence of a mutagen would lead to a substantial decline in viral fitness but found instead that, after 200 generations, fitness had increased despite a mutation rate two to three orders of magnitude above baseline. Although the researchers agree that extremely high mutation rates will mostly lead to viral extinction, they caution that forcing viruses to undergo rapid mutation could, if the mutation rate is not high enough, lead to well adapted ‘superviruses’.

The study is published in the journal Genetics.

The pandemic swine flu (H1N1) virus has proved to be less lethal than originally feared but, although most infected individuals experience relatively mild and self-limiting symptoms, some patients with no previous underlying medical condition have died. An international team of researchers has now found a possible explanation of why some people develop severe pneumonia when infected with the H1N1 virus. The team profiled immune mediators in 20 patients with severe symptoms, 15 patients with mild symptoms and 15 healthy controls. A typical innate antiviral response with increased levels of chemokines IP-10, MCP-1 and MIP-1β and an absence of anti-H1N1 antibodies characterised the early response in all infected individuals, but elevated levels of IFN-γ and mediators that stimulate Th17 and Th1 responses were found only in hospitalised patients. Both critical and non-critical hospitalised patients had increased levels of IFN-γ, Th17 mediators (IL-8, IL-9, IL17 and IL6) and Th1 mediators (TNF-α, IL-15 and IL-12p70) compared to outpatients. All hospitalised patients showed higher levels of IL-17 and TNF-α than controls but only the non-critical patients showed significant higher levels of IL-17 and TNF-α than those with mild symptoms. Levels of IL-15, IL-12p70 increased exclusively in critical patients who also showed the highest levels of IL-6.

Around half of hospitalised patients and nearly all outpatients tested positive for virus, with all those who tested positive having similar viral loads. Significantly higher levels of IL-13 and IL-17 were found in hospitalised patients with undetectable virus. IL6 was found to show a significant inverse association with arterial blood oxygen pressure in hospitalised patients and a similar inverse relationship was found for IL-8 in the critically ill patients.

Th1 and Th17 cells form an important part of host defence against pathogens but TH17 cells have also been linked to the pathogenesis of autoimmune and inflammatory diseases. It is presently unclear whether the increase in Th1 and Th17 responses reflects a vigorous antiviral defence necessary to clear lower respiratory infection or whether the inflammatory response contributes to disease severity. Although the ability of influenza viruses to evoke an inflammatory response is well known, this is the first study to link a Th17 response to severe influenza disease in humans. The authors suggest that immunomodulatory drugs which down-modulate Th1 and Th17 responses could be used to clarify the role of these pathways in the pathogenesis of the acute respiratory symptoms shown by patients with severe H1N1 disease. “Hypercytokinemia” of specific chemokines and cytokines has previously been shown to be associated with severe and often fatal cases of human H5N1 infections.

The study is published in the journal Critical Care.

Both HIV and cancer cells have found ways to evade the body’s immune system but researchers at Yale University have now found a way to boost the body’s ability to fight HIV and cancer. The team have identified bifunctional small molecules, termed “antibody-recruiting molecule targeting HIV” (ARM-H) and “antibody-recruiting molecule targeting prostate cancer” (ARM-P), which bind simultaneously to antibodies and to proteins on HIV, HIV-infected cells or cancer cells.

ARM-H molecules bind to gp120, a component of the Env glycoprotein on the surface of HIV and virus-infected cells and to anti-2,4-dinitrophenyl antibodies already present in the bloodstream. The ternary complex formed between the antibody, ARM-H, and gp120 is immunologically active, and leads to complement-mediated destruction of Env-expressing cells. ARM-H also prevents virus entry into human T-cells and so has the potential to inhibit viral replication by two mutually reinforcing mechanisms.

ARM-P molecules bind with high affinity to prostate-specific membrane antigen (PSMA) and, by inducing complexes of anti-2,4-dinitrophenyl antibodies with prostate cancer cells, mediate antibody-dependent killing of the cancer cells.

The team has begun to evaluate the ARM molecules in mice, and hope that the strategy of using antibody-recruiting small molecules to boost the immune response will prove useful for treating HIV, cancer, and other diseases.

Both studies are published in the Journal of the American Chemical Society (ARM-H and ARM-P).

Xenotropic murine leukemia virus-related virus (XMRV) was in the news a month ago as researchers provided new evidence that the virus could contribute to the development of prostate cancer. Now, scientists have linked XMRV to Chronic Fatigue Syndrome (CFS).

Knowing that patients with CFS can share an immune system defect with prostate cancer sufferers, the team looked for XMRV in blood samples from patients with CSF. In the study, which is published in the journal Science, XMRV was detected in blood samples from 67% of CFS patients and in only 4% of samples from healthy individuals. The infected blood samples not only contained viral DNA but were shown to produce viral proteins and infectious viral particles. Retroviral particles were also detected in patient samples using transmission electron microscopy. The virus, which is transmitted through body fluids and is not airborne, was found to be transmitted by both cell-to-cell and cell-free mechanisms. Secondary viral infections could be established in uninfected primary lymphocytes by exposure to activated PBMCs, B cells, T cells, or plasma derived from CFS patients.

The data demonstrate the first direct isolation of infectious XMRV from humans and raise the possibility that XMRV may be a contributing factor in CFS. Although the research provides a strong association between XMRV and CFS, it does not prove that XMRV causes CFS. If cause-and-effect is established, antiretroviral drugs could potentially be developed to treat CFS. Since the Science paper was submitted, the team have shown that 95% of plasma samples from CFS patients tested positive for XMRV antibodies. A clinically validated test to detect XMRV antibodies in plasma is currently under development, and the team plan to collect more data on the incidence of XMRV in the general population. The team are also investigating whether approved antiretroviral drugs are effective against XMRV and could benefit CFS patients.

Nexbio have recently presented an update on their new, broad-spectrum candidate for the prophylaxis and treatment of flu, DAS181 (Fludase®) [If this link is not working, please click here]. DAS181 is a recombinant sialidase fusion protein comprising the active domain of Actinomyces viscosus sialidase and a heparin binding sequence derived from the human protein, amphiregulin, to anchor the fusion protein to epithelial surfaces. As well as delivering DAS181 to airway epithelial cells, the anchoring domain may reduce the potential for systemic toxicity by limiting systemic absorption. DAS181 has been shown to be effective both prophylactically and therapeutically against seasonal influenza virus, the highly pathogenic H5N1 avian influenza virus, and multiple strains of parainfluenza viruses. The new study showed that DAS181 is also effective against strains of influenza virus that show resistance to the neuraminidase inhibitor, oseltamivir (Tamiflu®), both in vitro and in a mouse challenge study.

Unlike neuraminidase inhibitors that inhibit the viral neuraminidase, DAS181 prevents viral entry into cells by blocking binding of viral HA glycoproteins to sialic acids on cells in the respiratory tract. Cell-surface sialic acids act as entry receptors for all influenza virus A and B strains as well as for parainfluenza viruses. Antiviral drugs that target viral proteins lead to selection pressures that favour the emergence of resistant strains and it is hoped that targeting a host receptor may reduce the likelihood of resistance. Extensive, prolonged, nonclinical studies are reported not to show the development of any meaningful resistance.

A study carried out in collaboration with researchers at the University of Hong Kong and Imperial College, London and published in the September issue of Antimicrobial Agents and Chemotherapy has shown that DAS181 strongly inhibits infection of human lung tissue and cells by H5N1 virus. This study was also able to resolve mechanistic details of the action of DAS181. Human lung tissue and cells have two receptors that allow influenza virus to enter cells; α2-3-linked sialic acids, to which the H5N1 strain preferentially binds; and α2-6-linked sialic acids, to which the currently circulating pandemic H1N1 strain preferentially binds. DAS181 was shown to remove both α2-6-linked and α2-3-linked sialic acids found in human respiratory tissue from adjacent glycans, thereby suppressing viral entry.

DAS181 is administered by oral inhalation, using a device called ‘Cyclohaler’ and is currently undergoing phase I clinical studies.

A number of human cancers are linked to viral infection including cervical cancer (human papilloma virus), liver cancer (hepatitis B and C viruses), and lymphoma (Epstein Barr virus). The human retrovirus, XMRV (xenotropic murine leukemia virus-related virus) has previously been found in prostate cancers – most often in men with a defect in the antiviral defence protein, ribonuclease L – but, since only malignant tissues were analysed, a direct association with prostate cancer was not established. In a study published in the September 7^th online edition of PNAS, researchers at Columbia University and the University of Utah have now analysed specimens from 233 cases of prostate cancer for the presence of XMRV and compared them with 101 benign control specimens. XMRV infection was found to be associated with prostate cancer, especially with more aggressive tumours, and infection was also found to be independent of reduced activity of ribonuclease L. The virus was detected in 27% of prostate cancer specimens compared with 6% of benign tissue samples and was found almost exclusively in malignant cells.

XMRV is a member of the gammaretrovirus family, other members of which are known to cause cancers in rodents, cats and primates. The study suggests that XMRV infection could contribute to the development of human prostate cancer, although the mechanism by which the virus transforms cells remains to be fully elucidated. As with other retroviruses, XMRV integrates into host DNA and it may be that it inserts close to a gene that regulates cell growth. XMRV was found to replicate efficiently in a cell line derived from human prostate cancer but not in other human cell lines, suggesting a viral tropism that needs to be investigated further. If further studies provide a causal link between XMRV and the development of prostate cancer, opportunities for diagnostic tests, antiretroviral therapy, or ultimately a vaccine against prostate cancer, could follow.