Dengue fever is transmitted by the Aedes aegypti mosquito, which is found in more than 100 countries across Asia, North and South America, Africa and Europe.
Image courtesy of CDC/Frank Hadley Collins
Remarkable advances in the diagnosis and management of dengue fever, the most common mosquito-borne infection globally after malaria, have been made in recent years. Nonetheless, the disease continues to plague many tropical and subtropical regions around the world, and at present no specific treatments or clinically approved vaccines for dengue fever exist.
Singapore is a hub in the fight against dengue, and A*STAR and its partners carry out some of the most advanced research into the disease. Current projects at A*STAR that target dengue include controlling the spread of Aedes aegypti mosquitoes, the primary vector of the dengue virus, research into disease genomics and platelet biology, and clinical studies. Additional recent work also holds the potential for a major breakthrough in dengue vaccine development.
The search for a vaccine
Researchers at the A*STAR Singapore Immunology Network (SIgN), in collaboration with Singapore’s Novartis Institute for Tropical Diseases (NITD) and the Beijing Institute of Microbiology and Epidemiology (BIME) in China, and supported by a STOP Dengue Translational and Clinical Research Programme grant, have proposed a unique strategy aimed at thwarting the dengue virus’s ability to hide from the body’s immune system by deactivating a key enzyme known as methyltransferase (MTase).
The development of a safe and effective dengue vaccine has so far proven elusive due to the notorious complexity of the dengue virus, of which there are four strains or ‘serotypes’: DEN-1, DEN-2, DEN-3 and DEN-4. These variations each produce different immune responses through their interaction with antibodies in human blood serum.
Primary dengue infection usually causes mild symptoms such as fever and muscle and joint pain. It also leads to lifelong immunity to the particular infecting serotype, but can only provide short-term protection against other strains. Secondary infection with a serotype that differs from the initial infection can either result in a simple fever or progress to a more severe — potentially fatal — form of the disease such as dengue hemorrhagic fever.
Katja Fink, team leader at the A*STAR Singapore Immunology Network.
© A*STAR Singapore Immunology Network
“Dengue disease is associated with a complication that is probably unique among viral diseases,” explains Katja Fink, team leader of the research group at SIgN. “Pre-existing immunity to heterologous dengue serotypes increases the risk of developing a more severe disease in some rare cases. This risk seems to increase with the number of years between the first and the second infection,” adds Fink.
Intensive research efforts have therefore focused on the development of a tetravalent vaccine — one that is capable of providing immunity against all four serotypes. In addition, there is a clear consensus that a live attenuated vaccine — which uses a live, weakened form of the virus and thus minimizes the risk of disease — may offer the best chance of protection.
A new approach
Flaviviruses, the group of RNA viruses to which dengue belongs, use the MTase enzyme to methylate their RNA. Methylated viral RNA is capable of ‘imitating’ the RNA of the host cells, so much so that the virus can remain undetected and evade the host’s normal defense systems.
The SIgN team’s novel research strategy involves introducing a genetic mutation that inhibits the activity of MTase, leaving the virus with nowhere to hide and giving the infected individual a better chance of tackling the disease. Fink explains: “We assumed that viruses lacking this ‘hiding strategy’ would trigger a robust immune response that would stop them in the early stages of infection, a requirement of live attenuated viruses used as vaccines.”
Already, the researchers have demonstrated that mice and rhesus monkeys are able to immediately detect MTase-inactivated virus strains and produce an immune response of an appropriate strength. The challenge ahead will be to combine all four attenuated dengue serotypes into one vaccine and to conduct further experiments in mice and monkeys. If successful, the next step will be to plan human clinical trials.
“The original team comprising researchers from the NITD, the BIME and SIgN is already working on the tetravalent formulation,” says Fink. “For further development, we plan to team up with A*STAR’s D3 platform to help with the clinical trial preparation. There will be plenty of basic research questions to address as well, and for those we plan collaborations with other institutes in Singapore and overseas.”
Utilizing technology in the fight against dengue
Dengue research is a top priority at SIgN, and correspondingly its experts are also working to improve the diagnosis and prevention of dengue and other tropical diseases. The institute recently launched the VereTropTM lab-on-a-chip diagnostic kit that is capable of detecting dengue fever and another twelve major tropical diseases from a single blood sample (see Fast and simple detection of tropical diseases).
Meanwhile, at the A*STAR Genome Institute of Singapore (GIS), researchers are developing and applying genomics technologies to study and combat dengue fever. In collaboration with the Wellcome Trust’s Vietnam Research Programme and the Oxford University Clinical Research Unit in Ho Chi Minh City, Vietnam, the GIS conducted the first genome-wide association study for the disease. By comparing the genomes of children with severe dengue against healthy controls, the team was able to identify genes that may increase a child’s susceptibility to dengue shock syndrome, another potentially life-threatening complication of severe dengue infection.
The GIS has also developed a novel method called LoFreq to detect and monitor mutations in cancer cells, microorganisms and viruses. LoFreq combines deep sequencing of DNA with computational analysis to rapidly and precisely track mutations. GIS researchers are now using the technique to examine changes in the dengue virus genome following treatment of the host with antiviral drugs.
In addition to monitoring how viruses develop resistance to drug therapies, the team points out that their method can be used to identify regions in viral genomes that either rapidly or never mutate. Nagarajan Niranjan, a principal investigator at the GIS and one of the project’s leaders, says, “LoFreq has really allowed us to look at viral genome evolution in fine detail and we hope to use it to construct better models for transmission of the dengue virus.”
The multiple approaches currently under development at A*STAR demonstrate that the overall outlook in the fight against dengue fever is steadily improving. SIgN’s novel vaccine candidate and the GIS’s investigations into the genetic basis of dengue virus’s resistance to drug treatment, among others, promise to improve our understanding of this, until recently, evasive tropical disease. Thanks to these advances, Singapore looks set to strengthen the available arsenal being used to reduce the global burden of dengue infection.
About the Singapore Immunology Network
The Singapore Immunology Network (SIgN) was launched by A*STAR with the aim of expanding and strengthening immunology research in Singapore by advancing human immunology research and participating in international efforts to combat major health problems. Researchers at SIgN investigate immunity during infections and inflammatory conditions, including cancer, using mouse models and human tissue and integrate the findings into clinical applications. Since its launch, SIgN has grown rapidly, and currently includes around 250 scientists from 26 countries working under 28 renowned principal investigators and supported by cutting-edge technological research platforms and core services.
About the D3 platform
The A*STAR D3 platform was established in 2012 to build strong bridges between basic science and clinical research and development by bringing early-stage scientific discoveries to ‘proof-of-concept’ clinical trials in humans and generating economic benefit through the licensing of clinical stage therapeutics. D3 builds on Singapore’s existing drug discovery capabilities and strengthens the local biomedical innovation landscape. It was founded to be a cost-effective and professional development partner able to advance and add value to early-stage projects on a ‘shared-risk, shared-reward’ basis. D3’s primary focus is on developing drugs targeted at oncology indications and infectious diseases but the door is open to other indications if a partner brings the necessary disease knowledge. D3 is jointly funded by A*STAR, the Singapore Ministry of Health’s National Medical Research Council and the National Research Foundation.
About the Genome Institute of Singapore
The A*STAR Genome Institute of Singapore (GIS) has a global vision that seeks to use genomic sciences to improve public health and public prosperity. Established in 2001 as a center for genomic discovery, the GIS is pursuing the integration of technology, genetics and biology towards the goal of individualized medicine. The key research areas at the GIS include computational and systems biology, stem cell and developmental biology, cancer stem cell biology, cancer therapeutics and stratified oncology, human genetics, infectious diseases, genomic technologies and translational technologies. The genomics infrastructure at the GIS is utilized to train new scientific talent, to function as a bridge for academic and industrial research, and to explore scientific questions of high impact.
