Research Groups

Mammalian Biology: Recombinant Gene Products

Research Interests and Description

Staff Research Scientist: S. Swaminathan

Research Interests

Dengue, adenovirus, dengue reporter viruses, RNAi.

Description of Research

Current research focuses on the use of adenovirus as a vaccine vector for dengue antigens, the development of dengue reporter viruses to aid in dengue vaccine and drug research efforts and the investigation of the utility of RNA interference as an antiviral strategy to attenuate dengue replication.
Adenovirus vectored-dengue vaccine development
As there are four serotypes of dengue viruses, each antigenically distinct from the others, an ideal dengue vaccine must be tetravalent, capable of conferring immunity to all four serotypes. Several of the current dengue vaccines in clinical trials are based on tetravalent mixtures of single, serotype-specific (monovalent), live attenuated vaccines. These have repeatedly manifested “interference” arising out of differential replication of the live attenuated monovalent vaccine viruses in the tetravalent formulation. Interference results in a skewed immune response predominantly to a single dengue virus serotype.
Our work is driven by the hypothesis that switching from a strategy reliant on four monovalent attenuated viruses carrying inherently unstable RNA genomes to a single tetravalent DNA virus-based vaccine may provide a means of circumventing viral interference. We have developed an experimental adenovirus vaccine vector expressing a single chimeric tetravalent antigen. Preliminary studies have shown that this adenovirus vector can elicit neutralizing antibodies to all four dengue virus serotypes. Work is underway to evaluate the protective efficacy of this vaccine using dengue virus-sensitive interferon α/β and γ receptor knock-out mice.
Dengue Reporter Viruses
The current gold standard assay to determine the antiviral potency of antibodies elicited by dengue vaccine and drug candidates is the Plaque Reduction Neutralization Test (PRNT). This assay which is designed to measure the residual dengue virus infectivity in response to the presence of neutralizing antibodies or antiviral drugs is labour-intensive, time-consuming and has very limited sample-handling capacity. If the dengue viruses are engineered to express a reporter such as the green fluorescent protein (GFP), this assay would become amenable to a rapid and high throughput format wherein residual infectivity can be measured in terms of reduction in reporter gene expression. To this end we are currently developing an infectious clone of dengue type-2 virus carrying the GFP gene in place of its structural genes. Work is underway to create a packaging cell line that would provide the structural proteins to rescue this infectious clone.
RNAi to target dengue replication
As the plus sense RNA genome of dengue viruses doubles as the template for both translation and replication, targeting this RNA for degradation by harnessing the potential of the endogenous RNAi system could provide a way of attenuating dengue replication. In order to explore if one could target multiple dengue virus serotypes using RNAi, we are developing shRNA vectors targeting several conserved regions of the dengue genome. However, the success of RNAi in achieving viral replication knock-down would depend upon the ability to deliver siRNA efficiently in vivo. Once we screen and identify conserved siRNA targets, we will create an adenovirus vector encoding the corresponding shRNA constructs and evaluate the utility of this vector in attenuating the replication of the four dengue virus serotypes.