Plant-made dengue virus-like particles produced by co-expression of structural and non-structural proteins induce a humoral immune response in mice.

Dengue virus (DENV) is an emerging threat causing an estimated 390 million infections per year. Dengvaxia, the only licensed vaccine, may not be adequately safe in young and seronegative patients; hence, development of a safer, more effective vaccine is of great public health interest. Virus-like particles (VLPs) are a safe and very efficient vaccine strategy, and DENV VLPs have been produced in various expression systems. Here, we describe the production of DENV VLPs in Nicotiana benthamiana using transient expression. The co-expression of DENV structural proteins (SP) and a truncated version of the non-structural proteins (NSPs), lacking NS5 that contains the RNA-dependent RNA polymerase, led to the assembly of DENV VLPs in plants. These VLPs were comparable in appearance and size to VLPs produced in mammalian cells. Contrary to data from other expression systems, expression of the protein complex prM-E was not successful, and strategies used in other expression systems to improve the VLP yield did not result in increased yields in plants but, rather, increased purification difficulties. Immunogenicity assays in BALB/c mice revealed that plant-made DENV1-SP + NSP VLPs led to a higher antibody response in mice compared with DENV-E domain III displayed inside bluetongue virus core-like particles and a DENV-E domain III subunit. These results are consistent with the idea that VLPs could be the optimal approach to creating candidate vaccines against enveloped viruses.

Use of genetically modified bacteria for drug delivery in humans: Revisiting the safety aspect.

The use of live, genetically modified bacteria as delivery vehicles for biologics is of considerable interest scientifically and has attracted significant commercial investment. We have pioneered the use of the commensal gut bacterium Bacteroides ovatus for the oral delivery of therapeutics to the gastrointestinal tract. Here we report on our investigations of the biological safety of engineered B. ovatus bacteria that includes the use of thymineless death as a containment strategy and the potential for the spread of transgenes in vivo in the mammalian gastrointestinal tract. We demonstrate the ability of GM-strains of Bacteroides to survive thymine starvation and overcome it through the exchange of genetic material. We also provide evidence for horizontal gene transfer in the mammalian gastrointestinal tract resulting in transgene-carrying wild type bacteria. These findings sound a strong note of caution on the employment of live genetically modified bacteria for the delivery of biologics.

Intrabodies as drug discovery tools and therapeutics.

Within the biomedical and pharmaceutical communities there is an ongoing need to find new technologies that can be used to elucidate disease mechanisms and provide novel therapeutics. Antibodies are arguably the most powerful tools in biomedical research, and antibodies specific for extracellular or cell-surface targets are currently the fastest growing class of new therapeutic molecules. However, the majority of potential therapeutic targets are intracellular, and antibodies cannot readily be leveraged against such molecules, in the context of a viable cell or organism, because of the inability of most antibodies to form stable structures in an intracellular environment. Advances in recent years, in particular the development of intracellular screening protocols and the definition of antibody structures that retain their antigen-binding function in an intracellular context, have allowed the robust isolation of a subset of antibodies that can function in an intracellular environment. These antibodies, generally referred to as intrabodies, have immense potential in the process of drug development and may ultimately become therapeutic entities in their own right.

Intracellular antibodies: a revolution waiting to happen?

Antibodies and their derivatives play a key role in modern drug development, as both research tools and therapeutic entities in their own right. The combination of high-affinity binding and exquisite specificity makes them ideal agents for controlled intervention in biological processes. Evolution has designed antibodies to function in the circulation and interstitial spaces of a tissue or organism, but many potentially valuable drug targets are intracellular and therefore beyond the reach of standard antibodies. Some of the recent advances and current pitfalls in attempts to adapt antibodies for intracellular use are described, and the ultimate potential of this powerful but underused technology is discussed.

Intrabodies: production and promise.

Antibodies are among the most powerful tools in biological research and are presently the fastest growing category of new drug entities. It has long been a dream to harness their power to probe and modulate activities inside living cells. The binding of an antibody to an intracellular molecule has the potential to block, suppress, alter or even enhance the process mediated by that molecule. In particular, intracellular use of antibody fragments can offer an effective alternative to gene-based knockout technologies, potentially with more control and subtlety of outcome. This article outlines progress in the development of intracellular antibodies or intrabodies and highlights their potential, both as drug-discovery tools and as drug entities in their own right.

Intrabodies: Turning the immune system inside out for new discovery tools and therapeutics.

Extract: The human immune system has evolved over millennia to effectively deal with a huge diversity of threats to the integrity of the body. Antibodies, which are the principal agents of the humoral immune system, are masterpieces of evolutionary engineering, combining precise discrimination of target molecules or structures with potent binding capacities. The function of an alien molecule can either be blocked directly by an antibody binding it, or the antibody can recruit effector functions from the immune system to bring about the neutralization, destruction, or removal of the molecule. The potential value of antibodies is nowhere more evident than in the production of new medicines. Technological developments have allowed for the isolation and large scale production of single antibody molecules that can target disease-relevant molecules or structures either in the body fluids or on the surface of cells, resulting in highly precise and potent therapeutic outcomes and, as a result, antibodies currently form the fastest growing group of new drugs being developed and brought to market.