cobra:bio

• High dosage delivery with a wide range of antigens
• Oral delivery route effectively targets the immune system (antigen presenting cells) in the gut
• Oral administration offers superior safety, better patient compliance and is more cost-effective than injections
• Suitable for protein or DNA vaccines
• Stabilises high copy number plasmids with no antibiotic resistance or other selectable marker genes
• Cost-effective cGMP manufacturing, as minimal downstream purification is required

• Infectious diseases (e.g. AIDS, tuberculosis, avian influenza, anthrax)
• Cancer

The ORT-VAC ^® technology employs a plasmid-mediated repressor titration to activate a host selectable marker, removing the requirement for a plasmid-borne marker gene.  Current ORT-VAC^® strains are engineered to contain an essential gene, dapD under transcriptional control of the lac operator/promoter (lacO/P), although any essential gene could be used. In the absence of an inducer such as IPTG, this strain cannot grow due to the repression of dapD by the LacI repressor protein binding to lacO/P. Transformation with a high copy number plasmid containing the lac operator (lacO) effectively induces dapD expression by titrating LacI from the operator.  Regulation of the essential gene ensures the growth of bacteria and maintenance of recombinant plasmids containing lacO and an origin of replication. ORT-VAC is Cobra's proprietary oral vaccine delivery technology based on ORT^® that allows rapid and simple construction of bacterial vaccine strains.

(Figure 1. An ORT-VAC^® cell without a plasmid will lyse due to the lack of dapD expression.  When transformed with a multi-copy plasmid, this titrates the repressor, enabling dapD expression and therefore plasmid selection and maintenance)

After oral administration the ORT-VAC^® bacterial vaccine strain passes through the stomach and into the intestine where it crosses the intestinal epithelia and enters the gut-associated lymphoid tissue (GALT). In the GALT, the vaccine strain is phagocytosed by immune system cells (macrophages and dendritic cells) called antigen-presenting cells (Figure 2).

During uptake, the ORT-VAC^® strain synthesizes the vaccine antigen protein within the host immune cell. The host immune cells then process the protein, resulting in the antigen being presented to antigen-specific T cells and cell mediated immunity being stimulated. The antigen is also recognised by antigen specific B cells and induces the production of antigen specific antibodies (humoral immunity). ORT-VAC delivery induces a strong systemic and mucosal immune response and works to stimulate the entire immune system (cell-mediated and antibody).

Figure 2: Recombinant vaccine delivery using live bacterial vectors. Bacteria expressing the antigen are engulfed by Antigen Presenting Cells (APCs) and activate the immune system after phagocytosis.

Pre-clinical proof of concept for bubonic plague and anthrax vaccines.
Using a rigorous plague challenge model, proof-of-principle results show that mice given a single oral dose of bacteria that expressed a plague antigen achieved a high level of immunity against plague. In addition, plasmid maintenance was very stable and maintained over the course of the investigation whereas maintenance in a conventional strain was greatly diminished (Garmony et al., 2005).

Conventional vaccine technologies rely on either integrating the antigen gene(s) into the bacterial chromosome or using antibiotics and antibiotic resistance genes to amplify plasmids containing the antigen genes. However, the former approach leads to poor strain productivity and the latter to plasmid instability. Use of antibiotics also creates the risk of passing on the antibiotic resistance genes to pathogens in the environment and creating superbugs e.g. MRSA strains, which are difficult to manage clinically. ORT-VAC^® technology avoids these problems as it is extremely stable and safe (no antibiotics or antibiotic resistance genes employed).

Cobra is seeking partners for the development of ORT-VAC® vaccine applications in humans.  In particular, companies with an interest in developing attenuated bacteria strains for humans or interesting and commercially viable antigen genes. ORT-VAC may also be applicable for DNA vaccine delivery. Partners with clinical expertise in the vaccine arena would be advantageous. Cobra facilitates commercialisation for its partners by providing a highly targeted and safe ORT-VAC delivery system and a cost effective cGMP manufacturing process.
 

Garmory, H. S., Leckenby, M. W., Griffin, K. F., Elvin, S. J., Taylor, R. R., Hartley, M. G., Hanak, J. A. J., Williamson, E. D. and Cranenburgh, R. M., 2005. Antibiotic-free plasmid stabilisation by Operator-Repressor Titration for live vaccine delivery with Salmonella. Infect. Immun. 73: 2005-2007.