High Dosage Oral Delivery System (ORT-VAC)

ORT-VAC System: A gene-based oral attenuated bacterial vaccine delivery technology.

Features and benefits

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

Potential indications

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

Cancer

Technical design

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)

 

Mechanism of Action

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.



Clinical status

The F1 antigen from Yersinia pestis (bubonic plague) was expressed from a plasmid in ORT-VAC Salmonella and evaluated in a murine model. This provided good protection against a challenge with lethal Y. pestis. (Garmory et al. 2005, IAI 73: 2005-2007).


The alternative to multi-copy plasmids is chromosomal integration of a single-copy antigen gene, but this limits antigen production. The protective antigen of Bacillus anthracis was inserted in a plasmid in ORT-VAC and into the chromosome of unmodified Salmonella; ORT-VAC gave greatly enhanced protection against an anthrax challenge (Leckenby et al. 2009, Microb. Pathog. 46: 201-206).

Advantages over conventional technologies

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).

Partnering Opportunities

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.
 

References

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.
 


"Live bacterial vaccines offer huge benefits both to patients and vaccine manufacturers, and we are delighted to be working with Cobra to evaluate the use of Cobra's ORT-VAC technology in creating oral vaccines for diseases where there are major unmet clinical needs."

Professor Simon Cutting of the Royal Holloway


 

News Alert

View privacy policy

Copyright © 2012 cobra biologics. All rights reserved.