Prima touts DCtag success in vaccine development

Prima BioMed subsidiary Panvax has reported that recent trials of its DCtag vaccine technology in sheep have confirmed its potential for developing novel vaccines and immunotherapies for human diseases including cancers, viral infections, malaria and tuberculosis.

DCtag -- the 'DC' refers to dendritic cells -- is a novel adjuvant technology that promotes a rapid, strong immune response to vaccine antigens by delivering them directly to the sentry cells that initiate the immune response.

Panvax has already demonstrated that vaccines and immunotherapies employing DCtag effectively induce both of the immune system's primary defensive responses: neutralising antibodies, and the so-called cellular response, involving cytotoxic T-cells.

The T-cell response is crucial for eliminating cells that have already been infected by viruses or other microbes, and also play a critical role in preventing cancer, by targeting and killing mutant cells displaying mutant proteins on their surface.

Prima BioMed's R&D manager, Dr John Bates, said most modern vaccines did not elicit the strong T-cell response of traditional 'live' vaccines.

The problem is common with genetically engineered sub-unit vaccines, which induce a focused immune response against specific 'strong' antigens.

DCtag solves the problem by addressing vaccine antigens directly to dendritic cells, with a small, synthetic molecular tag that 'docks' with a surface molecule expressed on dendritic cells. Rather than dendritic cell finding the antigen, the antigen finds the cell.

DCtag exploits an original discovery by Prof Magda Plebanski, of Melbourne's Austin Research Institute, who went searching for a way to deliver vaccine antigens directly to dendritic cells.

Panvax conducted a large-animal trial in sheep, using an experimental vaccine, after demonstrating that DCtag effectively elicited both antibody and cell-mediated responses in mice.

In the sheep trial, the vaccine was well tolerated, and the cell-mediated response was enhanced to a greater degree than the antibody response.

Difficult to induce

In a statement, the company said the nature and strength of the cellular immune responses induced by DCtag, when compared to currently licensed adjuvants and those in development, have "encouraged Panvax to focus its immediate development program on diseases where the induction of immune responses of this type are considered to be essential and where they have been difficult to induce."

The fact that DCtag works the same way in a small and a large mammal suggests it should also work in humans.

However, Bates said that when DCtag had been shown to have "all the features we want", its first commercial product was likely to be a veterinary vaccine, because it would provide a quicker way of validating the technology, and a faster path to market.

He said DCtag was a platform technology, and Panvax, in addition to developing its own in-house vaccines, would also enter third-party arrangements with other companies that wished to exploit DCtag for their own vaccines.

Prima BioMed CEO Marcus Clark said data from the sheep experiment were consistent with Prima's objective of exploiting DCtag to prevent or treat diseases where conventional vaccines and immunotherapies had been unsuccessful or of limited clinical benefit, such as cancer, viral diseases, malaria and tuberculosis.

Clark said work was already in progress to evaluate the benefits of DCtag in preventing viral disease, and in oncology applications -- results should be available by the end of April.