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Mar 1, 2009 (Vol. 29, No. 5)

DNA Vaccines Inch Toward Human Use

West Nile Virus Equine Product Gains Foothold for a Burgeoning Field

  • Scaled-Up PCR

    Vandalia Research has developed a PCR system that scales DNA sequence production from the bench to commercialization. Triathlon™, a continuous, large-scale PCR system, is the heart of this system. As Derek Gregg, vp of business development, explained, “DNA vaccines have a lot of potential advantages, especially in manufacturing, but they are mainly based on plasmid DNA, which is propagated in bacteria. Therefore, removing the bacteria remnants is important.” And, he added, “Often, only one-third of the plasmid is used because much of the sequence is required for replication in bacteria and isn’t used by the vaccine.”

    Using PCR to amplify the DNA, however, could eliminate many of the challenges associated with plasmid purification. As yet, PCR hasn’t become popular for this use because of the many heating and cooling steps, the large quantities of plasmids needed, and the time required for processing.

    Triathlon resolves those issues through a continuous process that currently produces about 50 mg of DNA per day. The PCR reagents are transported through tubing that wraps around a cylinder, which rapidly heats and cools the solution, saving 40 to 90 seconds per cycle. The flow is continuous, eliminating the need to pool products from plates. The process results in reduced labor, decreased turnaround time, and reduced risk of contamination. The Triathlon is scalable, and the next-generation machine is expected to be able to produce up to 1 g or more of DNA per machine, per day, Gregg noted.

    PCR also produces linear DNA, so researchers can work with only the fragments of interest. “Some studies have shown that it’s easier to get smaller DNA fragments into the cell, which allows researchers to get better expression,” Gregg said. “The resulting vaccine also may be more transient,” he continued, allowing the DNA fragment to do its job and leave.

    Speed is a major benefit of this approach to plasmid production. Scaling up for manufacturing can be accomplished in a few days, versus the weeks or months needed for fermentation processes, Gregg said. “Therefore,” he pointed out, “this method could be particularly valuable in a pandemic. Vandalia offers large-scale PCR as a service.”

  • Vectors

    VIRxSYS is working to boost DNA delivery efficiency using lentiviral vectors, which, using its system, can deliver therapeutic payloads into human cells with more than 90% efficiency, Franck Lemiale, Ph.D., director of vaccines and immunology, said. Other vectors used for gene therapy range from 20 to 50% efficiency, he noted.

    According to Dr. Lemiale, VIRxSYS is seeing good results using the HIV virus as a vector. Obviously, “the vector is non-pathogenic.”

    One of the benefits of this approach is that “people have immunity against adenoviruses, but not against HIV,” explained Gary McGarrity, Ph.D., executive vp of research and clinical affairs. Consequently, an HIV vector can deliver its payload without the immune response that thwarts adenovirus and other vectors.

    Payloads have been delivered successfully to several targeted human cell types. Results so far have shown highly efficient gene transfer and genetic stability of the payload in dividing and nondividing cells. And, from a production standpoint, the HIV viral vector can be manufactured readily.

    One trial involving VRX496 as an AIDS treatment is in Phase II trials now. It uses antisense as a payload in a similar lentiviral backbone. Patient safety monitoring to date shows no safety concerns, Dr. McGarrity said. VRX496 inhibited HIV replication by more than 99% in laboratory studies, and data from clinical trials is encouraging. Early preclinical studies for an HIV vaccine have been completed, and Dr. Lemiale says VIRxSYS expects to enter clinical trials for that vaccine by 2010. Results from nonhuman primate studies are showing that the approach provides immunity against HIV. He added that the question remains as to whether the degree of immunity is sufficient to provide protection.

Readers' Comments

Posted 05/15/2009 by Engineer

This is a very interesting article.

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