Tuesday, September 15, 2009
Scientists at Oregon
State University
have developed a new "adjuvant" that could allow the creation of
important new vaccines, possibly become a universal vaccine carrier and help
medical experts tackle many diseases more effectively.
Adjuvants are substances that are not immunogenic
themselves, but increase the immune response when used in combination with a
vaccine.
However, due to concerns about safety and toxicity, there's
only a single vaccine adjuvant—aluminum hydroxide, or alum—that has been
approved for human use in the United
States. It's found in such common vaccines
as hepatitis B and tetanus. But even though widely used, alum is comparatively
weak and will only work with certain diseases.
The new adjuvant is based on nanoparticles prepared with
lecithin, a common food product. In animal models, it helped protein antigens
to induce an immune response more than six times stronger than when alum was
used. Researchers also showed that the lecithin nanoparticles were able to help
induce a reasonable antibody response after only one shot, whereas it took at
least two shots for the alum adjuvant to work.
Based on their studies, researchers believe the lecithin
nanoparticles have wide potential applications and possibly a good safety
profile. Their findings were just published in the Journal of Controlled
Release, a professional journal in the field of pharmaceutics, in work
supported by the National Institute of Allergy and Infectious Diseases.
"In many cases, to make progress with vaccine
development we need new adjuvants," said Zhengrong Cui, an assistant
professor of pharmaceutics at OSU and corresponding author on the new study.
"The material has to be safe, and lecithin is a common food product that's
already widely used in pharmaceuticals. This new form of using lecithin
nanoparticles as an adjuvant is promising and could become very
important."
Vaccine development has always been difficult and at times
controversial, Cui said, because of concerns about adverse effects when giving
vaccines to healthy people.
Because of that, the U.S. Food and Drug Administration has
been conservative about approving new vaccine adjuvants, he said. But even the
safety issue is complex – to help avoid risk, new vaccines are based on
purified compounds from microbes, but these provoke a very weak immune response
and often need an adjuvant to boost them. Vaccines could be made based on dead
or live attenuated microbes, but that would have a higher level of risk. The
ultimate solution is new and improved adjuvants that help address both concerns
about safety and efficacy.
Another problem, he said, is that the alum adjuvant that is
common in some U.S.
vaccines has very limited value in the development of many potential vaccines
against viruses or tumors.
By contrast, the lecithin-based nanoparticle adjuvant is
more effective. The extraordinarily small particles move easily to the
lymphatic system that plays a key role in development of immune response, and
they physically "look like" a pathogen to the immune system, which
quickly gears up to fight them.
"Our early studies with laboratory animals seem to
suggest that a vaccine based on the lecithin nanoparticle adjuvant would not
only be more effective, but be tolerated by the body more readily than one
using alum," Cui said. "Lecithin is very non-toxic, it's one of many
compounds 'generally recognized as safe' by the FDA, and at the injection site
we saw none of the nodules and tissue hardening you sometimes see with vaccines
that use alum."
If the new adjuvant is ultimately shown to be safe and is
approved following clinical trials, Cui said, it could become the basis for a
revolution in the production of vaccines and serve as a universal carrier.
Oregon State University