Tiny Spheres Boost Vaccines

SAN FRANCISCO--A single injection of microscopic plastic capsules could someday eliminate the need for vaccination booster shots. The new technique, described here yesterday at the annual meeting of the American Chemical Society, could save health care dollars by reducing the need for repeated doctor visits.

Vaccines against diseases such as polio and tetanus currently are given in several small doses spaced weeks or months apart. But this can pose logistical problems in developing countries, and even in some urban areas of the United States, a significant fraction of children fail to return for booster shots. Five years ago, a team led by Jeffrey Cleland of the biotech firm Genentech in San Francisco set out to simplify the procedure with microspheres, plastic balls just a few tens of micrometers across that slowly release drugs as they dissolve inside muscle or other tissue.

To mimic a booster shot, the microspheres had to be designed to survive for months in the body, then quickly release vaccine. The key turned out to be using a thicker rind of plastic--polylactidglycolide, the same stuff used in medical sutures--to encapsulate smaller vaccine droplets. The researchers tested the thicker hulled microspheres with an experimental AIDS vaccine, called GP120, developed by Genentech. They injected a group of baboons with a normal dose as a first vaccination, combined with a booster shot tucked into microspheres that would dissolve after 40 days. This group had a much higher and more prolonged immune response than those given the traditional booster shot by injection after 40 days had. Cleland speculates that the microspheres, which took several days to release the vaccine, did a better job of stimulating the immune system. "The longer you can keep the antibody levels up, the better off you are," he says.

Experts are happy to see the progress. "I'm very positive, very pleased" by the work, says chemical engineer Bob Langer of Massachusetts Institute of Technology. "Ideally, you could use this method for any vaccine." Haro Hartounian, a specialist in drug-delivery technologies at DepoTech in San Diego, predicts that microspheres will prove more potent than traditional booster shots and--by eliminating that second visit to the doctor--could lower the cost. Cleland says the technology is ready to be licensed to vaccinemakers willing to give it a shot.