Vaccines aim to prevent diseases by stopping microbes from getting
a toehold in your body in the first place. Traditional vaccines
use a variety of approaches, including using weakened or killed
microorganisms or portions of them to "teach" the immune system
to attack if it ever encounters the real thing. Unfortunately,
some microbes can elude these methods. HIV, for example, infects
the very immune cells that arrive to fight it, making effective
vaccine design a particular challenge. But new strategies for developing
vaccines are in the works and 2005 saw significant advances in
the field.
DNA vaccines are showing great promise, and are already being
used to help protect some animals. While none have yet been licensed
for human use, DNA vaccines against HIV, Ebola, West Nile virus
and SARS are currently being tested at NIAID's Dale and Betty Bumpers
Vaccine Research Center (VRC). DNA vaccines can be manufactured
more quickly than traditional vaccines. They also result in antigens
being presented by the body's own cells, so they're more likely
than some traditional vaccines to stimulate both antibody and cell-based
attacks from the immune system. One trial that opened earlier this
year, for example, is testing an experimental vaccine against West
Nile virus. The vaccine, which consists of a DNA plasmid with genes
coding for two key viral surface proteins, is injected into muscle,
where muscle cells can read the DNA, produce the two proteins and
display them on their surfaces.
A safe, effective HIV vaccine is perhaps the most prominent vaccine
research goal and several HIV vaccines are now in the pipeline.
One such vaccine, developed by scientists at the VRC, moved into
its second phase of clinical testing in October. This vaccine contains
synthetic genes representing HIV subtypes found in Europe, North
America, Africa and Asia that comprise about 85 percent of HIV
infections worldwide. For greater potency, the researchers are
using a one-two punch strategy, starting out by vaccinating with
naked gene fragments, then following up with a booster shot using
weakened adenovirus to deliver selected genes.
An innovative vaccine strategy funded by NHLBI aims to bypass
the need for helper T cells, normally a key component in the immune
response. Researchers at Children's Hospital of Pittsburgh focused
on a molecule on the surface of helper T cells called CD40L that
signals other cells like antibody-producing B cells to mount their
attack. The team combined CD40L with a key antigen from pneumocystis
pneumonia and showed that the vaccine was able to protect mice
lacking helper T cells from pneumocystis. The ability to develop
vaccines for humans that could bypass helper T cells would be a
major breakthrough for people with compromised immune systems like
those with HIV or organ transplants.
Another interesting area of vaccine development comes from the
cancer research arena. The immune system generally doesn't recognize
tumors to mount attacks against them. But with a little help, unique
or unusually abundant molecules on the surface of cancer cells
can prompt the immune system to act. New vaccines are now showing
promise for stimulating the immune system to attack cancer cells.
According to NCI, several clinical trials are under way to test
vaccines for a wide variety of cancers. For more information, visit www.cancer.gov/cancertopics/factsheet/cancervaccine.
