Yesterday I talked about a new kind of immunization: passive immunization with neutralizing antibodies. This approach may be effective against many different strains of a virus. It may also allow large amounts of a vaccine to be stored, ready to nip an exploding epidemic in the bud.
Traditional vaccines against HIV (the virus that causes AIDS) and influenza (flu) virus face a tough problem: The virus keeps changing many (but not all) of its antigens. That makes it hard for a vaccine to keep up.
With the Ebola virus, there are several strains. They are different enough that scientists have doubted that a vaccine could be made that was effective against all of them.
Several years ago, scientists made an important discovery. During infection with flu virus, HIV and Ebola, the immune system makes antibodies to antigens that do not change. In large amounts, these antibodies will kill (neutralize) all strains of the virus. For that reason, they are called “broadly neutralizing” antibodies.
Unfortunately, the body makes these natural broadly neutralizing antibodies in small amounts — too small to neutralize the large number of viruses (and their antigens) that are in a person’s body. So scientists have begun making large amounts of these antibodies in the laboratory. Then they test to see if the antibodies are effective when injected into animals infected with these viruses.
This is called “passive” immunization. The traditional approach to immunization is “active.” A person (or animal) is given an antigen, in hopes of stimulating the immune system to make antibodies against the antigen. With passive immunization, you give the antibodies themselves.
About five years ago, scientists tested broadly neutralizing antibodies against HIV in mice. HIV doesn’t infect normal mice, but it does attack human immune cells. So the scientists used special laboratory mice: Their immune systems were composed of human cells. The broadly neutralizing antibodies reduced the amount of virus in the animals to a much greater degree than did traditional vaccines.
The antibodies also greatly lowered levels of the virus in monkeys, which are more like humans than mice. In 2015, the antibodies were given to humans infected with HIV — and levels of the virus plummeted.
Similarly encouraging results have occurred with broadly neutralizing antibodies against flu virus, in studies in animals. Even the strain of flu virus that caused the terrible pandemic of 1918 was neutralized. In early 2016, the same approach was shown to protect mice and guinea pigs against all the strains of the Ebola virus.
Recently, scientists have tried a whole new type of vaccine. It’s not a shot of a virus’s antigens (an “active” vaccine). And it’s not a shot of broadly neutralizing antibodies (a “passive” vaccine). Instead, it’s a shot of the genes that make the broadly neutralizing antibodies. Those genes cause the animal to make large amounts of the antibodies. The technique has protected mice with human immune systems from HIV infection.
While more research is needed, new twists to vaccines may make major advances against many serious infectious diseases.