by Skip Derra

Vaccines have always been thought of as a great gift to humankind. Ever since Edward Jenner, an English country doctor developed the first vaccine from cowpox fluid and demonstrated it’s use in 1796, vaccines have held great promise for wiping out the scourges of Earth and promoting health and long life.

But the irony of vaccine’s great promise cannot be any sharper than in poor, under developed countries. In those countries, many children die from diseases that were once thought eradicated, diseases like polio and tuberculosis, continue to ravage the young and the weak. And in a cruel twist, while these diseases flourish most among the populations that are most vulnerable, the vaccines to combat them already exist.

But, these vaccines don’t always make their way to the world’s poorest countries. According to the World Health Organization, one quarter of the world’s children still have no protection from common preventable diseases. Nearly 3 million people (almost 2 million of them children) die every year from these diseases.

Roy Curtiss wants to inoculate as many children in impoverished nations as he possibly can to save them from these common, yet deadly diseases. His goal is to develop vaccines that can be delivered orally, and can be easily dispensed. But to do that, he will first have to convince those people to allow their children to drink Salmonella-laced liquids.

Curtis is a professor in the School of Life Sciences at Arizona State University. He also is co-director of the Center for Infectious Diseases and Vaccinology at ASU’s Biodesign Institute. As odd as it sounds, Curtiss and his colleagues are exploring the use of a “salmonella vector” as a delivery method to vaccinate children.

Salmonella is an entire genus of organisms. The tiny rod-shaped bacteria are bad news. They are responsible for diseases ranging from food poisoning to typhoid fever.

Curtiss is recognized internationally as an eminent biologist and as one of the leading microbial virulence experts in the United States. People listen to his ideas, no matter how unconventional they may sound.

The ASU biologist is a member of the National Academy of Sciences. He has been actively exploring the use of salmonella bacteria as a delivery method since the late 1970s when Jimmy Carter was President. He has been interested in it since before Elvis made it big.

“I’ve worked with salmonella since 1948. My first exposure to it was with chickens,” Curtiss says. “I’ve done a lot of work to figure out how Salmonella infects and causes all kinds of diseases in humans and in farm animals.”

“About 25 years ago, I got this idea that we could genetically modify salmonella. We would kind of fix it so it would induce an immune response to give life-long immunity against salmonella itself. Then we could use this modified Salmonella to induce immunity to other pathogens.”

His latest twist is to develop a vaccine to prevent infection in children by the bacteria Streptococcus pneumonia, the bacteria that cause pneumonia and meningitis. He also is working on a similar vaccine for avian flu. The ASU scientist believes his group is onto to something.

“We now have some technologies that are gang-busters,” Curtiss says.

Trojan horse

You’ve witnessed the scene. The child sitting in a clinic grimaces in anticipation of the needle pinch in his or her upper arm. Curtiss has a better idea. He’d like to have that child simply take a small drink. The catch? The liquid concoction will include a neutralized salmonella bacterium laced with pneumonia bacteria or flu virus genes.

The ASU biologist likes the use of salmonella as a type of Trojan horse. Why? Because salmonella is capable of inducing immunity in the airways and other key parts of the human body that are susceptible to bacteria and viruses that cause disease. The genetic makeup of salmonella also is well understood. And scientists now have effective methods for inserting genes into the bacterium.

“We undoubtedly will have some tweaking to do on our bacterial strains,” Curtiss says. “But some of our vaccine constructs appear to be safe in mice that are only two days old.

“Part of our goal is to develop a vaccine that is safe for newborns or infants,” Curtiss explains. “Most people would say you have got to be kidding me! With a bacteria like salmonella? Yes. We can tame it so it will be a friend of a newborn and not cause any harm.

“Our tests so far have gone pretty well,” he adds. “While mice are not humans, we have made some key observations that could lead to neat breakthroughs.”

Curtiss and his colleagues have shown that their vaccine protects mice from dying when exposed to the Streptococcus bacteria that causes pneumonia. It protected them even when they were exposed to a dose 100 times what would be needed to cause a fatal infection in unimmunized mice.

The aim of the work is to develop a vaccine for infants and very young children that prevents pneumonia. The vaccine will be effective against all strains of bacteria causing the disease and hopefully can be given in a single dose.

People living in under-developed countries are often spread out over large geographic areas. There are few health clinics, poor modes of available transportation, and a shortage of trained healthcare workers. The current anti-pneumonia vaccine for infants and toddlers requires four doses of an injected vaccine given at specific intervals. Curtiss says that a single dose oral vaccine would eliminate many of the current barriers to vaccination in very poor nations.

In addition, current pneumonia vaccines are expensive to produce. They cost an average of $40 per dose. A live bacterial vaccine proposed by Curtiss would cost only about $1 per dose.

The ASU scientist wants to use salmonella’s well-evolved and often elegant genetic machinations for getting past the human body’s immune defense system. The idea is to use salmonella itself at the means to deliver the vaccine to where it will be most effective. Delivery made, the salmonella then destroys itself, never infecting the patient or causing any disease symptoms.

When Curtiss explains how the vaccines will work, you see his inquisitiveness in action. You also see the reverence he has for the organism he’s working with. In his brightly lit office at the Biodesign Institute, the ASU biologist holds up a vial of brown murky pond water. Salmonella in a glass, perhaps. He describes in detail what the organism encounters during its journey through a human body.

If you pour some of the liquid in your mouth, he says that the salmonella organisms sense the temperature change and realize they are in a hostile environment. They immediately turn on expression of a number of genes to make new proteins that allow them to adapt to this environment.

Once swallowed, the organism encounters bacteria in the stomach. The pH is very low in the human stomach (our stomach is basically an acid pit). The organism turns on another 50 genes and becomes tolerant to the acid stress. It survives.

The contents of the stomach empty into the upper small intestine. This is where the bile duct delivers bile. Bile is a detergent at an 8 or 9 percent concentration.

“Have you ever swam underwater in a solution that is 10 percent detergent,” Curtiss asks. “You’d be in a bad way if you did. Salmonella organisms just shrug their shoulders and turn on some new genes to cope with the bile. They are expressing proteins they may need 20 minutes later when they get to the lower intestine. This is where they cross the intestine barrier and make you sick,” Curtiss adds.

The osmotic pressure increases once the salmonella organisms reach the lower intestine.

“Now they feel like they are 300 feet under water,” Curtiss continues. “They are in a high pressure environment with high concentrations of unabsorbed iron, which is toxic. Now is when they invade and attach to the cells that line your intestine in order to get inside. They get the cells to take them up and force their entry. However, once inside, they face an entirely new environment with all new stresses,” he says.

“In the course of an hour, the organisms that cross the intestine barrier have turned on one third of all of their genetic makeup. The sequences are very sophisticated,” Curtiss says admiringly. “They all work in response to specific stresses.”

Curtiss and his team have determined a genetic strategy for delaying the expression of all the information needed to cause disease. However, the strategy still allows the organism to express the necessary genetic information to withstand the stresses encountered on its journey through the body. That is important.

“Conceptually, that is a breakthrough. We have found five ways to do this. We will probably use three or four of them in each vaccine to ensure their safety,” Curtiss says.

“We have also designed our bacteria so they have a finite life,” he adds. “We have them so they are on a string. After about 10 cell divisions they lyse and explode. They liberate their contents,” he adds.

“In the past, we would put anywhere from two to four genetic modifications into some of these live salmonella vaccines. The ones we make now have 15 to 25 genetic alterations. They are very different critters.”

Vaccine research at the ASU Biodesign Institute is supported by the Bill and Melinda Gates Foundation. For more information about specific projects, visit the Institute’s web site at http://www.biodesign.asu.edu/

To learn more about Roy Curtiss, read "Help for the helpless."