Environmental pollutants can cause all kinds of health problems — from cancer to disrupted hormones. But can lingering environmental toxins like DDT and PCBs also interfere with the effectiveness of tools that keep us safe from disease, like vaccines?
That question is at the heart of a new five-year study being launched in September. A collaboration between Fred Hutchinson Cancer Research Center and the Chinese Center for Disease Control and Prevention, or China CDC, the study just received $4.4 million in funding from the National Institute of Environmental Health Sciences.
“It’s new ground,” said Dr. Steven Self, executive director of Fred Hutch’s China Initiative and lead investigator of the ChinaPOPs study (Childhood Immunity and Neonatally Assessed Persistent Organic Pollutants).
“We’re following up on an interesting signal in one study that found an association between persistent organic pollutants — or POPs — and vaccine response,” he said. “We’ve designed a study that [will] give a really comprehensive look at how prenatal exposure to these pollutants could impact the kinetics of vaccine responses across a wide range of vaccines. Not just one vaccine and not just one point in time, but a truly comprehensive look.”
Self and his collaborators, including Fred Hutch public health scientist Dr. Parveen Bhatti, plan to recruit 600 healthy Chinese women during the first trimester of their pregnancy, monitoring them until their babies are born. Researchers will collect umbilical cord blood samples at delivery and then track those infants for two years, collecting and analyzing the children’s blood at various points along the way. The team plans to measure the levels of POPs in the cord blood at birth as well as the immune response to various childhood vaccinations at multiple times during their first two years of life.
Infants in China receive many if not all of the same vaccinations that U.S. infants receive, including inoculations against various strains of hepatitis as well as measles, mumps, diphtheria, polio, tetanus, whooping cough, chicken pox, and more.
“We’re doing the study in China, but it’s relevant globally,” said Self. “If infants that we think are protected are actually not protected, based on exposure to these pollutants, then something will need to be done.”
Persistent pollutants
Although the U.S. and other countries have been working to reduce the manufacture and use of some of the most toxic persistent organic pollutants — including pesticides like DDT and industrial chemicals like polychlorinated biphenyls (PCBs) — they are still very much with us.
Highly fat soluble, most POPs accumulate in the fatty tissue of animals and “biomagnify,” or travel up the food chain. Humans become exposed to POPs when they eat meat, fish or dairy products containing them; babies are exposed to POPs through breast milk or while in their mothers’ womb, since POPs easily cross the placenta. Despite bans and tighter regulation, POPs continue to be found in the blood and tissue of people living in the U.S.
“They get in the environment and they stay there; they get in the body and they stay there,” Self said of these persistent pollutants. “They’ve basically circulated around the globe and virtually everybody is exposed to them on some level.”
A study conducted in north Atlantic’s Faroe Islands — where people have a traditional diet high in POP-laden whale blubber — found that children there had both higher levels of POPs as well as reduced antibody levels in their blood after vaccination, indicating a lower immune response than is typically triggered by a vaccine.
“In this small, highly exposed population, they only looked at a couple of vaccines — diphtheria and tetanus — but it got people thinking that maybe even lower concentrations of these environmental pollutants could have negative impacts on vaccine response, which would have major implications for vaccination efforts around the world,” said Bhatti, a co-investigator on the ChinaPOPs study who researches environmental and occupational risks of cancer and other disease.
POPs include dioxins and furans, PCBs, organochlorine pesticides such as DDT and perfluorinated compounds (PFCs). The compounds can cause cancer, neurobehavioral deficits, and reproductive and immune dysfunction.
A perfect study site
Self and Bhatti, who met during a Fred Hutch scientific retreat, started discussing the possibility of tracking the effect of POPs on vaccine response, then shared the idea Dr. Xin Sun of the Chinese CDC, with whom Self collaborates on a regular basis.
“Sun also happens to be an occupational and environmental health epidemiologist and he loved the idea,” said Self.
The Chinese scientist also knew the perfect site to conduct the study: a residential area surrounding an abandoned chemical manufacturing plant in an industrial district near Tianjin, China. Closed in 2003, the plant at its peak produced 17,000 tons a year of pentachlorophenol, a fungicide and wood preservative. During 50 years of operation, it also spewed about 1,000 tons of waste into the environment, including high levels of dioxins and furans.
Self and Bhatti looked at the levels of POPs found in the blood of residents who lived near the plant and saw that those who lived closer to the site had higher levels of POPs than those who lived further away.
“That’s hard to find in the general population,” said Bhatti. “We had a source [of pollution] that we could now tie to peoples’ exposure. As you moved away, you had a gradient exposure from high to low. That allows you to do a very efficient study of the effect of exposure on antibody levels.”
Self said people living farthest from the plant had an ambient level of POP exposure that was “not that different from what most of us have here in the U.S.”
“It’s important that we have anchors at high as well as lower levels of exposure,” he said. “That whole range will help us reconstruct a curve. And the mid- and lower levels of that curve will be relevant for populations in the U.S. and many places around the world.”
Making sure vaccines ‘take’
Most vaccines have a standard antibody response — a regulatory threshold — that needs to be reached for a child to be protected against disease. If the immune response is above the threshold, they’re considered to be protected. If it’s not, they may not be protected.
“One of the goals of this study is to use this regulatory threshold apparatus to determine what fraction of the population of vaccinated kids don’t meet that threshold for protection due to their exposure,” Self said. “If we find that [a number of these] kids aren’t being protected by vaccination because of exposure, then that problem will have to be addressed.”
Children who aren’t sufficiently protected from infectious diseases like chicken pox, whooping cough and hepatitis might receive additional booster immunizations, he said, or public health researchers could develop a different vaccine regimen for those living in highly polluted areas.
Self said the study is part of a larger effort to assess exposures to different pollutants and track their effects on our neurobehavioral and physical growth/development outcomes in children.
“The main message we’re trying to convey is that this data is applicable around the world, including the U.S.," Bhatti said. "We can take what we learn from China and look at our exposure levels here. They’re not that different. It will help us make decisions.”
Diane Mapes is a staff writer at Fred Hutchinson Cancer Research Center. She has written extensively about health issues for NBC News, TODAY, CNN, MSN, Seattle Magazine and other publications. A breast cancer survivor, she also writes the breast cancer blog doublewhammied.com. Reach her at dmapes@fredhutch.org.
