mBiosphere

Using Foodborne Bacteria in the War Against Cancer

Can bacteria that cause food-borne illness be used to fight cancer? Ongoing research suggests this is the case. 

“There has long been interest in using genetically engineered microbes to target and destroy cells within solid tumors,” said Roy Curtiss, III, PhD, University Professor of Microbiology and Director, Center for Infectious Diseases and Vaccinology and Center for Microbial Genetic Engineering, the Biodesign Institute, Arizona State University. His group has been working on turning Salmonella into a cancer-fighting machine.

The idea that bacterium can be used as an anticancer agent dates back to the turn of the century. In 1890, William B. Coley, MD, a surgeon at what is now known as Memorial Sloan-Kettering Cancer Center, observed that cancer patients who developed bacterial infections after surgery had better outcomes than those who did not. Dr. Coley developed Coley’s toxins, mixtures of dead bacteria that were used to treat cancer patients. While the treatment was controversial, different formulas of Coley toxins were made by several drug companies in the United States and used in cancer patients until the early 1950s. At that point, better forms of cancer treatment became available.

 In recent years, there has been a re-emergence of interest in using bacteria to kill cancer. In the March/April issue of mBio, an American Society for Microbiology online-only, open access journal, researchers show that genetically modified Salmonella can be used to kill cancer cells. Salmonella enterica Serovar Typhimurium has been shown to not only colonize solid tumors, but also to exhibit an antitumor effect. However, in order to use Salmonella as a weapon against cancer in humans, researchers must find a balance between allowing it to kill the cancer and be safe for the patient. The bacteria, commonly known for causing severe food poisoning, can lead to sepsis and death in humans.

In the new study, researchers from Germany and the United States teamed up to modify the lipopolysaccharide structure (LPS) of the Salmonella strain to make the bug less toxic. LPS, found in the outer membrane of bacteria, is one of the major inducers of sepsis, a life-threatening infection. The researchers used genetic engineering to delete genes involved in the synthesis of the LPS, and then tested various modified Salmonella strains to see how they performed in test tube studies with human cancer cells and in tumor bearing mice. They identified a particular mutant strain that was the most effective at killing cancer cells and shrinking tumors, and also unable to cause disease. However, this mutant strain was less able to colonize the tumors, although being most effective in killing tumor cells when getting there.

To address this problem, the researchers then added another genetic modification, an inducible arabinose promoter. The modification allowed the Salmonella to be injected in the mouse in a form that would not harm normal, healthy cells, was effective at colonizing tumors, and after entering cancer cells, would turn toxic. "This transition from a benign, invasive Salmonella that doesn't hurt normal cells to the toxic type occurs very rapidly (time wise) in the tumor due to the very rapid growth and cell division that occurs when Salmonella enters a tumor," said Dr. Curtiss. In a normal cell, Salmonella grows very slowly, dividing once or twice in a 24-hour period, but in a tumor, the bacteria divide every hour. 

 The researchers believe their study is a significant step in developing a strategy that will help in the overall means of using Salmonella as part of a cancer therapy. The investigational therapy would probably be used in conjunction with chemotherapy and radiation therapy, once it gets to human trials, according to the scientists.

--Kate O'Rourke

Seasonal Flu Vaccines Boost Immunity To Many Strains of Influenza

Paul Thomas was merely trying to develop a more reliable test for exposure to avian influenza viruses when he made a fairly startling finding: Seasonal flu vaccines may protect individuals not only against the strains of flu they contain but also against many additional types.

An immunologist who works with T cell biology, Thomas hypothesized that T cell responses would provide greater specificity than antibody-based tests in terms of determining if an individual had been infected, because for a T cell response to be made, the virus has to have invaded the body. While this hypothesis turned out to be incorrect, his team did find among a group of bird scientists studied that those who reported receiving flu vaccines had a strong immune response not only against the seasonal H3N2 flu strain from 2010, when blood samples were collected for analysis, but also against flu subtypes never included in any vaccine formulation.

The results, published this week in mBio, are exciting “because it suggests that the seasonal flu vaccine boosts antibody responses and may provide some measure of protection against a new pandemic strain that could emerge from the avian population,” said Thomas, an Associate Member in the Department of Immunology at St. Jude Children’s Research Hospital in Memphis, Tenn. “There might be a broader extent of reactions than we expected in the normal human population to some of these rare viral variants.”

Because avian influenza viruses have an important role in emerging infections, Thomas and colleagues tested whether exposure to different types of birds can elicit immune responses to avian influenza viruses in humans. They studied blood samples from 95 attendees of the 2010 annual meeting of the American Ornithologist Union. They exposed plasma from the samples to purified proteins of avian influenza virus H3, H4, H5, H6, H7, H8 and H12 subtypes using ELISA and hemagglutination inhibition (HAI) to see how many different viruses participants reacted to, and how strongly.

In the ELISA tests, 77 percent of participants had detectable antibodies against avian influenza proteins. Most individuals had a strong antibody response to the seasonal H3N2 human virus-derived H3 subtype, part of the 2009-2010 vaccine. However, many also had strong measurable antibody responses to group 1 HA (avian H5, H6, H8, H12) and group 2 HA (avian H4, human H7) subtypes. Sixty-six percent of participants had some level of detectable antibodies against four or more HA proteins that sit on viral surfaces, and a few had responses to all subtypes tested, most of which have not previously been detected in humans.

The team also found that participants who had significant antibody responses did not necessarily also have significant T cell responses to avian viruses, indicating that these two immunity arms can be independently boosted after vaccination or infection; that individuals who reported receiving seasonal influenza vaccination had significantly higher antibodies to the avian H4, H5, H6, and H8 subtypes; and that participants with exposure to poultry had significantly higher antibody responses to the H7 subtype, but to no other subtypes. Exposure to other types of birds did not play a role in immunity.

A person’s immune response on the ELISA test did not necessarily predict response on the HAI test, and vice versa. As HAI antibodies only target the “head” of the HA while ELISA antibodies can be against the head or the relatively conserved “stalk” domain, this result indicated that some individuals were more likely to target the conserved stalk region (i.e. show greater reactivity in ELISA than in HAI).

The work has opened up a lot of questions in figuring out why people mount different types of responses, and potentially how the seasonal vaccine may play a role in boosting these responses, Thomas said. He has started additional studies in other groups of people with varied vaccination and infection histories to tease apart what exposures boost immunity against avian influenza viruses.

Seasonal Flu Vaccines Boost Immunity To Many Strains of Influenza

Paul Thomas was merely trying to develop a more reliable test for exposure to avian influenza viruses when he made a fairly startling finding: Seasonal flu vaccines may protect individuals not only against the strains of flu they contain but also against many additional types.

An immunologist who works with T cell biology, Thomas hypothesized that T cell responses would provide greater specificity than antibody-based tests in terms of determining if an individual had been infected, because for a T cell response to be made, the virus has to have invaded the body. While this hypothesis turned out to be incorrect, his team did find among a group of bird scientists studied that those who reported receiving flu vaccines had a strong immune response not only against the seasonal H3N2 flu strain from 2010, when blood samples were collected for analysis, but also against flu subtypes never included in any vaccine formulation.

The results, published this week in mBio, are exciting “because it suggests that the seasonal flu vaccine boosts antibody responses and may provide some measure of protection against a new pandemic strain that could emerge from the avian population,” said Thomas, an Associate Member in the Department of Immunology at St. Jude Children’s Research Hospital in Memphis, Tenn. “There might be a broader extent of reactions than we expected in the normal human population to some of these rare viral variants.”

Because avian influenza viruses have an important role in emerging infections, Thomas and colleagues tested whether exposure to different types of birds can elicit immune responses to avian influenza viruses in humans. They studied blood samples from 95 attendees of the 2010 annual meeting of the American Ornithologist Union. They exposed plasma from the samples to purified proteins of avian influenza virus H3, H4, H5, H6, H7, H8 and H12 subtypes using ELISA and hemagglutination inhibition (HAI) to see how many different viruses participants reacted to, and how strongly.

In the ELISA tests, 77 percent of participants had detectable antibodies against avian influenza proteins. Most individuals had a strong antibody response to the seasonal H3N2 human virus-derived H3 subtype, part of the 2009-2010 vaccine. However, many also had strong measurable antibody responses to group 1 HA (avian H5, H6, H8, H12) and group 2 HA (avian H4, human H7) subtypes. Sixty-six percent of participants had some level of detectable antibodies against four or more HA proteins that sit on viral surfaces, and a few had responses to all subtypes tested, most of which have not previously been detected in humans.

The team also found that participants who had significant antibody responses did not necessarily also have significant T cell responses to avian viruses, indicating that these two immunity arms can be independently boosted after vaccination or infection; that individuals who reported receiving seasonal influenza vaccination had significantly higher antibodies to the avian H4, H5, H6, and H8 subtypes; and that participants with exposure to poultry had significantly higher antibody responses to the H7 subtype, but to no other subtypes. Exposure to other types of birds did not play a role in immunity.

A person’s immune response on the ELISA test did not necessarily predict response on the HAI test, and vice versa. As HAI antibodies only target the “head” of the HA while ELISA antibodies can be against the head or the relatively conserved “stalk” domain, this result indicated that some individuals were more likely to target the conserved stalk region (i.e. show greater reactivity in ELISA than in HAI).

The work has opened up a lot of questions in figuring out why people mount different types of responses, and potentially how the seasonal vaccine may play a role in boosting these responses, Thomas said. He has started additional studies in other groups of people with varied vaccination and infection histories to tease apart what exposures boost immunity against avian influenza viruses.

Immune Reaction to Infection Leads to Autism-like Disorders in Mice

Could an immune reaction to a virus cause autism? We still don’t know the answer to that question, but a new study shows that, in mice, infecting a pregnant mother with an artificial virus can spark a chain of events that leads to autism-like disorders in her offspring.

The study, just released on the mBio website, uses mouse models to follow up on previous studies that indicated infecting a mother with any of a wide range of viruses during pregnancy is associated with increased risk for disorders like autism and schizophrenia. In the latest study, De Miranda et al. explored the effects of infection using a totally fabricated double-strand of RNA that mimics a replicating virus.

In pregnant mice, the fake virus inhibited fetal neuronal stem cell replication and population of the superficial layers of the neocortex of the brain by neurons. In terms of behavior, these offspring had impaired locomotor development and once they reached adulthood, they were less able to filter sensory stimuli and make sense of their environment. Sensory impairments like these, called “abnormal sensorimotor gating responses”, are a hallmark of schizophrenia and autism.

To investigate the mechanisms behind these neural effects, the authors followed up with experiments in mice deficient in Toll-like receptor 3 (TLR3), a component of the innate immune system that also plays a pivotal role in development. The offspring of TLR3-deficient pregnant mice exposed to the virus did not have any of the neural problems, indicating a prominent role for TLR3 in the adverse effects that afflicted the wild type offspring. What’s more, a drug can actually head off these effects: pre-treating wild-type dams with a COX inhibitor called caprofen suppresses the inflammatory response of TLR3 to the artificial virus and allows the fetal stem cells to develop normally.

“This work advances the molecular understanding and not just the association,” between infection and neural and behavioral defects, says Christine Biron, Professor of Molecular Microbiology and Immunology at Brown University and member of mBio’s Board of Editors. Biron says the links between certain infectious agents and behavioral disturbances, like influenza and schizophrenia, have been explored, but research that actually addresses the pathways and mechanisms at work is rarer.

Biron cautions that scientists must be very careful about extrapolating results from mouse studies to humans, particularly in studies of behavior, but the idea that a virus could cause an immune response that leads to neural and developmental problems in children is a sobering one and deserves further analysis.

“The next thing they’re going to try to do is figure whether the immune signal is in the mother or the fetus; that’s a very important point,” says Biron.