Staph Vaccines Could Leverage Immune Cells & Early Immunization

Washington University study finds staphylococcus aureus α-toxin suppresses antigen-specific T cell responses

blood testing

A new study from Washington University School of Medicine in St. Louis, Missouri, may help explain why previous attempts to develop a staph vaccine have failed.

These Washington University researchers are also suggesting a new approach to vaccine design which focuses on activating an untapped set of immune cells, as well as immunizing against staph in utero or within the first few days after birth.

This pre-clinical study in mice published on December 24, 2019, found that T cells — one of the body’s major types of highly specific immune cells — play a critical role in protecting against staph bacteria. 

Most vaccines rely solely on stimulating the other main type of immune cells, the B cells, which produce antibodies to attack disease-causing microorganisms such as bacteria, said these Washington University researchers in a press release.

“Across the globe, staph infections have become a pervasive health threat because of increasing antibiotic resistance,” said senior author Juliane Bubeck Wardenburg, M.D., Ph.D., director of the university’s Division of Pediatric Critical Care. 

“Despite the medical community’s best efforts, the superbug has shown a consistent ability to elude treatment. Our findings indicate that a robust T cell response is absolutely essential for protection against staph infections.”

Highly contagious, staph survives and thrives on human skin and can be spread through skin-to-skin contact or exposure via contaminated surfaces. Generally, the bacteria live harmlessly and invisibly in about 33 percent of the population, says the Centers for Disease Control and Prevention (CDC).

From their residence on the skin, the bacteria can cause red, pus-filled sores. Ever persistent, the superbug will deliver recurrent infections in about half of its victims.

Staph strains can enter the bloodstream, bones or organs and lead to pneumonia, severe organ damage and other serious complications in hundreds of thousands of people each year. 

The CDC says nearly 20,000 people died with bloodstream staph infections in 2017.

“The focus in the vaccine field for Staphylococcus aureus during the past 20 years has been on generating antibody responses, not on specific T cell responses,” Dr. Bubeck Wardenburg said. 

“This new approach shows promise.”

For nearly 15 years, Dr. Bubeck Wardenburg has studied a single toxin — called alpha-toxin — made by staph. This toxin plays a role in tissue damage in multiple forms of infection. 

“An important thing about the alpha-toxin is that it is found in all staph strains, meaning those that are and are not antibiotic-resistant,” she said. 

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“Understanding this allowed us to devise studies in mice that examined the effect of alpha-toxin on the immune response in minor skin infections as well as in more serious infections that spread in the bloodstream.”

The researchers found that the immune cells did not protect mice that had minor staph infections on their skin. 

However, mice that were exposed to life-threatening staph infections in the bloodstream did develop protection.

“We discovered a robust T cell response targeting staph in the bloodstream,” Dr. Bubeck Wardenburg said. “By contrast, T cells were diminished in skin infections as a result of the toxin. Because skin infection is very common, we think that staph uses alpha-toxin to prevent the body from activating a T cell response that affords protection against the bacteria.”

In terms of the big picture, Dr. Bubeck Wardenburg said blocking the toxin in skin infections may yield a healthy T cell response.

Further, protecting the T cell response from the time of birth may reprogram the bacteria’s overall effect on the immune system. 

“This bug is deliberate and acts in a sinister way early on,” she said. “The bug appears to be using the toxin to shape the T cell response in a way that’s favorable for the bug but not for humans.”

Previous vaccine development efforts have focused on adults. 

However, Bubeck Wardenburg said, a vaccine may be more likely to succeed if administered before infants first encounter staph. Therefore, immunization should happen before initial exposure to staph, to block the toxin and generate a vigorous T cell response.

“We envision two strategies,” Bubeck Wardenburg said. 

“One is immunizing pregnant women so they can transfer antibodies that protect infants against the toxin at birth. The second involves immunizing infants within a day or two after birth. Neither of these strategies has been considered for staph vaccines to date.”

The study was supported by the National Institutes of Health, grants AI097434 and T32 HD007009; the Burroughs Wellcome Foundation Investigators in the Pathogenesis of Infectious Disease Fellowship; and the University of Chicago Growth, Development, and Disabilities Training Program. No conflicts of interest were disclosed.

Washington University School of Medicine’s 1,500 faculty physicians are also the medical staff of Barnes-Jewish and St. Louis Children’s hospitals.

Vaccine development news published by Precision Vaccinations