NEW YORK (Reuters Health) – An mRNA vaccine against 19 proteins found in tick saliva produces an immune response in guinea pigs, new research shows.
The vaccine impairs the ticks’ ability to feed and decreases the risk of contracting Lyme disease, according to findings published in Science Translational Medicine.
“Depending on how the experiments were performed in guinea pigs, the efficacy was over 95%,” Dr. Erol Fikrig of Yale University School of Medicine in New Haven, Connecticut, told Reuters Health by email.
The vaccine is composed of nucleoside-modified mRNAs that encode 19 proteins found in tick salivary glands that are secreted when the ticks bite. The mRNA technology is similar to that used in the Pfizer-BioNTech and Moderna COVID-19 vaccines.
The proteins targeted are found in Ixodes scapularis, the black-legged ticks responsible for much of the Lyme disease in North America. Rather than seeking to protect against Borrelia burgdorferi, the bacterium that causes North American Lyme disease, the researchers are developing this vaccine against tick bites with the potential to protect against a range of tick-borne infections. Those include babesiosis, anaplasmosis and Powassan virus, among others.
“Fostering immunity by people to the ticks themselves, rather than each specific pathogen they transmit, is an excellent approach. We now know that individual ticks are often co-infected with two or more tick-borne pathogens, and so, a vaccine targeting one pathogen generally won’t help against the others,” Dr. Richard Ostfeld, a disease ecologist at the Cary Institute of Ecosystem Studies in Millbrook, New York, who was not involved in the research, told Reuters Health by email.
To test the vaccine, the researchers compared six immunized guinea pigs with five control guinea pigs. The vaccinated guinea pigs had antibodies to 10 of the 19 proteins targeted by the vaccine, while the control animals had none of the antibodies.
The researchers then placed tick nymphs on vaccinated and unvaccinated animals, noting that redness developed within 18 hours on the vaccinated animals, but not on the controls.
The vaccinated animals also showed other signs of protection against ticks. The ticks began to detach early, 48 hours after they were placed, and by 96 hours 80% of the ticks had detached. In comparison, only 20% of the ticks had detached from the control animals during that time.
The ticks placed on vaccinated guinea pigs fed poorly, as revealed by their average weight of 1.02 mg, less than half that of the ticks placed on the controls (P<0.0001).
To test the vaccine’s effect on Lyme disease transmission, the researchers placed ticks infected with B. burgdorferi on vaccinated and unvaccinated guinea pigs. They removed the ticks when the bite sites became red, emulating an approximation of human behavior when irritated by a tick. After three weeks, none of the 16 vaccinate guinea pigs were infected, while six of the 13 controls were infected.
A repetition of the experiment found that three of five immunized guinea pigs were infected compared to four of five controls. The results suggest that removing ticks at the onset of erythema can protect against Lyme disease, the researchers write.
In another experiment, inoculated mice did not develop erythema and there was no effect on the ticks’ feeding. The difference may be that mice are important to the ticks’ life cycle, while guinea pigs are not. Mice are not known to develop resistance to tick bites naturally, in contrast to guinea pigs and humans.
Humans may react to the vaccine more similarly to guinea pigs than to mice, the researchers speculate.
“A big remaining question is whether human immune response is more like guinea pigs or more like mice,” Dr. Ostfeld said.
The study had no commercial funding. Some of the authors are co-inventors on a related patent application.
SOURCE: https://bit.ly/3soNy1J Science Translational Medicine, November 17, 2021.
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