Although it's crucial that people get vaccinated against tuberculosis (TB), the vaccine isn't always very effective – at least, not when injected through the skin. New research, however, shows that it works much better when delivered directly into a vein.
The study was conducted by scientists from the University of Pittsburgh School of Medicine and the National Institute of Allergy and Infectious Diseases. They were utilizing the only commercially-available human TB vaccine, known as Bacille Calmette-Guérin (BCG). It's made of a live but weakened form of TB bacteria – Mycobacterium bovis – which occurs in cattle.
For the experiment, the researchers started with 52 macaque monkeys, and divided them into six groups. One of those groups remained unvaccinated, while the others received a standard human-dose hypodermic injection, a stronger-dose injection, an inhaled vaccine mist, a mist plus an injection, and finally a shot of the stronger dose straight into a vein – intravenously, in other words.
Six months later, the scientists exposed the primates to tuberculosis-causing bacteria.
It was subsequently found that the monkeys who received the standard-dose injection experienced almost as much lung inflammation as those who received no vaccine at all. The groups that got the higher-dose injections or the mist did a little better, but only slightly. In the intravenous group, though, virtually no bacteria was detected in the lungs of the animals, and only one of the 10 monkeys developed any lung inflammation at all.
"The effects are amazing," says Prof. JoAnne Flynn, senior author of a paper on the study. "The reason the intravenous route is so effective is that the vaccine travels quickly through the bloodstream to the lungs, the lymph nodes and the spleen, and it primes the T cells before it gets killed."
T cells, which are a type of white blood cell, play a key role in the immune response.
The scientists now plan on seeing if a standard dose of intravenously-administered BCG would be just as effective, without producing as many side effects. They're also assessing the practicality and safety of the delivery method, as it requires more skill on the part of the clinician, and poses a higher risk of infection.
A paper on the research was recently published in the journal Nature.
Source: University of Pittsburgh
