When an effective vaccine against the Human Immunodeficiency Virus (HIV) becomes available, it may well be given through a puff from an inhaler rather than as an injection.
Two years back, Darrell Irvine of the Massachusetts Institute of Technology in the U.S., along with a team of other scientists, reported that a potent vaccine could be made by enclosing immunity-inducing substances in tiny capsules with several fatty layers.
Many germs, including HIV, gain entry into the body through moist tissue — the mucosa — that line the airways, alimentary canal, and the reproductive tract.
Dr. Irvine and colleagues have now demonstrated that such a nanocapsule vaccine can be administered in a needle-free manner at one mucosal site and produce immune protection at other mucosal surfaces as well.
The nanocapsules they tested in mice contained ovalbumin, an egg-white protein often used in immunology studies, along with two molecules to enhance the immune response. The ovalbumin played the part of an ‘antigen’, the bit of a pathogen that sets off the immune system’s alarm signals.
When the vaccine was administered to the airway of mice, immune cells patrolling the lining of the respiratory tract efficiently took in the nanocapsules and produced a strong immune response. Moreover, immune cells primed by the vaccine were detected in the gut and reproductive tract as well.
“We found that the nanocapsule vaccine promoted greater immunological memory at multiple mucosal tissue sites” than when the same vaccine components were given in solution, remarked Dr. Irvine in an email.
He and the other scientists also showed that mice immunised with an appropriate nanocapsule vaccine were much better protected when infected with the vaccinia virus.
“To date, strategies to enhance responses elicited by synthetic nanoparticle vaccines have largely focused on engineering the vaccine carrier itself, for example, to obtain optimal surface chemistry or particle size,” the scientists observed in their paper. “However, the site of vaccine administration may also play a critical role in the response to particulate vaccines.”
The safety and efficacy of their approach needed to be evaluated in a large-animal model closer to humans, such as monkeys, using relevant disease antigens, the scientists noted.
Besides HIV, this approach could be of interest for vaccines against many other mucosal pathogens, such as the human papillomavirus, herpes simplex virus, influenza and tuberculosis, said Dr. Irvine in his email.