Needless to say, vaccines have been an absolute boon to human populations since their inception, helping curtail such diseases as smallpox, polio, and measles. However, when it comes to infections like HIV-1 and malaria, their efficacy goes down significantly. One reason for that could be the timing of antigen and adjuvant presentation to the immune system.
To circumvent this problem, authors a paper recently published in the journal ACS Central Science have developed an injectable hydrogel that could be used to ensure sustained release of vaccine components, thereby improving potency, quality, and duration of immune responses in mice.
Most vaccines work by exposing the immune system to parts of a pathogen (called an antigen) for a period of time, which enables the body to generate antibodies to be deployed in fighting the infection. Later, when a vaccinated person encounters the same pathogen, their immune system can recognise and dispose of the invader more quickly and with less effort.
In natural infections, the immune system is typically exposed to antigens for 2-3 weeks, allowing it to form a formidable response, whereas vaccines rarely provide more than 1-2 days of exposure. And while, in many cases, that is perfectly sufficient, it may be lacking in others.
With all of this in mind, Eric Appel and his colleagues set out to create an injectable hydrogel that would release vaccine components over a longer period of time – more akin to what happens in natural infections – and hopefully lead to a more robust immune response.
In the study, Appel and his team describe a vaccine-infused polymer-nanoparticle hydrogel which they had injected under the skin of mice. The injection resulted in localised inflammation which brought certain types of immune cells to the area of injury, giving the hydrogel a chance to trickle out the antigen and adjuvant over several days.
Results showed that, compared to mice which received standard immunisation, mice injected with the hydrogel-vaccine mixture produced more antibodies over a longer period of time. In addition, the antibodies produced by mice in the intervention group had about 1,000-fold higher affinity for the antigen.
According to the authors, while the new system still needs further testing to ascertain its ability to confer vaccine protection against specific diseases, these findings demonstrate a simple, effective method for administering vaccines in a more effective manner that also ensures immunity for longer periods of time.