Bovine viral diarrhea virus (BVDV) vaccines have an obvious job: prepare cattle to respond when they encounter the virus. Researchers, however, are looking at whether they can get an even broader response from vaccination, including stronger defenses at the mucosal surfaces where BVDV can enter and replicate.
A new study tested an experimental adjuvant designed to do just that. The formulation, called an Alhagi honey polysaccharide-Alum Pickering emulsion (AHPPE), was combined with an inactivated BVDV vaccine and tested in calves.
Researchers combined Alum and a plant-derived polysaccharide called Alhagi honey polysaccharide with a squalene oil phase containing all-trans retinoic acid. Alhagi honey is a natural, sugar-rich secretion produced by camelthorn plants (Alhagi species) growing in arid regions like Northwest China and Central Asia. The resulting particles were designed to carry the vaccine antigen while also influencing how immune cells take up and respond to it.
Putting the Approach to the Test in Calves
The researchers vaccinated 24 healthy Holstein-Friesian calves, dividing them into four groups. Calves received saline, BVDV antigen alone, BVDV antigen with conventional Alum, or BVDV antigen with the new AHPPE formulation.
Each calf received a single 1-mL intramuscular injection containing 50 µg/mL of BVDV antigen. Blood and fecal samples were collected on days 7, 14, 21 and 28 to track the immune response.
The formulation itself performed well during development. The researchers reported particles approximately 2,000 nanometers in size and an antigen-loading efficiency of nearly 90%. The formulation also maintained relatively consistent particle characteristics during the testing period.
The more important question, though, was what happened after vaccination.
By day 28, calves receiving AHPPE had significantly higher BVDV-specific serum IgG than calves receiving the conventional Alum formulation. The AHPPE group also produced significantly more BVDV-specific IgA in fecal samples than the other vaccinated groups throughout the study.
That IgA response is particularly interesting because BVDV can infect through mucosal surfaces. The researchers were looking for evidence that an intramuscular vaccine could influence immunity beyond the traditional systemic antibody response.
The study also found changes in several molecules that help the immune system communicate and direct immune cells. By day 28, AHPPE-vaccinated calves had higher levels of IL-10 and IL-17, which help regulate immune responses; CCR6 and CCR9, which help immune cells navigate to different tissues; and CCL20 and CCL28, which help attract and position immune cells, compared with control calves.
Looking for Clues to How It Works
The researchers also looked at what happened when the formulation was exposed to dendritic cells, which play an important role in initiating immune responses.
The AHPPE particles were taken up by monocyte-derived dendritic cells, and gene-expression analysis showed changes in pathways involved in antigen uptake, Toll-like receptor signaling, antigen presentation and chemokine activity. In other words, the formulation appears to influence how antigen-presenting cells interact with the vaccine, although the study does not establish exactly which mechanisms are responsible for the enhanced response.
The work builds on an earlier mouse study from the same research group. Using the same AHPPE approach, researchers found increased IgA-positive cells and IgA expression in several sections of the intestine following intramuscular vaccination. That provided some of the initial evidence behind the idea that this type of adjuvant could influence intestinal immune responses.
More broadly, researchers are exploring Pickering emulsions and other particulate adjuvants as ways to combine antigen delivery and immune stimulation in a single vaccine formulation. Other work has tested similar concepts with polysaccharide-based adjuvants and vaccines for other animal diseases.
The Next Step: Does It Protect?
The interesting part isn’t necessarily the chemistry behind the particle, but the possibility of getting more from an injectable vaccine. An adjuvant that can strengthen the systemic antibody response while also encouraging mucosal-associated immunity could eventually provide another tool for improving protection against pathogens such as BVDV.
There are important caveats, however. This was a small study, with only six calves per group, and animals were followed for just 28 days after a single vaccination. Most importantly, the researchers did not challenge the calves with BVDV, so the study cannot tell us whether the stronger antibody responses would translate into less viremia, reduced viral shedding or better protection following exposure.
The fecal IgA findings also shouldn’t be interpreted as definitive proof of increased intestinal immunity. Fecal antibodies can come from both local and systemic sources, and the study did not directly measure protection at the intestinal surface.
Still, the results offer an interesting look at where BVDV vaccine research may be headed: not simply toward stronger antibody responses, but toward designing vaccines that can influence multiple parts of the immune system at once.
