In Vivo Study Results from a Prototype Single-Shot Hepatitis B Vaccination
To show the potential of the single-shot approach, prototypes were tested in in vivo studies. The results reveal the impact of the composition of the formulation on the immune response.
The OctoVAX microsphere technology is applied with the objective to reduce the number of injections to a single-shot vaccination
that confers full protection against a specific infection for a period at least similar to the conventional regimen. For proof
of concept of the single-shot vaccine approach, prototype vaccines were developed using the HBsAg antigen. Current practice
for hepatitis B vaccination is either a two- or a three-injection regimen, consisting usually of a prime injection followed
by two booster injections at 1–2 months and 3–12 months after the first administration. This vaccine consists of aluminum-adjuvanted
Based on the in vitro release profiles, prototype microsphere formulations were selected for further investigation of the concept. Proof of concept
studies were performed by immunizing Balb/c mice with prototype microsphere vaccine formulations that combine a prime dose
with a single microsphere component. This microsphere component represents the booster dose with a delayed antigen release
around day 30. In these studies, the prototype single-shot vaccines were compared with two injections at day 0 and 28, representing
the prime and booster dose. The potency of the vaccines to induce an antibody immune response was determined by analyzing
the development, over time, of serum anti-HBsAg immunoglobulin concentration using a commercial immunoassay.
The results of these animal studies show that the single-shot HBsAg vaccines based on the OctoVAX controlled release technology
induce responses that are similar to those induced by the representative two-injection control vaccination by subcutaneous
administration. Figure 8 shows that vaccines with differences in physical aspects and adjuvant presence induce antibody responses
with different kinetics. Formulation A induced the desired levels of antibodies without a prime component, in contrast to
formulation B, which needed an adjuvanted prime. However, even with formulation B, the data show that OctoVAX microspheres
can provide a booster dose on initiation of an immune response by a prime component, providing proof of concept for the single-shot
controlled delivery principle. In additional experiments, it has been shown that intramuscular application results in similar
or better immune responses, which may ultimately be the preferential choice for route of administration (data not yet published).
Figure 8. Antibody titers induced by prototype single-shot HBsAg vaccines based on microspheres of formulation A or B, which
differ in their physical characteristics. Microspheres were either administered by themselves or mixed with aluminum hydroxide
(AlOH)-adjuvanted HBsAg. Control mice received two injections of AlOH-adjuvanted HBsAg. Antibody titers are represented as
geometric mean titers per group of 10 animals in relation to an international reference standard at 28, 56, and 84 days after
In addition to the efficacy data, animal studies have revealed that OctoVAX microspheres are well-tolerated and induce no
systemic toxicity effects.9 Furthermore, local reactogenicity was limited to minor foreign body reactions, as to be expected for any biodegradable implanted
material. Therefore, it can be concluded that OctoVAX microspheres are well-tolerated and safe controlled-release vehicles
that can be applied for the development of single-shot vaccines.
The development of a single-shot vaccine technology could contribute to a significant increase in vaccination coverage worldwide
by improving patient compliance and lowering administration costs. To achieve this innovation, single-shot vaccines must
be rationally designed. To facilitate this, complex factors in the development and manufacturing process that have a significant
influence on the efficacy of the immune response must be controlled precisely during the development and manufacturing phases.
The concept of single-shot vaccination is applicable to various types of antigens and vaccines. Further research is required
to investigate the influence of adjuvants and release characteristics in various vaccination regimens.
Bas Kremer, PhD, is a scientist in vaccine development, Rianne Roukema is a manager of corporate communications, and Leo de Leede is a director of preclinical research and development, all at OctoPlus NV, Leiden, the Netherlands, +31.71.5241071, email@example.com
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