Oil-based emulsion vaccine adjuvants.

Vaccine adjuvants are critical components in experimental and licensed vaccines used in human and veterinary medicine. When aiming to evoke an immune response to a purified antigen, the administration of antigen alone is often insufficient, unless the antigen contains microbial structures or has a natural particulate structure. In most cases, the rationale to use an adjuvant is obvious to the experimental immunologist or the professional vaccinologist, who is familiar with the nature of the antigen, and the aim of the vaccine to elicit a specific antibody response and/or a specific type of T cell response. In this unit, we describe protocols to formulate antigens with oil-based emulsions. Such emulsions represent a major prototype adjuvant category that is frequently used in experimental preclinical vaccines, as well as veterinary and human vaccines.

Safety and immunogenicity of a recombinant Plasmodium falciparum AMA1 malaria vaccine adjuvanted with Alhydrogel, Montanide ISA 720 or AS02.

BACKGROUND: Plasmodium falciparum Apical Membrane Antigen 1 (PfAMA1) is a candidate vaccine antigen expressed by merozoites and sporozoites. It plays a key role in red blood cell and hepatocyte invasion that can be blocked by antibodies. METHODOLOGY/PRINCIPAL FINDINGS: We assessed the safety and immunogenicity of recombinant PfAMA1 in a dose-escalating, phase Ia trial. PfAMA1 FVO strain, produced in Pichia pastoris, was reconstituted at 10 microg and 50 microg doses with three different adjuvants, Alhydrogel, Montanide ISA720 and AS02 Adjuvant System. Six randomised groups of healthy male volunteers, 8-10 volunteers each, were scheduled to receive three immunisations at 4-week intervals. Safety and immunogenicity data were collected over one year. Transient pain was the predominant injection site reaction (80-100%). Induration occurred in the Montanide 50 microg group, resulting in a sterile abscess in two volunteers. Systemic adverse events occurred mainly in the AS02 groups lasting for 1-2 days. Erythema was observed in 22% of Montanide and 59% of AS02 group volunteers. After the second dose, six volunteers in the AS02 group and one in the Montanide group who reported grade 3 erythema (>50 mm) were withdrawn as they met the stopping criteria. All adverse events resolved. There were no vaccine-related serious adverse events. Humoral responses were highest in the AS02 groups. Antibodies showed activity in an in vitro growth inhibition assay up to 80%. Upon stimulation with the vaccine, peripheral mononuclear cells from all groups proliferated and secreted IFNgamma and IL-5 cytokines. CONCLUSIONS/SIGNIFICANCE: All formulations showed distinct reactogenicity profiles. All formulations with PfAMA1 were immunogenic and induced functional antibodies. TRIAL REGISTRATION: (Clinicaltrials.gov) NCT00730782.

The use of oil adjuvants in therapeutic vaccines.

Water in oil emulsions represents one of the new promising generations of adjuvants for immunotherapy. Fifty years ago, incomplete freund adjuvant (IFA) has been used in clinical trials for prophylactic vaccines like poliomyelitis or flu vaccine because of its strong potency. However, even if the quality of the raw materials has been improved in order to avoid secondary reactions, the risk benefit ratio was not favorable to its use for prophylactic vaccines. Moreover, emulsions were highly viscous with a weak stability. The development of new adjuvants concepts like liposomes, oil in water emulsions, bacterial immunostimulating compounds has induced a loss of interest for such formulations. The emergence of immunotherapy treatments for cancer, AIDS or other diseases leads to the re-emergence of these adjuvants, as the risk benefit ratio is more favorable. Then, safety of these adjuvants has been improved by the use of more specific surfactants and refined oils but also by improving their manufacturing process, allowing even sometimes their use in clinical trials for prophylactic vaccines.

Surfactants in vaccine adjuvants: description and perspectives.

Amphiphilic molecules, called surfactants, are made of a lipophilic part linked to a hydrophilic part. These substances have physicochemical properties of self-aggregation, solubilisation or emulsification. Their ability to be attracted at the same time by polar and non-polar compounds forces them to be at the interface. Surfactants most frequently used in vaccines can be of natural or synthetic origin, non-ionic, cationic or amphoteric with a formula weight between 600 and 4000 g/mol. They can be used as adjuvants, solubilisers or stabilisers of emulsions. Physicochemical properties are defined through solubility parameters or solution behaviours and hydrophilic lipophilic balance (HLB). Application properties are assessed through placebo formulations simulating the final use. Synthetic products are preferred to products of natural origin for quality reasons. Development of a new generation of surfactant with precise chemical definition and consistency may generate new candidates for potential vaccine adjuvants.