Inactivated vaccines usually contain an adjuvant which potentiates the immune response to the
antigen. During the last 70 years
aluminium salts have been the only adjuvant licensed for human use. The adjuvanting activity is based on their serving as an
antigen depot and inducing a localized inflammatory response. Our efforts to develop a potent and well tolerated adjuvant has focussed on the use of immunopotentiating reconstituted
influenza virosomes (IRIV). The IRIV base is a
liposome with a mean diameter of 150 nm, comprising
phosphatidylcholine (PC) and
phosphatidylethanolamine (PE). These mammalian
phospholipids are virtually non-immunogenic and have enjoyed a long history of use in human pharmaceutical preparations. The haemagglutinin (HA) and trace quantities of viral
neuraminidase and
phospholipids from the A/Singapore 6/86 virus strain are intercalated within the
phospholipid bilayer. The presence of the HA is necessary to enhance the immunopotentiating effect to
antigen associated with IRIV The excellent characteristics of IRIVs as adjuvants have been demonstrated in several systems. IRIVs as alternative adjuvant system for human use are registered by most European, Asian and American countries in commercial
hepatitis A and
influenza vaccines. IRIVs were first used in the manufacture of a
hepatitis A vaccine. This contains
formalin-inactivated and highly purified hepatitis A virus (HAV) of strain RG-SB, cultured in human diploid cells, which is coupled to the IRIV vesicle. For a new
influenza vaccine the surface spikes (HA and NA) of three currently circulating
influenza strains were jointly inserted into the vesicle membrane of the IRIVs and successfully tested clinically. In
Epaxal Berna, the first commercially available liposomal
vaccine is expected to be the inactivated hepatitis A virus adsorbed to IRIV particles. In the virosomal
hepatitis A vaccine, the
antigen is believed to be attached to the IRIV by interacting with
phospholipids which are considered to correspond to its natural receptor on hepatocytes. The present investigation includes data based on light scattering measurements which show the binding of the virions to vesicles.