The vaccine adjuvant known as ‘MF59’ [1-3] is a submicron oil-in-water emulsion of squalene, polysorbate 80 (also known as Tween 80), and sorbitan trioleate (also known as Span 85). It may also include citrate ions e.g. 10 mM sodium citrate buffer. The composition of the emulsion by volume can be about 5% squalene, about 0.5% Tween 80 and about 0.5% Span 85. The adjuvant and its production are described in more detail in Chapter 10 of reference 4, chapter 12 of reference 5 and chapter 19 of reference 6.
As described in reference 7, MF59 is manufactured on a commercial scale by dispersing Span 85 in the squalene phase and Tween 80 in the aqueous phase, followed by high-speed mixing to form a coarse emulsion. This coarse emulsion is then passed repeatedly through a microfluidizer to produce an emulsion having a uniform oil droplet size. As described in reference 6, the microfluidized emulsion is then filtered through a 0.22 μm membrane in order to remove any large oil droplets, and the mean droplet size of the resulting emulsion remains unchanged for at least 3 years at 4° C. The squalene content of the final emulsion can be measured as described in reference 8.
Oil-in-water emulsions contain oil droplets. The larger oil droplets contained in these emulsions may act as nucleation sites for aggregation, leading to emulsion degradation during storage.
It is an object of the invention to provide further and improved methods for the production of microfluidized oil-in-water emulsions (such as MF59), in particular methods that are suitable for use on a commercial scale and which provide improved microfluidization to provide emulsions with fewer large particles.