In Part III of our series on “Strategies for Improving Viral Yield in Vaccine Manufacturing,” we will examine the use of manufacturing strategies to improve viral yield and lower cost of production. Improving viral yield and lowering cost is critical for improving access to vaccines in the developing world where even minor medical expenses are prohibitive. Improving viral yield also enables a faster response time in case of a pandemic. Improving cell culture media is one way to increase virus yield and was examined in Part I titled “Improving Media to Increase Virus Yield in Vaccine Production.” In Part II titled “Utilizing Bioreactors to Increase Virus Production in Vaccine Manufacturing,” we discussed the role of bioreactors and accompanying technology as another way to achieve higher yield. In Part III we will look at additional strategies that can be employed as part of the manufacturing process to achieve higher yield and reduce cost.
In vaccine manufacturing keeping viruses stable during culture, purification, and formulation is critical. Some viruses are inherently unstable and these require even more care. Host cells (most often Vero or MDCK) are subjected to fluidic shear forces generated during shake, wave or bioreactor culture. These forces can reduce cell health including growth and yield and can damage the cell membrane. Adding stabilizing proteins to cell culture media can reduce the shear force damage. Stabilizing proteins can also help keep the virus stable in culture and in the final product formulation. One of the most successful stabilizing proteins used in media is albumin. Albumin is often used in formulation, as well, to stabilize attenuated viral vaccines and protein based vaccines. Other stabilizing proteins such as bovine gelatin are used as an excipient in some vaccines. However, the use of gelatin raises potential safety concerns due to the bovine source. Albumin can increase safety risks as well if it is animal or human derived. Fortunately now there are recombinant forms of albumin available, which provide the benefits of albumin without any safety issues or problems of inconsistency. Several companies including Sigma, Fisher Scientific, InVitria, Sheffield Bioscience and Mediatech supply recombinant albumin that can be added to provide stability.
Loss of viral yield during purification is a problem for many viruses. Many viruses, in particular enveloped viruses, are “sticky” and difficult to purify with high yield because the virus sticks to filters and surfaces. Albumin has been known to help increase the yield of virus after purification either by preventing non-specific binding to filters and surfaces or by directly stabilizing the virus. Similar to mammalian viruses, albumin as been shown to increase the spread and titer of baculovirus in culture by preventing non-specific binding of the virus to the cell surface .
Another strategy that can reduce cost is the use of adjuvants. While adjuvants do not improve yield, they allow vaccines to be effective with less virus antigen used per vaccine dose. Depending on the adjuvant and virus, antigen requirements with an adjuvant can be as low as one fourth the amount needed without the adjuvant present.
Aluminum salts or alum have been used as adjuvants for almost a hundred years to reduce the antigen needed to illicit the desired immune response. These adjuvants are currently being used in many childhood vaccines including Hepatitis A, Hepatitis B, Diphtheria-Tetanus-Pertussis (DTaP), Haemophilus Influenza type B (HIB), Human Papillomavirus (HPV), and pneumococcus infection. However, aluminum based adjuvants are not effective in many vaccines, including the influenza vaccine and new adjuvants have been developed to meet the demand.
A new group of adjuvants have been developed that are different forms of lipids. GlaxoSmithKline (GSK) launched a new adjuvant Monophosphyoryl Lipid A (MPL), a bacterial lipid, in their cervical cancer vaccine Cervarix. GSK and Novartis have each also developed new adjuvants that are oil in water emulsions of squalene, a lipid found in the body. Novartis’ MF59 is an example and has been used in flu vaccines in Europe since 1997. GSK’s A503, also squalene based, is used in H1N5 vaccines in Europe. Intercell, an Austrian Company, is developing a new adjuvant for the influenza vaccine that consists of a patch worn by patients over the injection site.
For vaccines where the virus is very expensive to make or doesn’t elicit a strong immune response these new adjuvants could be the key to making new vaccines possible. In the case of a pandemic, adjuvants allow more people to have access much faster. During the 2009 H1N1 pandemic, the majority of influenza vaccines in Europe and most of the rest of the world contained this new class of adjuvant. While the United States opted not to include adjuvants for fear of public rejection of the vaccine, adjuvants are becoming more commonplace in the rest of the world.
These are just a few examples of work being done to improve viral vaccine production and there are others. Does anyone have any other suggestions to recommend?
- Maranga, L., A.S. Coroadinha, and M.J. Carrondo, Insect cell culture medium supplementation with fetal bovine serum and bovine serum albumin: effects on baculovirus adsorption and infection kinetics. 2002. (12153321) Biotechnol Prog. 18 (4): p. 855-61.