Calling the shots
A new technology that could revolutionise vaccine manufacture is nearing commercialisation. Dr Bruce Roser, of Cambridge Biostability, described its potential to Hilary Ayshford.
A new technology that could revolutionise vaccine manufacture is nearing commercialisation. Dr Bruce Roser, of Cambridge Biostability, described its potential to Hilary Ayshford.
In the light of the potential threats posed by bioterrorism and a global avian influenza pandemic, vaccines have been much in the news lately. But vaccines are highly sensitive and must be stored and transported within a narrow temperature band between 2°C and 8°C from the time of manufacture to the point of use. Not only will they lose their potency over time, a process that accelerates if they are exposed to high temperatures, but they can be inactivated suddenly by freezing.Heat damage is less of a problem in developed countries, where refrigerators are widely available, than in the developing world, where there is a lack of sophisticated storage and distribution facilities. To overcome this, the World Health Organisation (WHO) set up a cold chain as part of its vaccines programme with the aim of ensuring that vaccines are maintained at the correct temperature until they reach the end-user.
Ironically, the cold chain itself has proved to be a major cause of vaccine wastage in developing countries, according to Dr Bruce Roser, chief scientific officer of UK-based Cambridge Biostability (CBL). The vaccines are packed in insulated boxes that use cold blocks to keep the temperature down, but unless the cold blocks are tempered by leaving them out of the freezer for a time before putting them in the packs, they will destroy all the vials of vaccines that come into close proximity with them.
'It is one of the horrifying statistics in the WHO outreach programme that 70% of all the vaccines delivered to local injection clinics are lost due to freezing,' says Roser. 'It is hard enough to get vaccines to people in the developing world, so writing off 70% of them due to freezing damage is atrocious.'
Of course, exposure to temperatures outside the required range is not the only reason why half of all vaccines manufactured every year are lost. Other causes include batch expiry; breakage or loss of vials; use of dirty needles that introduce contamination into the vials; use of incorrect diluent; surplus reconstitution (the vaccine can be kept for only six hours), and keeping the vaccine beyond the six hour limit, allowing any bacteria that may have entered the vial to grow.
reformulation
All these problems are addressed by an innovative technology from Cambridge Biostability that is set to revolutionise the way vaccines are manufactured, stored, distributed and used. It reformulates existing vaccines into stable liquids that need no refrigeration or reconstitution and are ready to inject.
Although anhydrobiosis is a process that occurs frequently in nature, this is the first time it has been applied to vaccines. The vaccine is spray-dried in sterile conditions to form microscopic glass spheres. These microspheres are then suspended in an approved, inert, anhydrous liquid ready to be injected. The glass softens when it comes into contact with bodily fluids and the vaccine is released and reactivated.
'Many people don't believe that it's possible to spray dry something as fragile as a vaccine, mainly because the temperatures we use are so high,' says Roser. The exhaust temperature of the spray dryer is 120°C, while the inlet temperature is 160-180°C. So how is the vaccine not destroyed when sprayed into air at those temperatures?
The answer, he explains, lies in the evaporative cooling process. When the liquid vaccine is sprayed into the chamber through a fine nozzle with the hot gases, the liquid breaks up into tiny droplets, increasing its surface area a thousand-fold. The rate of evaporation increases to the same degree, which keeps the vaccine cool until it forms a glass, at which point it is stable up to the softening point of the glass at around 100°C.
Heat damage to biological products is a function both of the temperature and the length of time during which it is exposed. Because spray drying is such a rapid process - each droplet spends only around three seconds in the drying chamber - the particle barely has time to register the temperature before it reaches a stable glass state and is collected in the cyclone. While it is in a liquid state it is cooled and as soon as it is a glass it is stable. 'So you can put the most unstable and fragile molecules through a spray dryer without damaging them,' Roser explains.
A glass is matter in an amorphous rather than a crystalline solid state. Many of the materials used by CBL in the spray dryer have been selected because during the drying process they prefer to become amorphous rather than crystalline; a so-called crystal poison can also be added to inhibit crystallisation in those substances that tend to crystallise more readily.
Glasses exhibit certain properties that lend themselves to this application. Unlike crystals, to melt them from the solid phase does not require large amounts of energy - the glasses produced during CBL's spray-drying process soften and melt at temperatures between 40°C and 120°C. They are also very stable: the rate of diffusion of molecules in a glass is measured in millimetres per century.
A product that is dried in a glass is physically immobilised, and because the molecules are unable to move together they cannot react chemically. Chemistry stops, degradation stops and the molecule is held in a state of suspended animation until the glass is softened and dissolved by injecting it into the body.
Since the glass microspheres have a large surface area and are extremely hygroscopic, CBL suspends them in anhydrous liquids in which they are insoluble. This effectively gives them a waterproof overcoat, Roser says, so even if they are exposed to high ambient humidity they are fully protected.
CBL deliberately chose liquids that have a very low viscosity and low surface tension, meaning they can be injected through a very narrow orifice. And since the liquid formulations are anhydrous, they are inherently bacteriostatic, eliminating the need for antiseptics such as thiomerosal.
density issues
The liquids used are already approved by the US FDA for multiple uses. The density of the microspheres is matched to that of the liquid to ensure that the particles remain in suspension. Recently, CBL has developed a method of not only increasing the density of the particles to match the fluoroether liquid it uses, but also of lowering their density by injecting each microsphere as it is formed with a known volume of gas for use in less dense oils. As the particles are mono-dispersed in the liquid they can be injected straight into the body without any reconstitution or agitation. The glass is made from amino acids that are part of the normal body protein metabolism and the oil is a rapidly metabolisable oil that is part of the normal body fat metabolism.
Although the technology can be applied to a variety of injectable, inhalable or ingestable liquid products, CBL is concentrating initially on the vaccine field. A major advantage of the technology is multivalency - its innate stability means that more than one vaccine can be delivered in the same dose without suppressing the response of any of them. As each vaccine is embedded in inert microspheres, no interaction is possible.
Furthermore, the glass can be tailored to dissolve at different rates, enabling the release of the individual component vaccines to be controlled. This makes it possible not only to offer multiple vaccinations in one injection, but also to deliver an initial dose and a booster at the same time - an important factor for compliance in developing countries where a trip to a clinic may involve a long, difficult journey.
With funding from the UK Department for International Development (DFID), CBL is developing a thermo-stable liquid penta-valent childhood vaccine for use in the developing world. The vaccine, which will inoculate children against diphtheria, tetanus, pertussis, Hib (Haemophilus influenzae type b) and hepatitis B in one dose, will be ready for clinical trials by 2008.
The company is also part of a major collaboration with US-based DynPort Vaccine Company for the development of thermo-stable multivalent vaccine formulations designed to provide protection against botulism, a neurotoxin identified as a potential bioweapon. There are seven serotypes of botulinum neurotoxin, each of which requires its own vaccine. A single vaccine formulation is being developed containing all seven vaccine antigens, each optimally formulated to maximise protection and stability.
Other projects under way include a collaboration with Aradigm Corporation to develop a thermo-stable measles vaccination for delivery via inhalation, and the development of a vaccine against enterotoxigenic E.coli (ETEC), one of the world's biggest causes of bacterial diarrhoea that accounts for 210,000,000 cases per year among children in the developing world and 40% of the cases among travellers from the developed world. The final composition of the vaccine is being established and Phase II trials will take place in 2006.
versatility
The technology has also been proven with a number of different pharmaceuticals, including erythropoetin (EPO), monoclonal antibodies, insulin and recombinant growth hormones. It can also be used for eye drops and for other forms of ballistic delivery, such as jet injections.
'We don't just have a technology that is looking for an outlet, we are trying to solve real problems in the real world,' Roser stresses.
Such is the company's confidence in its technology that it has invested £1m on commissioning the world's first commercial sterile spray drier for vaccines. Manufactured in Denmark by Niro, part of the process engineering division of the GEA Group, and installed at Nova Laboratories in Leicester, UK, the spray dryer will be operational in March and in full production by September. It will enable batches of up to 10,000 doses of vaccine to be produced in cGMP conditions for clinical trials and will be a precursor for large-scale commercial production of stable liquid vaccines.
'The plant allows us to address scale-up issues and refine the equipment. The next sterile facility will be for commercial production of stable liquid vaccines and will be 10 times bigger,' Roser predicts.
The spray dryer is about two metres high and one metre in diameter and will be housed in a large isolator. Input and exhaust gases will be passed through HEPA filters down to 0.2µm to ensure total containment. The isolator will be located in a Class 10,000 cleanroom and will operate under positive pressure. For CBL the aseptic sterile plant in Leicester represents the next step from having some good ideas to full-scale production of sterile and validated pharmaceuticals made to GMP standards. 'You have to grow up sometime,' said Roser. 'We had lots of good laboratory-based ideas and now we think we need to be seen to be a real player.'
moving to trials
The company's strategy is to work with partners to convert their vaccines into stable liquids and enable them to go through preclinical trials and Phase I and Phase II clinical trials using CBL's equipment and facilities. This should convince the vaccine manufacturers that there is no risk involved in adopting the new technology and encourage them to order and build their own production facilities.
'But we are not asking them to take that risk before they have proved the technology,' Roser stresses. 'This is a big jump for people to take on the word of a laboratory-based company, no matter how strong our patent position. We have to scale this up and make sure that it works. To make vaccines in a way that they have never been made before is a very big step for us.'
The new facility will also demonstrate to potential purchasers of such vaccines, such as the WHO and the US government, that they can be supplied consistently and in large quantities, and will open the way to supply contracts as well as development contracts.
The speed of the spray drying process is expected to prove very attractive to the major vaccine manufacturers. To make 10,000 doses of vaccine in one of the four small machines at CBL's premises in Cambridge would take 6-8 hours - significantly less than the 3-4 days it would take to produce a similar size batch of conventional freeze-dried vaccine, such as measles. 'If all vaccines were made by spray-drying we could overcome the problems of shortages, enabling production to be linked more precisely to demand,' Roser claims.
resistance
Some of the major vaccine manufacturers have expressed great interest in the tech-nology, but others are proving more resistant, particularly when it comes to accepting how stable the products are. But CBL does not see the vaccine and pharma companies as their real market. Rather, it sees its customers as those who feel the pain of funding the cold chain - organisations such as the WHO and Unicef - who will then put pressure on the vaccine manufacturers to supply stable liquid vaccines.
The WHO estimates the cost of the cold chain at $200-300m per year - enough to vaccinate an additional 10 million children worldwide.
CBL calculates that the technology adds about US$0.11 to a dose of vaccine - but additional costs have been kept to a minimum by using FDA-approved materials. This added cost is relatively insignificant for penta-valent vaccines costing $3-4 per injection, but for single dose vaccines like diphtheria or tetanus it represents almost a doubling of the cost. However, Roser believes this is balanced out by eliminating the high cost and wastage of the traditional cold chain.
'Innovation does not stop in the laboratory,' he asserts. 'It is also seen in the way we conduct our business. Our vision to become the world's leading virtual vaccine and drug company, enabling and licensing our technology across the globe, is supported by our Third-World-First business strategy: one that commits to delivering our technology first to those who need it the most.'
