Horizons in vaccine production

The scramble for a coronavirus vaccine over the last two years has demonstrated how important vaccines are to containing infectious disease. The coronavirus vaccine has broken the link between infections and hospitalisations, and this remains a vital part of the strategy for combatting Covid-19 and for any future pandemics. Despite the incredible speed of vaccine development, vaccine production capacity remains a serious bottleneck. There is a clear and pressing need to increase vaccine production capacity, not only for the current coronavirus vaccines, but the next generation and those against the next major emerging disease.

Vaccine Production

Vaccine production involves three broad steps. Firstly, the active agent, or a precursor to it, is produced. For the vast majority of vaccines, this involves some form of cell culture. Whether it is for whole pathogen and toxoid vaccines, which require incubating host mammalian cells, or recombinant protein vaccines produced by bacteria and yeasts, cell culture requires a sterile environment and stringent controls of incubation conditions in order to ensure reliable production of suitably pure vaccine. These must be optimised for every new vaccine or agent, and re-optimised for every change in batch size.

The antigen must then be harvested from culture and purified. This involves ultracentrifugation (to separate components by weight), multiple rounds of filtration (to remove unwanted residual products), chromatography (to further remove smaller contaminants based on size or electric charge), and ultrafiltration (to control the pH and formulation of the vaccine). Purification steps are expensive, employing costly filters and reagents, and are significantly time consuming, as vaccines must be free of impurities that could result in an adverse response or destabilise the finish product.

The purified antigen, however, is rarely suitable as a finished vaccine. The antigen is formulated with immune response boosting adjuvants, stabilisers, preservatives, buffers, and lipids, before bottling in a glass or plastic vial, all of which have their own production and purification chains. As some vaccines combine multiple different antigens at this stage, the number of production steps to make a finished vaccine can be vast.

Avoiding Cell Culture

Whilst improvements can be made throughout the antigen production and purification steps, one method of scaling up vaccine production involves focusing on simplifying antigen production and, in particular, removing the need for a cell culture phase.

mRNA vaccines, such as those crucial in the fight against Covid-19 so far, can help streamline this production significantly. Making the antigen-encoding mRNA itself is a relatively straightforward process. A polymerase produces the mRNA from free ribonucleobases according to a DNA template, which is subsequently degraded. This is a cell-free process, but still must be performed within a laboratory setting, with the corresponding hygiene and safety standards. However, some vaccine manufacturers are working to bring the production processes outside the lab and, potentially, outside altogether.

Canadian firm Medicago, in collaboration with GlaxoSmithKline, have developed a coronavirus vaccine which, instead of requiring cell culture, is produced in plants. Whilst these plants are not grown in open fields as with regular crops, the growing conditions are never-the-less far simpler than those of tissue culture, and can tolerate broader conditions without the requirement high sterility. The fact that plants unlike the host cells cannot be infected by human viruses reduces the risk of contamination by adventitious agents. If vaccine producing plant parts such as leaves, fruits or tubers to be dried, frozen or otherwise stored and distributed using the regular agricultural-grade processes, the costs of storing and shipping throughout the supply chain could be reduced. The WHO posit that similar technologies may one day allow vaccines to be produced cheaply in very high amounts.

Faster purification

Purification, as a time-consuming and expensive step, can significantly slow down production. It also reduces the However, regulatory standards rightly set high purities which must be achieved. Conventional purification techniques employ batch processes, such as ultracentrifugation, whereby mixtures are spun at high speeds to precipitate out heavier contaminants. This can be seen as a “negative” approach, whereby contaminants are removed.

The EU-funded DIVINE product, which finished in February 2020, aimed to devise new techniques for speeding up vaccine production. This primarily concerned a “positive” technique of removing the desired compounds from a mixture containing them and reformulating these at high purity, rather than trying to remove all contaminants from such a mixture. One approach is to use Nanofitins, antibody mimetics devised by French company Affilogic which capable of binding vaccine antigens with high affinity. Once immobilised into a resin in an affinity chromatography column, this allows capture of vaccines in a single step process. These can be tailored for specific antigens on demand, allowing the technology to be applied to a wide range of vaccines. Also part of the DIVINE project, Danish firm Aquaporin employed their membrane technologies to repurify waste water, further reducing waste quantity and overall purification costs.

In the future, further improvements in purification speed and efficiency can be achieved through a shift away from batch-based approaches and towards ones such as chromatography and aqueous two-phase extraction which are amenable to continuous manufacturing. However, it remains to be seen if suitably pure solutions can be produced using these methods, and any widescale deployment will need to be accompanied by changes in regulatory frameworks.

Scaling up vs Scaling out

As there are several obstacles to increasing the scale of production at existing facilities, one

alternative is to build more facilities – this is known as “scaling out”. On the face of it, one would expect this to be more difficult. Quality and sterility of production, and a reliable supply of inputs, are difficult to replicate consistently. Particularly with cell culture, it is common that new bioreactors produce substandard yields at first and require significant optimisation. However, many of these difficulties also apply to scaling up production on site.

Vaccine production can draw from experience in other high technology fields where extreme precision is required. Semiconductor manufacturing is a field as complex as vaccine production, if not more so, and it is not possible to simply scale up production at every process step whilst maintaining uniform production at the sub-micron scale. Indeed, when operating at such a fine scale, tolerances are so tight that seemingly mundane changes such sub-degree differences in temperature at each and every step of the process could result in unforeseen consequences for production. As chips became smaller, more variables became relevant, which resulted in an increased amount of experimentation to troubleshoot any problems which emerged. As a result, new production facilities typically faced long periods of substandard yield as this process unfolded.

As such, so as to speed up technological transfer, in the early 1990s Intel developed the “Copy Exactly!” approach. Under this philosophy, everything which might affect the process, or how it is run, is copied and replicated to the finest detail. Over time, the reach of this process expanded to encompass the entire fabrication plant. The results of this method were marked, allowing new sites to reach full productive capacity in record time. Unlike “scaling up”, scaling out in this manner takes advantage of the wealth of knowledge already gathered in optimising the initial production site – we already know how the parameters that achieve high yields from the first site, whereas scaling up requires significant optimisation and troubleshooting. The approach can be used to replicate existing facilities within a firm, or with partner organisations.

Applying this to the vaccine industry would mean encapsulating the production chain into highly defined modules, which could be reproduced exactly. Suggesting that innovators freely share their production processes in exhaustive detail may seem alien in an industry better known for keeping a tight grasp on its IP and intangible technical knowhow; however, strong IP rights have a significant role to play in this process. Simply having an licence and the information contained in a patent is insufficient to produce a viable vaccine – a patent is not intended to be an exhaustive “recipe”, and significant technical knowhow and internal knowledge is needed to reduce it to practice. A Copy Exactly approach would seem a natural partner for a licencing pool, providing a single mechanism for licencing all patents and knowhow required to produce a vaccine. Such a pool could even be collaborative, with multiple stakeholders contributing their IP rights to the overall package to provide an optimal workflow.

One attractive aspect to innovators of a Copy Exactly approach is that it would not be clear to third parties which (if any) of the factors were relevant to the overall process and, as such, would make unauthorised reproduction impossible. Indeed, it might be possible to provide collaborators with the exact instructions for an isolated step of the production process, without divulging critical knowhow about the process as a whole. In these circumstances, rights to the observation data generated during manufacture would need to be tightly controlled.

Conclusion

Covid-19 remains in general circulation, and future pandemics are, unfortunately, inevitable. This threat is exacerbated by climate change, including warming to which we have already committed. Our success in combatting infectious disease, both now and in the future, will be at least in part contingent not only on whether or not vaccines can be developed, but how quickly translates into jabs in arms. Increasing production capacity now so as to ensure higher availability and reduced costs when needed is a vital tool in our arsenal of preparedness.

Andrew originally spoke about the Covid-19 outbreak back in March 2020 in his blog Coronavirus (COVID-19): a case study in emerging disease.

This blog was originally written by Andrew Tindall.