Membranes unlock potential to increase cell-free vaccine production

In February, the researchers introduced a new biomanufacturing platform​​ - called in vitro conjugate vaccine expression (iVAX) – that they had developed. That platform is designed, they said, to quickly make shelf-stable vaccines at the point of care, ensuring they will not go to waste due to errors in transportation or storage.

In a new study, published in Nature Communications​​​ today [April 22], the team discovered that enriching cell-free extracts with cellular membranes - the components needed to made conjugate vaccines - vastly increased yields of this platform.

The work, they said, sets the stage to rapidly produce medicines that address rising antibiotic-resistant bacteria as well as new viruses at 40,000 doses per liter per day, costing about $1 per dose. At that rate, the team could use a 1,000-liter reactor to generate 40 million doses per day, reaching 1 billion doses in less than a month, noted the synthetic biologists.

BioPharma-Reporter caught up with Michael Jewett, who led the study. He is a professor of chemical and biological engineering at Northwestern's McCormick School of Engineering and director of Northwestern's Center for Synthetic Biology. "This work will transform how vaccines are made, including for bio-readiness and pandemic response,”​ he said.

Limitations in cell-based manufacturing 

We asked him to first outline the benefits of the iVAX manufacturing platform:

“iVAX is based on cell-free protein expression. Cell-free protein expression—the synthesis of proteins in crude extracts without living intact cells—offers a compelling solution to existing limitations in cell-based manufacturing.”​

He said existing limitations based on using living hosts include:

• High product variability created by glycoform (micro- and macro-) heterogeneity
• Batch-to-batch consistency can be a problem because living cellular factories are used
• Expensive centralized facilities are needed for good manufacturing practice (GMP)
• Going from a finalized DNA sequence to vials of drug takes at least 18 months due in large part to development/banking of cell lines
• Protein medicines must be prepared in advance of an anticipated, specific threat, which results in wasted materials, labor, and money when that threat is not realized; and
• Cold-chain requirements that limit distribution.

“iVAX based cell-free systems address these limitations. Indeed, iVAX offers a new approach. iVAX is a cell-free platform for portable, on-demand, and scalable production of protective conjugate vaccines.”​

Increasing yields and reducing costs of vaccine production ​

The Northwestern’s team previous study showed synthesis of conjugate vaccines at a level of around 20 micrograms per milliliter, said Jewett.

“Increasing yields and lowering costs could enable even greater access enhance disaster responsiveness, allow timely response to emergent/pandemic threats, and enable distributed biomanufacturing anywhere on earth and even beyond. This is what we addressed in this new paper.”​

In previous work, Jewett's team used the iVAX platform to produce conjugate vaccines to protect against bacterial infections. At the time, they repurposed molecular machinery from Escherichia coli to make one dose of vaccine in an hour, costing about $5 per dose. "It was still too expensive, and the yields were not high enough. ​We set a goal to reach $1 per dose and reached that goal here. By increasing yields and lowering costs, we thought we might be able to facilitate greater access to lifesaving medicines."​

So how did the team leverage the iVAX platform then to produce conjugate vaccines at the much lower cost range?

The team said the key to reaching that goal lay within the cell's membrane, which is typically discarded in cell-free synthetic biology. When broken apart, membranes naturally reassemble into vesicles, spherical structures that carry important molecular information. The researchers said they characterized these vesicles and found that increasing vesicle concentration could be useful in making components for protein therapeutics such as conjugate vaccines, which work by attaching a sugar unit - that is unique to a pathogen - to a carrier protein. By learning to recognize that protein as a foreign substance, the body knows how to mount an immune response to attack it when encountered again, they said.

Attaching this sugar to the carrier protein, however, is a difficult, complex process. The team found that the cell's membrane contained machinery that enabled the sugar to attach to the proteins more easily. By enriching vaccine extracts with this membrane-bound machinery, the researchers said they were able to significantly increase yields of usable vaccine doses.

“In iVAX, membrane vesicles form during cell lysis and enable cell-free glycoprotein synthesis. We hypothesized that increasing vesicle concentration in the cell-free system would increase membrane-bound components and improve glycosylation efficiency. Here, we showed that extract processing provides a handle to enrich extracts with vesicles. Increasing vesicle concentrations enriched with glycosylation machinery improves glycoprotein synthesis by a factor of 5 to more than 100mg/L. Thus, the overall costs of iVAX are reduced from around $5 per dose originally to $1 per dose here,” ​explained Jewett.

While there isn’t yet a company dedicated to the iVAX technology, it is on the horizon, he told us. Jewett founded SwiftScale Biologics to accelerate time to market of protein therapeutics, including glycosylated protein therapeutics.

Regulatory hurdles 

How challenging will it be to get such vaccines regulated?

“I believe that commercialization of cell-free synthesized vaccines is on the horizon. Importantly, iVAX is comprised of detoxified lysates that contain endotoxin levels well below those in FDA-approved products. While further safety and efficacy trials will be needed, we are excited by the robustness and consistency of cell-free synthesized products. Notably, cell-free systems enable consistent product quality by avoiding stochastic cell growth and mutation issues associated with cell-based manufacturing.”​

Conjugate vaccines

Jewett said that conjugate vaccines work by combining a weak antigen, such as the polysaccharide antigen of a pathogenic bacteria to a strong antigen, an immunogenic carrier protein, to invoke an immune response.

“This approach has been very successful for invoking responses to polysaccharide antigens of bacteria for protection. That said, cell-free systems generally provide exciting opportunities for manufacturing vaccine antigens of viruses, such as proteins – the spike protein - that trigger an immune response. This can be done in a rapid way and used with stockpiled reagents to respond pandemic threats. Indeed, the ability to readily store, distribute, and activate freeze-dried cell-free systems by simply adding water or one of a catalog of freeze-dried DNA templates opens new opportunities for on-demand, agile, and modular biomanufacturing.”​

Typically, which bacterial infections could such vaccines protect against?

“Drug resistant bacteria are predicted to threaten up to 10 million lives per year by 2050, necessitating new strategies to develop and distribute antibiotics and vaccines. ​

“Conjugate vaccines are among the safest and most effective methods for preventing life-threatening bacterial infections. In principle, conjugate vaccines can be developed for many bacterial pathogens and have so far proven greater than 90% effective. For example, implementation of meningococcal and pneumococcal conjugate vaccines has significantly reduced the occurrence of bacterial meningitis and pneumonia worldwide.”​