Continuous Tubular Bioreactor (CTB) System

Fully continuous virus production in suspension cells

for gene therapy and vaccine applications

What is it?

The lack of virus supply for gene therapies can be tackled by using continuous production, however, the biopharmaceutical industry mostly relies today on batch systems that cannot cope with the current and future product demands.


The move from batch to continuous virus production with commercially available technologies will be, however, challenged by two biological constraints: the risk of unwanted viral mutations after weeks of production, and the low virus production yields that arise when defective interfering particles (DIPs) accumulate in the virus population.

We have developed a continuous tubular bioreactor (CTB) system that enables stable and efficient virus production. It consists of a continuous stirred tank reactor (CSTR) for suspension cell growth coupled to a plug-flow tubular bioreactor (PFBR) segment for fully virus propagation.

The unique design of our CTB system increases volumetric output 20× compared to the size of a batch STR and can be twice as fast as batch. Also, thanks to the use of a PFBR for unidirectional virus propagation and a defined virus residence time, the CTB system is the only truly-continuous bioreactor that not only enables virus production without risk of mutations, but also is capable of avoiding the negative impact of DIPs.

Our CTB system can theoretically be used for any virus that can be propagated in suspension cells, such as influenza viruses or AAV.

Tubular segment

for virus propagation

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Our Approach to Continuous Virus Production

Suspension cells are continuously cultivated in a CSTR operated as a chemostat. The cells are then mixed in-line with a virus/plasmid stock and fed into a tubular bioreactor segment, where the cells will flow in a one direction. Virus replication occurs along the tube and at the end the virus harvest is collected.

Production performance with our CTB system


volumetric output per month compared to a batch STR

No titer loss

due to accumulation of DIPs as observed in batch systems


faster virus production than batch

demonstrated with a 0.5 L working volume device

of ~10 L per month production capacity

Increase production capacity with minimal footprint
Our CTB is almost twice as fast as batch

5E13 influenza virus particles

produced in

27 days with CTB system


50 days running 11 batches

Our CTB minimizes the risk of virus mutations

Our CTB system offers the following benefits compared to existing virus production technologies:

Increase capacity with existing footprint

  • Increases volumetric output up to 20× without increasing bioreactor size (10 L per month with a 0.5 L stirred tank). A 5 L STR coupled to a tubular segment can produce 100 liters in one month.

Use the STRs you already have

  • The tubular module can be coupled to any existing STR in your lab/facility, transforming your batch process into a more efficient fully continuous system.



  • Our CTB can be used from lab to manufacturing scale, eliminating the need of changing/revalidating processes at larger scales. For example, a 1 L-scale CTB can provide 10 L per month which may be enough for pre-clinical or early clinical-phases. A 5 L-scale CTB can provide 100 L per month, and a 50 L-scale CTB can produce volumes of 1000 L or more.



  • Avoids impurity carry-over and cross-contamination.

  • Reduces CapEx and OpEx.


Simultaneous product manufacturing

  • Our CTB can produce different viruses simultaneously by connecting several tubular modules to one cell seeding reactor.


Higher virus titers

  • Our CTB avoids the accumulation of defective interfering particles that drastically reduce virus titers in batch processes and even semi-continuous systems (e.g. for influenza virus) and that makes the virus population genetically heterogeneous.


Future single-use industrial manufacturing made possible

  • Coupling a continuous tubular module to a 2000 L single-use STR can potentially produce up to 40 000 L per month, a product volume that today is only possible with stainless-steel systems.


Genetically stable virus production with minimal risk of mutations

  • Virus mutations can occur if viral particles stay in the bioreactor long enough and keep infecting new cells over days or weeks, as observed in other continuous bioreactors such as cascades of CSTRs. Our CTB system ensures higher virus homogeneity thanks to a unidirectional plug-flow in the tube that avoids back-mixing. The viruses produced along the tubular section cannot infect freshly produced cells entering the tube, avoiding the accumulation of genetically-aberrant viruses, greatly reducing the risk of mutations and producing a genetically stable and homogeneous virus harvest.