Can CHO Bioreactors Be Used For Plant-Based Protein Production?

A conversation with Andreas Schaaf, Ph.D., Eleva

A company developing protein therapies otherwise challenging to make by traditional means is pursuing the ideal mix of standard, well-characterized equipment and a moss-based expression platform.

Eleva, a German biopharmaceutical company, uses Physcomitrium patens to produce the recombinant version of human glycoproteins, with its lead candidates targeting Fabry disease (RPV-001) and glomerulopathies (CPV-104).

For newcomers to moss-based recombinant production, it’s easy to imagine something exotic like soupy green tanks and piles of fouled filter cartridges. In practice, it’s run in controlled bioreactor environments like CHO. Eleva Chief Scientific Officer Andreas Schaaf, Ph.D., describes a process that makes the most of P. patens' knack for producing glycoproteins and the prior knowledge of traditional infrastructure.

Eleva began dosing patients in a clinical trial for CPV-104 to treat C3-glomerulopathy and other kidney-related diseases in July. It’s also exploring CPV-104 for dry AMD. The company is advancing RPV-001, an alpha-galactosidase therapy for Fabry disease, which has completed a positive Phase 1b single-dose trial.

To help us better grasp the production platform, Schaaf offered to answer some questions. Here’s the conversation edited for clarity.

Moss struggles with producing meaningful yields. How has Eleva solved this issue with P. patens?

Schaaf: Eleva is focused on exploring those situations where conventional methods such as CHO or microbial expression platforms fail – and there are far more of them than most people realize. In these projects, we don’t really play the "numbers game" as the direct comparison with the other systems doesn’t apply.

Within this group of so-called "unproducibles" lie numerous molecules with tremendous therapeutic potential. Our proprietary project, Factor H (CPV-104), is a prime example of this opportunity. Internally, we are pursuing a dedicated initiative to systematically screen this group for promising therapeutic candidates. Over time, we are building a comprehensive collection of product candidates and expert know-how.

Of course, it is nonetheless essential to achieve commercially attractive yields in these projects, and for this purpose, we have continuously optimized our system and are already achieving commercially viable yields for formerly unproducible therapeutics.

Walk us through the production cycle and help us understand where Eleva has innovated.

Schaaf: The most important innovation is the ability of our platform to integrate seamlessly into the established industry-standard production cycles. Unlike other plant-based systems, for example, we don't require greenhouses. There is no need to grow, harvest, and dismantle complex plants as our moss cell line grows in a 3D suspension culture.

This allows us to operate in standard fermenters. In this way, we have incorporated the advantages of plant-based expression into a conventional process.

Proteolytic by-products are a common issue when using moss. Has Eleva encountered them?

Schaaf: Quite rarely, to be honest. In my view, the formation of these proteolytic byproducts is often nothing more than a stress response. In fact, we see this more as an issue of immortalized cell cultures, such as CHO, which, physiologically speaking, are permanently in an “alarm state.” Our moss cells are not immortalized; essentially, they grow like natural moss – as a complete, intact organism. I would say that in nine out of 10 cases, such by-products are not an issue with moss.

What has been done to mitigate their influence on the product?

Schaaf: In those rare cases where we see such by-products, another beauty of the moss platform comes into play. Since it is a haploid organism, with only one copy for each gene, we can easily switch off the gene that encodes the protease, for example, that causes the issue. While CHO engineering is picking up speed, moss is still well ahead in in terms of ease of adaptability to such scenarios.

What types of proteins are especially well suited to production in P. patens?

Schaaf: While there is no limitation per se to what we can do, some protein classes indeed benefit more than others.

In the antibody therapeutics space, as an example, standard monoclonals are being well served with conventional methods. But as soon as these molecules become more complex, moving into the bi- and tri-specific arena and, for instance, when cytotoxic payloads are added, things can look a little different.

Similarly, there are advantages in using moss to produce certain cytokines and immune-cytokines. Mammalian cell lines often struggle with large-scale cytokine production due to toxic feedback effects – growth inhibition or apoptosis triggered by the cytokines themselves, which can overwhelm cellular machinery, limit secretion efficiency, and ultimately reduce yields. Moss cells on the other hand are largely unaffected by these toxic feedback effects.

The other two areas I would like to mention are complex blood proteins and enzymes. Recombinant Factor H, one of our two current clinical-stage proprietary programs, is such a complex blood protein, a natural regulator of the complement cascade.

Is there something unique about moss’ protein manufacturing infrastructure, e.g., endosomal reticulum or chaperone profile, that gives it an edge over other models?

Schaaf: Moss cells have indeed some unique features, including their efficient endosomal system, specialized chaperone profile, ability to perform complex post-translational modifications, and stability. The Golgi apparatus in moss, for instance, is less compartmentalized compared to mammalian cells, resulting in fewer processing steps and less opportunity for glycan diversification.

Unlike mammalian cells, which often generate heterogeneous glycan mixtures, moss produces more uniform glycosylation profiles due to its simplified glycan processing pathway. This reduces batch-to-batch variability, a critical advantage for therapeutic proteins where consistency is paramount. Moss bioreactors also maintain glycosylation consistency even at large scales, unlike some microbial or plant systems where environmental stress can alter glycan profiles.

Chaperones, as you know, are essential proteins that assist in the folding or unfolding and the assembly or disassembly of other macromolecular structures. Moss cells have a unique set of chaperones including plant-specific heat shock proteins (e.g., Hsp70 and Hsp90 isoforms) and folding assistants like protein disulfide isomerases (PDIs) that help prevent protein aggregation and ensure that proteins achieve their correct three-dimensional structures.

In moss cells, there is also an unconventional protein secretion pathway that bypasses the classical ER-Golgi route, enabling the export of proteins that lack a signal peptide. This pathway relies on specialized vesicles or direct translocation across the plasma membrane, often facilitated by unique membrane transporters or autophagy-related mechanisms. It expands moss cells’ versatility for producing difficult-to-express proteins, including those requiring non-canonical modifications.

The funny thing is, even after decades of research, some level of – shall we say – “mystery” remains as to exactly why certain proteins just work way better yield-wise in moss than in CHO or other systems. We are doing some advanced work internally using machine learning and AI tools to take the guesswork out of the process and predict how our moss platform will perform in advance. If successful, we could shave off weeks if not months from the time needed to run a feasibility study in the lab.

Talk specifically about the hardware Eleva is using. What kind of customization happened?

Schaaf: We use standard bioreactors equipped with an extra control loop for the added light. Therefore, it’s not so much customization on a case-by-case basis – it’s more like a once-and-done modification with an additional control technology that has now been tried and tested and standardized. If you turn the light off, the bioreactors would still be perfectly suited for a CHO-culture.

How did Eleva collaborate with vendors to optimize the tech stack?

Schaaf: We have been collaborating with Sartorius as the most important external party for some time, which led to the light-equipped fermenters that I mentioned. Essentially, these fermenters are now standardized "catalog products" at Sartorius that, in principle, anyone can order.

While not a "vendor" in the traditional sense, we recently launched a collaboration with 3PBIOVIAN, a leading European CDMO. As a result of the alliance, Eleva essentially triples its offering of GMP production capacity for programs based on its technology platform and 3PBIOVIAN, as an early adopter in the CDMO space, could bring a new solution to their customers struggling with unproducible target proteins.

Why P. patens? Why not just go with a method that's better at delivering higher yields?

Schaaf: We think P. patens is the perfect organism for what we are trying to achieve. Again, we are not necessarily competing on yield but offering a distinct alternative system, where we can offer a protein manufacturing solution not accessible with conventional methods. Any other platform wouldn’t give us the same differentiation we are establishing in the industry.

What does the future of moss-based recombinant protein production look like? Is it likely to remain a boutique approach?

Schaaf: We are aware of a few remaining limitations that we are constantly addressing. The goal is to achieve even higher scalability and to deliver yields in even more cases that are truly on par with conventional systems.

As it relates to questions on future “market share” of moss versus the other systems out there: Again, we are not really playing the game of replacing CHO or other systems in those cases where they deliver just fine nor are we just trying to be cheaper. Our relationship with 3PBIOVIAN, and potentially future deals with other CDMOs, should certainly help with raising the visibility and increasing market share.

Overall, we aim to be the platform of choice for all those cases where the traditional systems don’t deliver. Our industry tends to neglect proteins that fall into this category, and moss can come to the rescue.

If we are successful in mining this group of elusive otherwise inaccessible therapeutic molecules to fill our and our partners’ drug pipeline, we are going to create a lot of value for the industry and patients. If people consider that a niche, fair enough, but it could turn out to be a very valuable niche.

About The Expert:

Andreas Schaaf, Ph.D., is chief scientific officer and managing director at Eleva. Before joining Eleva as research scientist in 2009, he held positions at the University of Münster and Freiburg, Germany. At Eleva, he was responsible for advancing BryoTechnology to a fully viable biopharmaceutical platform. He has been chief scientific officer since 2015 and was appointed managing director in 2019. He has a Ph.D. in plant biology.