March 09, 2023

Manufacturing high-concentration mAbs: challenges and solutions

By Tom Watson, Aude Iwaneic, Gregor Kalinowski

This blog is a podcast transcript with insights from three subject matter experts in high-concentration mAbs. Brandy is the moderator.

BRANDY: Can you introduce yourselves?

TOM: I’m Product Management Group Leader for our direct flow sterilizing-grade filtration portfolio.

GREGOR: I’m a manager in Scientific and Laboratory Services, in our field support in Europe, and I’m specializing in new purification technologies.

AUDE: I’m a team leader in R&D bioprocessing.

BRANDY: Why are high-concentration mAbs an important topic in today’s biotech landscape?

TOM: We are always really excited by what is happening in the biotech industry. It is a mature industry and we have been serving it for a while, and we are highly motivated to support our customers as it continues to evolve. There’s plenty of innovation, so there’s innovation to help intensify processes in the upstream space and in purification, innovation at modality level, and also innovation at formulation level. And that’s where high-concentration drugs or high-concentration biotech drugs and HCDs come in.

They’re important because when a biotech drug can be prepared at high concentration that is administerable, it’s usually self-administered in a subcutaneous mode, and this brings lifestyle benefits to patients — it reduces healthcare costs because it negates the need for an intravenous treatment.

Subcutaneous biotech drugs have been available for a while but recently we’ve seen a lot of companies really looking to make sure they deliver these benefits. And as a consequence, they’re increasingly developing new drugs or formulating existing ones at high concentration, and now’s a great time for them to achieve this, thanks to contributions of formulation science and medical device science.

BRANDY: What are some of the differences in terms of manufacturing with high-concentration mAbs versus more traditional mAb production?

TOM: A high-concentration mAb or recombinant protein for subcutaneous delivery is going to be prepared at a high concentration starting with the final concentration steps, and when that happens, it's common for a highly viscous fluid to result in 10 to 30 centipoise at a concentration of greater than 100 grams per liter, often as high as 250 grams per liter.

This concentration step then reduces the volume of the fluid processed across the subsequent unit operations that are typical of a biotech process. Also, what we see then of course is a reduction in the dosage volume, since you only need one to two milliliters of a highly concentrated biotech drug to take its therapeutic effect.

So we typically see small dosage volumes, or in some cases, dosage volumes can be several milliliters to permit sort of a slightly longer-term infusion of a subcutaneous drug. But the viscosity makes processing the fluid more challenging across the unit operations including the concentration step itself, through filtration, mixing, freeze-thaw, formulation, and dispensing.

Also the smaller batch volumes that correspond with the increased concentration of the drug raise the cost of the active pharmaceutical ingredient (API) per unit volume, and this makes manufacturers more impacted by any product losses they encounter than with lower-concentration traditional biotech drug preparations.

BRANDY: What are some of the main challenges that exist in manufacturing workflow for high-concentration mAbs?

TOM: Talking on a high level, we repeatedly hear from our customers challenges relating to product loss in hold-up volume, aggregation of the molecules, limitations with analytical equipment and sampling procedures, and destabilization of filtered fluid due to the stripping out of formulation components — there’s quite a number of problems that they come to us and seek assistance with.

BRANDY: High concentration basically starts with a final ultrafiltration/diafiltration (UF/DF) step. As this is such a fundamental step, what are the specific challenges to achieving high product concentrations?

GREGOR: Product viscosity is increasing with increasing product concentration, plus for a given crossflow, the pressures are significantly increasing with increasing product concentration. Also, the permeate flux is decreasing with increasing product concentrations, and therefore the processing times become longer, and the number of pump passes are much higher, compared to low-concentration processes.

This combination of extended time and the increased concentration carries a significant risk of shear-related damage that may impact the product quality. And last but not least, the high viscosity typically results in a poor recovery from tangential flow filtration (TFF) systems because of limited drainability.

BRANDY: Which solutions can be applied to overcome these new challenges in the final UF/DF step?

GREGOR: First of all, an optimization of the TFF cassette screen type. For example, a more coarse screen or suspended screen can be applied to reduce the cassette pressure drop to be able to process such high-viscosity material.

Alternatively, single-pass TFF (SPTFF) significantly reduces the shear exposure because the entire concentration step is performed in a single pass, without a recirculation loop. Especially for sensitive products like sensitive plasma proteins, as well as shear-sensitive viral particles, single-pass TFF offers a significant reduction in cumulative shear exposure. We get high concentrations and high viscosities. We have demonstrated concentrations exceeding 250 mg per mL for IgG with SPTFF technology or even higher concentrations with plasma proteins. The SPTFF moreover applies a serialized flowpath and therefore the feed flow requirement of an SPTFF system is significantly reduced when compared to an all-parallel conventional TFF configuration.

Because of the serialized flowpath and reduced feed flow requirement of an SPTFF system, the system hold-up volume is significantly smaller when compared to a conventional TFF system with an all-parallel membrane configuration. The reduced hold-up volume of the SPTFF system when compared to a conventional system allows for enhanced product recovery and a higher step yield and higher final concentrations. Typical yields at high concentration from single-pass TFF systems are equal to or greater than 98%. Whereas conventional TFF system yields can be as low as 80% or even less

BRANDY: What about other types of filtration, including direct flow?

AUDE: As Tom and Gregor mentioned, this higher concentration causes a significant increase in viscosity, and that also affects the sterilizing-grade filtration that you find after your concentration step for the final formulation and filling. So, this higher viscosity has a direct impact on the filtration flux, and therefore that causes higher processing times. Another point is that with your higher concentration, there is a likelihood of having higher aggregate content compared to lower-concentration mAbs — this will in turn impact the sterile filter capacity, and it can cause your current filter size to block earlier than you would expect. So again, this means that it will increase your processing time, or in turn you might need a larger filter. So, the first approach you might consider to overcome those challenges might be to consider a larger device size for a specific batch size. However, you need to keep in mind that using a higher device size is likely to increase your non-recoverable volume at the end of the sterilizing-grade filtration process. And we know that high-concentration drugs are highly valuable, so the processing yield in each of the steps is a critical factor to keep in mind.

Something else to consider when thinking about larger device size — and therefore larger membrane surface area — is that it could also impact other product attributes such as your excipient concentration. So, we know from research that polysorbate which is used as an excipient in mAb formulation might absorb to sterile filters, and so using a larger device for the same batch size might affect your polysorbate concentration, in particular at the beginning of your filtration.

BRANDY: What else have you been working on over the past couple of years to provide solutions suited for high-concentration drug production?

TOM: We’ve got a diversity of products well-suited to late-stage processing of monoclonals and recombinant proteins, not just direct flow filters or tangential flow filters as discussed by Aude and Gregor. For example, our Freeze and Go storage and transport solutions, polymeric filling needles. and mixers — they all have attributes to help sustain critical-to-quality attributes for a concentrated drug and to help minimize costly losses that could be incurred by technologies that have limited performance with high-concentration feeds.

I shouldn’t forget our validation services. In complement to our product offering we have a Validation Services team, and they recognize that generating large sample volumes for process-specific validation can be difficult with these high-concentration feeds — they tend to be a bit more scarce. So, they are offering filter validation studies for fluid volumes in the range of several hundred milliliters, rather than the couple of liters that might traditionally be utilized for process-specific filter validation.

Finally, something we’re particularly proud to talk about today is our Allegro™ Connect Bulk Filling System. We have recently launched a system that permits the integration of direct flow filters with high capacity for viscous feeds into a bulk filling manifold, and this system automates this critical late-stage filtration and dispensing step. It has lots of features to maximize recovery of the high-value filtered fluid, so a really exciting launch for us I’m pleased to remark upon.

BRANDY: How can companies maximize productivity for their high-concentration drugs?

TOM: It’s all down to selection — making sure that you’ve implemented the right equipment in your unit operations. So, seek out crossflow or tangential flow filtration technologies that reduce shear and permit easy recovery of concentrated fluid. I suppose we could call them second-generation sterilizing-grade filters; sterilizing-grade filters with asymmetric membranes and very high filtration area per device can enable quite dramatic filtration system footprint reductions and have much lower dead volume to occupy any non-recoverable or hard-to-recover hold-up of a highly concentrated feed.

Another thing to do is always look towards vendors of single-use systems that are keen to explore your recovery challenge. Who, when presented with the challenge of line loss will try and come up with ideas to minimize them through clever system design, appropriate orientation or materials of construction of components that help facilitate fluid recovery. And of course, keep an eye on the newest products from established vendors or service providers in the biotech industry.

BRANDY: Can you give some examples from your work with customers on manufacturing problems, and solutions that were implemented to address these issues in real life?

TOM: We can’t really call out any customers by name, but one thing that we are doing is engaging with customers who are looking to adapt any existing manufacturing platforms they have to better handle high-concentration feeds, identifying those certainly that are using first-generation technology that wasn’t perhaps introduced in their facility to overcome some of the challenges we’ve described.

We recently had a customer let us know that they were looking to design a new filtration system that could filter low-concentration drugs as well as high. We had some great meetings with them, they discussed with us their expected batch volumes, process parameters, viscosity ranges and we set up a really thorough filtration study to help them determine suitable filtration setups for either scenario. So we future-proofed their facility for high-concentration drugs.

BRANDY: Could you describe some of the current trends in this space, and where you think we are going from here?

TOM: As I alluded to in the previous question there’s a trend towards customers adapting their production platforms to give them greater flexibility to produce final drugs for subcutaneous delivery. There has been quite a bit of talk around how high a high-concentration drug can be that can be practically manufactured and also reliably administered through a patient. We’re keeping an eye on that, and we’ll be ready to see how our products contend with fluids at higher concentrations in the upper end of the range of around 250 grams per liter that we tend to see today.

BRANDY: Do you have anything else you’d like to add?

TOM: I’d just like to take this opportunity to reaffirm how highly motivated we are to solve our customers’ challenges in biotech. The drug market is diversifying, there is certainly a lot going on in the advanced therapy space that we are paying attention to at the moment. But we are still firmly committed to biotech, we intend to be a big part of the development and manufacture of the next generations of biotech blockbuster drugs.

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