Protein A resin selection: alkaline tolerance and elution pH

Why does a catalog capacity say so little about cost?

Protein A resin is expensive because it is a protein-based capture tool, and its catalog capacity is easy to misread.

Protein A is a protein that Staphylococcus aureus carries on its cell surface. It binds strongly to the Fc region of an antibody (IgG), the stem of the Y-shaped molecule. Culture fluid is full of host cell protein (HCP), DNA and medium components, and Protein A lifts the antibody out of all that in one step. That is why most antibody drugs put it first, as the capture step. Think of pulling iron filings out of sand with a magnet. The difference is that the magnet has to be cleaned after every use.

A run has five stages: equilibration, load, wash, elution and regeneration. With the feed running at neutral pH, the antibody sticks to the beads and most impurities pass through. After the wash, an acidic solution releases the antibody, and that is elution. Finally the beads are washed with sodium hydroxide (NaOH) to remove leftover soil and microbes. This cleaning is called cleaning in place (CIP).

The cost comes from the "hand" that grips the antibody, which is a protein. The ligand, the binding part fixed on the bead, is made by recombinant DNA technology and attached precisely. In BioPharm International (2015), Protein A resin cost is estimated on the assumption that the resin is reused from dozens to several hundred times. The number of uses has a large effect on resin cost per gram of antibody.

The first number in a catalog is dynamic binding capacity (DBC): how many grams of antibody 1 liter of resin takes up while the liquid is flowing. The common mistake is to line up suppliers' numbers and compare them as they are. DBC changes with flow rate: slow flow gives a larger value, fast flow a smaller one. Each supplier measures at a different residence time (how long the liquid takes to pass through the bed), so the ranking can flip when you match conditions. You can work out the residence time at your own flow rate with the residence time calculator, and the steps for measuring under matched conditions are in measuring DBC (in Japanese).

Compare catalog DBC values only when they were measured at the same residence time.

Alkaline tolerance decides how many cycles you get

Sodium hydroxide is the standard cleaner because it dissolves leftover protein and lipid and also kills microbes and endotoxin. It is cheap and strong. The problem is that Protein A is itself a protein, so the alkali slowly damages it.

Native Protein A does not tolerate strong alkali, and a hard clean every cycle wears the resin out early. Suppliers therefore engineered the ligand by swapping amino acids to make it alkali-resistant. Most of today's leading products use an engineered ligand, but where and how the amino acids were swapped differs by supplier. Washed at the same concentration, products can last very different numbers of cycles.

Cytiva states that MabSelect PrismA keeps about 90% of its capacity after 150 uses when it is washed with 0.5 M NaOH for 15 minutes in every cycle. The comparison in which 0.1 M washing loses capacity faster than 0.5 M was shown on the same product. Both are results under Cytiva's conditions. The explanation offered is that soil that is not removed gradually accumulates on the beads and blocks the sites that bind antibody.

A kitchen sponge is a fair comparison. If the detergent is too weak, grease stays and clogs the sponge. If it is too strong, the sponge itself breaks down. The right strength differs by resin.

This is where purchasing and sales feel it. Comparing resins by price per liter does not tell you the cost per gram of antibody. Alkaline tolerance data from suppliers also come as combinations of concentration, soak time and number of cycles that differ from product to product. To compare, you have to restate each claim in your own cleaning conditions and ask again. When deciding how many cycles to run before replacing the resin, see Protein A resin lifetime and cost (in Japanese). When designing cleaning conditions, keep regeneration and CIP design (in Japanese) at hand.

A better question for a supplier than "What is the DBC?" puts your own conditions in it: "If we wash with 0.5 M every cycle, what percentage of capacity is left after 100 uses?" Answers to that kind of question can be compared across products.

Cost per gram of antibody depends less on the resin's price than on how many cycles it keeps its capacity under your own cleaning conditions.

Does a milder elution pH change the steps behind Protein A?

Yes. Releasing antibody from Protein A means making the liquid acidic, and with a general-purpose resin a buffer of about pH 3 to 4 is used. Many antibodies tolerate this. Some molecules do not. Acid partly unfolds the antibody, and after neutralization the antibodies stick to one another. The clumps that form are aggregates.

Aggregates are thought to risk an immune reaction in patients, so the final product keeps them under tight control. You check whether they rose after elution with size exclusion chromatography (SEC) in your purity assays, and you remove them in a later polishing (in Japanese) step. Many bispecific antibodies and Fc-fusion proteins are acid-sensitive, and for those molecules the loss at this point is not negligible.

That is why mild-elution resins appeared. Purolite (part of Ecolab) states that its Praesto Jetted A50 HipH has a redesigned ligand that releases antibody at a gentler pH of about 4.5 to 4.8, and it also claims fewer aggregates. The trade-off is the cleaning: the supplier limits NaOH for cleaning to 0.1 M. If you slot it into a process built around 0.5 M cleaning, the cleaning procedure has to be rebuilt. Before choosing this resin, confirm that 0.1 M cleaning keeps soil and microbes under control.

Side by side: a standard resin elutes at about pH 3 to 4, many products take cleaning at around 0.5 M NaOH, and it suits ordinary IgG antibodies that handle acid reasonably well. With it, you check the aggregate level after elution. A mild-elution resin such as Praesto Jetted A50 HipH can elute at about pH 4.5 to 4.8 (the supplier's test value) and takes NaOH only up to 0.1 M. It suits molecules that aggregate in acid, such as bispecific antibodies and some Fc-fusion proteins. With it, you check the cleaning procedure and whether virus inactivation must be redesigned.

The relationship to the step right behind is easy to miss. In antibody purification, the eluate is typically held at around pH 3.5 for roughly 30 to 60 minutes to inactivate virus. The eluate is already acidic, so only a little more acid is needed. Raise the elution pH and that premise breaks. If you add acid again for inactivation, the reason for choosing a milder resin gets thin. You have to decide with low-pH virus inactivation (in Japanese), including whether to switch to another method such as detergent-based inactivation. How the ligand design sets the elution pH is in elution pH and ligand design (in Japanese).

Choose the elution pH by how acid-sensitive your antibody is, and expect that choice to decide how the virus inactivation behind it is built.

Common mistakes, and a supplier base that keeps moving

The first mistake is choosing a resin by DBC and noticing afterward that cleaning does not fit. If your procedure assumes 0.5 M cleaning and you pick a resin that tolerates only 0.1 M, you redo the cleaning procedure and the checks that microbes are not growing.

The second is overlooking how hard it is to change the resin after approval. You have to show with comparison data that product quality is unchanged, and in many cases a change filing to the authority follows. This is why the resin picked at the start of development is often used through commercial production, so that first selection lasts for years.

The third is forgetting that Protein A itself ends up in the product. With every run, protease and other components in the culture fluid gradually strip fragments of ligand off the beads, and these stay attached to the antibody into the eluate. This is called ligand leaching. The residual Protein A is an impurity that is removed downstream, and its amount is measured and controlled (see ligand leaching (in Japanese)). For QA, the point to check is whether resin life is tracked by this leaching as well as by binding capacity.

The suppliers are moving too. In April 2026, MilliporeSigma, the life science business of Merck KGaA, announced that it had completed the acquisition of JSR Life Sciences' chromatography business, and Protein A resins such as Amsphere A3 moved into its portfolio. The product can stay the same while the contact for price negotiation and technical support changes.

The scale of purchasing is larger than it looks from outside. Danaher, which owns Cytiva, said on its July 2026 earnings call that shipments of chromatography resin totaling more than $100 million had slipped into 2027, citing among other things the readiness of customers' plants. Each shipment is said to be in the range of $10 million to $30 million. Resin for commercial plants is a purchase whose order timing moves together with the plant's start-up plan.

There are other options. Tosoh's TOYOPEARL Super A and Bestchrom's new top-grade Extrem A Diamond are also resins sold on alkaline tolerance. All of these numbers are the suppliers' own claims, and until you confirm them with your antibody and your cleaning conditions they are only a starting point.

Because a resin is usually kept through commercial production, choose it with the cleaning conditions, ligand leaching control and the supplier's own changes in view.

Steps to check this week

Start with your own batch records and procedures to fix the premises of your current process.

1. Find the resin name, the NaOH concentration and contact time used for cleaning, and the maximum number of uses you have set.
2. Check at which residence time the catalog DBC was measured.
3. Look at the elution pH, the time from elution to neutralization, and the aggregate level in the eluate.
4. Ask your quality contact whether resin life is monitored by recovery and ligand leaching as well as binding capacity.
5. Read the change notices that come from your supplier, such as acquisitions, site transfers and ligand changes.
6. When a supplier recommends a new resin, ask two questions: "After 100 uses under our cleaning conditions, what percentage of capacity is left?" and "What are the elution pH and the upper limit of NaOH for cleaning?" With those two answers you narrow candidates faster than by lining up catalogs.
7. If a mild-elution resin is on the shortlist, decide two more things with the resin choice: can 0.1 M cleaning control soil and microbes, and will virus inactivation stay acid-based or be rebuilt. Left until later, both mean redoing cleaning procedures and confirmations.

Candidate products can be compared in Protein A resins. To line up the published DBC of the main Protein A resins with their conditions, or to choose the ion exchange and other resins that follow, continue to how to choose purification resins.