After affinity capture, AAV polishing has two jobs: remove residual host cell protein, host cell DNA and process impurities, and enrich full capsids over empty ones. Anion exchange does both; cation exchange serves as an orthogonal step. Because an AAV capsid is roughly 25 nm across, it barely enters the pores of a packed-bed resin — so convective media are the usual choice. MonoCore™ Q (strong and weak anion exchange) and MonoCore™ S (strong and weak cation exchange) are cross-linked cellulose monoliths with a 15 µm channel size, supplied as 1.8 mL and 5.4 mL capsules with UNF 10-32 connectors that run on a standard FPLC system. For a 5 L harvest, the polishing step sits well within that range.
Why particle size decides the format
The argument is geometric, and it is the reason a polishing step for viral vectors looks different from a protein process.
A monoclonal antibody is about 10 nm across. It diffuses into the pores of a chromatography bead, which is where most of the surface area sits.
An AAV capsid is about 25 nm, a lentiviral vector about 100 nm. Both are largely excluded from that internal pore volume. What remains is the outer surface of the bead — a small fraction of the available area.
Two consequences follow. The usable capacity of a packed bed for viral vectors is far below its protein capacity. And the capacity that is still reachable depends strongly on residence time, because the particle has to travel a long way to reach it.
Convective media — monoliths and membrane adsorbers — carry the vector past the ligand in the flowing liquid instead. The ligand sits on the channel wall, in reach. That is why literature and suppliers converge on this class for viral vectors.
The polishing step in practice
Host cell protein, host cell DNA and process impurities are usually cleared by anion exchange (Q). Depending on the mode chosen, either the vector binds and impurities separate by charge, or the reverse.
Full versus empty capsid enrichment runs on anion exchange with a shallow salt or pH gradient. The separation is small, depends strongly on serotype, and requires method development.
An orthogonal polishing step can be added with cation exchange (S) where the anion exchange step alone does not clear a specific impurity.
Aggregate removal by hydrophobic interaction is less common in AAV than in protein processes.
Serotype matters. AAV8 behaves differently from AAV2 or AAV9 in surface charge and in how tightly it holds onto an anion exchanger. A gradient that separates full from empty capsids for one serotype rarely transfers unchanged to the next.
Being honest about the hard part: full-and-empty separation is the step where published methods vary most, and where our own data set is still thin. If that separation is the core of your process, ask us for the current state rather than relying on a general claim — ours or anyone else's.
MonoCore™ for AAV polishing
MonoCore™ Q — strong and weak anion exchange; polishing, impurity removal, full/empty enrichment.
MonoCore™ S — strong and weak cation exchange; orthogonal polishing.
Both on a cross-linked cellulose monolith, 15 µm standard channel size, 1.8 mL and 5.4 mL, larger on request, UNF 10-32 connectors.
Three properties matter in this step.
A hydrophilic cellulose backbone. Low non-specific adsorption keeps recovery up when the product is expensive and the load is small.
An open channel structure. A 15 µm channel does not block the way a fine-pored medium does when the feed carries debris or DNA. Fewer cleaning cycles, more reproducible runs.
Predictable scale-up. Pressure and flow profile stay consistent from the lab format to production, which means less method re-optimisation when volumes grow — less, not none.
Against membrane adsorbers, a monolith gives a more homogeneous flow path and a lower void volume, so the elution peak stays narrow and the product is less diluted. Against packed-bed resins, the gain is speed and robustness, not resolution: a monolith is resin-class in resolution, and we do not claim more.
Frequently asked questions
Is a monolith better than a membrane adsorber for AAV?
It is different. Membrane adsorbers are fast, disposable and cheap per run. A monolith has one continuous flow path rather than a stack of pleated layers, so flow distribution is more uniform and void volume smaller — which shows up as a narrower elution peak and less product dilution. Where a fully disposable flow-through step is the goal, a membrane is often the simpler answer.
Which media size handles a 5 L harvest?
After capture, the polishing load is small compared with the harvest volume. A 1.8 mL or 5.4 mL capsule usually covers this scale; the deciding numbers are the amount of vector to be bound and the cycle time you want, not the harvest volume.
Can anion exchange separate full from empty capsids?
Partially, and it is the most common approach. The two populations differ in surface charge because of the packaged genome. The separation is narrow, serotype dependent and requires careful gradient development.
Do I need to clarify the feed before polishing?
Polishing follows capture, so the feed is usually already clarified. The open channel structure tolerates residual turbidity better than fine-pored media, but it does not replace a clarification step.
How many cycles does a capsule last?
For ion exchange media the limit is set by cleaning, not by the number of bind-and-elute cycles. See the datasheet for validated cleaning conditions.