ATF vs TFF for Perfusion Cell Retention: Which Should You Pick?
For CHO mAb perfusion at 30-100 million cells/mL, pick ATF (Repligen XCell ATF) for sieving stability and lower lysis. The alternating diaphragm flow continuously backwashes the hollow fibre, holding mAb sieving at 88-95% across 14-30 day runs. Pick TFF when you need a vendor-independent filter housing, when integrating directly into a continuous downstream skid, or when you can drive the loop with a low-shear centrifugal pump such as Levitronix instead of a peristaltic head.
Key differences at a glance
- ATF (alternating tangential flow): diaphragm pump pulses suspension bidirectionally through hollow fibre, self-cleaning each stroke. Sieving 88-95% for full run. Lower shear. Repligen-only diaphragm hardware. 0.5 L to 5000 L scale.
- TFF (tangential flow filtration): one-directional cross-flow via peristaltic or centrifugal pump. Peristaltic-pump TFF sieving decays from 95% to 52% over 14 days from cell-lysis fouling; centrifugal-pump TFF closes most of the gap. Vendor-independent hardware.
- Cost difference: capital cost is similar at 80-200k USD; 3-year TCO within 15-20% when product loss is included.
- Best for CHO mAb perfusion (commercial cGMP): ATF.
- Best for integrated continuous bioprocess into capture chromatography: TFF, especially with a centrifugal pump and wide-surface-pore membrane.
Side-by-side comparison
| Factor | ATF | TFF |
|---|---|---|
| Flow direction | Alternating bidirectional (diaphragm) | One-directional cross-flow (peristaltic or centrifugal pump) |
| Self-cleaning mechanism | Reverse stroke backwashes lumen every 1-2 s | Cross-flow shear only; no backwash |
| Mature mAb sieving coefficient | 88-95% maintained across 14-30 days | Decays 95% to 52% over 14 days (peristaltic pump) |
| Cell lysis / shear | Lower; diaphragm imposes lower peak stress | Higher with peristaltic; comparable to ATF with centrifugal pump (Wang 2017) |
| Filter fouling rate | Slow; self-cleaning preserves flux | Faster with peristaltic-pump-driven lysis; mitigated by wide-pore membrane (Pinto and Brower 2020) |
| Demonstrated max cell density | ~1.3 x 10^8 cells/mL in WAVE (Clincke 2013); >1.5 x 10^8 in stirred-tank | 2.14 x 10^8 cells/mL in WAVE (Clincke 2013) |
| Vendor flexibility | Repligen XCell ATF only for diaphragm housing | Hollow fibre cartridges sourced from any supplier |
| Single-use capital cost (per system) | ~80-200k USD (XCell ATF 2-10) | ~80-180k USD (Repligen KrosFlo KPS or Cytiva FlexFactory loop) |
| Scale range | 0.5 L to 5000 L (ATF 1 to ATF 10) | 2 L to ~2000 L |
| Integration with continuous downstream | Possible but typically batched into surge tank | Direct loop feed into capture skid (Pinto 2020, 29-day run) |
Values reflect typical published specifications and peer-reviewed comparisons. Your vendor's current datasheet takes precedence.
ATF in detail
Alternating tangential flow filtration (ATF) is the dominant cell retention technology in commercial CHO monoclonal antibody perfusion. The Repligen XCell ATF system, originally developed by Refine Technology and acquired by Repligen in 2014, is deployed in over 40 commercial mAb processes and operates at scales from 0.5 L bench (XCell ATF 1) up to 5000 L production (XCell ATF 10).
How it works
An ATF device consists of a hollow-fibre filter housing connected to a diaphragm pump via a single port on the bioreactor. A pneumatic actuator drives the diaphragm upward and downward inside the pump head with a cycle time of one to two seconds. On the downstroke, cell suspension is pushed from the diaphragm chamber through the lumen of the hollow fibres and back into the bioreactor; on the upstroke, suspension is pulled from the bioreactor through the same fibres back into the diaphragm chamber. Permeate is drawn from the shell side of the hollow fibre continuously, while the alternating direction of the lumen flow continuously backwashes any deposited debris from the membrane surface. The single-use XCell ATF SU devices use 0.2 micron polyethersulfone (PES) fibres; stainless-steel housings offer 0.2 micron, 0.5 micron, or 50 kDa molecular weight cutoff options.
Commercial vendor presence is concentrated. Repligen XCell ATF is essentially the only mature ATF platform, sold either as a stand-alone system with its own controller or as the embedded XCell ATF module on the integrated Sartorius Biostat STR + XCell ATF platform launched in 2018 for 50-2000 L scale. Cytiva sells the predecessor Wave perfusion configurations with ATF; Thermo Fisher HyPerforma and Getinge / Applikon single-use bioreactors are also routinely paired with XCell ATF devices in process development.
When ATF wins
ATF wins decisively in three scenarios. First, commercial CHO mAb perfusion. The combination of stable 88-95% mAb sieving and low cell lysis means a 14-day run holds steady-state harvest titre with minimal high-molecular-weight species enrichment in the bioreactor. Pappenreiter et al. (2023) reported ATF sieving holding at 88-95% versus a decline to 52% in conventional peristaltic-pump TFF. Second, N-1 seed train intensification. Running an ATF-equipped N-1 reactor to 50-100 million cells/mL lets you seed the production bioreactor at 10x the conventional density, compressing the seed train by 15-30 days. Third, extended viral vector and vaccine campaigns. The reverse stroke prevents the filter from fouling on the high-DNA, high-debris broth typical of lentiviral and AAV production, extending filter life beyond what TFF can sustain on the same feedstock.
TFF in detail
Tangential flow filtration (TFF) drives cell suspension through a hollow-fibre cartridge in a single direction using an external pump, with permeate drawn through the membrane perpendicular to the bulk flow. The same physics that underpins TFF as a downstream concentration and diafiltration tool, covered in our TFF membrane sizing guide, is what makes it an option for upstream cell retention. The critical engineering question is which pump drives the cross-flow loop.
How it works
A TFF cell retention loop takes suspension out of the bioreactor through a recirculation port, pushes it across a hollow-fibre cartridge with a peristaltic or centrifugal pump, and returns the retentate back to the bioreactor. The cross-flow shear at the membrane surface prevents most cells from depositing onto the fibre wall, and permeate (cell-free supernatant containing product) is collected from the shell side. The dominant single-use systems are the Repligen KrosFlo KPS TFF (sold separately from XCell ATF), the Cytiva TFF perfusion configurations (FlexFactory recirculation loops), and Cytiva and Sartorius hollow-fibre cartridges (typically 0.2 micron PES or polysulfone). Hollow-fibre cartridges from Meissner and Merck Millipore are commonly substituted into vendor-agnostic skids.
The pump choice is the defining decision. A peristaltic pump pinches the tubing repeatedly with rollers, generating a pulsatile flow with high local shear at the roller contact points. Wang et al. (2017, Journal of Biotechnology) demonstrated that the peristaltic pump itself, not the absence of alternating flow, is the dominant source of cell lysis in TFF perfusion. Replacing the peristaltic pump with a low-shear centrifugal pump such as a Levitronix magnetically-levitated centrifugal pump restored cell viability, particle concentration, and product sieving to ATF-equivalent levels. This finding has reshaped TFF perfusion engineering since 2017, and most new TFF perfusion installations now specify a centrifugal pump rather than a peristaltic head.
When TFF wins
TFF wins in three contexts. First, very high cell density. Clincke et al. (2013) achieved 2.14 x 10^8 cells/mL with TFF in a WAVE bioreactor versus 1.32 x 10^8 cells/mL with ATF; the ATF ceiling was driven by diaphragm vacuum struggling against the viscous high-density broth rather than by ATF itself, but the difference is real at the extreme end of the density envelope. Second, integrated continuous bioprocessing. The TFF permeate loop can feed directly into a downstream capture chromatography skid without a surge tank intermediate, an architecture demonstrated by Pinto and Brower (2020, Biotechnology and Bioengineering) running 29 days uninterrupted with a wide-surface-pore microfiltration membrane. Third, vendor-independent hardware. TFF loops use commodity peristaltic or centrifugal pumps and off-the-shelf hollow-fibre cartridges, avoiding the Repligen-specific diaphragm housing of XCell ATF.
Pros and cons
ATF (alternating tangential flow)
Advantages
- Stable mAb sieving at 88-95% across full perfusion run; no decay from progressive fouling
- Lower hydrodynamic shear and cell lysis than peristaltic-pump TFF (Karst et al. 2016)
- Mature commercial cGMP track record: 40+ commercial mAb processes and 500+ deployed sites
- Linear scale-up from XCell ATF 1 (0.5 L) to ATF 10 (5000 L) without changing physics
Disadvantages
- Single-vendor lock-in on diaphragm hardware and controller (Repligen XCell ATF)
- Diaphragm pneumatic vacuum can struggle with viscous broth above 150 million cells/mL
- Single-port connection to bioreactor adds risk of gas bubble accumulation in dip tube
- Less natural fit for continuous-downstream integration than TFF permeate loop
TFF (tangential flow filtration)
Advantages
- Vendor-independent hardware: any commodity peristaltic or centrifugal pump plus any hollow-fibre cartridge
- Reached the highest published cell density in head-to-head WAVE comparison (Clincke 2013: 2.14 x 10^8 cells/mL)
- Centrifugal-pump TFF (Levitronix) brings sieving and lysis to ATF-equivalent levels (Wang 2017)
- Permeate loop integrates directly into continuous downstream capture skids
Disadvantages
- Classic peristaltic-pump configuration suffers progressive sieving decay (95% to 52% over 14 days)
- Higher cell lysis from peristaltic pump generates more debris, accelerating fouling
- HMW species accumulate in the bioreactor when product is partially retained, complicating quality
- Centrifugal-pump upgrade adds Levitronix-class hardware cost and validation effort
Which should you choose?
Pick based on the dominant constraint in your process. For most CHO mAb perfusion teams the answer is ATF; the TFF cases are real but specific.
CHO mAb perfusion, 50-1000 L
Steady-state 30-100 million cells/mL, 14-30 day production runs, commercial cGMP path. ATF gives stable sieving with low lysis; Repligen XCell ATF is the proven default with a 40+ commercial process track record.
Choose ATFIntegrated continuous downstream
Direct loop feed from upstream permeate into Protein A capture, no surge tank. The TFF permeate stream connects naturally; Pinto and Brower (2020) ran 29 days continuous from bioreactor to chromatography with a wide-pore TFF membrane.
Choose TFFVendor-independent procurement
Sourcing flexibility, multi-supplier risk reduction, or a process licensed to a CDMO using non-Repligen hardware. TFF with centrifugal-pump architecture lets you swap pumps and cartridges across vendors.
Choose TFFViral vector / vaccine perfusion
Lentiviral, AAV, or vaccine campaigns with high-DNA, high-debris broth. The reverse stroke on ATF prevents the filter fouling that limits TFF runs on the same feedstock; ATF extends filter life by 2-4x in lentiviral campaigns.
Choose ATFReal-world use cases
Typical setups where bioprocess teams have converged on one cell retention device or the other.
XCell ATF 6 on Biostat STR 200
Steady-state 60 million cells/mL, 21-day production, 1 vessel volume per day perfusion rate. Stable 90% mAb sieving from day 3 to day 21. The Sartorius + Repligen integrated platform is the default at 50-2000 L scale.
XCell ATF 4 on N-1 seed
5-day N-1 perfusion intensification to 50 million cells/mL, seeded into a 2000 L fed-batch production reactor at 5 million cells/mL. Compresses seed train by 15-30 days versus conventional N-1 batch.
Centrifugal-pump TFF, 50 L
HEK293 suspension producing LV at 1-2 million cells/mL with continuous harvest into downstream concentration. Levitronix centrifugal pump on a Cytiva XDR50 with 0.2 micron PES cartridge. Daily filter swap on heavily debris-laden broth.
Wide-pore TFF + Protein A capture
500 L perfusion bioreactor with Repligen KrosFlo KPS TFF on a centrifugal pump driving permeate directly into a Cadence BioSMB Protein A skid. 29-day integrated continuous campaign with no surge tank.
Sizing the perfusion loop and bleed for your retention device?
Run cell-specific perfusion rate (CSPR), vessel volumes per day (VVD), bleed rate, and steady-state VCD calculations for ATF or TFF cell retention efficiencies (95-99%+).
Open the Perfusion CalculatorCost and lifecycle considerations
Capital cost of the retention device and pump, recurring single-use consumables (hollow-fibre cartridges, tubing assemblies, single-use ATF housings), product loss in the retentate from sub-100% sieving, and labor/validation overhead. ATF wins on product loss and labor; TFF wins on procurement flexibility.
At 200 L production scale, capital cost is broadly similar between ATF and TFF. A single-use Repligen XCell ATF 6 controller plus device package lands in the 80-150k USD range; an equivalent Repligen KrosFlo KPS TFF or a centrifugal-pump TFF skid built on a Levitronix BPS-200 falls in the 80-180k USD range depending on whether the pump is commodity or magnetic-levitation. Both technologies use comparable hollow-fibre cartridge consumable economics (1-3k USD per cartridge, with cartridge lifetimes of 14-30 days).
The dominant cost differentiator is product loss. A peristaltic-pump TFF system holding mAb sieving at 70% on average across a 21-day run loses 10-15% more product than an ATF holding sieving at 92%. For a 200 L CHO perfusion at 1 g/L titre and 1 VVD, that is 200 g/day x 22% lost yield equals roughly 900 g of mAb across a 21-day run. At about 1000 USD per gram manufactured value, this single line item dwarfs the capital and consumable difference between the technologies.
| Cost component (200 L scale, single-use) | ATF | TFF (peristaltic) |
|---|---|---|
| Capital: controller + device | ~80-150k USD | ~80-180k USD |
| Consumables / 21-day run | ~2-4k USD (single-use cartridge + tubing) | ~1.5-3k USD (cartridge + tubing) |
| Operator labor / month | Low (single-port, integrated controller) | Medium (separate pump + sampler integration) |
| Product loss penalty (21-day run, 1 g/L) | ~5-10% (sieving 88-95%) | ~20-35% (sieving decay 95% to 52%) |
| 3-year TCO (10 runs/yr, with product loss) | ~1.4M USD | ~1.7M USD (peristaltic) / ~1.45M USD (centrifugal) |
Vendor landscape
Major vendors in each camp, with one-line positioning notes.
ATF vendors
- Repligen XCell ATF: the dominant and effectively only commercial ATF platform. Sizes ATF 1 (0.5-2 L) through ATF 10 (200-5000 L). Single-use PES or stainless-steel housings.
- Sartorius Biostat STR + XCell ATF integrated: co-developed single-control-interface package at 50-2000 L. The default cGMP path for new CHO mAb perfusion facilities since the 2018 launch.
- Cytiva Wave / Xcellerex: wave-mixed and stirred SU bioreactors routinely paired with Repligen XCell ATF devices in process development.
- Thermo Fisher HyPerforma and Getinge / Applikon: stainless-steel and single-use bioreactors that integrate XCell ATF through the standard pneumatic port.
TFF vendors
- Repligen KrosFlo KPS TFF: Repligen's dedicated TFF perfusion platform, sold separately from XCell ATF. Single-use PES hollow-fibre cartridges with broad flow-rate envelope.
- Cytiva FlexFactory TFF perfusion: hollow-fibre TFF cell retention as part of the Cytiva FlexFactory single-use upstream platform.
- Sartorius hollow-fibre cartridges: commodity 0.2 micron PES and polysulfone cartridges used in vendor-agnostic TFF perfusion skids.
- Levitronix centrifugal pumps: magnetically-levitated centrifugal pumps that replace the peristaltic head and close the TFF-vs-ATF lysis gap (Wang 2017).
- Meissner SepraPor and Merck Millipore: alternative hollow-fibre cartridge suppliers used in vendor-independent TFF skids.
Frequently asked questions
What is the main difference between ATF and TFF for perfusion?
Which gives higher cell density, ATF or TFF?
Why does TFF retain product (low sieving) and ATF does not?
Is ATF gentler on cells than TFF?
Can you scale ATF and TFF to commercial mAb manufacturing?
Does ATF or TFF foul faster?
What is the price difference between ATF and TFF cell retention?
Is TFF ever preferred over ATF?
Resources and references
- Clincke et al. (2013), Biotechnology Progress 29(3): 754-767 — Very high density CHO perfusion by ATF or TFF in WAVE bioreactor; peer-reviewed head-to-head reaching 2.14 x 10^8 cells/mL (TFF) and 1.32 x 10^8 cells/mL (ATF). DOI 10.1002/btpr.1704.
- Wang et al. (2017), Journal of Biotechnology 246: 52-60 — Shear contributions to cell culture performance and product recovery in ATF and TFF perfusion; identifies peristaltic pump (not alternating flow) as the dominant lysis source.
- Pinto and Brower (2020), Biotechnology and Bioengineering 117(11): 3567-3576 — Wide-surface pore microfiltration membrane solves the product-retention issue in filtration-based perfusion bioreactors; 29-day integrated continuous mAb run.
- Repligen XCell ATF Technology overview — manufacturer specifications: device sizes ATF 1 to ATF 10, single-use PES and stainless-steel housings, 0.2 micron / 0.5 micron / 50 kDa membrane options, 500+ deployed sites and 40+ commercial mAb processes.