Flow can contribute to product characterisation and release testing. Identity, viability and potency must remain distinct claims.
Original CFCM report: 26 August 2026. Expanded for pre-launch review; this is not a retrospective web-publication date.
Regulatory guidance: FDA, Potency Tests for Cellular and Gene Therapy Products, final guidance, January 2011. It describes a product-specific approach and does not prescribe a universal potency assay or release acceptance limit. FDA's cell-therapy characterisation research programme also describes flow cytometry among its analytical methods. These are regulatory and institutional sources, not a clinical trial.
These FDA recommendations are nonbinding guidance, not a product authorisation. Rechecked on 23 September 2026: Potency Assurance for Cellular and Gene Therapy Products (December 2023) and Potency Assessment of Active Immunotherapy Products (August 2026) are still labelled Draft / not for implementation by FDA. They should be tracked as evolving regulatory thinking and not described as final requirements.
The guidance supports developing potency evidence for the particular product. It does not declare that any marker-positive population is sufficiently potent or that flow alone can establish every release attribute. A flow assay may quantify cell identity, composition or viability; a proposed potency readout needs justification linked to the product's biological activity.
A high percentage of viable cells does not establish therapeutic function. Expression of a receptor can be an identity or characterisation measurement without proving downstream activity. The cited US guidance is not an EU marketing authorisation and supplies no universal cell-therapy release threshold. No sample size or performance percentage is claimed because these sources are not comparative assay studies.
CFCM development framework: define which release attribute each result supports and what decision follows from failure. Establish sample representativeness, stability, recovery, analysis rules and result review. Where a surrogate is proposed, investigate its relation to the relevant biological function across meaningful process variation. Predefine how changes in starting material, reagents, manufacturing or analysis trigger assessment. Ensure the assay can return a reliable result within the product's operational release window.
The opportunity lies in a defensible decision, not merely a complex panel. An elegant assay that cannot withstand process changes, time pressure or an investigation of an atypical batch is not operationally mature. Flow becomes valuable in release when its measurand, limitations and decision role are explicit and integrated with the rest of the product's quality evidence.
Professional background: Juan Manuel Ojeda has professional experience with Sysmex España in clinical flow cytometry and now works as a freelance consultant. CFCM is his independent editorial project; its views do not represent Sysmex or imply company endorsement. The same evidence standard applies to all manufacturers.
Related: validation and analysis resources →Clinical Notes →Expanded web version and source-check pass: 19 September 2026. This was not independent scientific review. The original-report date is preserved separately above.