- [Resource Hub](/) - [Blog](/?resource-type=blog-post#library) - In Cell Therapy, Your Cell Count Can Serve as a Release Assay Blog · 4 min read · Cell Therapy QC # In Cell Therapy, Your Cell Count Can Serve as a Release Assay In autologous CAR-T, the lot is one patient's cells. That changes what a count has to survive. Key takeaways - A release assay is a result you have to prove to an auditor, not just record. In cell-therapy manufacturing a cell count can now clear that bar, because 21 CFR Part 11 (audit trail, e-signatures, role-based access, and a logged record of any deletion) reaches the count once it is part of the batch record. - The lot is one patient's cells, so there is no re-run. Whatever you record at release is the count you answer for — which makes the record around the number matter as much as the count itself. - Accuracy is table stakes; provability is what gets a count released. The serious instruments are all accurate, so the useful question shifts from "is it accurate?" to "can you prove it?" Every QC scientist standing up a GMP cell-therapy workflow ends up in the same meeting. IT and Quality come to vet the cell counter, and their first questions have nothing to do with accuracy. They want to know who can change a result, and whether the system keeps a record when someone deletes one. Somewhere in that conversation a routine cell count stops being a lab measurement and becomes something you have to answer for. ## The count quietly changed jobs The cell count got promoted, and no one sent a memo. It used to be a convenience metric — the number you jotted down to decide whether to keep going. Now it can land on the certificate of analysis for a released lot. That is what lets it function as a release-assay result: a number an auditor can question and you have to stand behind. A cell count used to be a number you recorded. In cell-therapy manufacturing, it can now be a number you have to prove. ## Why the count grew up with the field The promotion is real because the field moved. Cell therapy came off the research bench and onto GMP manufacturing floors turning out autologous CAR-T. GMP brings 21 CFR Part 11, the data-integrity standard for electronic records. Part 11 asks for an audit trail, electronic signatures, role-based access, and a logged record of any change or deletion. Those requirements used to live on the big analytical instruments and the LIMS. Now they can reach the cell count, because at release the count is part of the batch record. Read against the count, the four Part 11 expectations get concrete: 21 CFR Part 11 requirement What it asks of the cell count Audit trail A time-stamped, computer-generated log of every action that creates, modifies, or deletes a count — recorded automatically, not by hand. Electronic signatures Each recorded count is attributable to the person who ran and approved it. Role-based access Only authorized roles can run, review, or change a count — and the system enforces it. Record of any deletion If a result is deleted, the trail still shows that it existed and that it was removed — raw data cannot quietly disappear. ## The gap shows up as one specific worry When IT and Quality vet a counter, the concern gets precise. The sharpest version comes up again and again: whether the audit trail would capture when data has been deleted. The count could be perfectly accurate and that concern would still hold, because the concern is about the record, not the arithmetic. What the worry is really about The system has to show that no one altered the number, and prove that to an auditor who was not in the room. An accurate count you cannot account for is, at release, not yet a result. ## The lot is one patient's cells, so there is no re-run CAR-T sharpens all of this, because the lot is one patient. The starting material is that person's own cells, the batch size is one, and the product is already spoken for. You cannot re-pull the sample and count again next week. Whatever you record at release is the only count there will ever be. ## The real question moved from accurate to provable So the useful question about a counting step has changed. Accuracy is table stakes. The serious instruments here are all accurate, and an auditor rarely doubts your arithmetic. What the auditor does test is whether the number holds up on the record: who touched it, whether the system logged the change, and whether a deletion would show. A count is only as good as what you can prove about it. Accuracy gets a count considered. Provability is what gets it released. ## Spec the count as a release assay from day one So treat the count as though it can serve as a release assay from the day you design the workflow. Choose an instrument that logs every action and keeps that record whole even when a result is deleted. Do that, and the count becomes the easy part of the release: the one number you can walk an inspector through, start to finish. Pick the counter for what it can prove, and the release takes care of itself. If you are writing this into an SOP, an [audit-ready cell counting guide](/resources/audit-ready-cell-counting-gmp-guide/) lays out what Part 11 actually asks of the count. ### Speccing a counter for a GMP cell-therapy workflow? Talk through what an auditor will ask of your cell count — audit trail, e-signatures, role-based access, and a record of every deletion — before it is written into your SOP. [Talk to a Specialist](https://precisioncellsystems.com/request-a-quote/) For research use only. Not for use in diagnostic procedures. On this page - [The count changed jobs](#count-changed-jobs) - [Why the count grew up](#why-the-count-grew-up) - [The one specific worry](#the-specific-worry) - [One patient, no re-run](#one-patient-no-rerun) - [Accurate vs. provable](#accurate-vs-provable) - [Spec it from day one](#spec-from-day-one) ### Counting for a released lot? See what Part 11 asks of the count before you pick an instrument. [Talk to a Specialist](https://precisioncellsystems.com/request-a-quote/) [Back to all resources](/#library) ## Similar resources [Blog](/resources/21-cfr-part-11-cell-counter-requirements/) Moxi GO II 2026 ### What 21 CFR Part 11 Requires of a Cell Counter The compliance explainer: what 21 CFR Part 11 actually demands of a cell counter — audit trail, e-signature, access control, and a Secure Mode. [Read Blog](/resources/21-cfr-part-11-cell-counter-requirements/) [Field Guide](/resources/audit-ready-cell-counting-gmp-guide/) Moxi GO II 2026 ### Audit-Ready Cell Counting for GMP Cell-Therapy QC An educational field guide to the audit-ready framing and the five requirements of a count you can defend. [Read Field Guide](/resources/audit-ready-cell-counting-gmp-guide/) [Blog](/resources/gmp-cell-therapy-qc-counting-audit-ready/) Moxi GO II 2026 ### GMP Cell-Therapy QC Counting: What Makes a Count Audit-Ready The evergreen guide to what makes a GMP cell-therapy count audit-ready — the hub for the Part 11 and volumetric-vs-image explainers. [Read Blog](/resources/gmp-cell-therapy-qc-counting-audit-ready/) [App Note](https://precisioncellsystems.com/wp-content/uploads/2026/02/Moxi-Applications-Compendium.pdf) Moxi GO II Moxi V Moxi Z 2026 ### Applications Compendium Scientists are concerned with speed, accuracy, and convenience, and those running the lab and industries are concerned with the cost typically associated with high-performing instruments. Our proprietary Coulter Principle-based system delivers on all three accounts, and is therefore a perfect fit for any cell biology benchtop. [Download App Note](https://precisioncellsystems.com/wp-content/uploads/2026/02/Moxi-Applications-Compendium.pdf) [Brochure](https://precisioncellsystems.com/wp-content/uploads/2025/12/Moxi_GO_II_Brochure.pdf) Moxi GO II 2025 ### Brochure - Moxi GO II [Download Brochure](https://precisioncellsystems.com/wp-content/uploads/2025/12/Moxi_GO_II_Brochure.pdf) [Publication](https://www.cell.com/iscience/fulltext/S2589-0042(25)01158-7) Moxi GO II 2025 ### Simulating CD8 T cell exhaustion: A comprehensive approach [View Publication](https://www.cell.com/iscience/fulltext/S2589-0042(25)01158-7) [Publication](https://pmc.ncbi.nlm.nih.gov/articles/PMC11259153/) Moxi GO II 2025 ### Streamlined measurement of chimeric antigen receptor T-cell concentration, size, viability and two-color phenotyping during manufacturing [View Publication](https://pmc.ncbi.nlm.nih.gov/articles/PMC11259153/) [Publication](https://pmc.ncbi.nlm.nih.gov/articles/PMC6167529/) Moxi GO II 2025 ### PET of adoptively transferred chimeric antigen receptor T cells with 89Zr-oxine [View Publication](https://pmc.ncbi.nlm.nih.gov/articles/PMC6167529/) [Field Guide](/resources/21-cfr-part-11-cell-counter-checklist/) Moxi GO II 2026 ### The 21 CFR Part 11 Cell-Counter Evaluation Checklist A practical one-page scoring tool to evaluate cell counters against 21 CFR Part 11. [Read Field Guide](/resources/21-cfr-part-11-cell-counter-checklist/) [Blog](/resources/volumetric-vs-image-based-cell-counting-cart-qc/) Moxi GO II 2026 ### Volumetric vs Image-Based Cell Counting for CAR-T QC The method explainer: volumetric vs image-based counting for CAR-T QC, and why the CV gap matters at lot release. [Read Blog](/resources/volumetric-vs-image-based-cell-counting-cart-qc/) [App Note](/resources/moxi-go-ii-cart-expansion-monitoring/) Moxi GO II 2026 ### CAR-T Expansion Monitoring: Consolidated Cell Characterization Using Moxi GO II Peer-reviewed concordance data showing the Moxi GO II consolidates cell counting, sizing, viability, and 2-color immunophenotyping into a single 15-second, at-bench measurement for CAR-T expansion monitoring — replacing the standard two-instrument core-lab workflow. In a University of Pennsylvania study (Pajarillo et al., Cytotherapy 2024), the Moxi GO II matched gold-standard reference instruments for viability (r² = 0.97), CD4+ T cell identification (r² = 0.997), and CAR19 transduction efficiency (r² = 0.90), eliminating the 3–6 hour turnaround for routine expansion checkpoints. For Research Use Only. [View App Note](/resources/moxi-go-ii-cart-expansion-monitoring/) [Publication](https://pubmed.ncbi.nlm.nih.gov/40147445/) Moxi GO II 2026 ### A patient-derived T cell lymphoma biorepository uncovers pathogenetic mechanisms and host-related therapeutic vulnerabilities The authors used a Moxi GO II to count and monitor CAR T cells (including cell size/growth kinetics) throughout expansion, advancing the products into in vitro cytotoxicity assays and in vivo PTCL PDX studies only once the cells’ kinetics/size indicated they had “rested” from stimulation. [View Publication](https://pubmed.ncbi.nlm.nih.gov/40147445/)