Cell viability, identity, sterility and potency explained
These four words appear on every certificate of analysis and almost never get explained to patients. Each answers a different question: are the cells alive, are they the right cells, is the product clean, and do the cells still function?
Viability — are the cells alive?
Viability is the percentage of intact, living cells in the dose. It is measured by dye exclusion or flow cytometry, and it matters twice: at release, and again after thawing, because freezing and thawing kill some cells. A dose quoted as "100 million cells" means little without the viability figure and the time between thaw and administration.
Identity — are they the right cells?
Identity confirms the product is a mesenchymal stromal cell population and not something else that grew in culture. The standard reference is the ISCT minimal criteria: plastic adherence, expression of CD73, CD90 and CD105, absence of haematopoietic markers such as CD34, CD45 and HLA-DR, and demonstrated trilineage differentiation capacity. Ask which markers were measured and at what percentage.
Sterility, endotoxin and mycoplasma — is it clean?
Contamination is the failure mode with the clearest link to patient harm in the published record of unregulated clinics, which is why these three are non-negotiable.
- Sterility — validated culture-based testing for bacterial and fungal growth.
- Endotoxin — measured in endotoxin units per kilogram; a product can be sterile and still cause a fever reaction if endotoxin is high.
- Mycoplasma — small bacteria that pass standard filters and do not show on routine sterility tests; tested by PCR or culture.
Potency — do they still work?
Potency is a functional assay: for MSCs, commonly the ability to suppress activated T-cell proliferation, or measured secretion of a relevant factor such as IDO or PGE2 after stimulation. Cells that have been expanded too far can pass identity and viability while losing function, so potency is what distinguishes a controlled product from a cell count.
What a specification looks like
A failing batch means your treatment is postponed. A provider who has never postponed a treatment for a failed release is worth a second look.
| Test | Typical specification format | If it fails |
|---|---|---|
| Viability | ≥ defined % at release and post-thaw | Batch rejected or dose recalculated |
| Identity | ≥ defined % positive for CD73/CD90/CD105; ≤ defined % for CD34/CD45 | Batch rejected |
| تعقيم | لا يوجد نمو | تم إتلاف الدفعة |
| الذيفان الداخلي | أقل من حد الاتحاد الأوروبي/كجم | تم إتلاف الدفعة |
| مفطورة | لم يتم الكشف عنها | تم إتلاف الدفعة |
| الفعالية | نتيجة الفحص ضمن النطاق المحدد | تم رفض الدفعة |
الأسئلة المتداولة
هل العدد الأكبر من الخلايا أفضل دائمًا؟
لا. يتم اختيار الجرعة وفقًا للبروتوكول ولكل كيلوغرام من وزن الجسم حيثما كان ذلك مناسبًا؛ بعد نقطة معينة، تضيف المزيد من الخلايا تكلفة وحِملًا على الحقن بدلاً من الفائدة، وتعتبر الحيوية والفعالية أهم من العدد الإجمالي.
ما هو رقم المرور ولماذا هو مهم؟
يحسب رقم المرور عدد المرات التي تم فيها زرع الخلايا بشكل ثانوي. تؤدي الأعداد العالية من المرور إلى المزيد من الخلايا ولكنها تخاطر بالشيخوخة وفقدان الفعالية، ولهذا السبب يتم تحديد حدود المرور في العملية.
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