In-house reference material for stem cell product development

by Alexey Bersenev on September 12, 2015 · 1 comment

in cell product, consensus

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We have been discussing standards and reference material in stem cell-based product development for the last few years. There are several ongoing projects, conducted by few organizations (NIST, USP, FDA, NIH, ISO, ASTM…) to address necessity of standards in cell therapy field. If the most discussions have been focused on development of consensual standards, the article, published this year in Stem Cells TM, highlights importance of in-house (product-specific) reference materials.

The following graph from the article, perfectly illustrates types of standards and their relations (modified by me):


The authors nicely outlined WHY do we need reference material (RM) and WHAT can be used as such. Ass you can see from the graph, RM could be for a specific product and for the methods. The key word to the first question “WHY?” is comparability:

“Product” RMs should be representative of the product and are used to validate comparability assessments throughout the product’s lifecycle, including process change and optimization, and to detect process drift (Fig. 2A). Individual RMs will be designed to assist in the assessment of the product identity or its biological potency, and the respective purpose for the RMs must be clear at the outset.

Comparability here is all over the place: after/ during process changes, raw material heterogeneity, batch-to-batch variability, stability… As authors pointed out, individual product-specific in-house RM could be primary and secondary (analogously to master and working cell banks). Primary (cellular) standard could be generated in pre-clinical development and cryopreserved as a bank. Secondary product RM is a working standard and could be always obtained from primary RM once depleted. Product RM also could be generated from pooled cellular material (from multiple donors or batches of product). Finally, product RM could be a biological equivalent, for example, well defined cell populations, sorted/ isolated from normal donors.

Now, important thing to notice is that the article dedicated to pluripotent stem cell-derived products. “These guys” are usually highly proliferative in culture and easy to bank. So, establishing product RM is nicely fit in allo-, industry- or/and pluripotent stem cell models. However, if we look at autologous highly personalized products, generation of product-specific in-house RM could be a challenge.

The second type of in-house RM, discussed in the article is a “method RM”. Essentially, the biggest part of method RM are “positive controls” for your assays. Depending on assays, method RM could be cellular (cell lines), noncellular (RNA, DNA, beads..) and virtual (gene expression or protein signatures).

“Method” RMs are used to qualify, validate, and define the accep- tance criteria for specific assays, to calibrate methods and equip- ment, and to identify method drift over time (Fig. 2B).

Even though, you as a cell product developer may have very unique assays, most of QC testing for product release are pretty similar between developers. In this case, I think, the concept of “in-house method RM” is overstated. For example, beads to calibrate flow cytometry instrument could be universal (you don’t need to make your own) and could be purchased from commercial vendors. The same thing with virtual method RM, such as gene expression signature PluriTest – anyone can test different stem cell-derived products via this software (again – you don’t need to make your own – use available database). Some method RM could be provided by standards-developing organizations. But, in some cases, method RM are desirable for your particular product. For example, I’d make “viability positive control” from my own product. I’d also try to make it for potency testing.

I think, consensus method RM still plays a huge role in detection of potential “drift over time” of your own in-house developed method RM and assays.

The method RMs we have described will typically display greater stability profiles than product RMs owing to the inherent plasticity of living cells and their responsiveness to the environment. Feasi- bility factors, including the ability to generate sufficient batch sizes, will also be more amenable to method RM approaches, which should, in general, also carry lower costs. A rational mix of method RMs for different assays within the overall characterization process and robust product RMs will be required.

Overall, this article is great and unique. Highly recommended for every stem cell product developer!

{ 1 comment… read it below or add one }

Christopher Bravery September 19, 2015 at 5:57 am

Hi Alexey, if you didn’t see it Anna and I also wrote a related article because I felt it would also be useful to have a more metrological discussion on reference materials.

We attempt to explain why some approaches would be unlikely to be successful, e.g. having a certified (consensus) living cell reference material. Its admittedly quite a complex discussion and relates to the issue of what is actually being measured in complex assays such as potency, and that a reference material can rarely be developed for more than one or two uses.


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