International Society for Cellular Therapy (ISCT) published a perspective on potency assay for immune function of mesenchymal stromal cells (MCS). This paper reflects position of international experts workshop, which was held during the past annual ISCT meeting. Unlike other ISCT’s papers, this one is paywalled (unfortunately!). I’ll try to summarize some important points here.
Challenges to assess potency of MSC-based products
At the beginning, article overviews definitions and regulatory requirements to potency assays for cellular products.
There is no single test that can adequately measure product attributes that predict clinical efficacy. Taking into consideration this limitation, the potency assay should represent the product’s mechanism of action (i.e., relevant therapeutic activity or intended biological effect). However, many CGT products, including MSC-like cells, have complex (e.g., rely on multiple biological activities) and/or not fully characterized mechanisms of action, making it difficult to determine which product attributes are most relevant to measuring potency.
The major challenges in development of potency assays for MSC products could be also extrapolated to other cellular products:
- Inherent variability of starting material (donor-to-donor variability)
- Complex mechanism of actions (MOA)
- Limited material for testing (low lot size/ low volume)
- Limited stability
- Lack of appropriate reference material
- Complex in vivo fate of the product (biodistribution, “dividing drug”, differentiation)
What type of assays to consider?
- Bioassays (using animals or cell culture) are frequently not feasible to perform, therefore, analytical surrogate assays (example: ELISA, PCR, FACS…) should be considered as more practical. Surrogate assay should clearly correlate with biological activity of the product.
- Few complementary potency assays should be considered when single assay “may not provide an adequate measure of potency”.
- Assay matrix is a combination of potency assays, which could be used in development or for release of the product. The best published example of such assay matrix is angiogenic assay for product MultiStem (Athersys).
- Qualitative assay (pass/ fail readout) should be accompained by quantitative assay(s) (units of activity readout).
Immunopotency assays for MSC products
The paper is challenging wildly used in research mixed lymphocyte reaction (or any responder immune cells) assay for MSC potency. Recommended assay matrix approach is the following:
- Quantative RNA analysis of gene products
- Flow cytometry of functionally relevant markers
- Measuring proteins in secretome
So-called “static” MSC markers are not relevant to immunopotency, therefore, in order to measure biological activity-relevant markers cells should be activated in vitro (licensed). Importantly, “resting MSC” should serve as a “cell ruler” or “in-house” control for “activated” MSC.
Perspective statement: A focused analysis of selected markers robustly deployed by in vitro cytokine licensing (e.g., IFNγ) of MSCs and metricized with a complementary matrix of assays (fluorescence-activated cell sorting, quantitative RNA and proteomic [ELISA]) using “resting” MSCs as controls (from the same lot) should be responsive to requirements from Regulator Authorities regarding release potency assay…
Call for openess
ISCT perspective paper is proposing openess in sharing MSC potency assays by manufacturers and regulatory agencies:
It is also desirable that unfettered open access of Regulatory Authority–approved release potency assay systems for MSC-like cells by Manufacturers engaged in clinical trials be encouraged and embraced by the cell therapy community. Public access of these elements can only be achieved by voluntary public disclosure by Manufacturers, and this shared regulatory data will further advance the field by allowing stakeholders to adopt rationally developed and validated common standards and assays.
The reason why this information is not currently shared and not published, because:
…Regulatory Authorities are not at liberty to publicly disclose otherwise confidential IND disclosure made by Manufacturers…
Well, too bad for community – too bad for the patients! How could such important, but paywalled paper promote openess? I hope, developers, regulators and ISCT will hear and make it all OPEN for public good!