The importance of reference standards in biosimilar development

Biosimilar – Recently, I had the opportunity to visit a biotechnology company to review their development of a vaccine.  I discovered that they had no reference standard, and hence, could not quantify the potency of their drug substance and finished product. Their justification was that no international reference standard was available; consequently, they could not develop an in-house standard. Dosing of their product was based entirely on protein concentration. The problem with this is that the assay used to measure protein concentration is a biochemical assay (Lowry method), which does not discriminate between active and inactive protein – it measures the total protein content in a sample. As we know, product-related impurities such as aggregates and fragments are generally inactive and other variants, such as oxidised and deaminated product species may be less active than the parent intact protein drug substance.  Protein concentration can, therefore, not be used as a measure of potency of a biological medicine – whether it is a vaccine or biopharmaceutical product. This reminded me of a biosimilar application I assessed a few years ago in which the applicant used a batch of the innovator product as their reference standard.  This too is not acceptable, as the reference standard must be independent of both the test (biosimilar) and reference (innovator) products in comparability assays.  In such a case, any variation observed in assay results of the reference product from that of the standard will simply reflect assay variability and not batch-to-batch variability in the reference product. In comparability studies the objective is always to show that results for critical quality attributes (CQAs) of the biosimilar ideally fall within the range of results for those CQAs obtained with several batches of the reference product. 

So what should biosimilar companies do if an international or compendial reference standard is not available? The simple answer is that they must do the same as the innovator companies – establish their own in-house primary and secondary reference standards. According to ICH Q71 an in-house primary reference standard is defined as “a substance that has been shown by an extensive set of analytical tests to be an authentic material that should be of high purity. “ In most cases, material is prepared from a clinical batch (Phase 3); sometimes with additional purification.  The material is then characterised, not only through release tests but also through extensive structural and identity tests using orthogonal methods. The primary reference standard is used mainly for calibration of secondary standards (two-tiered approach). An in-house secondary reference standard (also referred to as a working standard), is an appropriately characterized material prepared from representative commercial lot(s) to support routine testing of product lots for quality.  The reason for a two-tiered reference system is to prevent drift in quality attributes as it involves a comparison of each new reference standard with a primary reference standard so that it is linked to clinical trial material and the current manufacturing process2.

An approach that could be used, particularly early on in the biosimilar development program before the clinical comparability study has commenced, is to use a mixture of three or more reference product batches from the same manufacturing site or a batch of the reference product from a different site in a different jurisdiction as reference standard3. Batch-to-batch variability or the variability that is often seen between batches manufactured at different manufacturing plants will ensure that assay results obtained for individual reference product batches will differ from such reference standards.   


  1. ICH Q7, “Good Manufacturing Practice Guide for Active Pharmaceutical Ingredients,” 2000.
  2. White paper. Reference standards biopharmaceutical products. Do you have your reference standard program in place? 2019. Femke Jacobs.
  3. Development of Therapeutic Protein Biosimilars: Comparative Analytical Assessment and Other Quality-Related Considerations. May 2019.