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The Four Pillars of Critical Quality Attributes

The Four Pillars of Critical Quality Attributes

July 15, 2021
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Cell and gene therapies (CGT) have changed the landscape of precision medicine and continue to emerge at a rapid pace. These therapeutic strategies are both specific and precise compared to prior conventional medicines, and offer tremendous potential for the treatment of syndromes and diseases caused by genetic mutations.

The personalized nature of CGT approaches requires greater quality control metrics, which are achieved by identifying and meeting defined Critical Quality Attributes (CQAs). CQAs are a set of criteria to which a drug product should conform to be considered acceptable for its intended use. These attributes include in-process product identity, as well as potency, purity and safety.

In-process identity

As the name would imply, in-process identity is focused on ensuring the correct target is identified – for example, a specific viral vector. Protein characterization is particularly important for identity verification, as well as sizing and quantification of any post-translational modifications such as glycosylation.


Ensuring consistent potency, for example quantification of viral titer or nucleic acid/protein effective concentration, is another important CQA.

Variations in potency can have a significant impact on both research and product development, and undermine confidence in a specific therapy. Potency is a measure of activity per concentration, and the clinical viability of a new product is almost always dependent on a risk-benefit analysis comparing its activity at a given concentration to various safety factors, such as its therapeutic window and prevalence of side effects at certain blood or tissue concentrations. For research conclusions to be valid, they must be based on data that is both quantitatively accurate and precise.

Developments in PCR platforms have been instrumental in helping labs regulate potency, as newer technology allows for more precise identification of molecular targets for amplification, as well as overall improvement in accuracy of quantification.


Purity is a critical attribute for CGT approaches and related products to deliver a safe and reliable therapeutic option. When assessing the purity of a product, it is necessary to evaluate all possible contributors to variability, from host cell lines to baseline reagent purity. Contamination at any step along the product development or manufacturing pathway can result in alteration of the final version, and deviation from expected outcomes.

Looking one step ahead, it is also important to try to prevent contamination through consistency of product preparation and reduced disruption to workflow. Solutions such as no-wash protein assays can reduce the steps in sample preparation, and in many cases these assays can be paired with advanced plate reading platforms for a more precise and efficient approach to analysis.


Recipients of CGT may be immunosuppressed and/or immunocompromised, with greater susceptibility to opportunistic pathogens. Hence, the products used in CGT approaches must be free of contamination from pathogens as well as mycoplasma. The commonly-used PCR workflows for detection of contaminating agents can be supported by liquid handling workstations and microfluidic and detection technologies for both precision quantification and QC measures.

A good example of a safety consideration is the detection of pathogenic biological contaminants such as mycoplasma species. Mycoplasma is a known contaminant in cell cultures, and can be somewhat challenging to detect given its nearly month-long pathogen incubation time. This often supersedes the shelf-life of the cell or gene product. The use of PCR as a detection modality can remedy this issue, producing more timely results that ultimately decrease risk to product recipients.

The future remains bright for ongoing innovation of cell and gene therapy approaches and products, especially with continuous rollout of improved lab equipment and software. However, to ensure success, it is important for drug developers and manufacturers to commit to the four pillars of CQAs: in-process identity, potency, purity, and safety. Read our infographic to learn more.


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