ISO has published two cell counting standards as guidance to improve cell counting results
A wide range of biological sample types, dynamic and heterogeneous samples, and various formulations and bioprocessing steps mean that cell counting needs for cell and gene therapies are highly unique and complex. Furthermore, the fact that there are no ground truth reference materials for live cells increases the difficulty for determining the accuracy of cell counting defined in the ICH Harmonised Tripartite Guideline – Validation of Analytical Procedures: Text and Methodology Q2 (R1). Therefore, in order to increase the confidence of cell counting results, it is critical to follow the two recently published ISO cell counting standards, and ISO 20391 – 2:2019 Biotechnology – Cell Counting – Part I: General Guidance on Cell Counting Methods and ISO 20391 – 2:2019 Biotechnology – Cell Counting – Part II: Experimental Design and Statistical Analysis to Quantify Counting Method Performance, to ensure cell counting methods are tailored to the specific sample and purpose.
It is important to note that after the initial selection and evaluation of a cell counting method, method development, optimization, validation, and continuous verification following the Validation of Analytical Procedures are also critical for downstream processes for cell-based product manufacturing. In order to tailor cell counting methods to specific experimental needs, the focus of the current discussion is to provide insights and guidance for the ISO standards for method selection and evaluation (Figure 1). To that end, the important aspects of the ISO cell counting standards have been distilled to six key factors that can influence the quality of the cell counting results, which should be considered to select the appropriate cell counting methods that are fit-for-purpose. These key factors are divided into three specific categories: Knowledge Collection, Cell Counting Method, and Operation Assurance (Figure 1). Attention to these details will allow researchers to more easily adhere to the ISO recommendations to ensure high quality cell counting measurements, and in doing so, sites can meticulously document their rationale, process, and data for reporting FDA compliance.