Abstract
Cell and gene therapies are rapidly emerging as promising approaches for treating a wide range of diseases, including cancer, genetic disorders, and autoimmune conditions. These therapies often involve the transfer of genetic material into a patient's cells or tissues, and they require precise and accurate measurement of nucleic acids to determine things like gene expression, cell count, and viral titers.
To help ensure the safety and efficacy of these therapies, biopharmaceutical manufacturers need reliable tools for monitoring and analyzing their products. Digital PCR (dPCR) has emerged as a powerful technology for precise and accurate quantification of nucleic acids in complex mixtures, making it an essential tool for cell and gene therapy manufacturing. However, since therapeutic developers and manufacturers must achieve the utmost certainty to be confident in their products and regulatory submissions, they must be discerning when choosing a dPCR system and applying it to their workflow.
Not all digital PCR data is created equal
Overall, digital PCR technology generally outperforms other nucleic acid quantification approaches like quantitative PCR (qPCR). However, achieving the greatest precision and accuracy requires experts to differentiate between the different dPCR methods and platforms, each with their strengths and limitations.
Droplet Digital™ PCR (ddPCR™) has become increasingly popular due to its ability to overcome some of the limitations of other dPCR methods. Unlike other dPCR methods, which generally use chips, plates, or microarrays to partition the sample into individual reaction chambers, ddPCR assays use a water-oil emulsion technique to partition the sample into thousands of droplets. This methodology lowers the risk of cross-contamination and produces more precise and accurate results, with a higher signal-to-noise ratio and less amplification bias.
Another advantage of ddPCR technology is that it is more tolerant of inhibitors, which can interfere with the PCR reaction and lead to false negative results. ddPCR assays are also less sensitive to variations in reaction conditions, such as the amount of input DNA or RNA, which can affect the accuracy and precision of other dPCR methods. When these issues produce low-quality data, biopharma scientists must either repeat the experiment—thereby wasting time and reagents—or seek an advanced user to manually set thresholds and interpret results, introducing greater potential for human error. Minimizing these issues with ddPCR technology helps experts be confident in their results, which is especially critical for advanced biopharmaceuticals.
Top-notch data is critical for many cell and gene therapy steps
Precise and accurate digital PCR data is crucial in cell and gene therapy development and manufacturing due to the high stakes involved. These therapies can potentially provide life-changing treatments to patients, but any errors in manufacturing or dosing could have serious consequences. Inaccurate or imprecise data can lead to suboptimal dosing or potentially harm patients. Additionally, the complex nature of these therapies, involving multiple cell types and genetic modifications, requires precise quantification of the target nucleic acids. ddPCR technology provides a powerful tool for detecting and quantifying these targets across every step of the biopharmaceutical production journey.
Viral Titer Determination
Adeno-associated viruses (AAV) are one of the most commonly used viral vectors in gene therapy. Accurately quantifying the viral titer is essential for optimizing the dosing of AAV-based therapies. Unfortunately, traditional assays for AAV titer determination can be time-consuming, labor-intensive, or inadequately sensitive, with results affected by several variables. Conversely, ddPCR technology can offer more precise and accurate quantification of AAV genomes per mL, making it a powerful tool for AAV titer determination.
Potency Quantification
The number of functional transgene copies or viral particles present in a sample determines cell and gene therapy products' potency. The potency of these products is critical, as it impacts the efficacy of the therapy and its overall safety. While traditional qPCR-based methods have been used for potency quantification, they are not always accurate and reliable. In contrast, ddPCR technology can provide absolute quantification of the number of target sequences present, resulting in more precise and reliable potency determinations.
Contaminant Detection
Contaminants are all too common and can enter a therapeutic batch at any point in the workflow; however, no matter where they enter, they can seriously compromise the final product's safety and efficacy. In particular, mycoplasma bacteria are a common contaminant in cell culture that can evade detection through traditional microscopic methods due to their small size. In addition, standard culture-based detection techniques are laborious, lack sensitivity, and can take up to four weeks to produce results. In contrast, ddPCR technology offers a reliable means of same-day detection through the use of specific probes that can target the unique genetic signatures of 112 species of mycoplasma.
Another important contaminant to monitor in cell and gene therapy manufacturing is host cell DNA, particularly in systems that use the commonly employed HEK293 cell line. While HEK293 cells are widely used for their ability to produce high levels of recombinant proteins or viral vectors, they also carry a risk of DNA contamination in downstream products. This is where ddPCR technology can provide an advantage over other PCR techniques, as it can accurately analyze host cell DNA levels to ensure the fragment size and quantity fall within acceptable limits. By providing a more specific and precise measurement of host cell DNA, ddPCR can help minimize the risk of immune responses or other adverse events in patients receiving the final gene therapy product.
Copy Number Quantification
Cell therapy products, such as chimeric antigen receptor (CAR) T cells, have shown great promise in cancer treatment. However, the efficacy of these therapies can be affected by the number of transgene copies present in the cells. Without any transgenes, a cell will not contribute to effective treatment, but cells with too many transgenes may behave abnormally once injected into a patient. Traditional qPCR-based methods for determining copy number are often not precise enough for cell therapy manufacturing. However, ddPCR assays can confirm that therapeutic cells contain transgene numbers that fall within the range recommended by regulators.
An all-in-one solution for biopharma
The QX ONE™ Droplet Digital PCR (ddPCR) system from Bio-Rad is a fully automated ddPCR system designed specifically to meet the needs of biopharmaceutical customers. The QX ONE system has been validated for use in AAV titer determination, potency quantification, mycoplasma and host cell DNA contaminant detection, and cell therapy copy number determination, among other applications.
The system is user-friendly and fully automated for walk-away operation, reducing the risk of human error and variability. In addition, the intuitive software and simple workflow make it accessible to a wide range of users, from experienced molecular biologists to those with little or no PCR experience.
The QX ONE ddPCR system enables advanced multiplexing that can analyze up to 480 samples in a single day, allowing for efficient and cost-effective analysis. It also offers regulatory edition software, which includes tools to assist in compliance with regulatory requirements for data integrity and traceability, making it suitable for use in a GMP environment. Together, the features of the QX ONE ddPCR system make it an ideal instrument for cell and gene therapy manufacturing.
