In our final blog post on double-stranded RNA (dsRNA), we turn our attention to the chemical building blocks of mRNA therapeutics—modified nucleotides. These seemingly minor changes to the RNA sequence play a crucial role in the success of mRNA-based vaccines and treatments. However, they also introduce complexities in accurately detecting and quantifying unwanted dsRNA byproducts— key steps in ensuring the therapeutic efficacy of your mRNA product. 

What Are Modified Nucleotides? 

Modified nucleotides are ribonucleotides containing chemically altered nucleosides — like specialty ingredients swapped into a classic recipe to improve taste and nutrition. Just as a chef might use a lactose-free milk or gluten-free flour to make a dish easier to digest without changing its core structure, scientists use chemically altered nucleosides during in vitro transcription (IVT) to improve how mRNA therapies perform. These modifications replace their natural counterparts (e.g., uridine or cytidine) in the final RNA product. Their incorporation improves the performance and safety of mRNA therapeutics in several ways: 

As mRNA therapeutics continue to expand across clinical pipelines, one persistent challenge remains for developers: reducing double-stranded RNA (dsRNA) contaminants that can compromise safety and efficacy. These unintended byproducts of in vitro transcription (IVT) can trigger unwanted immune responses and reduce the potency of the final product. Developers must prioritize dsRNA detection and control as essential steps in the process. In our previous blog post we offered a high-level discussion of what is double-stranded RNA (dsRNA), its biological function, and importance of detection in a therapeutic context.  Here, we’ll take a closer look at origins of dsRNA contamination, quality control measures, and improvement strategies.

Large-scale production of single-stranded RNA (ssRNA) for mRNA-based therapeutics is primarily done through in vitro transcription (IVT), an enzymatic process designed to generate high-yield, functional mRNA transcripts from a DNA template. This process uses purified RNA polymerase enzymes, such as T7, that recognize specific promoter sequences in the DNA template, generating the RNA transcripts of interest. However, IVT reactions also generate unwanted dsRNA byproduct. Below, we delve into some of the major quality control (QC) considerations and strategies to reduce dsRNA byproducts.