The Collection, Storage, and Processing of Human Milk Samples as a Source of mRNA: A State of the Science Review

Background: Human milk contains messenger ribonucleic acid (mRNA), a key player in protein production and a source of gene expression information for understanding lactation physiology. The mRNA is renowned for its fragility and exists in several milk fractions, creating practical challenges for mRNA isolation and analysis. While research teams have developed protocols for the use of human milk samples in transcriptomic applications, it is unclear whether there are best practices in sample collection, storage, and processing procedures for the collection of the highest quality mRNA. Research Aim: We aim to review current practices in the collection, storage, and processing of human milk relevant for its use in transcriptomic applications (using mRNA) in the last 10 years. Method: The PubMed database was systematically searched for publications addressing methodological considerations or the use of mRNA derived from human milk samples. Results: Most sources described the collection of human milk from small cohorts of term mothers in a mature lactational stage. While fresh collection of human milk was common, some was frozen or preserved. Several centrifugation protocols exist, and considerations for collection, storage, and processing may vary by transcriptomic application. There is inconsistency in the description and reporting of mRNA quality used in analyses that obfuscates the determination of best practices for best mRNA quality. Conclusions: Research into the effects of human milk collection, processing, and storage on mRNA quality metrics is warranted.