Circular RNAs (circRNAs) are single-stranded, covalently closed RNA molecules that widely exist in various organisms. Unlike traditional linear mRNAs, circRNAs lack 5' and 3' ends and are resistant to RNA exonucleases-mediated degradation. Thus, they are more stable both in vivo and in vitro.

For a long time, circRNAs have been considered a long non-coding RNA. The CirCode team recently found that circRNAs can produce functional proteins in a cap-independent manner using IRESs, RNA modifications, or IRES-like elements (ref 1-3). CircRNA is an ideal platform for next-generation mRNA therapies due to its high stability, low immunogenicity, and cell-specific translation.