Self-amplifying RNAs (saRNAs) can be used for vaccination, protein therapy and to engineer cell-based therapies. However, saRNAs are very stressful for cells as they cause strong inflammation, which triggers flu-like side effects in vaccinees. To unlock the full potential of saRNA vaccines, saRNA that are less stressful for cells are needed. Messenger RNA-based protein therapy has recently been explored to address the limitations of current approved viral-based protein therapies and cell therapies. However, the use of mRNA as an alternative to viral-based therapies presents some challenges. First, non-replicating mRNAs only express proteins for a short period of time (1-2 weeks). On the other hand, saRNAs, which cause a much longer expression period (4 to 8 weeks), are currently not a clinical options as they are too inflammatory. This IOF-project aims to make saRNAs with improved properties.