Peter Liljeström and colleagues at Karolinska Institutet performed seminal work in the early 1990s on development of mRNA replicon vaccine technology based on the Semliki Forest virus genome. Since then, the platform has been extensively developed and tested and now represents a robust and versatile vaccine platform that can be rapidly mobilised against emerging pathogens.


The platform is based on a fully synthetic, self-replicating RNA molecule. This RNA replicon encodes the genes for the viral RNA replicase but lacks the genes coding for the structural proteins of the virus. Instead, the replicon will carry the gene(s) encoding the antigen of interest (Fig 1). When delivered into cells during vaccination, this recombinant RNA molecule will replicate in the same fashion as it would during an alphavirus infection with the difference that new virus particles are not formed. Cell-intrinsic responses to RNA replication provoke immune signaling, thus acting as a natural adjuvant such that an appropriate response is generated. Broad and vigorous adaptive immune responses that engage both the humoral and cellular arms of the immune system are induced. Memory responses are long-lasting with high potential of re-call.

The platform has been extensively evaluated in animal models, including mice, domestic livestock, non-human primates, and in clinical trials in humans (ongoing). Infectious disease models include Toxoplasma gondii and influenza, louping ill, respiratory syncytial, chikungunya, Ebola, hepatitis C, Zika and human immunodeficiency viruses, as well as SARS-CoV-2. For all (except HIV and HCV, where it was not investigated) challenge models were able to demonstrate complete protection from disease.


These self-replicating vaccines can be delivered as naked DNA (DREP) or RNA (RREP). Furthermore, this platform can be implemented as a rapid response to sudden outbreaks of emerging diseases as all its components ranging from disease target (antigen) identification and vaccine vector construction are fully synthetic. This makes this platform robust, allergen and contaminant-free, customizable, fully controllable, and low-cost. It also makes the vaccine components of the platform highly stable and safe and large numbers of vaccine doses can easily and rapidly be produced. Thus, vaccine production times could be reduced by years, making the platform ideal as a defense against emerging viruses.


Current Work

In 2019, Prof Liljeström’s research group merged with that of Prof McInerney. We are working with a number of partners (see below) to develop the system for better antigen expression, immunogenicity and exploring state-of-the-art delivery methods.


Collaboration Partners

The European HIV Alliance (EHVA)

HDT Bio 

International Vaccine Institute


Fig 1. Schematic illustration of alphavirus replicon vaccines. Top, an infectious cDNA clone of an alphavirus showing the replicase and structural genes encoded by separate viral RNAs. To make a general self-replicating vaccine vector, the structural genes of the virus are replaced by the foreign antigen, which is placed under the viral subgenomic promoter (black arrow). In the cell cytoplasm, these vectors amplify the recombinant viral RNA (by virtue of the encoded replicase) however no virus particles are formed and there is thus no possibility to spread infection. When the cDNA is placed on a plasmid under the SP6 promoter (RREP), in vitro transcription is used to produce large amounts of full-length RNA replicons. The RREP is directly administered for immunization as naked RNA. When replicon vaccine constructs are to be delivered as naked DNA replicon (DREP), the construct is placed under the CMV promoter.