Recombinant arterivirus replicon systems and uses thereof

A nucleic acid molecule comprising a nucleotide sequence encoding a modified equine arterivirus genome or replicon RNA, wherein the modified equine arterivirus genome or replicon RNA comprises:

• a sequence encoding an arterivirus replicase;
• an expression cassette comprising a transcriptional regulatory sequence (TRS) operably linked to a sequence encoding a gene of interest;
• a sequence fragment encoding an equine arterivirus open reading frame ORF7, wherein said sequence fragment is devoid of an ATG start codon or comprises an inactivated ATG start codon;
• a mutated T7 transcriptional termination signal sequence comprising a nucleotide substitution selected from the group consisting of T9001G, T3185A, G3188A and combinations of any two or more thereof;
• and
• one or more spacer regions operably positioned adjacent to the TRS;
• wherein the modified equine arterivirus genome or replicon RNA does not comprise an equine arterivirus open reading frame ORF2a.