The present invention provides use of an isolated RNA molecule comprising: a) an alphavirus 5' replication recognition sequence, wherein at least one initiation codon has been removed from the 5' replication recognition sequence； b) a nucleotide sequence encoding an alphavirus structural protein； and c) an alphavirus 3' replication recognition sequence, with the proviso that the RNA molecule does not contain a promoter that directs transcription of the nucleotide sequence of (b), and wherein the alphavirus 5' and 3' replication recognition sequences of (a) and (c) direct replication of the RNA molecule in the presence of alphavirus nonstructural proteins in inducing an immune response in a subject or for use in immunizing a subject or for treating a subject.
