An expression system, comprising: a first nucleic acid molecule having a cell-specific promoter； a second nucleic acid molecule which encodes a transcriptional activator； a third nucleic acid molecule having a first recognition sequence of the transcriptional activator； a fourth nucleic acid molecule having a first promoter and a first regulatory element； a fifth nucleic acid molecule which encodes a first regulatory protein； a sixth nucleic acid molecule having a second recognition sequence of the transcriptional activator； a seventh nucleic acid molecule having a second promoter and a second regulatory element； an eighth nucleic acid molecule which encodes a second regulatory protein； as well as a ninth nucleic acid molecule which is configured to conditionally inhibit the expression of the first regulatory protein, and a tenth nucleic acid molecule which is configured to conditionally inhibit the expression of the second regulatory protein； the first regulatory element is adapted to inhibit the function of the first promoter by means of binding to the second regulatory protein, and the second regulatory element is adapted to inhibit the function of the second promoter by means of binding to the first regulatory protein.
