The present invention refers to an immunosuppression-reverting oligonucleotide hybridizing with a nucleic acid sequence of tryptophan-2,3-dioxygenase (TDO) and a pharmaceutical composition comprising such immunosuppression-reverting oligonucleotide and a pharmaceutically acceptable carrier, excipient and/or diluent. The oligonucleotide and the pharmaceutical composition, respectively, is used in a method for preventing and/or treating an autoimmune disorder, an immune disorder, a psychiatric disorder and/or cancer.