Interleukin-2 (IL-2), as an important cytokine in immune response, has been demonstrated to have therapeutic activity in several cancer models. In our previous study, we showed that the pBV22210 vector containing a chloramphenicol resistance gene and the cryptic plasmid, pMB1, from the Bifidobacterium longum (B. longum) strain could stably replicate and did not significantly affect the biological characteristics of B. longum. In this study, B. longum was transfected by electroporation with pBV22210 containing IL-2 (B. longum-pBV22210-IL-2), its growth curve was determined, and its inhibitory effect on tumor xenografts in mice was examined. The results showed that B. longum‑pBV22210‑IL-2 reduced the tumor size and prolonged the survival time of H22 tumor-bearing mice. In addition, when cyclophosphamide (CTX), B. longum‑pBV22210‑endostatin, or B. longum-pBV22210‑TRAIL was combined with B. longum-pBV22210-IL-2, the antitumor effect was significantly enhanced. The survival times of the mice in the combination groups of B. longum-pBV22210-endostatin or B. longum-pBV22210-TRAIL were longer than those of the mice in the B. longum-pBV22210-IL-2 alone group. However, when CTX was added, the survival times of the mice showed no statistically significant difference compared with those of the mice in the dextrose-saline solution group. These results suggest that B. longum-pBV22210-IL-2 has potent antitumor effects that could be enhanced when combined with chemotherapeutic drugs or other antitumor genes.

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