Abstract: Objective To study the expression of VEGF and the microvascular density in breast cancer tissue of mice transfected with IL-23（mIL-23）and to examine whether the expression of VEGF is affected by IL-23 gene transfection.MethodsIL-23 gene was transfected into two packing cell lines（ecotropic ψ2 and amphotropic PA317）,respectively,with a retrovirus vector（LXSN）.Positive cellular clones that can produce retroviruses carrying IL-23 gene were screened by G418.Retroviruses were used to transduce the mIL-23 gene into mouse mammary cancer cells（MA-891）.After screened by G418,IL-23/MA-891 cells expressing IL-23 protein were obtained.Expression of IL-23 protien in IL-23/MA-891 cells was detected by ELISA.Proliferation of MA-891,LXSN/MA-891 and IL-23/MA-891 cells was detected by MTT in vitro.Three kinds of inoculated tumor were harvested on day 30 after s.c injection.Expression of mRNA and protein of VEGF was detected by RT-PCR and immunohistochemistry.Microvascular density（stained with CD34）in the grafted tumor tissues was detected by immunohistochemistry,observed under optical microscope and the value of MVD was calculated.ResultsIn the IL-23 gene-transfected tumor group,the expression of mRNA and protein of VEGF was lower than that in LXSN/MA-891 and MA-891 groups.Meanwhile,the microvascular density was lower in IL-23/MA-891 tumor cell group（18.23±6.92）than in LXSN/MA-891 group（36.13±10.40）and MA-891 group（38.16±12.30,P＜0.01）.ConclusionIL-23 secreted from IL-23/MA-891 cells exerts its anti-tumor effect by reducing the expression of VEGF and MVD,and by inhibiting the angiogenesis in tumors.