【Objective】To investigate the efficacy of oncolytic herpes simplex virus (HSV) vector

G47Δ for the treatment of the human breast cancer through the observation of cytotoxicity on human primary breast cancer cells and its stem cells in vitro. 【Methods】 Human primary breast cancer cells and breast cancer stem cells from 6 breast invasive ductal carcinoma samples were cultured and inoculated with G47Δ of two different multiplicities of infection (MOI)

MOI=0.01 and MOI=0.1. The condition of cell growth was observed every day. G47Δ contained the LacZ gene

and expression in infected cells was detected with X-gal histochemistry. 【Results】 It was confirmed that G47Δ can multiply and disseminate in breast cancer cells with X-gal histochemistry. G47Δ was cytotoxic for human primary breast cancer cells and breast cancer stem cells in vitro

but the cytotoxicity for human primary breast cancer cells was stronger than its stem cells. X-gal staining of infected tumor cells in vitro illustrated the replication and spread of the virus. In the MOI=0.01 group and 0.1 group

on the fourth day after infection

91% and 96% human primary breast cancer cells were killed

43% and 78% human primary breast cancer stem cells were killed. In the MOI = 0.01 and MOI = 0.1 group

on the sixth day after infection

the killing rates of human primary breast cancer cells were nearly 100% in both groups; the killing rates of human primary breast cancer stem cells were 92% and 98%

respectively. 【Conclusions】 Oncolytic herpes simplex virus (HSV)vector G47Δ was effective at killing human primary breast cancer cells and breast cancer stem cells in vitro. Breast cancer cells were more sensitive to G47Δ than its stem cells.