Objective To study the inhibitory effect of T lymphocytes secreting EphrinAl-Caspase-3 in vivo and on the growth of cancer cells in nude mice with breast cancer. Methods Nude mice (n = 35) were inoculated with breast cancer cells to construct a nude mouse model of breast cancer. When the tumor volume reached 0. 1 cm3, 30 nude mice with average size tumor tissue were randomly divided into PBS group, uninfected adenovirus group, T lymphocyte infected with Ad-EphrinAl-Caspase-3 group, and intratumoral transplantation. Tumor size was measured every day 2 to 3. Three groups of tumor-bearing nude mice were selected. After the above-mentioned cell transplantation, the subcutaneous tumor tissue homogenate was obtained every day 2 to 3, and the content of EphrinAl-Caspase-3 was detected by ELISA. At the end of the experiment, the animals in each group were sacrificed by cervical dissection and sliced. The presence of T lymphocytes expressing green fluorescent protein was observed under a fluorescence microscope, and Caspase-3 and Ki-67 were detected by immunofluorescence. Results After one week of inoculation of breast cancer cells into nude mice, the presence of subcutaneous tumors could be touched by hand, which proved that the tumor-bearing animals of breast cancer cells were successfully modeled. On the 8th day after inoculation, the tumor volume of the nude mice in each group became larger, and the difference between the treatment group and the PBS group/T lymphocyte group was extremely significant ( P<0.05). Although the tumor volume of the T lymphocyte transplantation group was slower than that of the PBS control group, there was no statistically significant difference between the two. The expression of EphrinAl-Caspase-3 was detected in the EphrinAl-Caspase-3 treatment group on the 2nd day, reached the peak on the 8th day, and then the secretion decreased gradually. No expression of EphrinAl-Caspase-3 was detected in the PBS control group and the T lymphocyte group. The presence of dispersed green fluorescent protein-labeled EphrinAl-Caspase-3-T lymphocytes was observed in the tumor tissues of the treatment group, while the presence of green fluorescent protein was not detected in the PBS group and the T lymphocyte groups. In the infected cells of the treatment group, the proportion of Caspase-3 positive cells was up- regulated, and the proportion of Ki-67 positive cells was down-regulated. No expression of EphrinAl-Caspase-3 was detected in the PBS group and the T lymphocyte group. Conclusion EphrinAl-Caspase-3 can significantly inhibit the growth of breast cancer cells, thereby exerting an anti-tumor effect.