Abstract： Objective To develop a BP26 recombinant BCG (rBCG-BP26) vaccine,and to observe the effects of rBCG-BP26 on CD4+,CD8+ T cells in immunized mice.Methods The recombinant shuttle vector pMV261-Ag85B-BP26 was constructed by using traditional molecular biological technology.The recombinant strains were obtained by kanamycin resistance screening and PCR identification after electroporation.Western blotting was used to detect the expression of recombinant BP26 vaccine in immunized mice.Safety experiment was carried out in three different groups:the target experiment(rBCG-BP26) group,the positive control(BCG) group and the negative control(PBS) group,15 BALB/c mice in each group.Intradermal inoculations of 100 μl rBCG-BP26 [containing 106 colony forming units(CFU)],BCG,and PBS were carried out,respectively.Signs of mice in each group were observed.After immunization for 10,20,30,and 40 days,body weight was weighed,and tail blood was collected to observe the change of peripheral blood CD4+ and CD8+ T cells by flow cytometry.Results The rBCG-BP26 was successfully constructed.The expression of BP26 protein was detected in the liquid medium and the bacteria cells.The results of safety test analysis showed that there were no significant differences in signs and body weights(F=2.468,0.331,1.520,0.739,all P＞ 0.05),between PBS group[ (19.24 ± 0.54),(21.37 ± 0.66),(22.83 ± 0.62),(25.06 ± 0.37)g],BCG group[ (19.90 ± 0.02),(21.53 ± 1.57),(21.95 ± 0.55),(24.70 ± 0.39)g]and rBCG-BP26 group[ (19.16 ± 0.55 ),(20.89 ± 0.20),(22.15 ± 0.76),(24.60 ± 0.64)g].The results of flow cytometry showed that the percentages of CD4+ T cell level were lower in BCG group(26.70％,33.07％) and rBCG-BP26 group( 13.40％,26.70％) than that of the PBS group(33.85％,29.33％) and the values of CD4+/CD8+ T cells increased in rBCG-BP26 group (0.69％,1.27％,1.57％,1.70％ ) 10,20 and 30 days after immunization.Conclusions Recombinant BCG-BP26 vaccine strain can express brucella BP26 protein efficiently.Furthermore,its virulence is mild,and it can activate CD4+,CD8+ T cells in the body.It can be used as one of candidate vaccine strain against brucellosis.