AIM: To explore the possibility of the replacement of the gag gene between human immunodeficiency virus and bovine immunodeficiency virus, to achieve chimeric virions,and thereby gain a new kind of AIDS vaccine based on BHIV chimeric viruses.METHODS: A series of chimeric BHIV proviral DNAs differing in the replacement regions in gag gene were constructed, and then were transfected into 293T cells. The expression of chimeric viral genes was detected at the RNA and protein level. The supematant of 293T cell was ultra centrifuged to detect the probable chimeric virion. Once the chimeric virion was detected, its biological activities were also assayed by infecting HIV-sensitive MT4 cells.RESULTS: Four chimeric BHIV proviral DNAs were constructed. Genes in chimeric viruses expressed correctly in transfected 293T cells. All four constructs assembled chimeric virions with different degrees of efficiency. These virions had complete structures common to retroviruses and packaged genomic RNAs, but the cleavages of the precursor Gag proteins were abnormal to some extent. Three of these virions tested could attach and enter into MT4 cells, and one of them could complete the course of reverse transcription. Yet none of them could replicate in MT4 cells.CONCLUSION: The replacement of partial gag gene of HIV with BIV gaggene is feasible. Genes in chimeric BHIVs are accurately expressed, and virions are assembled. These chimeric BHIVs (proviral DNA together with virus particles) have the potential to become a new kind of HIV/AIDS vaccine.