Objective. To investigate the anti- tumor effects of human single chain interleukin- 12 （hscIL- 12）. Method. pcDNA/ hscIL- 12 recombinant was transfected into human hepatic carcinoma cells （7721 cells） by lipofectin method. The 7721/hscIL- 12 cells which secrete hscIL- 12 stably

were obtained via G418 selection

and in vitro the influence of hscIL- 12 gene transduction on the growth of tumor cells was evaluated by cell cycle analysis. In vivo

genetically engineered 7721 cells （7721/hscIL- 12

7721/pcDNA） and parental cells were implanted into BALB/c nude mice

respectively. 7721/pcDNA and 7721/hscIL- 12 groups were divided into two sub- groups on day 8: one was administered with hPBL twice

6 days at interval; the other was given equal volume of PBS. Mice were sacrificed on day 26

and spleens and tumors were taken out for histologic assay. Results. hscIL- 12 produced stably by 7721/hscIL- 12 cells had bioactivity

and it was proved by Western blot

immunocytochemistry

and in situ hybridization. In vitro

compared with 7721 and 7721/pcDNA

the 7721/hscIL- 12 grew much more slowly. FACS assay showed apparent G1 arrest of 7721/hscIL- 12 cells. In animal experiment

on day 8 after inoculation

the tumors of 7721 and 7721/pcDNA group were up to 5～ 7mm

while those of 7721/hscIL- 12 group were 2～ 4mm.When treated with hPBL

the tumor of 7721/hscIL- 12 group disappeared completely. Histologically

the tumors from 7721/hscIL- 12 without hPBL treatment had numerous lymphocyte infiltration

the tumor cells displayed depression looking

atrophy

focal necrosis and apoptosis

whereas the tumors of 7721 and 7721/pcDNA groups grew thrivingly. Conclusion. hscIL- 12 transduced 7721 cells could induced significant antitumor immune response which resulted in tumor regression totally when the hPBL was inoculated

and also hscIL- 12 has certain effects on mice immune system. These findings suggest that hscIL- 12 and hscIL- 12 gene therapy might have promising prospects in clinical application.