Abstract: A recombinant plasmid p91-HuLT was constructed with a human lymphotoxin (HuLT) g ene 2.4kb EcoRI fragment and a mammalian cell expression vector plasmid p91023.T he HuL'T EcoRI DNA fragment covers entire coding sequence and some 3 1 non-trans lated region sequence of the gene.p91-HuLT DNA was used to transfect Chinese ham ster cell line CHO-DHFR- cells by using calcium phosphate-DNA coprecipitation me thod,and DHFR+ trasfectants were obtained RNA dot blot hybridization analysis sh owed that the HuLT mRNA was produced by p91-HuLT in transfectants.The results of MTT dye reduction assay indicated that the DHFR+ cell lines we obtained constit utively synthesize and secrete the HuLT with the cytotoxic activity of at least 200 units per mL of medium.

Key words: Recombinant plasmid p91-Hu LT, Human lymphotoxin (LuLT) gene, Cytotoxic activity, DHFR