[Expression of human lymphotoxin gene in CHO-DHFR- cells]

A recombinant plasmid p91-HuLT was constructed with a human lymphotoxin (HuLT) gene 2.4 kb EcoRI fragment and a mammalian cell expression vector plasmid p91023. The HuLT EcoRI DNA fragment covers entire coding sequence and some 3(1) non-translated region sequence of the gene, p91-HuLT DNA was used to transfect Chinese hamster cell line CHO-DHFR- cells by using calcium phosphate-DNA coprecipitation method, and DHFR+ transfectants were obtained. RNA dot blot hybridization analysis showed 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 constitutively synthesize and secrete the HuLT with the cytotoxic activity of at least 200 units per mL of medium.