Expression and characterization of biologically active human Fas ligand produced in CHO cells

We describe an expression system for high-yield production of recombinant soluble human FasL (rsh- FasL) in CHO cells. After one round of selection for gene amplification, cell lines producing rsh-FasL up to 60 microg/L x 10(6) cells in 24 h were obtained. Cell lines were grown in protein-free medium as suspension cultures. The protein secreted into growth medium was purified by immunoaffinity. The rsh-FasL thus obtained was further fractionated by gel filtration and a form of approx 140 kDa was isolated and characterized. Mass spectral analysis yielded a main peak of 28,321.15 Da, while, although to a lesser extent, dimeric and trimeric forms were also detected according to the described oligomerized state of native FasL. Our procedure permits consistent production of biologically active rsh-FasL as shown in tests on FasL-sensitive cells and in in vitro binding assays.