DHFR and plasma cell myeloma: The main cell types are used in this system include Chinese hamster ovary (CHO) cells, various mouse myelomas such as NS0 murine myeloma cells, baby hamster kidney (BHK) cells, insect SF-9 cell line, green monkey kidney cells and human cell lines such as human embryonic kidney (HEK) cells.56 The mEs and tagged-fusion-mEs (his6-mEs) were produced by CHO cells via inserting cDNA of endostatin in upstream of the amplifiable marker gene, dihydrofolate reductase (DHFR).