a silent single nucleotide substitution the dna fragment encoding the transmembrane and cytoplasmic domains of epor was then used to replace the portion of pvegfr2bgl encoding the transmembrane and cytoplasmic domains of vegfr2 thus a single reading frame was generated which encoded the chimeric receptor consisting of the vegfr2 extracellular domain and the epor transmembrane and cytoplasmic domains the dna fragment encoding the chimeric receptor was subcloned into the expression vector pbos and co transfected into the ba f3 cell line with plasmid pgk neo at a ratio of 1 20 cells expressing the vegfr2 epor protein were selected by flow cytometry analysis using a monoclonal antibody to the vegfr2 extracellular domain mab 4h3 this monoclonal antibody is described in australian patent application no pm 3794 filed 10 feb 1994 cell lines expressing higher levels of vegfr2 epor were selected by growing the cells in 5 u03bcg ml mab 4h3 or 25 ng ml of recombinant vegf a cell line expressing high levels of vegfr2 epor designated ba f3 nyk epor was used for the bioassay the ba f3 nyk epor cells described above were washed three times in pbs to remove all il 3 and resuspended at a concentration of 1000 cells per 13.