Response of cultured mammalian cells to diphtheria toxin. IV. Isolation of KB cells resistant to diphtheria toxin.

KB cell strains which are resistant to the lethal effects of diphtheria toxin were isolated from the toxin-sensitive KB cell line. For one such strain, KB-R2, the concentration of diphtheria toxin required to cause a 50% reduction of incorporation of amino acids into protein was more than 2,000 times that required in the sensitive KB-S cell. The KB-R2 strain was cloned by a single-cell isolation method to yield uniform strains with an even greater resistance to toxin. Resistance is a stable, inheritable property, providing a good genetic marker, and appears to be related to some alteration in the cell membrane. Preliminary studies showed that these cell strains are resistant to poliovirus and vesicular stomatitis virus as well as to toxin.