Selection of recombinant antibody-producing E. coli cells by means of toxin conjugates

The toxicity of hapten–toxin conjugates can be neutralized by steric hindrance using antibodies or other molecules binding to the hapten part of the conjugates. This principle was proven by neutralization of the growth-inhibiting effect of fluorescein–ampicillin and biotin–ampicillin conjugates on E. coli cells after binding of the anti-fluorescein antibody B13-DE1 or streptavidin to the corresponding conjugates. In addition to that E. coli cells producing a single-chain B13-DE1 antibody fragment (scFv B13-DE1) are resistant to the growth-inhibiting effect of a fluorescein–ampicillin conjugate, and scFv B13-DE1-producing E. coli cells can be selected out of a majority of E. coli cells producing other single-chain antibody fragments. This principle offers therefore a general possibility for the selection of cells producing antibodies or other binding molecules.