Ribosome display: an in vitro method for selection and evolution of antibodies from libraries

Combinatorial approaches in biology require appropriate screening methods f or very large libraries. The library size, however, is almost always limite d by the initial transformation steps following its assembly and ligation, as other all screening methods use cells or phages and viruses derived from them. Ribosome display is the first method for screening and selection of functional proteins performed completely in vitro and thus circumventing ma ny drawbacks of in vivo systems. We review here the principle and applicati ons of ribosome display for generating high-affinity antibodies from comple x libraries. In ribosome display, the physical link between genotype and ph enotype is accomplished by a mRNA-ribosome-protein complex that is used for selection. As this complex is stable for several days under appropriate co nditions, very stringent selections can be performed. Ribosome display allo ws protein evolution through a built-in diversification of the initial libr ary during selection cycles. Thus, the initial library size no longer limit s the sequence space sampled. By this method, scFv fragments of antibodies with affinities in the low picomolar range have been obtained. As all steps of ribosome display are carried out entirely in vitro, reaction conditions of individual steps can be tailored to the requirements of the protein spe cies investigated and the objectives of the selection or evolution experime nt. (C) 1999 Elsevier Science B.V. All rights reserved.