Isolation of antigen specific Llama V-HH antibody fragments and their highlevel secretion by Saccharomyces cerevisiae

Recently the existence of 'heavy chain' immunoglobulins in Camelidae has be en described. However, as yet there is no data on the binding of this type of antibody to haptens. In addition, it was not a priori predictable whethe r the binding domains (V-HH) of these antibodies could be produced and secr eted by the lower eukaryotic micro-organism Saccharomyces cerevisiae. In th e present study these questions are addressed. Heavy chain immunoglobulins directed against two hapten molecules, the ate-dyes RR6 and RR120 as well a s the (proteinaceous) human pregnancy hormone, have been raised in Lama gla ma. We were able to select specific V-HH fragments for all three antigens b y direct screening of Escherichia coli or yeast libraries, even without pri or enrichment via bio-panning. This is the first example of the isolation o f llama anti-hapten V-HH domains. Surprisingly, the affinities of the llama V(HH)s for the RR6 hapten obtained in this way are in the low nM range. Fu rthermore, some of the antigen specific V(HH)s were secreted by S. cerevisi ae at levels over 100 mg l(-1) in shake flask cultures. These two findings extend the possible application areas for the llama V-HH fragments signific antly. (C) 2000 Elsevier Science B.V. All rights reserved.