Use of antibody gene library for the isolation of specific single chain antibodies by ampicillin-antigen conjugates

Single-step colony assay for screening antibody libraries

We describe a method, single-step colony assay, for simple and rapid screening of single-chain Fv fragment (scFv) libraries. Colonies of Escherichia coli expressing the scFv library are formed on a hydrophilic filter that is positioned in contact with a membrane coated with an antigen. scFv expression is triggered upon treatment of colonies with an induction reagent, following which scFvs are secreted from the cells and diffused to the antigen-coated membrane. scFvs that exhibit binding affinity for the antigen are captured by the membrane-immobilized antigen. Lastly, detection of scFv binding of the antigen on the membrane allows identification of the clones on the filter that express antigen-specific scFvs. We tested this methodology by using an anti-rabbit IgG scFv, scFv(A10B), and a rat immune scFv library. Experiments conducted using scFv(A10B) revealed that this method improves scFv expression during the colony assay. By using our method to screen an immune library of 3×10³ scFv clones, we established several clones exhibiting affinity for the antigen. Moreover, we tested 7 other antigens, including peptides, and successfully identified positive clones. We believe that this simple procedure and controlled scFv expression of the single-step colony assay could make the antibody screening both rapid and reliable and lead to successful isolation of positive clones from antibody libraries.

How to avoid pitfalls in antibody use

Antibody use is ubiquitous in the biomedical sciences. However, determining best research practices has not been trivial. Many commercially available antibodies and antibody-conjugates are poorly characterized and lack proper validation. Uncritical application of such useless tools has contributed to the reproducibility crisis in biomedical research. Despite early initiatives such as MIAPAR or PSI-PAR, a best practice guideline for antibody characterization is still not in prospect. Here, we analyze 24 antibody-related databases and compare their content with regard to validation aspects and coverage. We also provide a flowchart for end-users with all necessary steps to facilitate finding and choosing specific and sensitive antibodies for their experiments. Based on a growing demand for better and standardized validation procedures and characterization guidelines for antibody molecules we have summarized our findings in a five-point plan. We intend to keep the discussion alive and hope that properly used antibodies will remain as central to biomedicine as they are today.