Efficient selection of scFv antibody phage by adsorption to in situ expressed antigens in tissue sections

The present report describes the development and application of an efficient method for the direct adsorption/selection of antibody phage using antigens expressed in situ in cryostat tissue sections. In a model system, scFv phage directed towards an epitope on the GA733-2 epithelial glycoprotein expressed in colorectal carcinoma tissue could be specifically enriched up to 1500 fold in single-pass experiments and a million fold after three rounds of selection. Enrichment efficacy was directly proportional to the fraction of antigen positive area over the total area. Sufficient enrichment was achieved at an area fraction of less than four percent, thereby permitting the selection of antibodies to sub-populations of cells or to tissue sub-structures. The general usefulness of the method was demonstrated when a combinatorial scFv antibody phage library derived from melanoma immunized non-human primates was selected in tissue sections of metastatic melanoma. Individual scFv antibodies from enriched phage populations demonstrated different binding specificities, reflected in extracellular and cellular tissue staining patterns which included tumor cell surface reactivity. This method should be particularly useful for the identification of antigens which are only expressed during specific in vivo conditions, and overcomes a major limitation of currently used selection protocols.