SURFACE DISPLAY OF A FUNCTIONAL SINGLE-CHAIN FV ANTIBODY ON STAPHYLOCOCCI

Two different host-vector expression systems designed for fell surface display of chimeric receptors on Staphylococcus xylosus and Staphyloc occus carnosus have been evaluated for surface display of a mouse immu noglobulin G1(kappa) [IgG1(kappa)] anti-human IgE single-chain Fv (scF v) antibody fragment. To achieve surface anchoring of the chimeric rec eptors containing the scFv, the cell surface attachment regions from S taphylococcus aureus protein A were used in both expression systems. T he different chimeric receptors could be recovered from cell wall extr acts of both S. xylosus and S. carnosus, and surface localization was demonstrated by taking advantage of a serum albumin-binding reporter r egion present within the two types of receptors. In addition, the two different recombinant staphylococci carrying hybrid receptors containi ng the scFv were demonstrated to react with the antigen, which was hum an IgE, in whole-cell enzyme-linked immunosorbent assays. This is the first report of an antibody fragment expressed in a functional form an chored to the surface of gram-positive bacteria. The potential use of recombinant gram-positive bacteria as whole-cell diagnostic devices or alternatives to filamentous phages for surface display of scFv librar ies is discussed.