Creative Biolabs provides high-quality service in phage display antibody library construction and screening. In order to select antibodies with high affinity and specificity, we have developed a series of selection strategies including epitope masking. Blocking the immunodominant epitope is effective in screening a high-afﬁnity Fab which targets the non-dominant epitope on the antigen or has a selective disadvantage.
Phage display technology has offered an efficient route to obtain a diverse set of monoclonal antibodies with the desired specificity. However, the selected Ab clones may only target certain epitope since the epitope is immunodominant or the Abs against that epitope have a selective advantage in the panning process. Therefore, the procedure becomes inefficient and requires screening of a large number of clones for the production of desired specific Abs. Epitope masking strategy can avoid this problem. Fabs or single-chain Abs targeting the corresponding immunodominant epitope will be retrieved from an initial library screening and then be used to block the antigen. With this initial selection of the phage libraries, the following screening refocuses the selection against other epitopes on the masked antigen (Ag).
Creative Biolabs develops this straightforward, effective and amenable strategy to produce Abs with high affinity and specificity. One advantage of this strategy is that it does not require predetermined knowledge about the antigenic epitopes on the Ag and it can be used cumulatively to retrieve Abs recognizing noncompeting epitopes from the same library. In addition, if we know prior knowledge of epitopes to be avoided, we can use already existing intact Abs or other proteins that recognize this epitope as masking reagents, thereby avoiding the initial direct selection of the library. The screening process of this strategy is shown in Fig.1. Firstly, the phage display library is applied to the immobilized antigen. After incubation, unbound phages are washed away, and then the antigen-specific phages are eluted and amplified. If individual clones appear in high frequency in the library or some special epitopes on the antigen are more exposed, certain Abs may dominate Ab clones. These clones are converted to soluble Ab and are used to mask the corresponding epitopes on the Ag before reselection. Since the dominating epitopes are blocked, phage recognizing this site will not bind and be washed away. Instead, minor phage specificities may bind to their epitopes on the Ag. At last, phage Abs have these minor specificities are then eluted and amplified.
Fig.1 Library selection using an epitope-masking strategy (Ditzel 2002).
Creative Biolabs’ scientists have extensive experience in phage display library screening based on epitope masking strategy. It is a valuable approach by which Abs, small proteins, or peptides against minor epitopes from phage libraries can be identified. By masking highly immunogenic epitopes with Abs, we can rescue a broader range of specific Abs from combinatorial libraries, which could be widely applied for various purposes.
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