A bidirectional phage display vector for the selection and mass transfer of polyclonal antibody libraries

Extensive restrictions in the VH sequence usage of the human antibody response against the Rhesus D antigen

Anti-Rhesus D immunoglobulin purified from human sera is used as a prophylactic reagent in Rhesus D negative women at risk of alloimmunization during pregnancy. We are currently developing a Rhesus D antigen-specific recombinant polyclonal antibody drug lead for replacing the existing blood derived-products. By analyzing the RhD-specific antibody VH repertoires from eight alloimmunized women we found, in agreement with previous studies, a strong preference for the VH 3-33 "superspecies" gene segments which encompasses the IGHV3-30-3*01, IGHV3-30*18, and IGHV3-33*01 VH alleles. Even more extensive genetic restriction was observed among five donors, which produced antibodies of identical V-D-J usage and CDR3 loop length and joining regions of similar amino acid composition. In addition, we find a high degree of sequence relatedness to previously isolated anti-Rhesus D antibodies. Such close homology in VH domains indicates that significant structural restrictions are operating in the selection of antibodies recognizing RhD as seen for T cell receptors. Moreover, some VH domains were isolated in their germline configuration indicating that anti-RhD antibodies of relatively high affinity are present in the naïve antibody repertoire of Rhesus negative individuals which offers an explanation for the strong and clinically significant immunogenicity of the Rhesus D.

Isolation of Human Antibody Repertoires with Preservation of the Natural Heavy and Light Chain Pairing

The humoral immune system in higher vertebrates is unique in its ability to generate highly diverse antibody responses against most pathogens as well as against certain malignancies. Several technologies have been developed to exploit this vast source of potentially therapeutic antibodies, including hybridoma technology, phage display and yeast display. Here, we present a novel, high-throughput technology (the Symplex Technology) for rapid direct cloning and identification of human antigen-specific high-affinity antibodies from single antibody-producing cells of immune individuals. The utility of the technology was demonstrated by isolation of diverse sets of unique high-affinity antibodies against tetanus toxoid and influenza virus from immunized volunteers. Hence, the Symplex Technology is a new method for the rapid isolation of high-affinity antibodies directly from humans.

Rapid generation of functional human IgG antibodies derived from Fab-on-phage display libraries

We introduce a procedure for the rapid generation of fully human antibodies derived from "Fab-on-phage" display libraries. The technology is based on the compatibility of display vectors and IgG expression constructs, and allows reformatting of individual Fab clones to IgG, as well as reformatting of antibody repertoires. Examples of batch reformatting of an uncharacterized Fab repertoire and of a pool of Fabs, previously analyzed at the phage level, are presented. The average transient expression levels of the IgG constructs in HEK293T cells are above 10 microg/ml, allowing the use of conditioned media in functional assays without antibody purification. Furthermore, we describe a high-throughput purification method yielding IgG amounts sufficient for initial antibody characterization. Our technology allows the generation and production of antigen-specific complete human antibodies as fast or even faster than raising monoclonal antibodies by conventional hybridoma techniques.

Generation and preliminary characterization of an antibody library with preferential reactivity to human colorectal cancer cells as compared to normal human blood cells

We are developing recombinant polyclonal antibody libraries (PCALs) reactive to human colorectal cancer cells as an anti-cancer therapeutic approach. To test the hypothesis that PCALs with preferential recognition of tumor cells as compared to normal cells could be generated, a Fab phage display library reactive to human colorectal cancer cell lines was absorbed with normal human blood cells. ELISA analysis of the absorbed Fab phage display library showed that 70% of tested clones reacted to colorectal cancer cells. Reactivity of the library to blood cells was reduced 4-10-fold, with many clones unreactive to one or more of the blood cell types. DNA fingerprint analysis of colorectal cancer-binding clones showed that the absorbed library remained polyclonal. The H and L chain V region gene pairs of the absorbed library were transferred in mass from the Fab phage display vector to a mammalian vector and expressed as IgG following transfection into Sp2/0 myeloma cells. ELISA analysis showed that 79% of transfectants expressed IgG and of those 74% were positive for binding to the SW480 human colorectal cancer cell line. A template of 95 SW480-reactive wells was assembled, designated Lib-Col2.1, and IgG purified from a consolidated mass culture. The purified Lib-Col2.1 IgG was compared to the clinically used anti-colorectal cancer mAb 17-1A, by ELISA and flow cytometry, for binding density on SW480 colorectal cancer cells and on normal human blood cells. The results showed that Lib-Col2.1 bound to SW480 cells at higher density than mAb 17-1A and that its binding to normal human blood cells was reduced 2.4-24-fold relative to an unabsorbed anti-SW480 serum. Furthermore, Lib-Col2.1 was more effective than mAb 17-1A at inhibiting the growth of SW480 cells in culture. These results suggest that a polyclonal antibody library with preferential reactivity to cancer cells as compared to normal cells could be generated.

Polyclonal anti-colorectal cancer Fab phage display library selected in one round using density gradient centrifugation to separate antigen-bound and free phage

A combinatorial Fab phage display library generated from antibody variable (V) region genes of BALB/c mice immunized with the human colorectal cancer cell lines SW480, SW948, and SW837, was used to isolate an anti-colorectal cancer library. In an attempt to preserve as many anti-colorectal cancer specificities as possible, the original Fab phage display library was selected for binding to a suspension of the human colorectal cancer cells using density gradient centrifugation, instead of washes, to separate cell-bound and free phage. The method consists of placing the cell-phage mixture on a layer of fetal bovine serum (FBS) which had been overlaid on a "cushion" of percoll density medium in a soft, polyallomer tube. After centrifugation, free phage remain on top of the serum layer, whereas the colorectal cancer cells with bound phage are recovered from the serum-percoll interface with a syringe. Analysis of the selected phage display library by enzyme linked immunosorbent assay (ELISA) and diagnostic restriction enzyme digests of individual members (fingerprinting), revealed about 90% anti-colorectal cancer diverse clones after only one round of selection. After conversion to a library of full-length antibodies, such an anti-cancer polyclonal library could be useful for therapeutic and/or diagnostic applications. The density gradient centrifugation method presented here holds great promise for the generation of polyclonal antibody libraries (PCALs) to complex antigens. It is also applicable for selection of peptide or other phage display libraries on any insoluble ligand.