The primary antibody repertoire of normal, immunodeficient and autoimmune mice is characterized by differences in V gene expression

Facile Discovery of a Diverse Panel of Anti-Ebola Virus Antibodies by Immune Repertoire Mining

The ongoing evolution of Ebolaviruses poses significant challenges to the development of immunodiagnostics for detecting emergent viral variants. There is a critical need for the discovery of monoclonal antibodies with distinct affinities and specificities for different Ebolaviruses. We developed an efficient technology for the rapid discovery of a plethora of antigen-specific monoclonal antibodies from immunized animals by mining the VH:VL paired antibody repertoire encoded by highly expanded B cells in the draining popliteal lymph node (PLN). This approach requires neither screening nor selection for antigen-binding. Specifically we show that mouse immunization with Ebola VLPs gives rise to a highly polarized antibody repertoire in CD138(+) antibody-secreting cells within the PLN. All highly expanded antibody clones (7/7 distinct clones/animal) were expressed recombinantly, and shown to recognize the VLPs used for immunization. Using this approach we obtained diverse panels of antibodies including: (i) antibodies with high affinity towards GP; (ii) antibodies which bound Ebola VLP Kissidougou-C15, the strain circulating in the recent West African outbreak; (iii) non-GP binding antibodies that recognize wild type Sudan or Bundibugyo viruses that have 39% and 37% sequence divergence from Ebola virus, respectively and (iv) antibodies to the Reston virus GP for which no antibodies have been reported.

Diversity of the antibody response to tetanus toxoid: comparison of hybridoma library to phage display library

Monoclonal antibodies are important tools in research and since the 1990s have been an important therapeutic class targeting a wide variety of diseases. Earlier methods of mAb production relied exclusively on the lengthy process of making hybridomas. The advent of phage display technology introduced an alternative approach for mAb production. A potential concern with this approach is its complete dependence on an in vitro selection process, which may result in selection of V(H)-V(L) pairs normally eliminated during the in vivo selection process. The diversity of V(H)-V(L) pairs selected from phage display libraries relative to an endogenous response is unknown. To address these questions, we constructed a panel of hybridomas and a phage display library using the spleen of a single tetanus toxoid-immunized mouse and compared the diversity of the immune response generated using each technique. Surprisingly, the tetanus toxoid-specific antibodies produced by the hybridoma library exhibited a higher degree of V(H)-V(L) genetic diversity than their phage display-derived counterparts. Furthermore, the overlap among the V-genes from each library was very limited. Consistent with the notion that accumulation of many small DNA changes lead to increased antigen specificity and affinity, the phage clones displayed substantial micro-heterogeneity. Contrary to previous reports, we found that antigen specificity against tetanus toxoid is encoded by both V(κ) and V(H) genes. Finally, the phage-derived tetanus-specific clones had a lower binding affinity than the hybridomas, a phenomenon thought to be the result of random pairing of the V-genes.

IgG variable region and VH CDR3 diversity in unimmunized mice analyzed by massively parallel sequencing

Most antigen-specific mouse antibodies have been derived by hybridoma technology, predominantly through use of the Balb/c strain. Much of the Balb/c germline repertoire of variable genes (V regions) is known. However, there is little information about the background expressed repertoire of IgG antibodies in mice, which reflects the baseline against which antigen-specific antibodies are generated through immunization. To assess this baseline repertoire, RNA was isolated from splenic B-cells enriched for expression of IgG from three mice. The RNA was individually amplified with three distinct PCR primer sets for comprehensive recovery of the heavy and light chain variable regions. Each PCR product was independently subjected to deep sequencing using 454 pyro-sequencing technology and analysed for redundancy, open reading frame, germline representation, and CDR3 sequence of the heavy chain variable region (VH CDR3) within and across the primer sets and mice. A highly skewed abundance of heavy and light chain variable gene usage was observed for all three primers in all three mice. While showing considerable overlap, there were differences among these profiles indicative of primer bias and animal-to-animal variation. VH CDR3 sequences were likewise highly skewed indicating that the heavy chain genes profiles substantially reflected individual antibodies. This observation was confirmed through analysis of randomly selected complete heavy chain variable sequences. However, there was very little redundancy in VH CDR3 sequences across the different mice. We conclude that the background IgG repertoire in young, unimmunized mice is highly skewed within individual mice and is diverse among them, a pattern similar to that observed in highly immunized mice.

Antibodies in a heavy chain knock-in mouse exhibit characteristics of early heavy chain rearrangement

Studies in autoantibody transgenic mice have demonstrated receptor editing rearrangements at Ab H and L chain loci. However, the physiologic role of H chain editing (V(H) replacement and rearrangement on the second allele) has been called into question. It is unclear if additional rounds of H chain rearrangement are driven by BCR specificity. In this study, we analyze the manner in which B cells undergo additional H chain rearrangements in an anti-DNA H chain knock-in mouse, B6.56R. We find that rearrangements in 56R(+) B cells tend to involve the D gene locus on both alleles and the most J(H)-proximal V(H) gene segments on the endogenous allele. As a result, some B cells exhibit V(D)J rearrangements on both H chain alleles, yet allelic exclusion is tightly maintained in mature 56R B cells. As B cells mature, a higher proportion expresses the nontransgenic H chain allele. Rearrangements on both H chain alleles exhibit junctional diversity consistent with TdT-mediated N-addition, and TdT RNA is expressed exclusively at the pro-B cell stage in B6.56R. Collectively, these findings favor a single, early window of H chain rearrangement in B6.56R that precedes the expression of a functional BCR. B cells that happen to successfully rearrange another H chain may be favored in the periphery.

Age-related loss of bone marrow pre-B- and immature B-lymphocytes in the autoimmune-prone flaky skin mutant mice

Defective B-lymphopoiesis has been associated with development of auto-antibodies and auto-immunity in a number of autoimmune-prone strains of mice. The flaky skin (fsn) mutation results in development of chronic inflammation and auto-immunity. Associated with the development of auto-immunity is the hyperactivation of B-lymphocytes and production of auto-antibodies. We, therefore, undertook a detailed examination of B-lineage precursors in the bone marrow of fsn/fsn mice. We observed a rapid age-related loss of the pre-B and immature B cells. It was also noted that an accumulation of early precursor populations occurs coincident with the loss of Fr.D and Fr.E bone marrow B cell populations indicating a developmental block or accumulation of pro-B cells in 7 and 10 week old fsn/fsn mice. Our data suggests changes in the fsn/fsn bone-marrow microenvironment that results in senescence of B cell development.

Production of recombinant ScFv antibodies against methamidophos from a phage-display library of a hyperimmunized mouse

A recombinant phage display library was generated using splenocyte mRNA isolated from a Balb/c mouse hyperimmunized with a hapten conjugate that mimicked the structure of methamidophos, one of the most acutely toxic organophosphate pesticides. Three recombinant single-chain variable fragment (scFv) antibodies with the highest specificity for methamidophos, termed 28D4, 29D0, and 36B2, were produced via a stringent selection protocol. In a competitive enzyme-linked immunosorbent assay, the IC50 values for 28D4, 29D0, and 36B2 were 46.25, 35.39, and 17.99 ng/mL, respectively. The cross-reactivity of the three scFv antibodies with other organophosphate pesticides was below 0.1% except for acephate (O,S-dimethyl acetylphosphoramidothioate). Nucleotide and deduced amino acid sequences indicated that the respective heavy chains and light chains of the three scFvs were involved in the distinctive VDJ segment rearrangements associated with somatic hypermutations during the process of several immunizations with higher dosages of immunogen. Taken together, these data constitute the first detailed description of an immunoassay that utilizes scFvs against the methamidophos, an analyte with a simple structure and low molecular mass (141 Da).

Characterisation of the immunoglobulin variable region gene usage encoding the murine anti-ganglioside antibody repertoire

Neuropathogenic murine antibodies reactive with terminal disialylgalactose epitopes are innate and preferentially encoded by the VH7183.3b gene. Here we have studied antibodies reactive with internal galactose-linked disialosyl epitopes and the terminal trisaccharide of GT1b. Antibodies were of moderate affinity and unmutated. Anti-GD1b antibodies were often encoded by the VH10.2b heavy and gj38c light chain genes. Anti-GT1b antibodies with broader glycan binding patterns were encoded by VHQ52 and VHJ558 family genes. These data indicate that the discrete specificities of ganglioside-binding antibodies are dictated by particular patterns of V gene usage residing within the innate B cell repertoire.

The inhibitory Fcgamma receptor modulates autoimmunity by limiting the accumulation of immunoglobulin G+ anti-DNA plasma cells

Deletion of the gene encoding the Fc immunoglobulin G receptor IIB (FcgammaRIIB) results in a fulminant, lupus-like disease in C57BL/6 but not BALB/c mice. Here we have investigated this strain-specific, epistatic loss of tolerance using gene-targeted immunoglobulin variable heavy-chain (V(H)) alleles 3H9 or 56R, which encode DNA-specific heavy chains, expressed on the C57BL/6 or BALB/c background. The combination of C57BL/6 and V(H) 56R (B6.56R) resulted in a loss of tolerance; hybridoma and single-cell analysis indicated an FcgammaRIIB-independent difference in immunoglobulin light-chain usage, consistent with an alteration in receptor editing. FcgammaRIIB deficiency resulted in an increase in immunoglobulin G (IgG) antibodies to DNA in the serum, an increased frequency of anti-DNA-reactive IgG(+) B cells with a plasma cell phenotype and immune complex deposition in the glomeruli and renal disease in B6.56R mice. Thus, FcgammaRIIB provides a distal peripheral checkpoint to limit the accumulation of autoreactive plasma cells, thereby maintaining tolerance.

Characterization of an antibody Fv fragment that binds to the human, but not to the rat neurotensin receptor NTS-1

The cDNAs coding for the heavy and light chain variable domains of an antibody, recognizing the human G-protein-coupled receptor for neurotensin, NTS-1, were obtained from a hybridoma cell line, B-N6. The Fv B-N6 fragment was expressed in Escherichia coli and purified. To characterize the properties of the antibody fragment, human and rat high-affinity neurotensin receptors were expressed in E. coli in functional form, linked at their N-termini to the maltose-binding protein. Fv B-N6 was found to compete for [3H]neurotensin binding to the human neurotensin receptor, but not to the rat neurotensin receptor, with IC50 values of 1.6 microM (membrane-bound receptor) and 1.9 microM (detergent-solubilized, purified receptor). The formation of a relatively stable complex of Fv B-N6 with purified human neurotensin receptor fusion protein was also demonstrated by gel filtration experiments. The Fv B-N6 fragment will be used to isolate a high-affinity binder to the human neurotensin receptor as a valuable tool for cocrystallization and receptor structure determination.

Synthesis of ligand-specific phage-display ScFv against the herbicide picloram by direct cloning from hyperimmunized mouse

Immunoglobulin genes were directly isolated from the splenocytes of a BALB/C mouse hyperimmunized with the auxinic herbicide picloram conjugated to bovine serum albumin. Variable light and heavy domain DNA were joined to produce single-chain Fv (scFv) DNA, which was cloned into phage vector fd-tet-GIIID to display multiple copies of scFv on the filamentous phage minor coat protein gIIIp. The phage-display scFv library (10(4) clones) was selected against picloram conjugated to ovalbumin. After five rounds of panning, individual clones were analyzed. ScFv with different affinities to picloram (IC(50) values ranging from 20 ppb to 10 ppm) were detected in the final enriched pool. The increased avidity of the phage vector enhanced the selection (i.e., panning) of multiple picloram-specific recombinant antibodies. Stringent selection was required to isolate the clones with the highest affinity. Nucleotide sequence analysis of six isolated clones revealed that all of the V(L) belonged to the V kappa 9A family joined to J kappa 2 segments. All of the V(H) belonged to the V(H)()7183 family and joined to two different J segments (i.e., J(H)()2 or J(H)()4). Different from the immune response to large molecular weight molecules (MW > 10,000 Da), which requires both VDJ segment rearrangement and somatic hypermutations, production of high-affinity antibodies to picloram, a small ligand having a formula weight of 241.5 Da, predominantly requires somatic hypermutations.

V lambda-light chain genes reconstitute immune responses to defined carbohydrate antigens or haptens by utilizing different VH genes

The contribution of the lambda-light chain to the development of peripheral B cell repertoire and generation of specific antibodies to haptens and polysaccharide antigens was studied in genetically manipulated kappa-deficient and lambda 2-transgenic mice. The results clearly demonstrate a non-stoichiometric VH gene family expression in the absence of k-light chain and suggest a non-stochastic pairing between VH and V lambda genes, expressed in the peripheral B cell repertoire. A shift in VH gene utilization in the case of VI lambda + antibodies was evident in response to beta 2-6 fructosan and TNP hapten. These observations demonstrate the availability of compensatory mechanisms in the absence of VK genes and are consistent with the hypothesis that VH gene family expression is controlled by genetic factors from inside the VH locus. Furthermore, genetic factors from outside the VH locus, namely restricted available light chain diversity, may lead to a shift in VH gene utilization in the peripheral B cell repertoire.