A genetic approach to the generation of antibodies with enhanced catalytic activities

A hydrolytic catalytic antibody, generated against a nitrophenyl phosphonate transition state analogue, has been cloned and expressed in Escherichia coli for use as a model system to demonstrate the feasibility of using genetic selections to enhance catalytic activity. Conditions were found that permit the secretion of active recombinant antibody into the periplasm of a strain of E. coli deficient in the biotin biosynthetic genes (delta bio-gal). A number of substrates were synthesized that, upon hydrolysis by the antibody, yield free biotin, which is required for cell growth. The substrates and selections can be used to identify mutants of the antibody with altered activities. This approach should be generalizable to a wide number of hydrolytic reactions including the selective cleavage of peptide, polysaccharide, phosphodiester, and ester bonds.

Biologic properties of a CH2 domain-deleted recombinant immunoglobulin

Monoclonal antibody (MAb) B72.3 reacts with TAG-72, a high-molecular-weight mucin expressed on several types of human carcinoma, and is currently being used in clinical trials for the diagnosis and therapy of human carcinoma. An expression construct containing cDNA encoding an immunoglobulin (Ig) heavy chain, with the variable region of murine MAb B72.3 and a human Ig constant region with a deletion of the CH2 domain, was generated. Immunoglobulin from the transfectoma with the highest expression of the TAG-72 immunoreactive antibody was designated MAb chimeric (c) B72.3 delta CH2. The pharmacokinetics of serum clearance of iodine-labeled MAbs cB72.3 delta CH2 and the intact cB72.3 were compared in athymic mice. By 24 hr, less than 1% of the cB72.3 delta CH2 was left in the plasma, while 36% of the cB72.3 still remained. The T1/2 alpha values of the cB72.3 delta CH2 and cB72.3 MAbs were 1.7 and 2.4 hr, respectively. The T1/2 beta values were 7.8 hr for the domain-deleted cMAb and 48.9 hr for cB72.3. Biodistribution studies in athymic mice bearing LS-174T xenografts showed a reduction in the percentage of injected dose per gram in tumor with 131I-cB72.3 delta CH2; however, the 131I-cB72.3 delta CH2 both localized to tumors faster and cleared from the blood faster than the 125I-cB72.3 MAb. Only trace amounts of the 131I-cB72.3 delta CH2 were detected in normal tissues, including kidney. The faster clearance rate, more rapid tumor targeting and lack of metabolic uptake in normal tissues demonstrated with the iodine-labeled CH2 domain-deleted cMAb may be an advantage for certain clinical protocols.

Efficient production of a functional single-chain antidigoxin antibody via an engineered Bacillus subtilis expression-secretion system

We have applied a Bacillus subtilis expression-secretion system to produce a functional antidigoxin SCA (single-chain antibody consisting of VL-linker-VH) and the individual variable domains of light (VL) and heavy (VH) chains. The secreted antidigoxin SCA can be affinity purified in one step by applying the culture supernatant directly to a ouabain-Sepharose column. N-terminal sequence determination indicated that the protein has the expected N-terminus with the signal peptide properly processed. Affinity and ligand specificity studies demonstrated that the engineered antidigoxin SCA has almost identical properties as those of the parental monoclonal antibody. The use of B. subtilis WB600, an engineered, six-extracellular protease-deficient strain, is vital for the production of antidigoxin SCA in high quality and quantity (5 mg/liter in a shake flask culture). All the secreted SCAs are biologically active. The ability to produce secreted SCAs by the B. subtilis expression system provides a simple and efficient means to analyze the binding properties of engineered antibodies generated through rational design or site-directed mutagenesis.

Isolation and preparation of antisera to ovine IgE

Elevated levels of ovine reaginic antibody were induced by immunization with Ascaris suum antigens. The PCA activity of this antibody persisted in the skin of sheep for 20 days and was abolished by heating to 56 degrees C, suggesting that it was immunoglobulin E. Attempts to isolate IgE from this hyperimmune serum by gel filtration, ion exchange and affinity chromatography resulted in the preparation of a PCA-positive fraction containing proteins with molecular weights of 70, 56 and 22 kD on SDS-PAGE. This preparation was used to raise an antiserum in a rabbit to IgE which was rendered specific by absorption. An antiserum to the heavy chain of ovine IgE was also raised in a rabbit by immunization with a fraction prepared from the 68- to 80-kD region of SDS-PAGE by excision and electroelution. Both antisera were positive in reverse cutaneous anaphylaxis tests and recognized a single protein with a molecular weight of 70-72 kD on SDS-PAGE immunoblotting. The presence of this protein in reaginic sheep serum, the molecular weight of its heavy chain, its heat lability and long-term skin-sensitizing ability are characteristic of IgE.

Construction and purification of domain-deleted immunoglobulin variants of the recombinant/chimeric B72.3 (y1) monoclonal antibody

Chimeric antibodies have been produced against a pancarcinomic tumor associated antigen, TAG-72, by fusing the genes for the variable region of mouse MAb B72.3 to the genes for the constant region of human IgG. In our efforts to optimize the pharmacokinetics of plasma clearance and the efficiency of tumor localization and penetrance of cB72.3, we have now developed truncated versions of immunoglobulin heavy chains. The domain-deleted antibodies are produced by transfecting cells that produce chimeric kappa chains with expression vectors that encode chimeric heavy chains lacking the sequences that encode the CH2 domain, CH3 domain, or both. Despite the absence of these domains, the transfectomas secrete H2L2 tetramers with appropriate antigenic specificity. All the domain-deleted immunoglobulins can be purified by chromatography on Protein G Sepharose which binds to a site on the Fab region that is retained in the domain-deleted antibodies. The CH2CH3 domain-deleted immunoglobulin produced in cell culture is analogous in size to enzymatically produced F(ab')2.

Expression and characterization of hepatocyte growth factor receptor-IgG fusion proteins. Effects of mutations in the potential proteolytic cleavage site on processing and ligand binding

The receptor for hepatocyte growth factor (HGF) is the product of the c-met proto-oncogene, a membrane-spanning tyrosine kinase receptor. To facilitate analysis of HGF and its receptor (HGFr), we expressed and purified a chimeric protein containing the extracellular domain (ECD) of the HGFr fused to the constant region of IgG heavy chain. This soluble form of the HGFr (sHGFr) bound HGF with an affinity similar to that of the authentic, membrane-associated receptor. The sHGFr also neutralized the binding of HGF to the HGFr expressed on A549 cells. Like the mature form of the HGFr, sHGFr is a heterodimer which arises by proteolytic processing within the ECD. In order to characterize the requirements for proteolytic processing of the ECD and the effects of cleavage on ligand binding, we expressed sHGFr variants containing amino acid substitutions in the putative processing site. Replacement of the P1 or P4 arginine, but not the P3 lysine, with alanine inhibited conversion to the alpha/beta heterodimer. This suggests that maturation is mediated by furin or a furin-like protease. Finally, we showed that processing of the sHGFr into the alpha/beta form is not required for high affinity binding to either pro- or mature HGF.

Immunoaffinity chromatography in biorecovery: an application of recombinant DNA technology to generic adsorption processes

The constant region of human kappa light chain (Ck) was linked to Escherichia coli beta-galactosidase, using standard molecular cloning techniques. The binding of Ck-beta-galactosidase fusions to a number of different murine monoclonal antibodies, specific for Ck, was improved by the insertion of spacers between Ck and beta-galactosidase: a cleavable linker was then introduced. Over-expressed Ck-beta-galactosidase fusion protein was purified using monoclonal antibodies immobilised on Sepharose 4B. Elution conditions were found that maintained beta-galactosidase activity so purified enzyme could be released on breaking the cleavable linker. A number of practical problems associated with maintaining stable fusion proteins and immunoaffinity column performance were identified.

Beta 2-microglobulin gene is mutated in a human colon cancer cell line (HCT) deficient in the expression of HLA class I antigens on the cell surface

The human colon cancer cell line HCT does not express any detectable HLA class I antigens on the cell surface. RNA blot analyses showed that HCT cells synthesize easily detectable levels of heavy chains as well as beta 2-microglobulin (beta 2m) transcripts. Experiments of immunoprecipitation revealed the presence of intracellular HLA heavy chains and the absence of beta 2m molecules. Sequencing studies, performed on polymerase chain reaction-mediated amplification of beta 2m-specific complementary DNAs, indicated that in HCT cells both beta 2m genes are mutated. The first mutation consists of an 11-base deletion, corresponding to the first 11 base pairs of the second exon of the beta 2m gene. This mutation alters the reading frame, starting from the third amino acid residue of the mature beta 2m protein, resulting in the synthesis of a 31-amino acid peptide with no remarkable homology to any of the sequences stored in the protein database. The second mutation is a point mutation (C----A), resulting in a UAA stop codon corresponding to the 10th amino acid residue of the mature beta 2m. Therefore, it would appear that in HCT cells the beta 2m genes have undergone two different mutational changes. This is the first molecular demonstration of beta 2m mutations in a human epithelial cell line.

Immunoglobulins secreted by a hybrid-hybridoma: analysis of chain assemblies

In addition to the bispecific antibody, the hybrid-hybridoma 28.19.8 secretes antibodies monospecific for carcinoembryonic antigen (CEA) and antibodies monospecific for vinca alkaloids. By exhaustive affinity purification, the immunoglobulins isolated by Protein A chromatography from ascitic fluid have been fractionated into four populations, three of which are immunoreactive. Studies on these fractions by FPLC, SDS-PAGE, and a variety of ELISAs have shown that seven of the ten possible combinations of heavy and light chains exist as immunoreactive forms. The results suggest that the other three inactive combinations are also secreted by the hybrid-hybridoma.

Propagation of a mouse myeloma cell line J558L producing human CD4 immunoglobulin G1

Transfected mouse myeloma cells are of increasing interest for the production of a wide variety of solubilised recombinant fusion proteins. A stably transfected J558L mouse myeloma subclone (J558L-CD4) secreting human CD4-immunoglobulin type G1 receptor (CD4-H gamma 1) was employed as a model system for cell suspension culture and expression of chimaeric molecules. Cells were grown up to 3-5 x 10(6) cells/ml in serum-free and protein-reduced DHI medium consisting of a mixture of DMEM, HamF12 and IMDM media supplemented with transferrin, insulin, Primatone RL and Pluronic F68. Primatone RL was the essential growth-promoting factor in protein-free medium. The soluble CD4-H gamma 1 receptor, the production of which was not growth-associated, accumulated in the medium to concentrations of 40 micrograms/ml with a specific formation rate of 0.18 micrograms/10(6) cells/h in conventional cultures. The cell density was further increased by growing the cells in dialysis tubing or by using a perfusion system with cell retention. Because of the continuous exchange of nutrients and metabolic end-products average concentrations of 35 x 10(6) cells/ml were achieved. CD4-H gamma 1 accumulated in the dialysis tubing up to 1.3 mg/ml. After an initial rapid growth period, a ten-fold reduction in specific nutrient consumption rates and metabolic end-product formation was observed. Chimaeric proteins purified by protein G chromatography from conventional and perfusion cultures were indistinguishable when compared by SDS-PAGE, limited proteolysis and isoelectric focusing analysis (isoelectric point: 8.5-8.6).

Protection against endotoxic shock by a tumor necrosis factor receptor immunoadhesin

Tumor necrosis factors (TNF) alpha and beta are structurally related cytokines that mediate a wide range of immunological, inflammatory, and cytotoxic effects. During bacterial infection of the bloodstream (sepsis), TNF-alpha induction by bacterial endotoxin is thought to be a major factor contributing to the cardiovascular collapse and critical organ failure that can develop. Despite antibiotic therapy, these consequences of sepsis continue to have a high mortality rate in humans. Here we describe a potent TNF antagonist, a TNF receptor (TNFR) immunoadhesin, constructed by gene fusion of the extracellular portion of human type 1 TNFR with the constant domains of human IgG heavy chain (TNFR-IgG). When expressed in transfected human cells, TNFR-IgG is secreted as a disulfide-bonded homodimer. Purified TNFR-IgG binds to both TNF-alpha and TNF-beta and exhibits 6- to 8-fold higher affinity for TNF-alpha than cell surface or soluble TNF receptors. In vitro, TNFR-IgG blocks completely the cytolytic effect of TNF-alpha or TNF-beta on actinomycin D-treated cells and is markedly more efficient than soluble TNFR (24-fold) or monoclonal anti-TNF-alpha antibodies (4-fold) in inhibiting TNF-alpha. In vitro, TNFR-IgG prevents endotoxin-induced lethality in mice when given 0.5 hr prior to endotoxin and provides significant protection when given up to 1 hr after endotoxin challenge. These results confirm the importance of TNF-alpha in the pathogenesis of septic shock and suggest a clinical potential for TNFR-IgG as a preventive and therapeutic treatment in sepsis.

Preparation of the Fv fragment from a short-chain mouse IgG2a anti-dansyl monoclonal antibody and use of selectively deuterated Fv analogues for two-dimensional 1H NMR analyses of the antigen-antibody interactions

The Fv fragment, a univalent antigen-binding unit with a molecular weight of 25,000, has successfully been prepared in high yield by limited proteolysis with clostripain of a short-chain mouse IgG2a anti-dansyl monoclonal antibody in which the entire CH1 domain is deleted [Igarashi, T., Sato, M., Takio, K., Tanaka, T., Nakanishi, M., & Arata, Y. (1990) Biochemistry 29, 5727-5733]. The Fv fragment obtained is stable at room temperature and retains its full antigen-binding capability. It has been shown that selective deuterium labeling of the Fv fragment, which is half the size of the Fab fragment, provides 1H NMR spectral data at a sufficient resolution for a detailed structural analysis of the antigen-combining site. NOESY spectra of an Fv analogue, in which all aromatic protons except for His C2'-H and Tyr C3',5'-H had been deuterated, were measured in the presence of varying amounts of dansyl-L-lysine. On the basis of the NOESY data obtained, it was possible to assign all the ring proton resonances for the dansyl group that is bound to the Fv fragment. It was also possible to obtain information about His and Tyr residues of the Fv fragment in the absence and presence of the antigen. On the basis of the NMR data obtained, we have shown that at least two Tyr residues along with one of the amide groups are directly involved in antigen binding. The mode of interaction of the dansyl ring with these residues in the Fv fragment has briefly been discussed.

Immunoglobulin heavy-chain-associated amyloidosis

Immunoglobulin- or multiple myeloma-associated amyloidosis has been distinguished by the tissue deposition of Congophilic, fibrillar protein consisting of light chains or light-chain fragments (AL amyloidosis). We now report the isolation and characterization of another form of immunoglobulin-associated amyloid obtained from a patient who had extensive systemic amyloidosis and in whom the amyloid deposits consisted not of light chains but rather of an unusual form of heavy chain. This component, isolated from splenic amyloid extracts, represented an internally deleted IgG1 heavy chain as evidenced by immunochemical, electrophoretic, and amino acid sequence analyses. A comparable immunoglobulin-related monoclonal protein, consisting only of IgG heavy chains, was present in the patient's urine. Based on serologic reactivity with a battery of anti-immunoglobulin antisera, these two immunoglobulin-related components were antigenically identical; however, when compared to normal IgG, both were deficient in Fc-associated gamma-chain determinants. The structural abnormality of the amyloid gamma-chain protein was further evidenced by SDS/PAGE and immuno-blotting analyses: An unusually low molecular mass of approximately 22 kDa was found for this material vs. the expected value of approximately 55 kDa for a normal gamma heavy chain. Despite the lack of certain Fc determinants, the amyloid and urinary heavy-chain proteins expressed the IgG1 subclass allotype marker G1m(a) located on the third constant region (CH3) domain of the internally deleted IgG1 heavy chains. That the amyloid protein contained an intact CH3 domain was established through amino acid sequence analyses of cyanogen bromide fragments and peptides generated by a lysine-specific protease. These studies also revealed that the gamma-chain amyloid protein contained the complete heavy-chain variable (VH) domain [including the diversity (DH) and joining (JH) segments] that was contiguous with the CH3 domain. The low molecular mass of the protein resulted from the total absence of the first (CH1), hinge, and second (CH2) heavy-chain constant regions. Such extensive CH deletions and the presence of a complete VH distinguish this amyloid-associated heavy chain from all other heretofore characterized gamma-heavy-chain disease proteins. This heavy-chain-related form of immunoglobulin-associated amyloidosis is tentatively designated AH amyloidosis.

Bacterial expression of antibody fragments that block human rhinovirus infection of cultured cells

Human rhinoviruses are the major causative agents of the common cold in humans and have been divided into major and minor groups based on receptor specificity. cDNAs encoding the light and heavy chains of a murine monoclonal antibody that recognizes the major group receptor were cloned, abundantly expressed in Escherichia coli, and renatured into Fab fragments that blocked virus binding and protected HeLa cell monolayers from rhinovirus infection. Elimination of the cysteines normally bridging the heavy and light chains yielded molecules indistinguishable from wild-type Fab fragments in virus binding assays. Single-chain antibodies with covalently linked light and heavy variable domains were also expressed and showed receptor binding and cell protection activities. These recombinant antibody fragments are potentially useful in preventing or treating common colds in humans.

Clonal diversity, somatic mutation, and immune memory to phosphocholine-keyhole limpet hemocyanin

Group II antibodies to phosphocholine (PC)-keyhole limpet hemocyanin in BALB/c mice are genetically diverse and of a defined binding phenotype which recognizes the hapten, phenyl-PC, and PC coupled to protein but not free PC. We sequenced the V regions of 14 kappa and lambda-bearing group II antibodies. Both types show extensive somatic mutations. The pattern of the mutations differs between kappa and lambda antibodies. The nature of the somatic mutation in lambda chains suggests strong Ag selection on the L chain but not the H chain of the lambda-bearing antibodies. The reverse pattern of selection was observed among kappa-containing antibodies wherein the accumulation of replacement mutations in the CDR of the H chain appears to result from selection while changes in the L chain appear unselected. From these findings it appears that somatic mutation plays a major role in anti-PC-keyhole limpet hemocyanin memory development because all 14 antibodies displayed changes from germ-line sequences.

A chimeric mouse-human antibody that retains specificity for HIV gp120 and mediates the lysis of HIV-infected cells

Murine mAb BAT123, which was made against the envelope glycoprotein gp120 of HTLV-IIIB strain of HIV type 1 (HIV-1), is capable of neutralizing HTLV-IIIB in vitro. It also inhibits the fusion between uninfected CD4+ cells and HIV-1-infected cells to form syncytia. As a step to explore the potential utility of the anti-HIV antibody in vivo, we have constructed a mouse-human chimeric antibody by rDNA techniques. The chimeric antibody, which bears the variable domains of mouse antibody BAT123 and constant domains Cr1 and C kappa of human Ig retains the Ag specificity of BAT123 as determined by its reactivity with HIV-1-infected H9 cells, gp120 in Western blot analysis, and the oligopeptide recognized by BAT123. The antiviral activities of the chimeric antibody in neutralizing HIV-1 infection as well as inhibiting the syncytia formation are also found identical to those of the parent murine antibody. Moreover, in the presence of human blood mononuclear cells, the chimeric antibody but not BAT123 (mouse IgG1) induces antibody-dependent cellular cytotoxicity. The findings point to the potential usefulness of the chimeric antibody in treating patients infected with HIV-1.

Sequence and fine specificity analysis of primary 511 anti-phosphorylcholine antibodies

The primary antibody response of mice to phosphorylcholine (PC) is dominated by antibodies using the T15 L chain. Anti-PC antibodies using the 511 L chain are prominent only in secondary responses to PC coupled to proteins, are somatically mutated, and all have an extra amino acid at the Vh-D junction, compared with T15 antibodies. The aim of the experiments reported here was to determine if the extra junctional amino acid alone was sufficient to generate a 511 PC-binding antibody, or if somatic mutation or other junctional changes were also necessary. We also wished to determine if unmutated 511 antibodies had sufficient affinity for PC to appear in the primary response. To increase the frequency of primary 511 antibodies, we generated a series of hybridomas from M167 L chain transgenic mice immunized 4 days earlier with either Streptococcus pneumonia R36a or PC-keyhole limpet hemocyanin (KLH). We determined the relative affinity of the antibodies, and sequenced their H chain V regions. The results showed that: 1) somatic mutations are not required for 511 antibodies to bind PC; 2) primary 511 antibodies all had lower relative affinities for PC than T15 while having similar affinities to T15 for TNP-aminophenyl PC, and higher affinities for the PC analogs nitrophenyl PC and choline; 3) all antibodies had the 511-specific insertion of an extra amino acid, usually Ala, at the VhD junction, compared with T15; 4) immunization with R36a, but not PC-hemocyanin, elicited antibodies with a specific Tyr----Asp substitution in the D region, indicating Ag selection based on fine specificity differences; 5) the total length of CDR3 was conserved in most anti-PC-hemocyanin antibodies, whereas the anti-R36a antibodies predominantly had longer CDR3 sequences; and 6) there were unique substitutions in most antibodies, including significant sequence heterogeneity in the D-Jh junction. We conclude that Ag selection on the basis of affinity for PC biases the primary anti-PC response in favor of T15, and that 511 precursors with their alternative fine specificities contribute the precursors that are expanded in the secondary anti-PC-KLH responses.

The productive gene for alpha-H chain disease protein MAL is highly modified by insertion-deletion processes

alpha-H chain diseases (HCD) is a human lymphoproliferative disorder, characterized by the production of truncated alpha-Ig H chains, without associated L chains. In this study, we have analysed the serum protein, the alpha-HCD mRNA and the rearranged alpha-HCD gene from the leukemic cells of a patient (MAL) with alpha-HCD. The abnormal MAL serum Ig consisted of short alpha 1-chains, lacking VH and CH1 domains (only CH2 and CH3 domains were present). The alpha-HCD mRNA (1.2 kb) was shorter than a normal alpha-mRNA (2 kb); the corresponding cDNA had sequences for the leader, a 84-bp sequence of unknown origin and the CH2 and CH3 exons. The establishment of the sequence of the productive alpha-HCD MAL allele revealed two major deletions; that of the VH region as well as that of the CH1 region. The JH region is altered by multiple mutations, small insertions and a duplication of the psi JH3 region. A large insert (INS1), of 360 bp (containing the 84 bp exon found in the cDNA), replaces the deleted VH region. INS1 is non-Ig related and apparently of nongenomic origin. A large second insert (509 bp), is located between the enhancer and the switch region. Insert2 contains repetitive non-Ig-related sequences and a small Ig-related sequence. All these alterations resulted in an abnormal mRNA, which comprises the leader, a 84-bp alien exon derived from INS1 and the CH2 and CH3 exons of the alpha 1-gene.

Molecular analysis of clonal stability and longevity in B cell memory

We used the antiphosphocholine response induced by Proteus morganii and an adoptive transfer protocol to study the contribution of individual clones to B cell memory. Spleen cells from donor mice immunized with P. morganii were injected into irradiated hosts. These recipients were then immunized and their spleen cells fused 12 to 14 wk thereafter. The sequences of hybridoma VH and VL were obtained and DNA rearrangements at both V region loci were studied to ascertain clonal relationships. In all three adoptive transfer experiments, each mouse of a pair receiving cells from the same donor contained hybridomas which were clonally related to each other. In two of these experiments paired recipients possessed cells that had identically mutated V genes. These results lead us to conclude that once a B cell clone(s) dominates a response, progeny of that clone form the memory cell population for many months. Moreover, stability appears to be generated in some memory B cells through inactivation of the hypermutation mechanism.

Nucleotide sequence of channel catfish heavy chain cDNA and genomic blot analyses. Implications for the phylogeny of Ig heavy chains

Our prior analyses defined the cDNA sequence on part of the CH2 domain, the complete CH3 and CH4 domains, and the 3'-untranslated region of a catfish H chain. To complete the catfish H chain mRNA sequence, a primer-extended H chain cDNA library was constructed. Analysis of this library has resulted in the definition of full-length clones encoding a 61-bp 5' untranslated region, a 51-bp leader sequence, the V region and the complete CH1 and CH2 domains. The high similarity defined with other vertebrate V regions readily allowed the catfish sequence to be divided into FR and CDR regions. Sequence comparisons with mammalian VH and JH genes strongly suggest that the catfish V region is the product of multiple genes. Using a catfish VH cDNA probe, at least 25 different genomic VH members were defined. Because this probe does not hybridize with other full-length H chain cDNA clones, additional VH families will likely be defined in catfish. Phylogenetic sequence comparisons of the catfish C region domains indicated that the CH1 and CH4 were the most highly conserved. In addition several important features were defined in genomic Southern blot analyses of catfish DNA. Gene titration experiments established that the catfish CH gene is represented by a single genomic copy. This finding provides clear evidence that the genomic organization of H chain genes in catfish must be different from that defined in sharks and suggests that the phylogeny of single copy CH genes may have been established at the level of the bony fishes. It is also likely that there is an additional CH gene in catfish. This gene is also represented by a single genomic copy, and based upon its relative signal intensity when compared with the known CH gene it appears to share higher similarity with the known CH1 domain than it does with the CH2 domain.

Absence of Ig V region gene somatic hypermutation in advanced Burkitt's lymphoma

Somatic hypermutation of rearranged Ig V region gene plays a major role in generating antibody diversity. Recently, V mutation has been established as a major mechanism of tumor escape from anti-Id immunotherapy. We cloned and sequenced the expressed Ig H and L chain V regions from a case of B acute lymphoblastic leukemia in order to evaluate B cell stages associated with V region mutation, and to determine which tumors would be better suited to Id directed immunotherapy. A consensus VH and V lambda sequence representing tumor at diagnosis was obtained by conventional cDNA cloning in lambda gt10 from a heterohybridoma. Primers which flanked both V regions were used in a modified polymerase chain reaction to generate multiple independent sequences from tumor cells harvested at relapse. In order to exclude mutations due to infidelity of the amplification procedure, single cDNA templates of known sequence were also amplified. The polymerase chain reaction proved to be an effective procedure to obtain multiple clones, but replication in M13 was associated with a low rate of base misincorporation. The results indicate that there is no evidence for biologically significant ongoing mutation in this t(8;14) B cell tumor when comparing sequences at diagnosis and relapse. Thus, V somatic mutation may be restricted to a discrete B cell stage whose malignant counterpart is follicular lymphoma.

Clonal characterization of the human IgG antibody repertoire to Haemophilus influenzae type b polysaccharide. II. IgG antibodies contain VH genes from a single VH family and VL genes from at least four VL families

To define the V gene family repertoire of human IgG anti-Haemophilus influenzae type b polysaccharide antibodies, we purified six IgG1 and nine IgG2 anti-Hib-PS antibodies to monoclonality from immune serum of six individuals and performed N-terminal amino acid sequence analysis. Of the 15 clonal antibodies we examined, all H chain V regions were of the VHIII family. In contrast, the L chains of these antibodies were clearly from at least four different VL families; VKI, VKII, VKIII, and V lambda. Interestingly. VL family expression correlated with the cross-reactivity of these antibodies to the capsular carbohydrate of Escherichia coli K100. VKII antibodies did not cross-react, whereas antibodies expressing V lambda, VKI, or VKIII generally cross-reacted. We conclude that L chain V regions are very important contributors to the limited heterogeneity in this antibody repertoire.

Interspersion of the VHQ52 and VH7183 gene families in the NFS/N mouse

Deletion mapping analysis has shown that members of the VH7183 and VHQ52 gene families are interspersed in the NFS/N mouse. To obtain direct evidence that members of these gene families are physically linked, an NFS/N liver library was constructed and genomic clones were analyzed for hybridization to both VHQ52 and VH7183 gene probes. Four clones were identified which contained both VHQ52 and VH7183 hybridizable restriction fragments. Two clones containing rearranged VHQ52 genes were also found to hybridize with the VH7183 gene probe. Sequence analysis of three of the VH7183-containing restriction fragments indicate that all are pseudogenes which contain interruptions at either the 5' and/or 3' ends of the VH coding region. Given the D-proximal location of at least a portion of the VHQ52 gene family relative to VH7183 in NFS/N mice, and the known correlation between D proximity and the frequency of VH gene utilization, 22 NFS/N-derived pre-B cell lines were analyzed for VHQ52 gene utilization. More than 40% of the identified H chain (VHDJH) rearrangements in this survey used members of this gene family. Furthermore, analysis of poly(A)+ RNA from NFS/N fetal liver and adult spleen also indicates preferential utilization of VHQ52 family in fetal liver. Kinetic studies show, however, that there are no changes in relative utilization throughout fetal ontogeny. The implications of these findings for the expression and randomization of the VH repertoire are discussed.

Nucleotide sequences of eight human natural autoantibody VH regions reveals apparent restricted use of VH families

Eight full length cDNA were isolated from EBV transformed human PBL derived from different normal individuals. Five were derived from antibodies with the characteristics of natural polyreactive antibodies. Three were either monoreactive or bireactive. The most striking feature of the structure of these molecules was their utilization of VH families. Although three used the large VHIII family and one used the large VHI family, the other four used genes derived from two of the recently defined small human VH families VHIV and VHV. Three of the molecules represent VHIV expressed sequences and one is the first example of a VHV gene used in an antibody of defined specificity. The nucleotide sequences of some of the molecules were remarkably similar in their VH gene segments to previously described VH genes. The data suggest that natural autoantibodies may use a restricted portion of the VH repertoire, and, in addition, that some polyreactive antibodies may be germ line encoded. The implication of these findings for the origin and diversity of the human B cell repertoire is discussed.