Construction and testing of mouse--human heteromyelomas for human monoclonal antibody production

Hybridoma technology a versatile method for isolation of monoclonal antibodies, its applicability across species, limitations, advancement and future perspectives

The advancements in technology and manufacturing processes have allowed the development of new derivatives, biosimilar or advanced improved versions for approved antibodies each year for treatment regimen. There are more than 700 antibody-based molecules that are in different stages of phase I/II/ III clinical trials targeting new unique targets. To date, approximately more than 80 monoclonal antibodies (mAbs) have been approved. A total of 7 novel antibody therapeutics had been granted the first approval either in the United States or European Union in the year 2019, representing approximately 20% of the total number of approved drugs. Most of these licenced mAbs or their derivatives are either of hybridoma origin or their improvised engineered versions. Even with the recent development of high throughput mAb generation technologies, hybridoma is the most favoured method due to its indigenous nature to preserve natural cognate antibody pairing information and preserves innate functions of immune cells. The recent advent of antibody engineering technology has superseded the species level barriers and has shown success in isolation of hybridoma across phylogenetically distinct species. This has led to the isolation of monoclonal antibodies against human targets that are conserved and non-immunogenic in the rodent. In this review, we have discussed in detail about hybridoma technology, its expansion towards different animal species, the importance of antibodies isolated from different animal sources that are useful in biological applications, advantages, and limitations. This review also summarizes the challenges and recent progress associated with hybridoma development, and how it has been overcome in these years to provide new insights for the isolation of mAbs.

Structural Comparison of Human Anti-HIV-1 gp120 V3 Monoclonal Antibodies of the Same Gene Usage Induced by Vaccination and Chronic Infection

Elucidating the structural basis of antibody (Ab) gene usage and affinity maturation of vaccine-induced Abs can inform the design of immunogens for inducing desired Ab responses in HIV vaccine development. Analyses of monoclonal Abs (MAbs) encoded by the same immunoglobulin genes at different stages of maturation can help to elucidate the maturation process. We have analyzed four human anti-V3 MAbs with the same VH1-3*01 and VL3-10*01 gene usage. Two MAbs, TA6 and TA7, were developed from a vaccinee in the HIV vaccine phase I trial DP6-001 with a polyvalent DNA prime/protein boost regimen, and two others, 311-11D and 1334, were developed from HIV-infected patients. The somatic hypermutation (SHM) rates in VH of vaccine-induced MAbs are lower than in chronic HIV infection-induced MAbs, while those in VL are comparable. Crystal structures of the antigen-binding fragments (Fabs) in complex with V3 peptides show that these MAbs bind the V3 epitope with a new cradle-binding mode and that the V3 β-hairpin lies along the antigen-binding groove, which consists of residues from both heavy and light chains. Residues conserved from the germ line sequences form specific binding pockets accommodating conserved structural elements of the V3 crown hairpin, predetermining the Ab gene selection, while somatically mutated residues create additional hydrogen bonds, electrostatic interactions, and van der Waals contacts, correlating with an increased binding affinity. Our data provide a unique example of germ line sequences determining the primordial antigen-binding sites and SHMs correlating with affinity maturation of Abs induced by vaccine and natural HIV infection.IMPORTANCE Understanding the structural basis of gene usage and affinity maturation for anti-HIV-1 antibodies may help vaccine design and development. Antibodies targeting the highly immunogenic third variable loop (V3) of HIV-1 gp120 provide a unique opportunity for detailed structural investigations. By comparing the sequences and structures of four anti-V3 MAbs at different stages of affinity maturation but of the same V gene usage, two induced by vaccination and another two by chronic infection, we provide a fine example of how germ line sequence determines the essential elements for epitope recognition and how affinity maturation improves the antibody's recognition of its epitope.

Ro52 autoantibodies arise from self-reactive progenitors in a mother of a child with neonatal lupus

The detection of cardiac conduction defects in an 18-24 week old foetus in the absence of structural abnormalities predicts with near certainty the presence of autoantibodies against 60kD and 52kD SSA/Ro in the mother regardless of her health status. Previous studies have emphasized these autoantibodies as key mediators of tissue injury. The aim of this study was to focus on the anti-Ro52 response to determine whether these autoantibodies originate from progenitors that are inherently self-reactive or from B-cells that acquire self-reactivity during an immune response. We traced the evolution of two anti-Ro52 autoantibodies isolated from circulating IgG1-switched B-cells from an asymptomatic mother of a child with third degree congenital heart block. The autoantibodies were expressed as their immune form and as pre-immune ancestors by reverting somatic mutations to germline sequence. The reactivity of pre-immune and immune antibodies for Ro52, Ro60, La and DNA was measured. Both anti-Ro52 autoantibodies exhibited a low frequency of somatic mutations (3-4%) and utilised the same heavy and light chain genes but represented distinct clones based on differing complementarity determining region sequences. Pre- and post-immune antibodies showed specific binding to Ro52 with no measurable reactivity for other autoantigens. Ro52 binding was higher for immune antibodies compared to pre-immune counterparts demonstrating that autoreactivity was enhanced by affinity maturation. These data indicate that Ro52 reactivity is an intrinsic property of the germline antibody repertoire in a mother with a pathogenic antibody defined by cardiac injury in her offspring, and implies defects in both central and peripheral tolerance mechanisms.

Comparison of Antibody-Dependent Cell-Mediated Cytotoxicity and Virus Neutralization by HIV-1 Env-Specific Monoclonal Antibodies

Although antibodies to the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein have been studied extensively for their ability to block viral infectivity, little data are currently available on nonneutralizing functions of these antibodies, such as their ability to eliminate virus-infected cells by antibody-dependent cell-mediated cytotoxicity (ADCC). HIV-1 Env-specific antibodies of diverse specificities, including potent broadly neutralizing and nonneutralizing antibodies, were therefore tested for ADCC against cells infected with a lab-adapted HIV-1 isolate (HIV-1NL4-3), a primary HIV-1 isolate (HIV-1JR-FL), and a simian-human immunodeficiency virus (SHIV) adapted for pathogenic infection of rhesus macaques (SHIVAD8-EO). In accordance with the sensitivity of these viruses to neutralization, HIV-1NL4-3-infected cells were considerably more sensitive to ADCC, both in terms of the number of antibodies and magnitude of responses, than cells infected with HIV-1JR-FL or SHIVAD8-EO ADCC activity generally correlated with antibody binding to Env on the surfaces of virus-infected cells and with viral neutralization; however, neutralization was not always predictive of ADCC, as instances of ADCC in the absence of detectable neutralization, and vice versa, were observed. These results reveal incomplete overlap in the specificities of antibodies that mediate these antiviral activities and provide insights into the relationship between ADCC and neutralization important for the development of antibody-based vaccines and therapies for combating HIV-1 infection.

IMPORTANCE

This study provides fundamental insights into the relationship between antibody-dependent cell-mediated cytotoxicity (ADCC) and virus neutralization that may help to guide the development of antibody-based vaccines and immunotherapies for the prevention and treatment of HIV-1 infection.

Use of Human Hybridoma Technology To Isolate Human Monoclonal Antibodies

The human hybridoma technique offers an important approach for isolation of human monoclonal antibodies. A diversity of approaches can be used with varying success. Recent technical advances in expanding the starting number of human antigen-specific B cells, improving fusion efficiency, and isolating new myeloma partners and new cell cloning methods have enabled the development of protocols that make the isolation of human monoclonal antibodies from blood samples feasible. Undoubtedly, additional innovations that could improve efficiency are possible.

Functional implications of the binding mode of a human conformation-dependent V2 monoclonal antibody against HIV

Data from the RV144 HIV vaccine trial indicated that gp120 V2 antibodies were associated with a lower risk of infection; thus, the mapping of V2 epitopes can contribute to the design of an effective HIV vaccine. We solved the crystal structure of human monoclonal antibody (MAb) 2158, which targets a conformational V2 epitope overlapping the α4β7 integrin binding site, and constructed a full-length model of V1V2. Comparison of computational energy stability to experimental enzyme-linked immunosorbent assay (ELISA) results identified a hydrophobic core that stabilizes the V2 region for optimal 2158 binding, as well as residues that directly mediate side chain interactions with MAb 2158. These data define the binding surface recognized by MAb 2158 and offer a structural explanation for why a mismatched mutation at position 181 (I181X) in the V2 loop was associated with a higher vaccine efficiency in the RV144 clinical vaccine trial.

IMPORTANCE

Correlate analysis of the RV144 HIV-1 vaccine trial suggested that the presence of antibodies to the second variable region (V2) of HIV-1 gp120 was responsible for the modest protection observed in the trial. V2 is a highly variable and immunogenic region, and structural information on its antigenic landscape will be important for rational design of an effective HIV-1 vaccine. Using X-ray crystallography, computational design tools, and mutagenesis assays, we carried out a detailed and systematic investigation of the epitope recognition of human V2 MAb 2158 and demonstrated that its epitope region overlaps the integrin binding site within V2. In addition, we propose a structure-based mechanism for mismatching of the isoleucine at position 181 and the increased vaccine efficacy seen in the RV144 vaccine trial.

Thermodynamic signatures of the antigen binding site of mAb 447-52D targeting the third variable region of HIV-1 gp120

The third variable region (V3) of HIV-1 gp120 plays a key role in viral entry into host cells; thus, it is a potential target for vaccine design. Human monoclonal antibody (mAb) 447-52D is one of the most broadly and potently neutralizing anti-V3 mAbs. We further characterized the 447-52D epitope by determining a high-resolution crystal structure of the Fab fragment in complex with a cyclic V3 and interrogated the antigen-antibody interaction by a combination of site-specific mutagenesis, isothermal titration calorimetry (ITC) and neutralization assays. We found that 447-52D's neutralization capability is correlated with its binding affinity and at 25 °C the Gibbs free binding energy is composed of a large enthalpic component and a small favorable entropic component. The large enthalpic contribution is due to (i) an extensive hydrogen bond network, (ii) a π-cation sandwiching the V3 crown apex residue Arg(315), and (iii) a salt bridge between the 447-52D heavy chain residue Asp(H95) and Arg(315). Arg(315) is often harbored by clade B viruses; thus, our data explained why 447-52D preferentially neutralizes clade B viruses. Interrogation of the thermodynamic signatures of residues at the antigen binding interface gives key insights into their contributions in the antigen-antibody interaction.

Cross-neutralizing activity of human anti-V3 monoclonal antibodies derived from non-B clade HIV-1 infected individuals

One approach to the development of an HIV vaccine is to design a protein template which can present gp120 epitopes inducing cross-neutralizing antibodies. To select a V3 sequence for immunogen design, we compared the neutralizing activities of 18 anti-V3 monoclonal antibodies (mAbs) derived from Cameroonian and Indian individuals infected with clade AG and C, respectively. It was found that V3 mAbs from the Cameroonian patients were significantly more cross-neutralizing than those from India. Interestingly, superior neutralizing activity of Cameroonian mAbs was also observed among the nine VH5-51/VL lambda genes encoding V3 mAbs which mediate a similar mode of recognition. This correlated with higher relative binding affinity to a variety of gp120s and increased mutation rates in V3 mAbs from Cameroon. These results suggest that clade C V3 is probably weakly immunogenic and that the V3 sequence of CRF02_AG viruses can serve as a plausible template for vaccine immunogen design.

Mining human antibody repertoires

Human monoclonal antibodies (mAbs) have become drugs of choice for the management of an increasing number of human diseases.  Human antibody repertoires provide a rich source for human mAbs.  Here we review the characteristics of natural and non-natural human antibody repertoires and their mining with non-combinatorial and combinatorial strategies.  In particular, we discuss the selection of human mAbs from naïve, immune, transgenic, and synthetic human antibody repertoires using methods based on hybridoma technology, clonal expansion of peripheral B cells, single-cell PCR, phage display, yeast display, and mammalian cell display.  Our reliance on different strategies is shifting as we gain experience and refine methods to the efficient generation of human mAbs with superior pharmacokinetic and pharmacodynamic properties.

Mining human antibody repertoires

Human monoclonal antibodies (mAbs) have become drugs of choice for the management of an increasing number of human diseases.  Human antibody repertoires provide a rich source for human mAbs.  Here we review the characteristics of natural and non-natural human antibody repertoires and their mining with non-combinatorial and combinatorial strategies.  In particular, we discuss the selection of human mAbs from naïve, immune, transgenic, and synthetic human antibody repertoires using methods based on hybridoma technology, clonal expansion of peripheral B cells, single-cell PCR, phage display, yeast display, and mammalian cell display.  Our reliance on different strategies is shifting as we gain experience and refine methods to the efficient generation of human mAbs with superior pharmacokinetic and pharmacodynamic properties.

Structural basis of the cross-reactivity of genetically related human anti-HIV-1 mAbs: implications for design of V3-based immunogens

Human monoclonal antibodies 447-52D and 537-10D, both coded by the VH3 gene and specific for the third variable region (V3) of the HIV-1 gp120, were found to share antigen-binding structural elements including an elongated CDR H3 forming main-chain interactions with the N terminus of the V3 crown. However, water-mediated hydrogen bonds and a unique cation-pi sandwich stacking allow 447-52D to be broadly reactive with V3 containing both the GPGR and GPGQ crown motifs, while the deeper binding pocket and a buried Glu in the binding site of 537-10D limit its reactivity to only V3 containing the GPGR motif. Our results suggest that the design of immunogens for anti-V3 antibodies should avoid the Arg at the V3 crown, as GPGR-containing epitopes appear to select for B cells making antibodies of narrower specificity than V3 that carry Gln at this position.

Preferential use of the VH5-51 gene segment by the human immune response to code for antibodies against the V3 domain of HIV-1

Human anti-V3 monoclonal antibodies (mAbs) generated from HIV-1 infected individuals display diversity in the range of their cross-neutralization that may be related to their immunogenetic background. The study of the immunoglobulin (Ig) variable region gene usage of heavy chains have shown a preferential usage of the VH5-51 gene segment which was detected in 35% of 51 human anti-V3 mAbs. In contrast, human mAbs against other envelope regions of HIV-1 (anti-Env), including the CD4-binding domain, the CD4-induced epitope, and gp41 preferentially used the VH1-69 gene segment, and none of them used the VH5-51 gene. Furthermore, the usage of the VH4 family by anti-V3 mAbs was restricted to only one gene segment, VH4-59, while the VH3 gene family was used at a significantly lower frequency by all of the analyzed anti-HIV-1 mAbs. Multivariate analysis showed that usage of VH gene segments was significantly different between anti-V3 and anti-Env mAbs, and compared to antibodies from healthy subjects. In addition, the anti-V3 mAbs preferentially used the JH3 and D2-15 gene segments. The preferential usage of selected Ig gene segments and the characteristic pattern of Ig gene usage by anti-V3 mAbs can be related to the conserved structure of the V3 region.

An optimized electrofusion-based protocol for generating virus-specific human monoclonal antibodies

We sought to develop and optimize a hybridoma-based technology for generating human hybridomas that secrete virus-specific monoclonal antibodies for clinical diagnosis and therapy. We developed a novel electrofusion protocol for efficiently fusing Epstein-Barr virus (EBV)-transformed human B cells with myeloma partners. We tested seven myeloma cell lines and achieved highest efficiency when the HMMA 2.5 line was used. We optimized the electrofusion process by improving cell treatments before and after electrofusion as well as varying cell ratios, fusion medium and other experimental parameters. Our fusion efficiency increased remarkably to 0.43%, a significant improvement over the efficiency of previous PEG-based or other electrofusion methods. Using the optimized protocol, we obtained human hybridomas that secrete fully human monoclonal antibodies against two major human respiratory pathogens: respiratory syncytial virus (RSV) and an influenza H3N2 vaccine virus strain. In conclusion, we have developed an efficient and routine approach for the generation of human hybridomas secreting functional human virus-specific monoclonal antibodies.

Cross-clade neutralizing activity of human anti-V3 monoclonal antibodies derived from the cells of individuals infected with non-B clades of human immunodeficiency virus type 1

The majority of global human immunodeficiency virus infections are caused by viruses characterized by a GPGQ motif at the tip of the V3 loop. Characterization of anti-V3 monoclonal antibodies (MAbs) that neutralize isolates with the GPGQ V3 motif is an important step in designing vaccines that will induce such Abs. Consequently, seven human anti-V3 MAbs derived from the cells of individuals infected with non-B-subtype viruses (anti-V3(non-B) MAbs) were generated from the cells of individuals from Africa infected with circulating recombinant forms CRF02_AG, CRF09_cpx, and CRF13_cpx, each of which contains a subtype A env gene. Sequence analysis of plasma viruses revealed a GPGQ motif at the apex of the V3 loop from six of the seven subjects and a GPGR motif from one subject. The MAbs were selected with fusion proteins (FP) containing V3(92UG037.8) or V3(JR-CSF) from subtype A or B, respectively. In virus binding assays, five of the seven (71%) anti-V3(non-B) MAbs bound to V3-FPs from both subtype A and subtype B, while only four of the nine (44%) anti-V3(B) MAbs recognized both V3-FPs. Using two neutralization assays, both the anti-V3(non-B) and the anti-V3(B) MAbs neutralized subtype B viruses with similar activities, while the anti-V3(non-B) MAbs exhibited a tendency toward both increased potency and breadth of neutralization against non-B viruses compared to anti-V3(B) MAbs. Statistical significance was not achieved, due in large measure to the sizes of the MAb panels, but the overall pattern of data strongly suggests that viruses with the GPGQ motif at the tip of the V3 loop induce anti-V3 Abs with broader cross-neutralizing activity than do viruses with the GPGR motif.

The V1/V2 domain of gp120 is a global regulator of the sensitivity of primary human immunodeficiency virus type 1 isolates to neutralization by antibodies commonly induced upon infection

A major problem hampering the development of an effective vaccine against human immunodeficiency virus type 1 (HIV-1) is the resistance of many primary viral isolates to antibody-mediated neutralization. To identify factors responsible for this resistance, determinants of the large differences in neutralization sensitivities of HIV-1 pseudotyped with Env proteins derived from two prototypic clade B primary isolates were mapped. SF162 Env pseudotypes were neutralized very potently by a panel of sera from HIV-infected individuals, while JR-FL Env pseudotypes were neutralized by only a small fraction of these sera. This differential sensitivity to neutralization was also observed for a number of monoclonal antibodies (MAbs) directed against sites in the V2, V3, and CD4 binding domains, despite often similar binding affinities of these MAbs towards the two soluble rgp120s. The neutralization phenotypes were switched for chimeric Envs in which the V1/V2 domains of these two sequences were exchanged, indicating that the V1/V2 region regulated the overall neutralization sensitivity of these Envs. These results suggested that the inherent neutralization resistance of JR-FL, and presumably of related primary isolates, is to a great extent mediated by gp120 V1/V2 domain structure rather than by sequence variations at the target sites. Three MAbs (immunoglobulin G-b12, 2G12, and 2F5) previously reported to possess broad neutralizing activity for primary HIV-1 isolates neutralized JR-FL virus at least as well as SF162 virus and were not significantly affected by the V1/V2 domain exchanges. The rare antibodies capable of neutralizing a broad range of primary isolates thus appeared to be targeted to exceptional epitopes that are not sensitive to V1/V2 domain regulation of neutralization sensitivity.

Human monoclonal antibodies specific for conformation-sensitive epitopes of V3 neutralize human immunodeficiency virus type 1 primary isolates from various clades

The epitopes of the V3 domain of the human immunodeficiency virus type 1 (HIV-1) gp120 glycoprotein have complex structures consisting of linear and conformational antigenic determinants. Anti-V3 antibodies (Abs) recognize both types of elements, but Abs which preferentially react to the conformational aspect of the epitopes may have more potent neutralizing activity against HIV-1, as recently suggested. To test this hypothesis, human anti-V3 monoclonal Abs (MAbs) were selected using a V3 fusion protein (V3-FP) which retains the conformation of the third variable region. The V3-FP consists of the V3(JR-CSF) sequence inserted into a truncated form of murine leukemia virus gp70. Six human MAbs which recognize epitopes at the crown of the V3 loop were selected with the V3-FP. They were found to react more strongly with molecules displaying conformationally intact V3 than with linear V3 peptides. In a virus capture assay, these MAbs showed cross-clade binding to native, intact virions of clades A, B, C, D, and F. No binding was found to isolates from subtype E. The neutralizing activity of MAbs against primary isolates was determined in three assays: the GHOST cell assay, a phytohemagglutinin-stimulated peripheral blood mononuclear cell assay, and a luciferase assay. While these new MAbs displayed various degrees of activity, the pattern of cross-clade neutralization of clades A, B, and F was most pronounced. The neutralization of clades C and D viruses was weak and sporadic, and neutralization of clade E by these MAbs was not detected. Analysis by linear regression showed a highly significant correlation (P < 0.0001) between the strength of binding of these anti-V3 MAbs to intact virions and the percent neutralization. These studies demonstrate that human MAbs to conformation-sensitive epitopes of V3 display cross-clade reactivity in both binding to native, intact virions and neutralization of primary isolates.

Preparation of human-mouse heterohybridomas against an immunising antigen

The production of murine monoclonal antibodies against specific antigens by hybridomas is a well utilised technique. The production of hybridomas secreting specific human antibodies would have many advantages in therapeutic applications of monoclonal antibodies. The immortalised human lymphocytes themselves would also provide valuable tools in research on lymphocyte development. Preparation of human-human hybridomas has been limited by a lack of suitable fusion partners. This protocol paper describes the production of human-mouse heterohybridomas by two independent laboratories. The purpose of this protocol is to provide a basis for the development of heterohybridoma technology in laboratories with limited hybridoma experience.

The development of monoclonal human rabies virus-neutralizing antibodies as a substitute for pooled human immune globulin in the prophylactic treatment of rabies virus exposure

To provide a more defined and safer replacement for the human rabies immune globulin (HRIG) from pooled serum which is currently used for treatment of exposure to rabies virus we have developed a series of human rabies virus-specific monoclonal antibodies. Mouse-human heterohybrid myeloma cells producing rabies virus-specific human monoclonal antibodies were prepared using B cells obtained from volunteers recently-immunized with a commercial rabies virus vaccine (HDCV). Cell lines producing antibody which neutralized the Evelyn-Rokitnicki-Abelseth (ERA) rabies virus strain in vitro were cloned and the resulting monoclonal antibodies characterized for isotype, specificity against a variety of rabies virus isolates, and neutralization capacity. The ability of the monoclonal antibodies to neutralize a variety of rabies virus strains in vitro correlated with their binding specificity for these viruses in an enzyme-linked immunoadsorbant assay (ELISA). A number of these antibodies have proven suitable for the formulation of a prophylactic human monoclonal antibody-based reagent which would provide significant advantages to the HRIG in having defined, reproducible specificity, lessened possibility of contamination with viral pathogens, and consistent availability.

Effects of oligomerization on the epitopes of the human immunodeficiency virus type 1 envelope glycoproteins

To understand the differential expression of epitopes on monomeric and oligomeric forms of the envelope glycoproteins, nine human monoclonal antibodies (mAbs) were derived from the cells of human immunodeficiency virus-infected subjects by selection with soluble oligomeric gp140 (o.140). These nine mAbs and 12 human mAbs selected with V3 peptides, viral lysates, and rgp120, specific for the V2, V3, C5, CD4-binding domain (CD4bd), and gp41, were tested in a binding assay to compare the exposure of these regions on monomeric gp120 or gp41 and on o.140. None of the 21 mAbs were oligomer specific. However, mAbs to V3 and CD4bd were "oligomer sensitive," whereas mAbs to V2 and the distal epitope of C5 tended to be "monomer sensitive" (i.e., to react better with the oligomer or monomer, respectively). The majority of anti-gp41 mAbs reacted similarly with monomer and oligomer. Although the uncleaved o.140 used in this study differs from the cleaved gp120/41 oligomer found on the native virus particle, these results suggest that new epitopes are not introduced by oligomerization of viral envelope proteins, that such oligomer-specific epitopes, if they exist, are not highly immunogenic, and/or that they are not efficiently selected using soluble o.140.

Recognition of auto- and exoantigens by V4-34 gene encoded antibodies

The antigenic specificities of 24 V4-34-encoded monoclonal antibodies were compared with the amino acid sequence. The specificities were divided into three categories, red blood cells, B lymphocytes and auto/exoantigens. Six anti-I monoclonal antibodies, with multiple substitutions in their VH region, did not bind B lymphocytes or auto/exoantigens. Reactivity to these two antigens segregated with the 16 anti-i monoclonal antibodies, which were derived from the near germline V4-34 gene. All anti-i monoclonal antibodies bound B lymphocytes, albeit with varying intensities. B-cell binding correlated with basic amino acids in the VH-CDR3. Reactivity to auto/exoantigens was demonstrated only by a subset anti-i monoclonal antibodies and did not correlate with B-lymphocyte or i-antigen binding. These anti-ssDNA reactive monoclonal antibodies had basic amino acids in the VH-CDR3, strongly supporting the suggested role of arginine in DNA binding. However, an arginine-rich CDR3 was not enough to ensure DNA reactivity, since six other anti-i monoclonal antibodies that fulfilled this criteria did not bind ssDNA. Thus it is possible that the anti-DNA reactivity of V4-34-encoded monoclonal antibodies is mediated by the classic antigen-binding groove generated by the CDRs of the heavy/light chains. In contrast, anti-B-cell/i-antigen reactivity is mediated, unconventionally, by the V4-34 protein with a dominant influence of the VH-CDR3.

Generation of neutralizing human monoclonal antibodies against parvovirus B19 proteins

Infections caused by human parvovirus B19 are known to be controlled mainly by neutralizing antibodies. To analyze the immune reaction against parvovirus B19 proteins, four cell lines secreting human immunoglobulin G monoclonal antibodies (MAbs) were generated from two healthy donors and one human immunodeficiency virus type 1-seropositive individual with high serum titers against parvovirus. One MAb is specific for nonstructural protein NS1 (MAb 1424), two MAbs are specific for the unique region of minor capsid protein VP1 (MAbs 1418-1 and 1418-16), and one MAb is directed to major capsid protein VP2 (MAb 860-55D). Two MAbs, 1418-1 and 1418-16, which were generated from the same individual have identity in the cDNA sequences encoding the variable domains, with the exception of four base pairs resulting in only one amino acid change in the light chain. The NS1- and VP1-specific MAbs interact with linear epitopes, whereas the recognized epitope in VP2 is conformational. The MAbs specific for the structural proteins display strong virus-neutralizing activity. The VP1- and VP2-specific MAbs have the capacity to neutralize 50% of infectious parvovirus B19 in vitro at 0.08 and 0.73 microgram/ml, respectively, demonstrating the importance of such antibodies in the clearance of B19 viremia. The NS1-specific MAb mediated weak neutralizing activity and required 47.7 micrograms/ml for 50% neutralization. The human MAbs with potent neutralizing activity could be used for immunotherapy of chronically B19 virus-infected individuals and acutely infected pregnant women. Furthermore, the knowledge gained regarding epitopes which induce strongly neutralizing antibodies may be important for vaccine development.

HLA (A*0201) Mimicry by Anti-Idiotypic Monoclonal Antibodies

Soluble MHC Ags and anti-Id (anti-anti-MHC) Abs have both been shown to inhibit MHC alloantigen-specific B cell responses in vivo. We hypothesized that some anti-idiotypic Abs function as divalent molecular mimics of soluble HLA alloantigen. To test this idea, we studied two well-defined anti-idiotypic mAbs, T10-505 and T10-938, elicited in syngeneic BALB/c mice by immunization with CRll-351, an HLA-A2,24,28-specific mAb. Each anti-Id induced “Ab-3” Abs in rabbits that cross-reacted with HLA-A2 but not with HLA-B Ags. Furthermore, each anti-Id could bind to and block Ag recognition by Ha5C2.A2, a human homologue of mAb CRll-351. Both anti-Id mAb displayed weak reactivity with the human mAb SN66E3, which recognized an overlapping but distinct determinant of HLA-A2 Ags; neither reacted with human mAb MBW1, which recognized a nonoverlapping HLA-A2 determinant. Amino acid sequence comparison of mAb CRll-351 heavy and light chain variable region complementarity-determining regions (CDRs) with those of mAb Ha5C2.A2 and SN66E3 revealed short regions of homology with both human mAb; a large insert in the light chain CDR1 of mAb SN66E3 distinguished it from both CRll-351 and Ha5C2.A2. The amino acid sequences of mAb T10-505 and T10-938, which differed markedly from each other, revealed no homology to the α2 domain sequence of HLA-A*0201 that contains the CRll-351 mAb-defined epitope. We conclude that structurally different anti-Id Abs can mimic a polymorphic conformational epitope of an HLA Ag. In the case of T10-505 and T10-938 mimicry was not based on exact replication of the epitope by the hypervariable loops of the anti-Id mAb.

A human monoclonal antibody against HLA-Cw1 and a human monoclonal antibody against an HLA-A locus determinant derived from a single uniparous female

Two human monoclonal antibodies (HuMAbs) with widely different HLA specificities were raised from a uniparous HLA-seropositive female. Screening against a large panel of serologically HLA-typed lymphocytes in the complement-dependent cytotoxicity test showed that one of these HuMAbs, VP6G3, was specific for HLA-Cw1, thereby constituting the first HuMAb against an HLA-C locus product. The second HuMAb, VP5G3, was directed against an HLA-A-encoded determinant shared by HLA-A11, -A25, -A26 and -A66. The epitopes responsible for binding were determined by comparing the aminoacid sequences and were pinpointed to the 6K/9F combination for HuMAb VP6G3, and 163R with a critical contribution of aminoacids present at positions 166/167 for HuMAb VP5G3.

The frequent expansion of a subpopulation of B cells that express RF-associated cross-reactive idiotypes: evidence from analysis of a panel autoreactive monoclonal antibodies

Preferential expression of VH gene segments is evident within the adult human primary B-cell repertoire. The repertoire may be influenced by genetic factors, e.g. VH gene segment polymorphisms, or in a temporal manner due to the exposure to environmental antigens. The molecular characteristics of 15 autoreactive human monoclonal antibodies (MoAbs) are reported. All antibodies were of the IgM isotype, and 12 of the 15 were polyreactive and included rheumatoid factor type specificity, i.e. reactivity with IgG. Nine of the 15 MoAbs are products of VH3 gene segments, as evidenced by staphylococcal protein A binding; four of these express the cross-reactive idiotype recognized by the mouse MoAb 3H7 and are thus products of the VH26 gene segment. One of the five remaining VH3 gene products expresses the cross-reactive idiotypes recognized by the mouse MoAbs B6 and D12. V-gene family usage, determined by polymerase chain reaction (PCR) amplification of cDNA and further hybridization with family-specific oligonucleotide probes, confirmed the cross-reactive idiotype studies and showed that only VH3-gene-encoded proteins bound staphylococcal protein A. Five of the six non-VH3 gene segment products express the cross-reactive idiotype recognized by the mouse MoAb LC1 and could be assumed to be products of the VH4.21 gene segment; however, one human MoAb is shown to be the product of a VH2 gene segment. This is interesting because it turns LC1 from being an anti-cross-reactive idiotype antibody into an anticlan reagent.

A human monoclonal antibody specific for the V3 loop of HIV type 1 clade E cross-reacts with other HIV type 1 clades

To ascertain the antigenic relationship between HIV-1 viruses belonging to various genetically defined subgroups (clades), shared epitopes need to be defined. Human monoclonal antibodies (MAbs) are particularly useful for this purpose because they can detect complex regions of viral proteins that may be missed by sequence analysis and because, by definition, they react with epitopes that stimulate the human immune system. Monoclonal antibodies derived from the cells of HIV-1 clade B-infected subjects have been used extensively for this purpose. Here we describe the first human MAb derived from a clade E-infected individual; the MAb is specific for the V3 loop, recognizing a core epitope represented by the amino acids TRTSVR on the N-terminal side of the crown of the V3 loop. The IgG1(kappa) MAb, designated 1324E, binds to the clade E consensus V3 loop, to rgp120 proteins from clade E and to peripheral blood mononuclear cells infected in vitro with the virus that infected the subject from whose cells the MAb-producing heterohybridoma was derived. Strong cross-reactivity of the MAb to the V3 peptides, rgp120 proteins, and native monomeric gp120s representing clades A and C, as well as to cells infected with a clade C primary isolate, revealed a shared V3 epitope between these clades. When tested for its neutralizing ability, MAb 1324E neutralized a clade E isolate that had been adapted for growth in H9 cells but failed to neutralize five clade E primary isolates.

Cytotoxicity of murine B lymphocytes induced by human VH4-34 (VH4.21) gene-encoded monoclonal antibodies

We have previously described specific binding and cytotoxicity of human B lymphocytes by VH4-34 gene-derived anti-i cold agglutinin (CA) mAbs. Here we demonstrate that the carbohydrate ligand recognized by human VH4-34 anti-i CA mAbs is also expressed on murine B lymphocytes. Similar to human B cells, binding of murine B lymphocytes by VH4-34-derived anti-i CA mAbs leads to rapid cytotoxicity of target cells as tested both in vitro and in vivo. Moreover, the mechanism leading to murine B cell death is also similar to human B cells, since morphologically identical membrane pores were detected within 15 min of mAb exposure by scanning electron microscopy. The conservation of the carbohydrate ligand across species provides an ideal system to study the function of human VH4-34 gene derived Abs in immune regulation.

Reactivity of twenty-two cytotoxic human monoclonal HLA antibodies towards soluble HLA class I in an enzyme-linked immunosorbent assay (PRA-STAT)

An ELISA, PRA-STAT was recently introduced for the detection of HLA class I specific antibodies of IgG isotype in patients' sera. We studied the antigenicity of the soluble HLA (sHLA) preparations that are used in this ELISA as the detection matrix, with the aid of a panel of complement binding human HLA monoclonal antibodies (HuMAbs). A total of 22 HuMAbs, including both IgG and IgM were used. CDC and PRA-STAT ELISA were in complete agreement on 9 of the mAbs tested, with 16 HLA-A and 16 HLA-B locus antigens or their splits identified identically on CDC and PRA-STAT. In 7 of the remaining 13 HuMAbs, there was a difference of one antigen in the specificity pattern of the two techniques three times a specificity call not made by CDC, and four times a call not made by PRA-STAT. For the remaining 6 HuMAbs the differences involve 2 antigens (4 HuMAbs), and 3 or 4 antigens (1 HuMAb each). This study shows the validity of PRA-STAT for detection of HLA-class I antibodies, irrespective of isotype, in serum. The immunological integrity of the sHLA preparations used in PRA-STAT is also confirmed, albeit with some slight discrepancies in antibody specificity seen between PRA-STAT and CDC.

Functional activities of 20 human immunodeficiency virus type 1 (HIV-1)-specific human monoclonal antibodies

Antibodies that are useful in the treatment of HIV infection should result in virus neutralization or lysis of infected cells but should not enhance infection. In this study, the potential clinical use of 20 HIV-1-specific human monoclonal antibodies (HuMAbs) was determined by measuring their enhancing (C-ADE) activities using HIVLAI as the target virus. Two HuMAbs mediated both C-ADE and ADCC, two exclusively neutralized, and five exclusively mediated ADCC. Ten HuMAbs demonstrated no activity in any of the three assays. Three antibodies that neutralized HIVLAI were tested against HIVSF2; all three also neutralized HIVSF2. Four of five HuMAbs mediating ADCC against HIVLAI that were also tested against HIVSF2 had ADCC activity against HIVSF2. These results demonstrate that many HuMAbs have unique functions, allowing the separation of potentially beneficial and harmful activities. Combinations of HuMAbs with ADCC and neutralizing functions may have therapeutic utility.

A human monoclonal antibody to a human self-antigen, CD2 derived from human peripheral blood lymphocytes engrafted in SCID mice

To establish human hybridoma lines, production of human immunoglobulin (Ig) and behavior of the implanted human peripheral blood lymphocytes (PBL) were characterized in severe combined immunodeficiency (SCID) mice. Human PBL from healthy donors were injected into the peritoneal cavity of SCID mice, and they were immunized with self-antigen, CD2. CD45+ cells (human PBL) migrated to lymphoid tissues in the mice as early as 4 days, accounting for more than half the lymph node cells and thymocytes. The number of cells releasing human IgG specific to the antigen increased 3.5 weeks after immunization without the usual constraint that production of the IgG, an autoantibody, is prohibited by immunological tolerance in humans. Therefore, we established several human hybridomas secreting human IgG to CD2, since splenocytes and lymph node cells from the implanted SCID mice at 3.5 weeks were fused with a human B lymphoblastoid cell line. A human anti-CD2 monoclonal antibody (MAb) was confirmed to bind to natural CD2 on human T cells by flow cytometric analysis. The epitope for the MAb was identical with a portion that the ligand LFA-3 binded, so that the MAb might reduce the inflammatory reaction caused by preventing activation of human T cells. Here, we report that the human immune system could be reconstituted in SCID mice to develop human hybridomas producing human MAb to a human self-antigen.

Antiphospholipid syndrome and the idiotypic network

To study whether monoclonal anticardiolipin antibodies (aCL), derived from patients with antiphospholipid syndrome (APS), have similar pathogenic potential, we have employed an experimental model of antiphospholipid syndrome. Monoclonal aCL were produced by the combined method of EBV transformation and somatic cell hybridization of lymphocytes, derived from patients with APS. The monoclonal aCL were used to immunize mice at the footpads and the mice were followed for serological and clinical manifestations of APS. The monoclonal antibody EY2C9, was found to bind weakly to cardiolipin and other phospholipids (i.e. phosphatidyl-serine, phosphatidyl-ethanolamine and phosphatidyl-inositol). The antibody TM1B9, although derived from a patient with SLE and with secondary APS, did not react with phospholipids. Immunization of naive BALB/c mice with EY2C9 was followed by production of sustained high titers of antiphospholipid antibodies associated with prolonged activated partial thromboplastin time (APTT) (46.8 +/- 5.0 s vs. 22.4 +/- 1.7 s, in the non-immunized mice). Mice immunized with TM1B9 had a more moderate titer of antiphospholipid antibodies and did not show prolonged APTT. The pregnant mice, that were immunized with EY2C9, had increased fetal resorption rate (the equivalent of fetal loss in the human) of 36.8 +/- 10% (vs. 2 +/- 4% in mice immunized with TM1B9). Our results confirm that monoclonal aCL, derived from a patient with APS, can have a pathogenic potential, dysregulating the idiotypic network and leading to the development of characteristic signs of APS.(ABSTRACT TRUNCATED AT 250 WORDS)

Autologous human B-cell immune response to pulmonary adenocarcinomatous polymorphic epithelial mucin

In order to investigate whether a B-cell immune response to the polymorphic epithelial mucin (PEM) is present in adenocarcinomatous patients, peripheral blood lymphocytes from 20 patients with adenocarcinomas from various sites were fused with the mouse-human heteromyeloma cell line SHM-D33. One IgM(K) monoclonal antibody derived from peripheral blood lymphocytes of a patient with a lung adenocarcinoma was generated with binding reactivity for bovine submaxillary mucin (BSM). The latter is one of the PEMs, and it contains a large amount of the tumor-associated sialosyl-Tn epitope. The generated antibody was designated KMD-2. Immunohistological studies on various tissues showed that KMD-2 reacted with 6/6 colorectal adenocarcinomas and 4/6 pulmonary adenocarcinomas. The antibody also displayed a slight degree of cross-reactivity with a limited number of normal tissues, especially those that elaborate mucin. Our data show that an autologous antibody response in the form of IgM to the immunosuppressive PEM is present in some adenocarcinomatous patients. The data also suggest that the KMD-2 (IgM/K) antibody may be of clinical importance for diagnostic purposes of adenocarcinomatous disease.

Functional expression of human and mouse low density lipoprotein receptors in hybridomas

Though a mouse.human-human heterohybridoma, N12-16.63, secreting an antitetanus toxoid human monoclonal antibody grew well in a serum-free medium, its high producing subclone N12-69 required SSGF-I, a low density lipoprotein (LDL) from swine serum, or human-LDL (h-LDL) for growth. The growth-promoting action of SSGF-I was caused by its lipid fraction, and SSGF-I could be replaced completely with cholesterol in the presence of bovine serum albumin (BSA). Thus, cell line N12-69 is a cholesterol auxotroph of the heterohybridoma. N12-69 cells express both mouse and human LDL receptors on the cell surface in a ratio of 1:4. SSGF-I bound to both receptors with the same binding affinity, and h-LDL was also take up by the same receptors, though the affinity constant of the receptors for SSGF-I was 1.5 times stronger than that for h-LDL. The growth of N12-69 cells was completely inhibited by the addition of dextran sulfate, which is known to inhibit the binding of LDL to LDL receptors, to an SSGF-I or h-LDL containing medium but was not inhibited at all when dextran sulfate was added to a serum-free medium supplemented with cholesterol and BSA. Furthermore, an anti-human LDL receptor monoclonal antibody partially inhibited the growth of N12-69 cells in an SSGF-I or h-LDL containing medium. These findings suggest that N12-69 cells express both biologically active mouse and human LDL receptors on their cell surfaces and that SSGF-I or h-LDL is taken up by the both receptors to be utilized as a cholesterol source for the growth.

Human anti-V2 monoclonal antibody that neutralizes primary but not laboratory isolates of human immunodeficiency virus type 1

A human immunoglobulin G1 lambda monoclonal antibody (MAb), 697-D, was developed that recognizes the V2 region of human immunodeficiency virus type 1 (HIV-1) gp120. Substitutions at amino acid positions 176/177, 179/180, 183/184, and 192 to 194 in the V2 loop of gp120 each completely abolished the binding capacity of 697-D in an enzyme-linked immunosorbent assay format. Competition analysis with three different neutralizing murine anti-V2 MAbs confirmed the specificity of 697-D. The 697-D epitope is primarily conformation dependent, although there was weak reactivity of the MAb with a V2 peptide spanning residues 161 to 180. Treatment of recombinant gp120 HIVIIIB with sodium metaperiodate, which oxidizes carbohydrates, abolished the binding of the MAb, showing the dependence of the epitope on intact carbohydrates. The broad reactivity of 697-D was displayed by its binding to the gp120 molecules from four of four laboratory isolates and five of five primary isolates. The MAb 697-D neutralized three out of four primary isolates but failed to neutralize any of four laboratory strains of HIV-1. 697-D and a human anti-V3 MAb, 447-52-D, displayed similar potency in neutralizing primary isolates, indicating that the V2 region of gp120, like the V3 region and the CD4-binding domain, can induce potent neutralizing antibodies against HIV-1 in humans.

beta 2-Glycoprotein I reactivity of monoclonal anticardiolipin antibodies from patients with the antiphospholipid syndrome

OBJECTIVE

To elucidate the specificity of anticardiolipin antibodies (aCL) from patients with the antiphospholipid syndrome (APS) to various phospholipids (PLs), DNA, and beta 2-glycoprotein I (beta 2-GPI).

METHODS

Five monoclonal aCL were established from peripheral blood lymphocytes of 3 patients with the APS. The reactivity of monoclonal aCL with various PLs, with DNA, and with beta 2-GPI was examined by enzyme-linked immunosorbent assay (ELISA).

RESULTS

All of the monoclonal aCL bound to anionic PLs, only in the presence of beta 2-GPI. Neither monoclonal aCL nor beta 2-GPI bound to DNA. Monoclonal aCL bound to solid-phase beta 2-GPI on polystyrene ELISA plates that had carboxyl groups on their surface, but did not react with solid-phase beta 2-GPI on ordinary polystyrene plates. A mixture of beta 2-GPI and CL inhibited the binding of monoclonal aCL to beta 2-GPI, but CL or beta 2-GPI alone did not.

CONCLUSION

Monoclonal aCL may recognize a cryptic epitope, which appears as a result of beta 2-GPI binding to anionic PLs or to polystyrene with carboxyl groups.

Human monoclonal antibody [1-1-2D] against cancer of the uterine cervix

To obtain a human monoclonal antibody (h-MAb) against cancer of the uterine cervix, lymphocytes from the regional lymph nodes of 14 patients with cervical cancer were fused with a mouse-human heterohybridoma [II]. Of 6,419 hybridomas, 1,295 produced human immunoglobulins (IgG 670, IgM 737). We isolated clone [1-1-2D], which has produced human IgM with stability for more than a year. This antibody reacted with three of five cell lines of cervical cancer but not with normal fibroblasts. Histoimmunostaining showed positive responses to 9/15 specimens of cervical cancer and in 2/7 specimens from cases of cervical dysplasia. Most of the normal human and fetal tissues showed no positive immune response. The positive immune response of [1-1-2D] to the cell membrane observed by the fluorescence antibody method disappeared after periodate treatment and was weakened by trypsin. Neuraminidase did not affect immune reactivity. This antibody showed a positive response by the thin-layer chromatography immunostaining method and precipitated a glycoprotein having a molecular weight of 38 kD. These results suggested that the epitope of the [1-1-2D] antibody is present on a carbohydrate moiety not containing sialic acid that is carried on protein and lipid moieties.

A novel human monoclonal antibody directed to a tumor-associated antigen

Twelve human monoclonal antibodies (HuMAb) were established by the fusion of (mouse x human) heteromyeloma cells with B-lymphoblastoid cells derived from the regional lymph nodes of three patients with squamous cell carcinoma of the lung. They were tested for reactivity to two kinds of proteins (purified protein derivatives and bovine serum albumin) by ELISA, Sq-19 (squamous cell carcinoma) culture cells by indirect membrane immunofluorescence tests, and Sq-19 tumor xenograft by immunohistological study. Among them, one HuMAb 904F (IgM, lambda) was selected. In indirect membrane immunofluorescence tests, this 904F antibody reacted with various kinds of cell lines, e.g. lung cancer, esophageal cancer, endometrial cancer, and stomach cancer. It did not react with malignant hematopoietic and diploid fibroblast cell lines. Immunohistologically, it stained the tumor nests of squamous cell carcinoma, adenocarcinoma, and large cell carcinoma of the lung. It also stained those of esophagus and colon, but not those of small cell carcinoma of lung, or stomach. On frozen-section specimens of normal tissues from various organs, it showed only limited areas of positive staining. Limited positive findings were observed at a reticular zone of the adrenal gland, at the esophagus as weak staining, and at islets of the pancreas as very weak staining. Western blotting analysis demonstrated that it recognized a 54 kDa trypsin-sensitive molecule which is expressed on the surface of tumor cells. These results suggest the 904F monoclonal antibody detects a novel tumor-associated antigen which is recognized by the human immune system.

Development of human monoclonal antibodies against human cytomegalovirus

Human monoclonal antibodies (HMAbs) against human cytomegalovirus (HCMV) have been developed by fusion of human spleen cells and human lymphoblastoid cell lines (NP101 and NP197). The cell line NP101 had great advantages in its high fusion frequency and the stability of the resultant hybridomas. The specificity of HMAbs was confirmed by enzyme-linked immunosorbent assay (ELISA) and immunofluorescence staining. Two of the six HMAbs obtained, which were IgG3 subclass, neutralized viral infectivity in the absence of complement. The neutralizing activity of one of these two HMAbs was enhanced in the presence of human complement, whereas the other was not. Another IgG1 subclass HMAb neutralized viral infection only in the presence of complement. The remaining three HMAbs showed no neutralizing activity. Those HMAbs may provide an important approach to studying human immune responses to HCMV. HMAbs having neutralizing activity may prove to be useful for passive immunotherapy of HCMV diseases.

Phase I study of antilipopolysaccharide human monoclonal antibody MAB-T88

Monoclonal antibody MAB-T88 is a human monoclonal immunoglobulin M antibody directed at the lipopolysaccharide of gram-negative bacteria. In this study, nine patients who were expected to become neutropenic from antineoplastic chemotherapy received an infusion of MAB-T88, three patients at each of three doses: 1, 4, and 8 mg/kg of body weight. MAB-T88 was shown to be safe, with an effective half-life in plasma of 25.4 h, and no patient developed immunoglobulin G antibody to MAB-T88.

Production of human monoclonal antibodies specific for conformational and linear non-V3 epitopes of gp120

Three IgG1 human monoclonal antibodies (MAbs) directed against conformational epitopes of the gp120 envelope protein of HIV-1 were produced, as was a single human MAb to a linear epitope spanning amino acids 487-509 in the C-terminal portion of gp120. All three conformation-dependent MAbs reacted optimally with recombinant gp120 (rgp120) captured on plastic via its carbohydrate moieties with Concanavalin A. These MAbs were able to block the interaction between recombinant CD4 (rCD4) and rgp120; they were also able to achieve 50% neutralization of HTLV-IIIB and MN strains of HIV-1 in a concentration range of 0.5-12.8 micrograms/mL. The MAb to the linear determinant is the first reported human MAb specific for the immunodominant portion of gp120; this MAb was most reactive with rgp120 when it was coated directly on plastic. It could neither inhibit rCD4-rgp120 binding nor neutralize either HTLV-IIIB or MN. The binding affinities of the four human MAbs for rgp120 in solution, reflected by their dissociation constants (Kd), ranged from 0.5 x 10(-8) to 7.5 x 10(-8) M.

A human monoclonal autoantibody to a nucleolar structure

Peripheral blood lymphocytes from a scleroderma patient (CDC) were isolated, transformed with Epstein-Barr virus and fused to the heteromyeloma SHM-D33. Supernatants from cultures were screened for autoantibody production against nucleoprotamine by ELISA. Positive wells were cloned by limiting dilution. After cloning, supernatants from two wells were positive for the nucleoprotamine assay. One named CDC-1 has been studied in our laboratory. CDC-1 recognized a nucleolar antigen by indirect immunofluorescence. By using an ELISA with purified recombinant antigens, CDC-1 reacted against Ro/SS-A, U1 (RNP) and Sm. By immunoblotting using a lysate of MOLT-4 cell line, CDC-1 was able to react against a structure of 60 kD. When the antigen recognized by CDC-1 was purified, SDS-PAGE under reducing conditions with purified antigen and subsequent silver staining of the gel allowed us to detect three bands at 60, 55 and 39 kD, respectively. A screening by ELISA with previously characterized antisera against our purified antigen demonstrated reactivity of the CDC-1 antigen with those antisera able to recognize Ro/SS-A.

Production of heterohybridomas secreting autoreactive and polyreactive human monoclonal antibodies

Peripheral blood lymphocytes from two polytransfused renal dialysis patients were transformed by Epstein-Barr virus, fused to a heteromyeloma and cloned. Eight human monoclonal antibodies from the resulting clones were tested for their binding to a variety of antigens by ELISA, indirect immunofluorescence and immunoblotting. Antigens tested included B-cell lines, T and B lymphocytes, red blood cells, chronic lymphocytic leukaemic B cells, IgG, ssDNA, dsDNA, histones, nucleoprotamine, sperm nuclei, thymus and spleen extracts, MOLT4 cell lysates, affinity purified autoantigens, tetanus toxoid, bacterial lipopolysaccharide, insulin, and a tissue section screen. These human monoclonal antibodies reacted with more than one antigen to varying degrees and were autoreactive and polyreactive. One of these heterohybridoma cell lines exhibited cytoplasmic staining with an anti-CD5 monoclonal. Our findings support the concept that in adult individuals a subset of B cells produce heterogeneous IgM antibodies which can bind to a variety of different autoantigens and also to foreign antigens. These monoclonals were different from the autoantibodies usually seen in renal dialysis patients in the sense that they were not lymphocytotoxic.

A human anti-Jkb monoclonal antibody

Peripheral blood mononuclear cells of an immunized patient were transformed with Epstein-Barr virus and then fused with P3X63Ag8 mouse myeloma cells by polyethylene glycol. After the cloning, a hybridoma cell line secreting specific anti-Jkb monoclonal antibody was isolated. The antibody was produced in supernatant form and tested for its use as a blood grouping reagent.

Polyreactivity of human monoclonal antibodies: human anti-Rh monoclonal antibodies of IgM isotype are frequently polyreactive

The specific aim of this study was to characterize human anti-Rh monoclonal antibodies cross-reacting with self-antigens. We studied supernatants from man-mouse hybridomas and from lymphoblastoid cell lines. Man-mouse hybridomas were established by fusion of peripheral blood lymphocytes from healthy individuals recently immunized against Rh alloantigens, with mouse myeloma (or man-mouse heteromyeloma) cell lines. Lymphoblastoid cell lines were produced by Epstein-Barr virus induction of lymphocytes from identical sources. Of the 55 monoclonal alloantibodies studied, 11 also reacted with intracellular self-antigens as demonstrated by immunofluorescence assay on cryostat sections of human tissues. This cross-reactivity was mainly a property of monoclonal alloantibodies belonging to the IgM isotype (among the 11 cross-reacting mAbs 10 were IgM). The cross-reactivities of these monoclonal antibodies were ascertained by absorption of alloreacting antibodies with red blood cells. Similar results were obtained on a panel of purified cellular antigens by ELISA. The results confirm that during an immune response against a foreign antigen (alloantigen), B cells that produce polyreactive antibodies are not excluded from the pool of responding cells. Therefore, polyreactive autoantibodies present in sera from healthy individuals may be the result of an immune response against foreign antigens.

Epitope mapping of two immunodominant domains of gp41, the transmembrane protein of human immunodeficiency virus type 1, using ten human monoclonal antibodies

Immunogenic regions of the gp41 transmembrane protein of human immunodeficiency virus type 1 (HIV-1) were previously mapped by examining polyclonal sera from HIV-infected patients and rodent polyclonal and monoclonal antibodies (MAbs) to peptides of gp41. To define the epitopes within these regions to which infected humans respond during the course of infection, the specificity of human MAbs to these regions had to be studied. Using 10 human MAbs identified initially by their reactivity to whole gp41 in HIV-1 lysates, the epitopes within the immunodominant region of gp41 and within a second immunogenic region of gp41 have been mapped. Thus, five MAbs (from five different patients) to the immunodominant domain of gp41 in the vicinity of the cysteines at positions 598 and 604 (hereinafter designated cluster I) reacted with a stretch of 11 amino acids from positions 590 to 600. Four of these five MAbs were reactive with linear epitopes, while one MAb required the conformation conferred by the disulfide bridge between the aforementioned cysteines. Three MAbs to cluster I revealed dissociation constants ranging from 10(-6) to 10(-8) M, depending on the MAb tested and the size of the synthetic or recombinant peptide used in the assay. Five additional MAbs reacted with a second immunogenic region between positions 644 and 663 (designated cluster II). Four of these five MAbs were specific for conformational determinants. Titration of sera from HIV-infected patients showed that there was about 100-fold more antibody to cluster I than to cluster II in patients' sera, confirming the immunodominance of cluster I.