Human immunodeficiency virus type 1-neutralizing monoclonal antibody 2F5 is multispecific for sequences flanking the DKW core epitope

Human monoclonal antibody 2F5 is one of a few human antibodies that neutralize a broad range of HIV-1 primary isolates. The 2F5 epitope on gp41 includes the sequence ELDKWA, with the core residues, DKW, being critical for antibody binding. HIV-neutralizing antibodies have never been elicited by immunization with peptides bearing ELDKWA, suggesting that important part(s) of the 2F5 paratope remain unidentified. The use of longer peptides extending beyond ELDKWA has resulted in increased epitope antigenicity, but neutralizing antibodies have not been generated. We sought to develop peptides that bind to 2F5, and that function as specific probes of the 2F5 paratope. Thus, we used 2F5 to screen a set of phage-displayed, random peptide libraries. Tight-binding clones from the random peptide libraries displayed sequence variability in the regions flanking the DKW motif. To further reveal flanking regions involved in 2F5 binding, two semi-defined libraries were constructed having 12 variegated residues either N-terminal or C-terminal to the DKW core (X(12)-AADKW and AADKW-X(12), respectively). Three clones isolated from the AADKW-X(12) library had similar high affinities, despite a lack of sequence homology among them, or with gp41. The contribution of each residue of these clones to 2F5 binding was evaluated by Ala substitution and amino acid deletion studies, and revealed that each clone bound 2F5 by a different mechanism. These results suggest that the 2F5 paratope is formed by at least two functionally distinct regions: one that displays specificity for the DKW core epitope, and another that is multispecific for sequences C-terminal to the core epitope. The implications of this second, multispecific region of the 2F5 paratope for its unique biological function are discussed.     

Epitope mapping of the human immunodeficiency virus type 1 gp120 with monoclonal antibodies.

A soluble form of recombinant gp120 of human immunodeficiency virus type 1 was used as an immunogen for production of murine monoclonal antibodies. These monoclonal antibodies were characterized for their ability to block the interaction between gp120 and the acquired immunodeficiency syndrome virus receptor, CD4. Three of the monoclonal antibodies were found to inhibit this interaction, whereas the other antibodies were found to be ineffective at blocking binding. The gp120 epitopes which are recognized by these monoclonal antibodies were mapped by using a combination of Western blot (immunoblot) analysis of gp120 proteolytic fragments, immunoaffinity purification of fragments of gp120, and antibody screening of a random gp120 gene fragment expression library produced in the lambda gt11 expression system. Two monoclonal antibodies which blocked gp120-CD4 interaction were found to map to adjacent sites in the carboxy-terminal region of the glycoprotein, suggesting that this area is important in the interaction between gp120 and CD4. One nonblocking antibody was found to map to a position that was C terminal to this CD4 blocking region. Interestingly, the other nonblocking monoclonal antibodies were found to map either to a highly conserved region in the central part of the gp120 polypeptide or to a highly conserved region near the N terminus of the glycoprotein. N-terminal deletion mutants of the soluble envelope glycoprotein which lack these highly conserved domains but maintain the C-terminal CD4 interaction sites were unable to bind tightly to the CD4 receptor. These results suggest that although the N-terminal and central conserved domains of intact gp120 do not appear to be directly required for CD4 binding, they may contain information that allows other parts of the molecule to form the appropriate structure for CD4 interaction.     

Identification and characterization of a new cross-reactive human immunodeficiency virus type 1-neutralizing human monoclonal antibody

The identification and characterization of new human monoclonal antibodies (hMAbs) able to neutralize primary human immunodeficiency virus type 1 (HIV-1) isolates from different subtypes may help in our understanding of the mechanisms of virus entry and neutralization and in the development of entry inhibitors and vaccines. For enhanced selection of broadly cross-reactive antibodies, soluble HIV-1 envelope glycoproteins (Envs proteins) from two isolates complexed with two-domain soluble CD4 (sCD4) were alternated during panning of a phage-displayed human antibody library; these two Env proteins (89.6 and IIIB gp140s), and one additional Env (JR-FL gp120) alone and complexed with sCD4 were used for screening. An antibody with relatively long HCDR3 (17 residues), designated m14, was identified that bound to all antigens and neutralized heterologous HIV-1 isolates in multiple assay formats. Fab m14 potently neutralized selected well-characterized subtype B isolates, including JRCSF, 89.6, IIIB, and Yu2. Immunoglobulin G1 (IgG1) m14 was more potent than Fab m14 and neutralized 7 of 10 other clade B isolates; notably, although the potency was on average significantly lower than that of IgG1 b12, IgG1 m14 neutralized two of the isolates with significantly lower 50% inhibitory concentrations than did IgG1 b12. IgG1 m14 neutralized four of four selected clade C isolates with potency higher than that of IgG1 b12. It also neutralized 7 of 17 clade C isolates from southern Africa that were difficult to neutralize with other hMAbs and sCD4. IgG1 m14 neutralized four of seven primary HIV-1 isolates from other clades (A, D, E, and F) much more efficiently than did IgG1 b12; for the other three isolates, IgG b12 was much more potent. Fab m14 bound with high (nanomolar range) affinity to gp120 and gp140 from various isolates; its binding was reduced by soluble CD4 and antibodies recognizing the CD4 binding site (CD4bs) on gp120, and its footprint as defined by alanine-scanning mutagenesis overlaps that of b12. These results suggest that m14 is a novel CD4bs cross-reactive HIV-1-neutralizing antibody that exhibits a different inhibitory profile compared to the only known potent broadly neutralizing CD4bs human antibody, b12, and may have implications for our understanding of the mechanisms of immune evasion and for the development of inhibitors and vaccines.     

Characterization and epitope mapping of neutralizing monoclonal antibodies produced by immunization with oligomeric simian immunodeficiency virus envelope protein

In an attempt to generate broadly cross-reactive, neutralizing monoclonal antibodies (MAbs) to simian immunodeficiency virus (SIV), we compared two immunization protocols using different preparations of oligomeric SIV envelope (Env) glycoproteins. In the first protocol, mice were immunized with soluble gp140 (sgp140) from CP-MAC, a laboratory-adapted variant of SIVmacBK28. Hybridomas were screened by enzyme-linked immunosorbent assay, and a panel of 65 MAbs that recognized epitopes throughout the Env protein was generated. In general, these MAbs detected Env by Western blotting, were at least weakly positive in fluorescence-activated cell sorting (FACS) analysis of Env-expressing cells, and preferentially recognized monomeric Env protein. A subset of these antibodies directed toward the V1/V2 loop, the V3 loop, or nonlinear epitopes were capable of neutralizing CP-MAC, a closely related isolate (SIVmac1A11), and/or two more divergent strains (SIVsmDeltaB670 CL3 and SIVsm543-3E). In the second protocol, mice were immunized with unfixed CP-MAC-infected cells and MAbs were screened for the ability to inhibit cell-cell fusion. In contrast to MAbs generated against sgp140, the seven MAbs produced using this protocol did not react with Env by Western blotting and were strongly positive by FACS analysis, and several reacted preferentially with oligomeric Env. All seven MAbs potently neutralized SIVmac1A11, and several neutralized SIVsmDeltaB670 CL3 and/or SIVsm543-3E. MAbs that inhibited gp120 binding to CD4, CCR5, or both were identified in both groups. MAbs to the V3 loop and one MAb reactive with the V1/V2 loop interfered with CCR5 binding, indicating that these regions of Env play similar roles for SIV and human immunodeficiency virus. Remarkably, several of the MAbs generated against infected cells blocked CCR5 binding in a V3-independent manner, suggesting that they may recognize a region analogous to the conserved coreceptor binding site in gp120. Finally, all neutralizing MAbs blocked infection through the alternate coreceptor STRL33 much more efficiently than infection through CCR5, a finding that has important implications for SIV neutralization assays using CCR5-negative human T-cell lines.     

A neutralizing monoclonal antibody previously mapped exclusively on human immunodeficiency virus type 1 gp41 recognizes an epitope in p17 sharing the core sequence IEEE.

We report here that a human immunodeficiency virus type 1 (HIV-1)-specific neutralizing monoclonal antibody (MAb 1575) mapped to the conserved putative intracellular region from amino acid residues 735 to 752 (735-752 region) of gp41 also recognizes a region in an extracellular portion of p17. Both epitopes have a core recognition sequence (IEEE) in a nonhomologous context. The IEEE motif found in HIV-1 p17 is located in a region known as HGP-30 (residues 86 to 115) which has been previously associated with virus neutralization, cytotoxic T lymphocyte activity, and mother-to-child transmission. An analysis of available gp41 and p17 sequences demonstrates that in these regions both IEEE sequences are highly conserved in different HIV-1 clades. The presence of the IEEE epitope in p17 allows us to explain some unexpected neutralizing characteristics of MAb 1575. In addition, the gp41 735-752 region has been previously reported both in intra- and extracellular locations. Our results suggest that the extracellular location was the result of cross-reactivity with p17.     

Human antibodies react with an epitope of the human papillomavirus type 6b L1 open reading frame which is distinct from the type-common epitope.

Recombinant proteins encoded by the human papillomavirus type 6b (HPV6b) L1 open reading frame react with sera from patients with condylomata acuminata and also react with rabbit antiserum raised against sodium dodecyl sulfate-disrupted bovine papillomavirus type 1 (BPV1) virions. To map the immunoreactive epitopes, a series of procaryotic expression plasmids was made which contained a nested set of 3' to 5' deletions in the HPV6b L1 open reading frame. The deleted plasmids expressed a set of carboxy to amino terminus truncated fusion proteins. Regions containing the immunoreactive epitopes were mapped by determining which of the deleted fusion proteins retained reactivity with sera in Western immunoblot assays. The coding sequence for a human antibody-reactive linear epitope mapped between HPV6b nucleotide coordinates 7045 and 7087, and the rabbit anti-BPV1-reactive epitope coding sequence mapped between coordinates 6377 and 6454. Synthetic peptides derived from the epitope mapping were reacted with sera in enzyme-linked immunosorbent assay. Human sera reacted with synthetic peptide QSQAITCQKPTPEKEKPDPYK (HPV6b L1 amino acids 417 through 437). Rabbit anti-BPV1 and rabbit antisera raised against HPV16 L1 recombinant proteins reacted with the synthetic peptide DGDMVDTGFGAMNFADLQTNKSDVPIDI (HPV6b L1 amino acids 193 through 220). Human sera which reacted with HPV6b L1 fusion proteins cross-reacted with an HPV11 L1 fusion protein but did not react with fusion proteins encoded by HPV1a, HPV16, or HPV18. Rabbit anti-BPV1 reacted with L1 fusion proteins encoded by all of these HPV types. In contrast to the type-common (rabbit anti-BPV1-reactive) epitope, the human antibody-reactive epitope appears to be relatively HPV type specific.     

Epitope mapping of monoclonal antibodies against human immunodeficiency virus type 1 structural proteins by using peptides.

Murine monoclonal antibodies directed against the structural proteins p17 and p24 of human immunodeficiency virus type 1 were investigated in an epitope mapping system. Overlapping peptides consisting of 15 amino acids of the p17 and p24 protein, respectively, were used as competitors in an enzyme-linked immunosorbent assay. Three different immunogenic regions (A, B, and C) could be defined, one on p17 and two on p24. Twenty monoclonal antibodies reacted with the human immunodeficiency virus type 1 peptides of region B, although differences in the reactivity of these antibodies with human immunodeficiency virus type 2 and simian immunodeficiency virus strain mac were detectable. Recognized epitopes were characterized by computer analysis as described by T.P. Hopp and K.R. Woods (Proc. Natl. Acad. Sci. USA 78:3824-3828, 1981) and P.Y. Chou and G.D. Fasman (Biochemistry 13:222-245, 1974).     

Monoclonal antibodies against human immunodeficiency virus type 1 integrase: epitope mapping and differential effects on integrase activities in vitro.

Human immunodeficiency virus type 1 (HIV-1) integrase (IN) catalyzes the integration of viral DNA into the host chromosome, an essential step in retroviral replication. As a tool to study the structure and function of this enzyme, monoclonal antibodies (MAbs) against HIV-1 IN were produced. Epitope mapping demonstrated that the 17 MAbs obtained could be divided into seven different groups, and the selection of MAbs representing these groups were tested for their effect on in vitro activities of IN. Four groups of MAbs recognized epitopes within the region of amino acids (aa) 1 to 16, 17 to 38, or 42 to 55 in and around the conserved HHCC motif near the N terminus of IN. MAbs binding to these epitopes inhibited end processing and DNA joining and either stimulated or had little effect on disintegration and reintegration activities of IN. Two MAbs binding to epitopes within the region of aa 56 to 102 in the central core or aa 186 to 250 in the C-terminal half of the protein showed only minor effects on the in vitro activities of IN. Three Mabs which recognized on epitope within the region of aa262 to 271 of HIV-1 IN cross-reacted with HIV-2 IN. MAbs binding to this epitope clearly inhibited end processing and DNA joining and stimulated or had little effect on disintegration. In contrast to the N-terminal-specific MAbs, these C-terminal-specific MAbs abolished reintegration activity of IN.     

Characterization of murine monoclonal antibodies to the tat protein from human immunodeficiency virus type 1.

A panel of murine monoclonal antibodies (MAbs) to the human immunodeficiency virus type 1 trans-activator tat protein were characterized. The anti-tat MAbs were mapped to the different domains of the tat protein by Western blot (immunoblot) and Pepscan analyses. One-half of the MAbs tested mapped to the amino-terminal proline-rich region, and one-third of the MAbs tested mapped to the lysine-arginine-rich region of tat. The individual MAbs were tested for inhibition of tat-mediated trans activation, using a cell-based in vitro assay system. MAbs which mapped to the amino-terminal region of the tat protein demonstrated the highest degree of inhibition, whereas MAbs reactive to other portions of the molecule exhibited a less pronounced effect on tat function.     

Characterization of human immunodeficiency virus type 1 p17 matrix protein motifs associated with mother-to-child transmission.

In order to determine if viral selection occurs during mother-to-child transmission of human immunodeficiency virus type 1 (HIV-1), we used a direct solid-phase sequencing method to sequence the p17 matrix protein-encoding regions of viral isolates from 12 HIV-1-infected mother-and-child pairs, 4 infected infants, 4 transmitting mothers, and 22 nontransmitting mothers and compared the sequences. The blood samples were collected during the delivery period for the mothers and during the first month of life for most of the children. The p17 nucleic sequences were distributed among several clades corresponding to the HIV-1 A, B, and G subtypes. At the amino acid level, no significant differences within the known p17 functional regions were observed among the subtypes. Statistical analyses could be performed with the B subtype. Within the major p17 antibody binding site, a constant KIEEEQN motif (amino acids 103 to 109) was found in all mother-and-child isolates from the B subtype. On the other hand, 9 of 17 nontransmitting mother isolates were variable in this 103 to 109 region. Thus, this motif was significantly associated with the transmitting status (chi square, P = 0.0034). A valine residue at position 104 was significantly associated with the nontransmitting phenotype (chi square, P = 0.014), suggesting that it has a protective role during vertical transmission. The C-terminal end of p17 was globally conserved among nontransmitting mother isolates (chi square, P = 0.0037). These results might improve the understanding of the pathogenesis of HIV-1 vertical transmission and might allow the screening of seropositive mothers by a rapid molecular or peptide test.     

Cross-reactive human immunodeficiency virus type 1-neutralizing human monoclonal antibody that recognizes a novel conformational epitope on gp41 and lacks reactivity against self-antigens

Broadly cross-reactive human immunodeficiency virus (HIV)-neutralizing antibodies are infrequently elicited in infected humans. The two best-characterized gp41-specific cross-reactive neutralizing human monoclonal antibodies, 4E10 and 2F5, target linear epitopes in the membrane-proximal external region (MPER) and bind to cardiolipin and several other autoantigens. It has been hypothesized that, because of such reactivity to self-antigens, elicitation of 2F5 and 4E10 and similar antibodies by vaccine immunogens based on the MPER could be affected by tolerance mechanisms. Here, we report the identification and characterization of a novel anti-gp41 monoclonal antibody, designated m44, which neutralized most of the 22 HIV type 1 (HIV-1) primary isolates from different clades tested in assays based on infection of peripheral blood mononuclear cells by replication-competent virus but did not bind to cardiolipin and phosphatidylserine in an enzyme-linked immunosorbent assay and a Biacore assay nor to any protein or DNA autoantigens tested in Luminex assays. m44 bound to membrane-associated HIV-1 envelope glycoproteins (Envs), to recombinant Envs lacking the transmembrane domain and cytoplasmic tail (gp140s), and to gp41 structures containing five-helix bundles and six-helix bundles, but not to N-heptad repeat trimers, suggesting that the C-heptad repeat is involved in m44 binding. In contrast to 2F5, 4E10, and Z13, m44 did not bind to any significant degree to denatured gp140 and linear peptides derived from gp41, suggesting a conformational nature of the epitope. This is the first report of a gp41-specific cross-reactive HIV-1-neutralizing human antibody that does not have detectable reactivity to autoantigens. Its novel conserved conformational epitope on gp41 could be helpful in the design of vaccine immunogens and as a target for therapeutics.     

Ultrastructural characterization of embryonic chick cartilage proteoglycan core protein and the mapping of a monoclonal antibody epitope.

The ultrastructure of embryonic chick cartilage proteoglycan core protein was investigated by electron microscopy of specimens prepared by low angle shadowing. The molecular images demonstrated a morphological substructural arrangement of three globular and two linear regions within each core protein. The internal globular region (G2) was separated from two terminally located globular regions (G1 and G3) by two elongated strands with lengths of 21 +/- 3 nm (E1) and 105 +/- 22 nm (E2). The two N-terminal globular regions, separated by the 21-nm segment, were consistently visualized in well spread molecules and showed little variation in the length of the linear segment connecting them. The E2 segment, however, was quite variable in length, and the C-terminal globular region (G3) was detected in only 53% of the molecules. The G1, G2, and G3 regions in chick core protein were 10.1 +/- 1.7 nm, 9.7 +/- 1.3 nm, and 8.3 +/- 1.3 nm in diameter, respectively. These results are similar to those described previously for proteoglycan core proteins isolated from rat chondrosarcoma, bovine nasal cartilage, and pig laryngeal cartilage (Paulsson, M., Morgelin, M., Wiedemann, H., Beardmore-Gray, M., Dunham, D., Hardingham, T., Heinegard, D., Timpl, R., and Engel, J. (1987) Biochem. J. 245, 763-772). However, a significant difference was detected between the length of the elongated strand (E2) of core proteins isolated from chick cartilage, E2 length = 105 +/- 22 nm, compared to bovine nasal cartilage, E2 length = 260 +/- 39 nm. The epitope of the proteoglycan core protein-specific monoclonal antibody, S103L, was visualized by electron microscopy, and the distance from the core protein N terminus to the S103L binding site was measured. The S103L binding site was localized to the E2 region, 111 +/- 20 nm from the G1 (N terminus) domain and 34 nm from the G3 (C terminus) domain. cDNA clones selected from an expression vector library of chicken cartilage mRNA also show this epitope to be located near the C-terminal region (R. C. Krueger, T. A. Fields, J. Mensch, and B. Schwartz (1990) J. Biol. Chem. 265, 12088-12097).     

Generation and characterization of neutralizing human monoclonal antibodies against human immunodeficiency virus type 1 Tat antigen

The human immunodeficiency virus Tat regulatory protein is essential for virus replication and pathogenesis. From human peripheral blood mononuclear cells of three Tat toxoid-immunized volunteers, we isolated five Tat-specific human monoclonal antibodies (HMAbs): two full-length immunoglobulin G (IgG) antibodies and three single-chain fragment-variable (scFv) antibodies. The two IgGs were mapped to distinct epitopes within the basic region of Tat, and the three scFvs were mapped to the N-terminal domain of Tat. The three scFvs were highly reactive with recombinant Tat in Western blotting or immunoprecipitation, but results were in contrast to those for the two IgGs, which are sensitive to a particular folding of the protein. In transactivation assays, scFvs were able to inhibit both active recombinant Tat and native Tat secreted by a transfected CEM cell line while IgGs neutralized only native Tat. These HMAbs were able to reduce viral p24 production in human immunodeficiency virus type 1 strain IIIB chronically infected cell lines in a dose-dependent manner.     

Characterization of monoclonal antibodies directed against distinct conserved epitopes of human immunodeficiency virus type 1 core proteins

Summary Two mouse hybridoma cell lines secreting antibodies to the Human Immunodeficiency Virus (HIV) p25 major core protein and its precursors p55 and p41, were developed after immunization with the highly cytopathic Zaïrian HIV-1 isolate, NDK. These monoclonal antibodies also react with the gag gene products from HIV-1-BRU prototype and present cross reaction with HIV-2-ROD, and SIV-AGM. They map into topographically distinct areas of p25 and define epitopic regions topographically separated from those recognized by four other anti-p25 mAb suggesting the existence of at least 6 spatially distinct epitopic regions on HIV-1-p25 core protein.Abbreviations HIV Human Immunodeficiency Virus - SIV Simian Immunodeficiency Virus - HTLVI Human T cell Leukaemia Virus - AIDS Acquired Immune Deficiency Syndrome - mAb Monoclonal Antibody - ELISA Enzyme Linked Immunosorbent Assay - PBS Phosphate Buffered Saline     

Immunochemical characterization of six monoclonal antibodies to human apolipoprotein A-I: epitope mapping and expression.

We have produced and characterized six murine monoclonal antibodies to human apolipoprotein A-I named A-I-9, A-I-12, A-I-15, A-I-16, A-I-19, and A-I-57. All monoclonal antibodies were specific for apolipoprotein A-I and bound between 55% and 100% of 125I-labeled high density lipoproteins (HDL) in a fluid phase radioimmunoassay. All antibodies possessed a higher affinity to apoA-I in HDL than to free, delipidated apoA-I. Two of them, particularly A-I-12 and A-I-15, which were directed to the same or very close epitopes on the molecule, recognized very poorly the delipidated protein. Binding of apoA-I to phospholipid restored the immunoreactivity of the monoclonal antibodies to the protein suggesting that lipids play an important role in determining the immunochemical structure of apoA-I. Using CNBr fragments and synthetic peptides, the epitopes for the antibodies were mapped as follows: A-I-19, CNBr fragment 1; A-I-12 and 15, CNBr fragment 2; A-I-9 and A-I-16, CNBr fragment 3; A-I-57, CNBr fragment 4. Antibody A-I-57 failed to recognized a mutant form of apoA-I, A-IMilano (Arg173----Cys) by immunoblotting and by competitive radioimmunoassay demonstrating that substitution of a single amino acid in human apoA-I may cause the loss of an antigenic determinant.     

Characterization of monoclonal antibodies identifying type and strain-specific epitopes of human immunodeficiency virus type 1

Summary Several hybridoma cell lines were raised against the highly cytopathic Zairian isolate of Human Immunodeficiency Virus (HIV), HIV1-NDK.The specificity of the secreted monoclonal antibodies (mAb) was demonstrated by immunoblotting, radioimmunoprecipitation and immunofluorescence. Two hybridoma cell lines secreted mAb reacting with independent epitopes of the NDK p17 capsid protein and its precursors. One, RL16.24.5, is specific for the NDK isolate whereas the other, RL16.45.1, along with anti-p25 RL16.30.1 mAb, bind all HIV1 isolates but not HIV2. Together with the previously described mAb RL4.72.1 those reagents define lentivirus subfamily (HIV1, HIV2, SIV) type/subtype (HIV1) and strain (HIVI-NDK) specific epitopes expressed on HIVl-NDK core proteins. The last mAb RL16.76.1 binds the env gene products gp160 and gp120.     

A monoclonal antibody to human immunodeficiency virus type 1 which mediates cellular cytotoxicity and neutralization.

Monoclonal antibodies (MAbs) were raised against human immunodeficiency virus type 1 gp120. One MAb, P4/D10, was found to mediate highly efficient antibody-dependent cellular cytotoxicity and virus neutralization. The reactivity was located to a major neutralizing region (amino acids 304 to 323) on gp120. Five other MAbs with a similar epitopic reactivity did not show any antibody-dependent cellulan cytotoxicity activity but had a virus-neutralizing capacity.     

Characterization of a human immunodeficiency virus neutralizing monoclonal antibody and mapping of the neutralizing epitope.

A monoclonal antibody was produced to the exterior envelope glycoprotein (gp120) of the human T-cell lymphotropic virus (HTLV)-IIIB isolate of the human immunodeficiency virus (HIV). This antibody binds to gp120 of HTLV-IIIB and lymphadenopathy-associated virus type 1 (LAV-1) and to the surface of HTLV-IIIB- and LAV-1-infected cells, neutralizes infection by cell-free virus, and prevents fusion of virus-infected cells. In contrast, it does not bind, or weakly binds, the envelope of four heterologous HIV isolates and does not neutralize heterologous isolates HTLV-IIIRF and HTLV-IIIMN. The antibody-binding site was mapped to a 24-amino-acid segment, using recombinant and synthetic segments of HTLV-IIIB gp120. This site is within a segment of amino acid variability known to contain the major neutralizing epitopes (S. D. Putney, T. J. Matthews, W. G. Robey, D. L. Lynn, M. Robert-Guroff, W. T. Mueller, A. J. Langlois, J. Ghrayeb, S. R. Petteway, K. J. Weinhold, P. J. Fischinger, F. Wong-Staal, R. C. Gallo, and D. P. Bolognesi, Science 234:1392-1395, 1986). These results localize an epitope of HIV type-specific neutralization and suggest that neutralizing antibodies may be effective in controlling cell-associated, as well as cell-free, virus infection.     

Synergistic neutralization of human immunodeficiency virus type 1 by combinations of human monoclonal antibodies.

The ability of antibodies to the V3 region and the CD4-binding domain (CD4bd) of human immunodeficiency virus type 1 (HIV-1) to act in synergy to neutralize HIV has been demonstrated previously. However, synergy between antibodies to other HIV-1 epitopes has not been studied. We have used 21 combinations of human monoclonal antibodies (MAbs) directed against different epitopes of the gp120 and gp41 proteins of HIV-1 to evaluate their ability to act in synergy to neutralize HIV-1. Combinations of anti-V3 and anti-CD4bd antibodies, anti-V3 and anti-gp120 C-terminus antibodies, anti-CD4bd and anti-C-terminus antibodies, anti-V3 and anti-gp41 antibodies, and anti-CD4bd and anti-gp41 antibodies were tested. Our results show that some, but not all anti-V3 antibodies can act in synergy with anti-CD4bd antibodies. In addition, for the first time, antibodies to the C-terminus region have been found to act in synergy with the anti-CD4bd antibodies. Various anti-CD4bd MAbs also act in synergy when used together. The use of such cocktails of human MAbs for passive immunization against HIV-1 may prove to be important for therapy in postexposure settings and for prevention of maternal-fetal transmission of the virus. The results also provide information on the types of antibodies that should be elicited by an effective vaccine.