Purified envelope glycoproteins from human immunodeficiency virus type 1 variants induce individual, type-specific neutralizing antibodies.

Repeated immunizations of goats, horses, or chimpanzees with envelope glycoprotein gp120 isolated from human immunodeficiency virus type 1 (HIV-1) resulted in type-specific neutralizing-antibody responses, which began to decay approximately 20 days following the administration of antigen. This was true repeatedly for serum samples from animals hyperimmunized with gp120s from either the HTLV-IIIB (IIIB) or the envelope-divergent HTLV-IIIRF (RF) HIV-1 isolates. Animals previously immunized with the IIIB gp120 were then inoculated with purified RF gp120. The first response in these animals was an anamnestic resurgence of neutralizing antibody to IIIB without detectable neutralizing antibody for RF. However, with later RF gp120 boosts, the IIIB neutralizing-antibody titers fell and an RF type-specific neutralizing-antibody response developed. When assessed with other HIV-1 variants, no group-specific neutralizing antibody was seen in any of the vaccination protocols evaluated. These results will pose real obstacles in the development of an effective vaccine for HIV.     

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.     

Specificity of chimpanzee antibodies binding a strain-specific HIV-1 neutralization epitope of the external envelope

Sera from three chimpanzees infected with a primary lymphadenopathy-associated virus (LAV-1) or human T-lymphotropic virus type III (HTLV-IIIB) passage, from two chimpanzees infected with blood from the primary infected chimpanzees, and from one chimpanzee infected with blood from a secondary passage animal all bound the peptides 3B and 3B/RF, sharing the sequence IQRGPGR, with equally high titers. Pepscan analysis confirmed the amino acids Q, R, G, P, and G as irreplaceable in order to retain antigenicity.     

Superinfection of a chimpanzee with a second strain of human immunodeficiency virus.

Two chimpanzees, one (C-499) infected with the acquired immunodeficiency syndrome-associated retrovirus type 2 (ARV-2) strain of human immunodeficiency virus (HIV) and one (C-560) infected with the lymphadenopathy-associated virus type 1 (LAV-1) strain of HIV, were inoculated with approximately 10(4) tissue culture infective doses of the reciprocal strain. At the time of the second inoculation, both chimpanzees had high titers of HIV-specific antibodies, including antibodies that neutralized both virus strains. After inoculation of the second strain of HIV, the antibody titers in both chimpanzees increased 4- to 10-fold, and in one chimpanzee (C-499), the numbers of infectious peripheral blood mononuclear cells (PBMC) increased 1,000-fold to levels that are comparable with those observed after primary HIV infections. By restriction enzyme analysis of virus recovered from PBMC, both ARV-2 and LAV-1 were identified in C-499, thus demonstrating that superinfection had occurred.     

Persistent infection of chimpanzees with human T-lymphotropic virus type III/lymphadenopathy-associated virus: a potential model for acquired immunodeficiency syndrome.

The lymphadenopathy-associated virus (LAV) prototype strain of human T-lymphotropic virus type III/LAV was transmitted to juvenile chimpanzees with no prior immunostimulation by (i) intravenous injection of autologous cells infected in vitro, (ii) intravenous injection of cell-free virus, and (iii) transfusion from a previously infected chimpanzee. All five animals that received more than one 50% tissue culture infective dose were persistently infected with LAV or chimpanzee-passaged LAV for up to 18 months. During this time they developed no illnesses, but they exhibited various degrees of inguinal and axillary lymphadenopathy and significant reductions in rates of weight gain. Detailed blood chemistry and hematologic evaluations revealed no consistent abnormalities, with the exception of immunoglobulin G (IgG) hypergammaglobulinemia, which became apparent in one animal 6 months postinfection and continued at more than 1 year postinfection. Transient depressions followed by increases in the numbers of T4 cells to levels greater than normal were observed in all animals after virus inoculation. However, the number of LAV-infected peripheral blood cells decreased with time after infection. Results of enzyme immunoassays showed that all infected animals seroconverted to IgG anti-LAV within 1 month postinfection and that antibody titers remained high throughout the period of observation. In contrast, only three of the five LAV-infected chimpanzees had detectable IgM antibody responses, and these preceded IgG-specific serum antibodies by 1 to 2 weeks. Virus morphologically and serologically identical to LAV was isolated from peripheral blood mononuclear cells of all infected animals at all times tested and from bone marrow cells taken from one animal 8 months after infection. One chimpanzee that was exposed to LAV only by sharing a cage with an infected chimpanzee developed lymphadenopathy and an IgM response to LAV, both of which were transient; however, no persistent IgG antibody response to LAV developed, and no virus was recovered from peripheral blood cells during a year of follow-up. Thus, LAV readily infected chimpanzees following intravenous inoculation and persisted for extended periods despite the presence of high titers of antiviral antibodies. However, the virus was not easily transmitted from infected to uninfected chimpanzees during daily cage contact.     

Polyvalent human immunodeficiency virus synthetic immunogen comprised of envelope gp120 T helper cell sites and B cell neutralization epitopes

In previous studies, we have used antisera raised to envelope (env)-gene-encoded synthetic peptides to identify a region of (HIV) glycoprotein (gp) 120 env protein designated SP10 that contains a type-specific neutralizing determinant. To develop a polyvalent, synthetic peptide inoculum that can evoke both neutralizing antibodies and T cell proliferative responses to more than one HIV isolate, synthetic peptides containing type-specific neutralizing determinants of gp120 from HIV isolates HTLV-IIIB (IIIB), HTLV-IIIMN (MN) and HTLV-IIIRF (RF) were coupled to a 16 amino acid T cell epitope (T1) of HIV-IIIB gp120 and used to immunize goats. Goat antisera to each T1-SP10 peptide derived from the SP10 region of gp120 of IIIB, MN, and RF neutralized HIV isolates IIIB, MN and RF in a type-specific manner. Moreover, peripheral blood T cells from immunized goats also proliferated in a type-specific manner to peptides derived from gp120 of IIIB, MN, and RF. When combined in a trivalent inoculum, T1-SP10 peptides from HIV-1 isolates IIIB, MN, and RF evoked a high titered neutralizing antibody response to isolates IIIB, MN, and RF in goats and as well induced immune T cells to undergo blast transformation in the presence of peptides derived from gp120 of all three HIV isolates. The T1 portion of the T1-SP10 construct was shown to induce a B cell antibody response against determinants within the T1 peptide in addition to inducing T cell proliferative responses in immune goat T cells. Moreover, the SP10 portion of the T1-SP10 constructs not only induced B cell antibody production but also induced type-specific T cell proliferative responses localized to the C-terminal variable sequences of the SP10 peptides. Finally, the T1-SP10 peptide construct induced memory T cell proliferative responses to native gp120 env protein. Thus, combinations of homologous SP10 region synthetic peptides containing type-specific neutralizing determinants and T cell epitopes of HIV gp120 may be useful in man to elicit high titered neutralizing B cell responses and, as well, T cell responses to more than one HIV isolate.     

Synthetic peptides containing T and B cell epitopes from human immunodeficiency virus envelope gp120 induce anti-HIV proliferative responses and high titers of neutralizing antibodies in rhesus monkeys.

We have previously described a synthetic peptide (T1-SP10) derived from two noncontiguous regions of HTLVIIIB envelope gp120 (T1, amino acids 428-443; SP10, amino acids 303-321) that induced type-specific anti-HIV neutralizing antibodies and T cell proliferative responses against native HIV gp120 when used as a carrier-free immunogen in goats. In this study, HTLVIIIB T1-SP10 synthetic peptides were used to immunize rhesus monkeys to determine if the peptides were capable of eliciting HIV-specific neutralizing antibody and proliferative responses in primates. Four compounds (alum, polyA:polyU, threonyl-muramyldipeptide (MDP) and IFA) were also compared for efficacy as adjuvants in this system. Rhesus monkeys immunized with T1-SP10 peptides generated high titers of antibodies against the immunogens and also against HTLVIIIB gp120. Sera from all four animals given T1-SP10 in IFA or threonyl-MDP neutralized infection by HTLVIIIB and blocked virus-dependent cell fusion events. A peak neutralization titer of 1:940 was seen in one animal given IFA (19600) and a titer of 1:900 was seen in one of the monkeys (17371) given threonyl-MDP. Proliferative responses of immune rhesus PBMC to T1-SP10 appeared after the first injection. After eight immunizations, two of eight monkeys (one injected with peptides in threonyl-MDP and one given peptides in IFA) had PBMC proliferative responses to native HTLVIIIB gp120. These data demonstrate that the carrier-free T1-SP10 synthetic peptide construct can induce high titers of neutralizing anti-HIV antibody responses and PBMC proliferative responses to HIV in primates.     

Challenge of chimpanzees (Pan troglodytes) immunized with human immunodeficiency virus envelope glycoprotein gp120.

The human immunodeficiency virus type 1 (HIV-1), the causative agent of acquired immunodeficiency syndrome, infects humans and chimpanzees. To determine the efficacy of immunization for preventing infection, chimpanzees were immunized with gp120 purified from human T-cell lymphotrophic virus type IIIB (HTLV-IIIB)-infected cell membranes and challenged with the homologous virus, HTLV-IIIB. A challenge stock of HTLV-IIIB was prepared by using unconcentrated HTLV-IIIB produced in H9 cells. The titer of the virus from this stock on human and chimpanzee peripheral blood mononuclear cells and in human lymphoid cell lines was determined; a cell culture infectivity of 10(4) was assigned. All chimpanzees inoculated intravenously with 40 cell culture infectious units or more became infected, as demonstrated by virus isolation and seroconversion. One of two chimpanzees inoculated with 4 cell culture infectious units became infected. Chimpanzees immunized with gp120 formulated in alum developed antibodies which precipitated gp120 and neutralized HTLV-IIIB. Peripheral blood mononuclear cells from gp120-vaccinated and HIV-infected animals showed a significantly greater response in proliferation assays with HIV proteins than did peripheral blood mononuclear cells from nonvaccinated and non-HIV-infected chimpanzees. Two of the gp120-alum-immunized chimpanzees were challenged with virus from the HTLV-IIIB stock. One animal received 400 cell culture infectious units, and one received 40 infectious units. Both animals became infected with HIV, indicating that the immune response elicited by immunization with gp120 formulated in alum was not effective in preventing infection with HIV-1.     

Vaccine-induced protection of chimpanzees against infection by a heterologous human immunodeficiency virus type 1.

The extraordinary genetic diversity of human immunodeficiency virus type 1 (HIV-1) is a major problem to overcome in the development of an effective vaccine. In the most reliable animal model of HIV-1 infection, chimpanzees were immunized with various combinations of HIV-1 antigens, which were derived primarily from the surface glycoprotein, gp160, of HIV-1 strains LAI and MN. The immunogens also included a live recombinant canarypox virus expressing a gp160-MN protein. In one experiment, two chimpanzees were immunized multiple times; one animal received antigens derived only from HIV-1LAI, and the second animal received antigens from both HIV-1LAI and HIV-1MN. In another experiment, four chimpanzees were immunized in parallel a total of five times over 18 months; two animals received purified gp160 and V3-MN peptides, whereas the other two animals received the recombinant canarypox virus and gp160. At 3 months after the final booster, all immunized and naive control chimpanzees were challenged by intravenous inoculation of HIV-1SF2; therefore, the study represented an intrasubtype B heterologous virus challenge. Virologic and serologic follow-up showed that the controls and the two chimpanzees immunized with the live recombinant canarypox virus became infected, whereas the other animals that were immunized with gp160 and V3-MN peptides were protected from infection. Evaluation of both cellular and humoral HIV-specific immune responses at the time of infectious HIV-1 challenge identified the following as possible correlates of protection: antibody titers to the V3 loop of MN and neutralizing antibody titers to HIV-1MN or HIV-1LAI, but not to HIV-1SF2. The results of this study indicate that vaccine-mediated protection against intravenous infection with heterologous HIV-1 strains of the same subtype is possible with some immunogens.     

Antibody-mediated in vitro neutralization of human immunodeficiency virus type 1 abolishes infectivity for chimpanzees.

This study was undertaken to establish whether antibody directed against the human immunodeficiency virus type 1 (HIV-1) principal gp120 type-specific neutralization determinant can abolish the infectivity of HIV-1 in chimpanzees. Challenge inocula of the IIIb virus isolate were mixed in vitro with either immunoglobulin G (IgG) from an uninfected chimpanzee, nonneutralizing IgG from an HIV-seropositive human, a virus-neutralizing murine monoclonal antibody directed against the HIV-1 IIIb isolate, or virus-neutralizing IgG from a chimpanzee infected with the IIIb isolate. Both neutralizing antibodies were directed against the principal neutralization determinant of the challenge isolate. Establishment of infection following inoculation of each virus-antibody mixture into chimpanzees was assessed by virus-specific antibody development and by virus isolation. No protective effect was noted either with the control IgG or with the nonneutralizing anti-HIV IgG. By contrast, the polyclonal chimpanzee virus-neutralizing IgG prevented HIV-1 in vivo infection, while the neutralizing monoclonal antibody notably decreased the infectivity of the challenge virus. Hence, antibody to the gp120 principal neutralization determinant is able both to prevent HIV-1 infection in vitro and to inhibit infection in vivo.     

Emergence of viruses resistant to neutralization by V3-specific antibodies in experimental human immunodeficiency virus type 1 IIIB infection of chimpanzees.

Emergence in two chimpanzees of human immunodeficiency virus type 1 (HIV-1) IIIB variants resistant to neutralization by the preexisting antibody is described. Viruses isolated from the HIV-1 IIIB gp120-vaccinated and -challenged animal were more resistant to neutralization by the chimpanzee's own serum than viruses isolated from the naive infected animal, indicating immune pressure as the selective mechanism. However, all reisolated viruses were 16- to 256-fold more neutralization resistant than the inoculum virus to antibodies binding to the third variable domain (V3) of the HIV-1 external envelope. Early chimpanzee serum samples that neutralized the inoculum strain but not the reisolated viruses were found to bind an HIV-1 IIIB common nonapeptide (IQRGPGRAF) derived from the gp120 isolate-specific V3 domain shown to induce isolate-specific neutralization in other animals. Amplification of the V3 coding sequence by polymerase chain reaction and subsequent sequence analysis of the neutralization-resistant variants obtained from in vivo-infected animals indicated that early resistance to neutralization by an HIV-1 IIIB monoclonal antibody (0.5 beta) was conferred by changes outside the direct binding site for the selective neutralizing antibody. The reisolated neutralization-resistant isolates consisted of the lower-replication-competent virus subpopulations of the HIV-1 IIIB stock, as confirmed by biological and sequence analyses. In vitro passage of the HIV-1 IIIB stock through chimpanzee and human peripheral blood mononuclear cell cultures void of HIV-specific antibody resulted in homogenic amplification of the more-replication-competent subpopulation preexisting in the original viral stock, suggesting a role for the immune system in suppressing the more-replication-competent viruses.     

Immunoelectrophoretic Analysis of Avian Ribonucleic Acid Tumor Virus Group-Specific Antigens

Tumors induced in pigeons by inoculation with the Schmidt-Ruppin strain of Rous sarcoma virus regressed after about 6 weeks. Sera from these pigeons, taken 8 weeks after inoculation, had complement-fixing group-specific antibody titers of 1:2 to 1:256. In immunoelectrophoresis with the pigeon serum, disrupted BAI strain A (myeloblastosis) avian tumor virus showed at least five precipitin arcs. The pattern of precipitin lines was dependent in part on the means used for virus disruption, and ethyl ether and nonionic detergents appeared to be both effective and relatively mild reagents. Immunoelectrophoretic comparison of pigeon serum with serum from a tumor-bearing hamster and that from virus-inoculated rabbits yielded similar, though not identical, results.     

Induction of neutralizing antibodies against human immunodeficiency virus type 1 primary isolates by Gag-Env pseudovirion immunization

A major challenge for the development of an effective HIV vaccine is to elicit neutralizing antibodies against a broad array of primary isolates. Monomeric gp120-based vaccine approaches have not been successful in inducing this type of response, prompting a number of approaches designed to recreate the native glycoprotein complex that exists on the viral membrane. Gag-Env pseudovirions are noninfectious viruslike particles that recreate the native envelope glycoprotein structure and have the potential to generate neutralizing antibody responses against primary isolates. In this study, an inducible cell line was created in order to generate Gag-Env pseudovirions for examination of neutralizing antibody responses in guinea pigs. Unadjuvanted pseudovirions generated relatively weak anti-gp120 responses, while the use of a block copolymer water-in-oil emulsion or aluminum hydroxide combined with CpG oligodeoxynucleotides resulted in high levels of antibodies that bind to gp120. Sera from immunized animals neutralized a panel of human immunodeficiency virus (HIV) type 1 primary isolate viruses at titers that were significantly higher than that of the corresponding monomeric gp120 protein. Interpretation of these results was complicated by the occurrence of neutralizing antibodies directed against cellular (non-envelope protein) components of the pseudovirion. However, a major component of the pseudovirion-elicited antibody response was directed specifically against the HIV envelope. These results provide support for the role of pseudovirion-based vaccines in generating neutralizing antibodies against primary isolates of HIV and highlight the potential confounding role of antibodies directed at non-envelope cell surface components.     

Synthetic peptides define the fine specificity of the human immunodeficiency virus (HIV) gp160 humoral immune response in HIV type 1-infected chimpanzees

The fine specificities of antibodies produced against human immunodeficiency virus type 1 (HIV-1) gp160 were examined in sera from 23 HIV-1-infected chimpanzees. These animals had been infected with one of six isolates of HIV-1. Sera were screened by enzyme-linked immunosorbent assay for reactivity against seven synthetic peptides corresponding to regions of gp160. Chimpanzees appear to remain healthy after infection with HIV-1, suggesting that these animals may prevent extensive spread of the virus in vivo through immunologic mechanisms. Antibody specificity to gp160 epitopes may play a key role in the defense against HIV-1-related disease. Approximately one-half of all chimpanzee sera contained antibodies reactive with peptide 846-860, which corresponds to the carboxyl terminus of gp41. Less than 10% of sera from HIV-1-infected humans that were examined contained antibodies reactive with peptide 846-860, suggesting that this region is not highly immunogenic in humans. Of the human sera containing antibodies reactive with this peptide, all were from individuals classified as Walter Reed stages 1 to 3. No sera from humans with advanced stages of the disease contained antibodies reactive with peptide 846-860. Peptide 600-611, which reportedly reacts with nearly all sera from HIV-infected humans, was reactive with less than one-half of sera from HIV-1-infected chimpanzees. The observed differences in antibody reactivity to gp160 peptides in sera from HIV-1-infected chimpanzees and humans suggest that each may generate antibodies against differing sets of HIV-1 epitopes. These differences may contribute to the lack of disease progression in chimpanzees after infection with HIV-1.     

Detection of rabies virus antibodies in Brazilian free-ranging wild carnivores

Rabies virus is a pathogen of major concern in free-ranging wild carnivores in several regions of the world, but little is known about its circulation in Brazilian wild carnivores. Sera from 211 free-ranging wild carnivores, captured from 2000 to 2006 in four locations of two Brazilian biomes (Pantanal and Cerrado), were tested for rabies antibodies. Twenty-six individuals (12.3%) had neutralizing antibody titers ≥0.10 IU/ml. The four sampled locations had antibody-positive animals, suggesting that Rabies virus circulates in all of these regions. Results underscore the risk posed by rabies for conservation of Brazilian carnivores and the possibility of the animals acting as reservoirs for the Rabies virus.     

A human immunodeficiency virus type 1 (HIV-1) infection-enhancing factor in seropositive sera

While testing sera for Human Immunodeficiency Virus neutralizing antibody titers, three sera were identified which had the ability to enhance infectivity of the virus. The sera were from three different individuals residing in Nashville, TN. The enhancing factor was not removed by either filtration through 0.05 micron filters or by incubation for one hour with a stoichiometric amount of protein A sepharose. Two of the sera were able to enhance infection by two divergent isolates (HTLV-IIIB and HTLV-IIIRF) while one was only capable of enhancing infection of target cells by HTLV-IIIB. None of the sera induced syncytium formation in chronic HIV-infected cells. The findings suggest that the substance is neither a virus nor an IgG class 1 or 2.     

Loss of CD4+ T Cells in Human Immunodeficiency Virus Type 1-Infected Chimpanzees Is Associated with Increased Lymphocyte Apoptosis

Supportive evidence that apoptosis contributes to loss of CD4⁺ lymphocytes in human immunodeficiency virus type 1 (HIV-1)-infected humans comes from an apparent lack of abnormal apoptosis in apathogenic lentivirus infections of nonhuman primates, including HIV-1 infection of chimpanzees. Two female chimpanzees were inoculated, one cervically and the other intravenously, with HIV-1 derived from the LAI/LAV-1b strain, which was isolated from a chimpanzee infected with the virus for 8 years. Within 6 weeks of infection, both recipient chimpanzees developed a progressive loss of CD4⁺ T cells which correlated with persistently high viral burdens and increased levels of CD4⁺ T-cell apoptosis both in vitro and in vivo. Lymph nodes from both animals also revealed evidence of immune hyperactivation. Intermediate levels of T-cell apoptosis in both peripheral blood and lymph nodes were seen in a third chimpanzee that had been infected with the LAI/LAV-1b strain for 9 years; this animal has maintained depressed CD4/CD8 T-cell ratios for the last 3 years. Similar analyses of cells from 4 uninfected animals and 10 other HIV-1-infected chimpanzees without loss of CD4⁺ cells revealed no difference in levels of apoptosis in these two control groups. These results demonstrate a correlation between immune hyperactivation, T-cell apoptosis, and chronic loss of CD4⁺ T cells in HIV-1-infected chimpanzees, providing additional evidence that apoptosis is an important factor in T-cell loss in AIDS. Furthermore, the results show that some HIV-1 strains are pathogenic for chimpanzees and that this species is not inherently resistant to HIV-1-induced disease.     

Glycosylation of immunodominant linear epitopes in the carboxy-terminal region of the caprine arthritis-encephalitis virus surface envelope enhances vaccine-induced type-specific and cross-reactive neutralizing antibody responses

This study evaluated type-specific and cross-reactive neutralizing antibodies induced by immunization with modified surface glycoproteins (SU) of the 63 isolate of caprine arthritis-encephalitis lentivirus (CAEV-63). Epitope mapping of sera from CAEV-infected goats localized immunodominant linear epitopes in the carboxy terminus of SU. Two modified SU (SU-M and SU-T) and wild-type CAEV-63 SU (SU-W) were produced in vaccinia virus and utilized to evaluate the effects of glycosylation or the deletion of immunodominant linear epitopes on neutralizing antibody responses induced by immunization. SU-M contained two N-linked glycosylation sites inserted into the target epitopes by R539S and E542N mutations. SU-T was truncated at 518A, upstream from the target epitopes, by introduction of termination codons at 519Y and 521Y. Six yearling Saanen goats were immunized subcutaneously with 30 microg of SU-W, SU-M, or SU-T in Quil A adjuvant and boosted at 3, 7, and 16 weeks. SU antibody titers determined by indirect enzyme-linked immunosorbent assay demonstrated anamnestic responses after each boost. Wild-type and modified SU-induced type-specific CAEV-63 neutralizing antibodies and cross-reactive neutralizing antibodies against CAEV-Co, a virus isolate closely related to CAEV-63, and CAEV-1g5, an isolate geographically distinct from CAEV-63, were determined. Immunization with SU-T resulted in altered recognition of SU linear epitopes and a 2.8- to 4.6-fold decrease in neutralizing antibody titers against CAEV-63, CAEV-Co, and CAEV-1g5 compared to titers of SU-W-immunized goats. In contrast, immunization with SU-M resulted in reduced recognition of glycosylated epitopes and a 2.4- to 2.7-fold increase in neutralizing antibody titers compared to titers of SU-W-immunized goats. Thus, the glycosylation of linear immunodominant nonneutralization epitopes, but not epitope deletion, is an effective strategy to enhance neutralizing antibody responses by immunization.     

Glycoprotein exchange vectors based on vesicular stomatitis virus allow effective boosting and generation of neutralizing antibodies to a primary isolate of human immunodeficiency virus type 1

Live recombinant vesicular stomatitis viruses (VSVs) expressing foreign antigens are highly effective vaccine vectors. However, these vectors induce high-titer neutralizing antibody directed at the single VSV glycoprotein (G), and this antibody alone can prevent reinfection and boosting with the same vector. To determine if efficient boosting could be achieved by changing the G protein of the vector, we have developed two new recombinant VSV vectors based on the VSV Indiana serotype but with the G protein gene replaced with G genes from two other VSV serotypes, New Jersey and Chandipura. These G protein exchange vectors grew to titers equivalent to wild-type VSV and induced similar neutralizing titers to themselves but no cross-neutralizing antibodies to the other two serotypes. The effectiveness of these recombinant VSV vectors was illustrated in experiments in which sequential boosting of mice with the three vectors, all encoding the same primary human immunodeficiency virus (HIV) envelope protein, gave a fourfold increase in antibody titer to an oligomeric HIV envelope compared with the response in animals receiving the same vector three times. In addition, only the animals boosted with the exchange vectors produced antibodies neutralizing the autologous HIV primary isolate. These VSV envelope exchange vectors have potential as vaccines in immunizations when boosting of immune responses may be essential.     

Evaluation of poliovirus antibody titers in orally vaccinated semi‐captive chimpanzees in Uganda

Background To understand immunological responses in chimpanzees vaccinated with live‐attenuated vaccine (oral polio vaccine; OPV), serum neutralizing antibodies against poliovirus types 1, 2, and 3 were investigated over time. Methods The neutralizing antibody titers against poliovirus types 1, 2, and 3 were determined by microneutralization test using 100 ID₅₀ of poliovirus types 1, 2, and 3 (Sabin strains). Results Neutralizing antibodies against poliovirus types 1, 2, and 3 were detected in 85.7%, 71.4%, and 65% of the serum from 42 chimpanzees tested 9 years post‐vaccination. The neutralizing antibody titers in chimpanzees were similar to the documented levels in human studies as an indicator of vaccine efficacy. Conclusions This study reveals persistence of neutralizing antibodies in chimpanzees for at least 9 years after vaccination with OPV. This first study in chimpanzees provides useful information for the evaluation of the success of vaccination with OPV in other captive apes.