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P Nara

Publications and source records attributed to P Nara.

At least 19 recordsLinked to original sources
PubMed2001

Stimulation of antiviral antibody response in SHIV-IIIB-infected macaques.

Three macaques infected with SHIV-IIIB and expressing the shared 1F7-idiotypic marker on antibodies against HIV-1 gp120, were injected intravenously with 1F7 monoclonal antibodies (MoAb). As controls, a SHIV-IIIB-infected macaque was injected with a HIV-unrelated mouse monoclonal isotype antibody (TEPC-183) and two healthy, noninfected macaques were injected with MoAb 1F7. 1F7-id-expressing antibodies against gp120-IIIB decreased in two of the three MoAb 1F7-treated macaques and then rebounded. Importantly, antibodies binding to envelope proteins of heterologous HIV-1 strains MN, CM, and SF2, which were low or not detectable before the MoAb 1F7 treatment, increased rapidly following MoAb inoculations in all three 1F7 MoAb treated macaques, but not in the macaque injected with control MoAb TEPC-183. Newly arising antibodies reacting with heterologous virus, i.e. HIV-1 gp120-MN, SF2, and CM did not express 1F7-id. Surprisingly, significant increases of antibodies were also observed in the 1F7-inoculated macaques' antibodies directed to non-HIV antigens (DNP, peptides and BSA). The noninfected control animals did not produce antibodies to these antigens despite MoAb 1F7 treatment. These data show that the MoAb 1F7 injections of chronically SHIV-IIIB-infected macaques resulted in idiotype-specific clonal suppression with broadening the antibody response to HIV envelope proteins.

Animals↗
PubMed2000

Human immunodeficiency virus (HIV)-positive sera obtained shortly after seroconversion neutralize autologous HIV type 1 isolates on primary macrophages but not on lymphocytes.

The aim of this study was to analyze the role of humoral immunity in early human immunodeficiency virus (HIV) infection. As neutralizing activities in HIV-positive sera are rarely detectable earlier than 9 to 12 months after infection using primary lymphocytes as target cells in neutralization assays, humoral immunity is generally thought not to contribute significantly to early virus control in the patients. Besides lymphocytes, cells of the monocyte/macrophage lineage are known to be important target cells for HIV in vivo during the establishment of the infection. Therefore, we studied the neutralization of early primary HIV isolates by autologous serum samples using primary macrophages as target cells in the neutralization assays. We analyzed neutralizing activities against the autologous HIV-1 isolates in 10 patients' sera taken shortly after seroconversion, both on primary macrophages and, for comparison, on lymphocytes. Viruses were isolated and expanded in primary mixed cultures containing macrophages and lymphocytes in order to avoid selection for one particular cell type. All viruses replicated to different degrees in macrophages and lymphocytes; nine had a nonsyncytium-inducing phenotype, and one was syncytium inducing. The detection of neutralizing antibodies in acute primary HIV infection depended on the target cells used. Confirming previous studies, we did not find neutralizing activities on lymphocytes at this early time point. In contrast, neutralizing activities were detectable in the same sera if primary macrophages were used as target cells. Differences in neutralizing activities on macrophages and lymphocytes were not due to different virus variants being present in the different cell systems, as gp120 sequences derived from both cell types were homogeneous. Neutralization activities on macrophages did not correlate with the amount of beta-chemokines in the sera. As affinity-purified immunoglobulin G preparations from an early patient serum also exhibited neutralization of the autologous virus isolate on primary macrophages, but not on lymphocytes, neutralization is very likely due to antibodies against viral epitopes necessary for infection of macrophages but not for infection of lymphocytes. Our data suggest that, along with cell-mediated immunity, humoral immunity may contribute to the reduction of primary viremia in the patient. This was further supported by a certain association between neutralizing antibody titers on macrophages and viral load in the patients.

Cells, Cultured↗
PubMed1999

HIV-specific immunity following immunization with HIV synthetic envelope peptides in asymptomatic HIV-infected patients.

OBJECTIVE: A phase I trial was conducted to evaluate the safety and immunogenicity of an HIV synthetic peptide vaccine in HIV-seropositive individuals. The immunogens used in this study were PCLUS 3-18MN and PCLUS 6.1-18MN envelope peptides. METHODS: Eight HIV-infected patients received six subcutaneous injections of 160 microg PCLUS 3-18MN in Montanide ISA 51 and were followed longitudinally for a year after the first immunization. Peripheral blood mononuclear cells (PBMC) were tested for peptide-specific T helper and cytotoxic T cell (CTL) responses, HIV-1MN neutralizing antibodies and antibodies against HIV PCLUS 3 and P18 MN peptides. RESULTS: PCLUS 3-1 8MN-specific T helper responses were significantly increased at 36 weeks (P < 0.05, after adjustment for multiple comparisons) following initial immunization with PCLUS 3-18MN. A P18MN-specific CTL response, not present prior to vaccination, was observed after immunization in one patient. Serum HIV-1 MN-neutralizing antibody titers increased in each of the three patients who had low titers prior to immunization. Plasma HIV RNA levels and CD4 cell counts did not change appreciably during the study period. CONCLUSIONS: This trial demonstrates that both peptides can be safely administered to HIV-infected individuals and that PCLUS 3-18MN induces increases in HIV peptide-specific immune responses.

AIDS Vaccines↗
PubMed1997

Challenge of chimpanzees immunized with a recombinant canarypox-HIV-1 virus.

To evaluate the potential protective efficacy of a live recombinant human immunodeficiency virus type 1 (HIV-1) canarypox vaccine candidate, two chimpanzees were immunized five times with ALVAC-HIV-1 vCP250, a recombinant canarypox virus that expresses the HIV-1[IIIB(LAI)] gp120/TM, gag, and protease gene products. One month after the last booster inoculation, the animals were challenged by intravenous injection of cell-associated virus in the form of peripheral blood mononuclear cells from an HIV-1[IIIB(LAI)]-infected chimpanzee. One chimpanzee with a neutralizing antibody titer to HIV-1[IIIB(LAI)] of 128 at the time of challenge was protected, whereas both the second animal, with a neutralizing antibody titer of 32, and a naive control animal became infected. At 5 months after challenge, the protected chimpanzee and a third animal, previously immunized with various HIV-1[MN] antigens, were given a booster inoculation. The two animals were challenged intravenously 5 weeks later with twenty 50% tissue culture infectious doses of cell-free HIV-1[DH12], a heterologous subtype B isolate. Neither chimpanzee had neutralizing antibodies to HIV-1[DH12], and neither one was protected from infection with this isolate. The immune responses elicited by vaccination against HIV-1[IIIB(LAI)] or HIV-1[MN] did not, therefore, protect the animals from challenge with the heterologous cell-free HIV-1[DH12].

AIDS Vaccines↗
PubMed1996

Immune strategies utilized by lentivirus infected chimpanzees to resist progression to AIDS.

HIV-1 infected chimpanzees are relatively resistant to the development of AIDS despite their close genetic relatedness to humans and their susceptibility to HIV-1 infection. We have systematically studied possible reasons for their relative ability to maintain T helper (Th) cell numbers and immune competence in the presence of chronic HIV-1 infection. Factors which may alone or together cause the loss in T-cell dependent immunity include: (i) the loss of Th cell function; (ii) the loss of Th cells; and (iii) the loss of capacity for Th cell renewal. Differences in the in vivo and in vitro responses of T lymphocytes from chimpanzees and humans were compared for evidence of HIV-1 related T-cell dysfunction. In contrast to HIV infected individuals, HIV-1 infected chimpanzees maintained strong Th cell proliferative and cytokine responses after receiving tetanus toxoid boosts. In addition there was no abnormal Th1 to Th2 shift as is suggested to occur in AIDS patients. There was no evidence of Th cell dysfunction such as increased level of programmed cell death (PCD) or immune activation in HIV-1 infected chimpanzees in contrast to HIV-1 infected asymptomatic humans. Anergy could be induced with HIV-1 gp120 in human but not chimpanzee Th lymphocytes. We then asked if there was a direct loss of chimpanzee CD4+ cells due to HIV-1 infection in vitro. Infection of chimpanzee CD4+ lymphocyte cultures with HIV-1 in the absence of CD8+ cells resulted in marked cytopathic effect with complete lysis and loss of cells within 3 weeks. We concluded that most chronic HIV-1 infected chimpanzees were able to maintain relatively stable CD4+ lymphocyte numbers despite CD4+ lymphocyte destruction due to direct effects of the virus. Furthermore, there was no evidence of indirect Th cell loss, since neither increased levels of anergy nor apoptosis were observed. Lymph node biopsies from HIV-1 infected chimpanzees revealed that MHC class II rich regions of lymph nodes remained intact, in contrast to the involution of these regions in infected humans. This suggested that chimpanzees may maintain the capacity for Th cell renewal by preserving this MHC class II lymphoid environment. The data presented in this paper suggests that chimpanzees may preserve this critical MHC class II-Th cell environment by dramatically suppressing extra-cellular virus load and that this may be in part mediated by soluble lentivirus suppressing factors.

Animals↗
PubMed1995

Insertion of primary syncytium-inducing (SI) and non-SI envelope V3 loops in human immunodeficiency virus type 1 (HIV-1) LAI reduces neutralization sensitivity to autologous, but not heterologous, HIV-1 antibodies.

The aim of the study was to investigate the influence of V3 loops from naturally occurring viruses on the neutralization sensitivity of a molecularly cloned virus. A selection of well-defined syncytium-inducing (SI) and non-SI V3 loops of a single human immunodeficiency virus type 1-infected individual (H594) and the V3 regions of two SI laboratory strains were inserted in an infectious molecular clone of human immunodeficiency type 1 LAI. Neutralization was performed with a heterologous serum pool and autologous patient serum, using the virus reduction neutralization assay and peripheral blood lymphocytes as target cells. High sensitivity of the chimeric viruses containing the laboratory strain V3 regions to neutralization by H594 sequential sera as well as the heterologous serum pool was found. A statistically significant correlation between the sensitivities of these viruses was seen. In contrast, insertion of the primary isolate NSI and SI envelope V3 loops significantly reduced the neutralization by autologous serum but not by the heterologous serum pool. No correlation was found between the neutralization of the viruses with laboratory strain-derived V3 regions and the viruses with primary isolate V3 domains. We conclude that heterologous antibodies are able to neutralize infectious molecular clones with V3 loops of both SI and NSI viruses, regardless of whether they originated from laboratory strains or primary isolates. However, serum of patient H594 discriminated between the two types of viruses and showed reduced neutralization of the viruses with the autologous NSI and SI primary isolate V3 loops. These results indicated that the neutralization sensitivity of the viruses depended on the capacity of the V3 region to influence the conformation of the virus envelope. These V3-dependent conformational changes partially explain the neutralization sensitivity of laboratory strains and the relative neutralization resistance of primary isolates.

Acquired Immunodeficiency Syndrome↗
PubMed1994

The natural history of HIV-1 infection: virus load and virus phenotype independent determinants of clinical course?

Virus load and virus phenotype have both been indicated as major determinants of disease progression in HIV-1 infection. In this study HIV-1 RNA copy numbers in serum, virus phenotype, and CD4+ cell counts were analyzed longitudinally in a group of 20 seroconverters progressing to AIDS within 5.5 years. In this group 12 individuals developed AIDS without syncytium-inducing (SI) viruses ever being isolated, while 8 individuals showed a non-SI (NSI) to SI phenotypic switch prior to AIDS development. HIV-1 RNA copy numbers in sera of all progressors were stable and high from seroconversion until development of AIDS. Twenty-one seroconverters remaining asymptomatic for more than 5.5 years were selected as nonprogressing controls, and both progressors and nonprogressors were evaluated at seroconversion and early in infection (3 years post seroconversion). Comparative analysis revealed that at the point of seroconversion HIV-1 RNA copy numbers in sera from NSI progressors, SI progressors, and nonprogressors were not significantly different, nor were their CD4+ cell counts. At seroconversion all individuals harbored viruses with an NSI phenotype. In contrast to the progressors, HIV-1 RNA copy numbers in sera of nonprogressors had declined significantly during the early period of infection. At the second time point RNA copy numbers in the sera of NSI progressors and nonprogressors differed significantly (P = 0.0005), while RNA copy numbers in the sera of SI progressors and nonprogressors did not. However, at this time point the CD4+ cell counts of SI progressors were significantly lower than those from nonprogressors (P = 0.002), while the CD4+ cell counts of NSI progressors and nonprogressors did not differ significantly. These results show that early in HIV-1 infection progressors and nonprogressors are distinguishable. NSI progressors can be distinguished from nonprogressors on the basis of serum HIV-1 RNA load and S1 progressors on the basis of CD4+ cell decline. In addition, a significant decrease in the number of HIV-1 RNA copies in the early phase of infection seems to postpone the development of AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Identification of a new neutralizing epitope conformationally affected by the attachment of CD4 to gp120.

We have developed a strategy to purify and characterize various anti-gp120 antibody populations in HIV+ sera by using anti-Id mAb. One preparation of human anti-gp120 antibody (ES+ Ab) isolated on an anti-Id mAb (ES)-conjugated immunoabsorbent exhibited a novel neutralizing epitope specificity. The ES+ Ab bound only to the native form of recombinant gp120SF2 and gp120IIIB and not to the third hypervariable region (V3) loop peptide. In contradistinction to other CD4-gp120-inhibiting and V3-specific neutralizing antibodies, ES+ Ab exhibited a dose-dependent enhancement of binding to recombinant gp120 in the presence of recombinant soluble CD4. In addition, flow cytometric analysis revealed a similar increase in the binding of ES+ Ab to the native form of gp120 expressed on the HIV-infected cells. The ES+ Ab competed with CD4 binding site- and V3-specific antibodies in binding to gp120, suggesting that the ES+ Ab epitope is located near the CD4 binding site epitope and the V3 region. The ES+ Ab neutralized six genetically distinct HIV-1 strains. The neutralizing activity of ES+ Ab on HIVIIIB was significantly increased in the presence of human anti-CD4 binding site mAb. These data suggest that the ES+ Ab epitope represents a conserved, conformational, neutralization target on gp120 that may be involved in viral infection in an event after the CD4-gp120 interaction and that is distinct from previously defined neutralizing epitopes of gp120. This finding may be important for the development of an AIDS vaccine and immunotherapy.

Amino Acid Sequence↗
PubMed1993

Qualitative and quantitative detection of HIV-1 RNA by nucleic acid sequence-based amplification.

AIM: To develop a method to detect HIV-1 viral RNA by amplifying a specific nucleic acid sequence. METHOD: The nucleic acid sequence-based amplification (NASBA) method uses the simultaneous activity of avian myeloblastosis virus reverse transcriptase, T7 RNA polymerase and RNase H to amplify a specific nucleic acid target sequence. VALIDATION: An in vitro cultured HIV-1 stock solution was used to validate the NASBA method and determine the variation in RNA measurement. CONCLUSION: Although NASBA is theoretically capable of specific amplification of RNA or DNA, it is most suitable for amplification of RNA, and therefore for detection of HIV-1 viral RNA.

Gene Amplification↗
PubMed1993

HIV experimental vaccines based on the iscom technology using envelope and GAG gene products.

In previous experiments gp160 incorporated into iscom was shown to induce neutralizing antibodies to the homologous as well as the heterologous isolates of HIV-1 (Akerblom et al., AIDS Res., 1991). In the present work we have incorporated into iscoms three defined recombinant DNA products of HIV-1. The carboxy-terminal part of gp120 expressed in E. Coli-PB-1; a chimera containing parts of both p24 and p15 expressed in E. coli-GAG; and baculovirus gp160 cloned in baculovirus and produced in insect cells. Immune responses were induced by the iscom preparations to the homologous antigen as well as to defined recombinant products and to the synthetic peptide RP135 (aa 304-328) harboring a neutralizing epitope. Sera from mice immunized with PB1-iscoms and gp160 (baculo) iscoms were tested in a syncytie inhibition assay. The serum from a mouse immunized with PB1 iscoms reacted strongly with the synthetic peptide RP135 and also neutralized the homologous isolate HIV-1/IIIB with a neutralization titer of 1/64. Three gp160 (baculo) iscom antisera were tested, of which two reacted strongly with the synthetic peptide RP135 but did not neutralize the homologous isolate HIV-1/IIIB. High serum titers were induced in mice by the gp160 iscoms (2 micrograms) to homologous antigen and the recombinant DNA E. coli construct p121 covering part of gp41. The ceilings of the antibody responses were reached after two immunizations. The PB1- and GAG-iscoms required three immunizations to reach the ceiling of the antibody response.

AIDS Vaccines↗
PubMed1992

Two major groups of neutralizing anti-gp120 antibodies exist in HIV-infected individuals. Evidence for epitope diversity around the CD4 attachment site.

The aim of this study was to dissect neutralizing anti-gp120 antibody populations in seropositive asymptomatic individuals. Murine anti-Id mAb were raised against polyclonal affinity-purified human anti-gp120 antibodies. These anti-Id mAb were used to fractionate anti-gp120 antibodies from a pool of HIV-positive sera into idiotypically distinct anti-gp120 antibody (Id+Ab) preparations. Immunochemical and neutralization studies indicated that all Id+Ab that neutralized HIV-1 in vitro interacted with either the V3 loop or the CD4 attachment site of gp120. The V3-specific Id+Ab neutralized HIV-1 in a strain-restricted manner. Id+Ab specific for the CD4 attachment site exhibited different spectra of neutralizing activities against multiple strains of HIV-1. This finding indicates that multiple, antigenically diverse epitopes reside around the CD4 attachment site of gp120. Significantly, depletion of the Id+Ab from affinity-purified total anti-gp120 antibodies abrogated most of the neutralizing activities of these antibodies, suggesting that neutralizing anti-gp120 antibodies consist of two major specificities, either to the V3 region or to the CD4 attachment site. The understanding of specificities and neutralizing activities of different anti-gp120 antibodies in seropositive healthy individuals will be helpful for designing effective vaccines and immunotherapeutic strategies for AIDS.

Animals↗
PubMed1992

Vaccine protection of chimpanzees against challenge with HIV-1-infected peripheral blood mononuclear cells.

Because human immunodeficiency virus (HIV) can be transmitted as cell-free virus or as infected cells (cell-associated virus), vaccines must protect against infection by both viral forms. Vaccine-mediated protection of nonhuman primates against low doses of cell-free HIV-1, HIV-2, or simian immunodeficiency virus (SIV) has been demonstrated. It is now shown that multiple immunizations of chimpanzees with HIV-1 antigens protected against infection with cell-associated virus. Protection can persist for extended periods (one animal had not been exposed to viral antigens for 1 year before challenge). These results show that it is possible to elicit long-lasting protective immunity against cell-associated HIV-1.

AIDS Vaccines↗
PubMed1992

Anti-idiotype monoclonal antibody elicits broadly neutralizing anti-gp120 antibodies in monkeys.

Murine monoclonal antibodies (mAbs) were raised against human, polyclonal, anti-gp120 antibodies (Ab1) and were selected for binding to broadly neutralizing anti-gp120 antibodies in sera positive for human immunodeficiency virus (HIV). One anti-idiotype mAb (Ab2), 3C9, was found to be specific for human anti-gp120 antibodies directed against an epitope around the conserved CD4 attachment site of gp120. The 3C9 reactive human anti-gp120 antibodies (3C9+ Ab) neutralized MN, IIIB, RF, and four primary isolates of HIV type 1 (HIV-1). Cynomolgus monkeys were immunized with 3C9 in adjuvant to test whether this anti-idiotype mAb could induce neutralizing anti-gp120 antibodies. The results show that purified anti-anti-idiotype antibodies (Ab3) from 3C9 immune sera bind to an epitope around the CD4 attachment site of gp120SF and gp120IIIB. Furthermore, purified gp120-specific Ab3 neutralize MN, IIIB, and RF isolates. These results demonstrate that primates immunized with an anti-idiotype mAb produce broadly neutralizing anti-HIV-1 antibodies. Since this anti-idiotype mAb was selected by identifying a clonotypic marker, its biological activity can be explained as the results of clonotypic B-cell stimulation.

Animals↗
PubMed1992

Clonal dominance: cause for a limited and failing immune response to HIV-1 infection and vaccination.

Oligoclonal and monoclonal antibody populations against different HIV-encoded proteins are common in sera from healthy HIV-1-infected individuals. This is especially important when it includes functional antibody repertoires directed at neutralizing cell free virus or inhibiting cell fusion of virus-infected cells. In the host, during the acute viral syndrome following HIV-1 infection, a rapidly replicating, cell-free and genotypically homogeneous viral population is known to arise from the transmitted viral inoculum. Dominant B and possibly T cell clones responsible for both functional and nonfunctional antibodies appear to arise early in response to this initially homogeneous cell-free viral population heralding seroconversion. During the viremic phase, deposition of cell-free virus as either complement coated or as immune complexes (iccosomes) within the germinal centers results in continued and long-term boosting of primed B cells. This saturation of antigen presenting germinal centers and the presence of limited, immunodominant cross-reactive epitopes on the envelope glycoprotein of the closely-related and immune selected viral quasispecies in the host appear to continue the boosting effect of the primed secondary response. This repertoire freeze appears to be responsible for limiting the recruitment of new uncommitted B cells to other functional epitopes or affinity maturation of B-cell clones to escape variants and the subsequent production and quality of functional antibody against the evolving/selected virus populations. This may include in addition to neutralizing and cell fusion inhibiting antibody, direct complement-fixing and/or NK-directed antibody-dependent cell-mediated antibody as well as various effector, helper, or T cell-mediated activity. In addition to antiviral antibody responses, antibody directed to other invading pathogens or opportunistic organisms may also be clonaly restricted. Antibody facilitating infectivity or blocking effective immunity may also be included in this phenomena and thus be over represented by such a mechanism. AIDS vaccines utilizing the envelope must identify these epitopes to avoid creating clonal dominance and therefore possibly limit the breadth and specificity of a humoral response following infection. Furthermore, immunotherapeutic approaches designed to recruit humoral immune effector function must be able to overcome the dominance of noneffective antibodies and restore a normal polyclonal immune response against HIV. Further research, therefore, into the humoral and cellular dysregulating properties of the HIV-1 envelope is warranted.

AIDS Vaccines↗