Modulation of the functions of dengue virus-specific human CD8+ cytotoxic T cell clone by IL-2, IL-7 and IFN gamma

Lymphokines play an important role in immune responses to viruses by modulating functions of T lymphocytes. In the present study, we examined the effects of interleukin-2 (IL-2), interleukin-4 (IL-4), interleukin-6 (IL-6), interleukin-7 (IL-7), and interferon gamma (IFN gamma) on proliferation, cytotoxic activity and lymphokine production of a dengue virus-specific CD8+ human cytotoxic T lymphocyte (CTL) clone. IL-2 and IL-7 induced proliferation of the CD8+ CTL clone in the presence or absence of specific antigen, while IFN gamma suppressed proliferation of the clone. IL-7 and IFN gamma augmented dengue virus-specific cytotoxic activity without inducing non-specific cytotoxic activity, and IL-2 induced non-specific cytotoxic activity. IL-2 induced IFN gamma production by the CD8+ CTL clone. IL-4 and IL-6 did not modulate the functions of the CD8+ CTL clone in these experimental conditions. These results suggest that functions of dengue virus-specific CD8+ CTL are modulated by IL-2, IL-7 and IFN gamma, and that IL-7 is a lymphokine useful to induce growth and to maintain specific cytotoxic activity of CD8+ CTL clones in vitro.

Dengue virus-specific, HLA-B35-restricted, human CD8+ cytotoxic T lymphocyte (CTL) clones. Recognition of NS3 amino acids 500 to 508 by CTL clones of two different serotype specificities

Dengue virus infections are a major cause of morbidity and mortality in tropical and subtropical areas of the world. We analyzed dengue virus-specific CD8+ CD4- CTL at the clonal level to further understand the role of CD8+ CTL in dengue virus infections. Dengue virus-specific CD8+ CTL clones were established from lymphocytes of a dengue 4-immune adult. Three patterns of dengue serotype specificities were identified: 1) specific for dengue 4, 2) cross-reactive for dengue 2 and dengue 4 (subcomplex-specific); and 3) cross-reactive for all four dengue virus serotypes. Three dengue 4-specific clones and one dengue 2/dengue 4 cross-reactive clone were further analyzed. All four of the clones were HLA-B35 restricted and recognized NS3. The epitopes were mapped to amino acids (aa) 483 to 618 of NS3. The epitope was then defined by using synthetic peptides. Three dengue 4-specific clones and one dengue 2/dengue 4 cross-reactive clone recognized the same peptide (TPEGIIPTL) encompassing aa 500 to 508 of dengue 4 NS3. The peptide encompassing aa 500-508 of dengue 2 NS3 was recognized by a dengue 2/dengue 4 cross-reactive clone but was not recognized by the dengue 4-specific clones. Dengue 4-specific and dengue 2/dengue 4 cross-reactive clones used different TCR. These results indicate that CD8+ CTL clones that use different TCR and demonstrate two distinct serotype specificities recognize the same 9-mer peptide in the context of HLA-B35.

Dengue virus-specific, HLA-B35-restricted, human CD8+ cytotoxic T lymphocyte (CTL) clones. Recognition of NS3 amino acids 500 to 508 by CTL clones of two different serotype specificities

Dengue virus infections are a major cause of morbidity and mortality in tropical and subtropical areas of the world. We analyzed dengue virus-specific CD8+ CD4- CTL at the clonal level to further understand the role of CD8+ CTL in dengue virus infections. Dengue virus-specific CD8+ CTL clones were established from lymphocytes of a dengue 4-immune adult. Three patterns of dengue serotype specificities were identified: 1) specific for dengue 4, 2) cross-reactive for dengue 2 and dengue 4 (subcomplex-specific); and 3) cross-reactive for all four dengue virus serotypes. Three dengue 4-specific clones and one dengue 2/dengue 4 cross-reactive clone were further analyzed. All four of the clones were HLA-B35 restricted and recognized NS3. The epitopes were mapped to amino acids (aa) 483 to 618 of NS3. The epitope was then defined by using synthetic peptides. Three dengue 4-specific clones and one dengue 2/dengue 4 cross-reactive clone recognized the same peptide (TPEGIIPTL) encompassing aa 500 to 508 of dengue 4 NS3. The peptide encompassing aa 500-508 of dengue 2 NS3 was recognized by a dengue 2/dengue 4 cross-reactive clone but was not recognized by the dengue 4-specific clones. Dengue 4-specific and dengue 2/dengue 4 cross-reactive clones used different TCR. These results indicate that CD8+ CTL clones that use different TCR and demonstrate two distinct serotype specificities recognize the same 9-mer peptide in the context of HLA-B35.

Preferential usage of T-cell receptor V beta 17 by dengue virus-specific human T lymphocytes in a donor with immunity to dengue virus type 4

In order to better understand human T-cell responses to dengue viruses (DV), we analyzed T-cell receptor (TCR) V beta gene usage in DV-specific T lymphocytes. Peripheral blood T lymphocytes from a DV type 4 immune donor were stimulated in vitro with DV type 4 antigen, and TCR usage was examined by reverse transcriptase PCR. TCR V beta 17 was preferentially used (P = 0.020) among T cells stimulated by DV type 4 in bulk culture. Furthermore, 8 of 19 DV type 4-specific CD4+ T-cell clones established from the peripheral blood mononuclear cells expressed V beta 17 (P = 0.008). Preferential usage of TCR V alpha was not found among T cells expressing V beta 17. These results indicate that there is preferential usage of TCR V beta 17 among DV-specific T cells in this donor and suggest that T cells with certain TCRs may be important in immune responses to DV.

Dengue virus-specific memory T cell responses in human volunteers receiving a live attenuated dengue virus type 2 candidate vaccine

A live attenuated dengue virus type 2 candidate vaccine (16681-PDK53) was evaluated in a phase I trial in 10 nonimmune adult volunteers. The dengue virus-specific memory T cell responses were analyzed as part of this study. Dengue virus-specific T cell proliferative responses were observed in all subjects after stimulating their peripheral blood mononuclear cells with live viruses or noninfectious viral antigens. The highest proliferative response was against dengue virus type 2, although cross-reactivity with other flaviviruses was detected to a lesser degree in some subjects. Dengue virus type 2-specific CD4+ and CD8+ cytotoxic T lymphocytes were generated in all vaccinees. This study investigated whether the candidate vaccine was efficacious in inducing dengue virus-specific CD4+ and CD8+ T cell memory after a single immunization in nonimmune recipients.

Subtype cross-reactive, infection-enhancing antibody responses to influenza A viruses

Antibody-dependent enhancement of the uptake of influenza A virus by Fc receptor-bearing cells was analyzed by using virus strains of the three human influenza A virus subtypes, A/PR/8/34 (H1N1), A/Japan/305/57 (H2N2), and A/Port Chalmers/1/73 (H3N2). Immune sera obtained from mice following primary infection with an H1N1, H2N2, or H3N2 subtype virus neutralized only virus of the same subtype; however, immune sera augmented the uptake of virus across subtypes. Immune sera from H1N1-infected mice augmented uptake of the homologous (H1N1) and H2N2 viruses. Antisera to the H2N2 virus augmented the uptake of virus of all subtypes (H1N1, H2N2, or H3N2). Antisera to the H3N2 virus augmented the uptake of the homologous (H3N2) and H2N2 viruses. These results show that subtype cross-reactive, nonneutralizing antibodies augment the uptake of influenza A virus strains of different subtypes. Antibodies to neuraminidase may contribute to the enhanced uptake of viruses of a different subtype, because N2-specific monoclonal antibodies augmented the uptake of both A/Japan/305/57 (H2N2) and A/Port Chalmers/1/73 (H3N2) viruses.

Recognition of envelope protein by dengue virus serotype-specific human CD4+ CD8- cytotoxic T-cell clones

We analyzed dengue virus-specific CD4+ CD8- cytotoxic T lymphocytes (CTL) at the clonal level to further understand their role in dengue virus infections. Stimulation of peripheral blood mononuclear cells from two dengue virus type 4 (D4V)-immune donors with live D4V or noninfectious D4V antigen generated 17 HLA class II-restricted CD4+ CTL capable of specific lysis of dengue virus antigen-treated autologous lymphoblastoid cell lines. Thirteen clones were D4V specific, three clones were cross-reactive for D2V and D4V, and one clone was cross-reactive for D1V, D3V, and D4V. Antigen recognition by six D4V-specific clones and three D2V- and D4V-cross-reactive clones was restricted by HLA-DR7. Five D4V-specific CD4+ CTL clones lysed autologous lymphoblastoid cell lines infected with a dengue virus-vaccinia virus recombinant containing the E gene of D4V, whereas three serotype-cross-reactive CTL clones did not. These results indicate that E-specific clones are serotype specific and HLA-DR7 restricted in these two donors and suggest that a common epitope on E protein may be recognized. E protein-specific CD4+ CTL may be important mediators of virus clearance especially during reinfection with the same serotype as that in primary infection by providing help for virus-specific antibody production and lysis of virus-infected cells.

Primary influenza A virus infection induces cross-reactive antibodies that enhance uptake of virus into Fc receptor-bearing cells

Sera of young children who had had a primary infection with influenza A virus or were immunized with a live attenuated influenza A virus vaccine were examined for antibody responses that neutralized virus or enhanced uptake of virus into Fc receptor-bearing cells, because antibodies that enhance uptake of influenza virus into Fc receptor-bearing cells have been reported using mouse immune serum and monoclonal antibodies. The neutralizing antibody titers to the homologous infecting virus and to another H1N1 virus isolated several years later were higher after natural infection than after infection with the live attenuated virus. Natural infection and the attenuated vaccine induced antibodies that enhanced uptake of homologous virus and H1N1 virus isolated several years later. These results demonstrate that primary influenza A virus infection results in the induction of infection-enhancing antibodies.

Immunopathologic mechanisms of dengue hemorrhagic fever and dengue shock syndrome

Dengue virus infections are a major cause of morbidity and mortality in tropical and subtropical areas of the world. The immunopathological mechanisms that result in severe complications of dengue virus infection, i.e. dengue hemorrhagic fever (DHF), are important to determine. Primary dengue virus infections induce serotype-specific and serotype-cross-reactive, CD4+ and CD8+ memory cytotoxic T lymphocytes (CTL). In secondary infections with a virus of a different serotype from that which caused primary infections, the presence of cross-reactive non-neutralizing antibodies results in an increased number of infected monocytes by dengue virus--antibody complexes. This in turn results in marked activation of serotype cross-reactive CD4+ and CD8+ memory CTL. We hypothesize that the rapid release of cytokines and chemical mediators caused by T cell activation and by CTL-mediated lysis of dengue virus-infected monocytes triggers the plasma leakage and hemorrhage that occurs in DHF.

Definition of an HLA-DPw2-restricted epitope on NS3, recognized by a dengue virus serotype-cross-reactive human CD4+ CD8- cytotoxic T-cell clone

We previously reported that the clone JK34 was cross-reactive for dengue virus types 1, 2, 3, and 4 and recognized NS3 (I. Kurane, M. A. Brinton, A. L. Samson, and F. A. Ennis, J. Virol. 65:1823-1828, 1991). In the present experiments, we defined the epitope at the amino acid level, with 93 15-mer overlapping peptides which cover the entire NS3. A peptide 4 which contains amino acids 251 to 265 of NS3 sensitized the autologous B lymphoblastoid cell line (LCL) to the lysis by JK34. The smallest peptide recognized by JK34 was a 10-mer peptide which contains amino acids 255 to 264 (EIVDLMCHAT). A monoclonal antibody to HLA-DP inhibited the lysis of epitope peptide-pulsed autologous LCL by JK34. Genotypic typing revealed that the HLA-DP of this donor is DPA1*01, DPB1*0201, which is serologically defined as HLA-DPw2. JK34 lysed peptide 4-pulsed allogeneic LCL which carried HLA-DPw2. These results indicate that HLA-DPw2 is the restriction allele for recognition of this epitope by JK34.

Dengue virus-specific human CD4+ T-lymphocyte responses in a recipient of an experimental live-attenuated dengue virus type 1 vaccine: bulk culture proliferation, clonal analysis, and precursor frequency determination

We analyzed the CD4+ T-lymphocyte responses to dengue, West Nile, and yellow fever viruses 4 months after immunization of a volunteer with an experimental live-attenuated dengue virus type 1 vaccine (DEN-1 45AZ5). We examined bulk culture proliferation to noninfectious antigens, determined the precursor frequency of specific CD4+ T cells by limiting dilution, and established and analyzed CD4+ T-cell clones. Bulk culture proliferation was predominantly dengue virus type 1 specific with a lesser degree of cross-reactive responses to other dengue virus serotypes, West Nile virus, and yellow fever virus. Precursor frequency determination by limiting dilution in the presence of noninfectious dengue virus antigens revealed a frequency of antigen-reactive cells of 1 in 1,686 peripheral blood mononuclear cells (PBMC) for dengue virus type 1, 1 in 9,870 PBMC for dengue virus type 3, 1 in 14,053 PBMC for dengue virus type 2, and 1 in 17,690 PBMC for dengue virus type 4. Seventeen CD4+ T-cell clones were then established by using infectious dengue virus type 1 as antigen. Two patterns of dengue virus specificity were found in these clones. Thirteen clones were dengue virus type 1 specific, and four clones recognized both dengue virus types 1 and 3. Analysis of human leukocyte antigen (HLA) restriction revealed that five clones are HLA-DRw52 restricted, one clone is HLA-DP3 restricted, and one clone is HLA-DP4 restricted. These results indicate that in this individual, the CD4+ T-lymphocyte responses to immunization with live-attenuated dengue virus type 1 vaccine are predominantly serotype specific and suggest that a multivalent vaccine may be necessary to elicit strong serotype-cross-reactive CD4+ T-lymphocyte responses in such individuals.

Direct detection of infectious human immunodeficiency virus type 1 (HIV-1) immune complexes in the sera of HIV-1-infected persons

The sera of human immunodeficiency virus type 1 (HIV-1)-infected subjects were examined for the presence of infectious HIV-1-antibody complexes by their ability to infect Fc gamma receptor (Fc gamma R)-bearing cells. Infection of Fc gamma R-bearing cells by a serum in which half of the p24 antigen was present in a form of immune complexes was inhibited by aggregated human immunoglobulin. Then in studies on 22 sera, 9 sera produced p24 antigen during 14 days of culture in U937 cells. HIV-1 p24 production was inhibited or delayed by the pretreatment of cells with aggregated human immunoglobulin in 6 of the 9 sera that were infectious. These results may reflect interactions between virus-antibody complexes and Fc gamma R-bearing cells in vivo because serum itself was used as the source of virus and virus-antibody complexes. The results indicate that infectious HIV-1 immune complexes are present in the circulation of HIV-1-infected patients.

Neutralization and infection-enhancement epitopes of influenza A virus hemagglutinin

We studied 18 mAb specific for the H3 hemagglutinin (HA) to analyze the relationships between neutralizing and infection-enhancing epitopes on the influenza HA. The mAb could be separated into three groups based on their neutralization (N) and enhancement (E) activity in assays with the prototype virus; group I (N+E+), group II (N+E-) and group III (N +/- E+). A representative mAb from each group was analyzed for its effect on the infectivity of a group of escape mutants, selected with mAb to three sites on the H3 HA, and wild-type H3 viruses to define the relationship between neutralizing epitopes and infection-enhancing epitopes. A group I mAb (N+E+), which recognized site A on the HA, neutralized virus infection at high concentrations of antibody and enhanced virus infection at low concentrations. A group II mAb (N+E-), which recognized site B, had high neutralizing but no enhancing activity. The failure of this mAb to enhance virus uptake was a result of the inability of the Fc portion of virus-mAb complexes to bind to Fc receptor. The addition of anti-murine IgG as a second antibody to these virus-mAb complexes augmented virus uptake. A group III mAb (N +/- E+), which recognized site C, had enhancing but little neutralizing activity. This is the first definition of distinct epitopes that induce neutralizing and/or enhancing mAb.

Neutralization and infection-enhancement epitopes of influenza A virus hemagglutinin

We studied 18 mAb specific for the H3 hemagglutinin (HA) to analyze the relationships between neutralizing and infection-enhancing epitopes on the influenza HA. The mAb could be separated into three groups based on their neutralization (N) and enhancement (E) activity in assays with the prototype virus; group I (N+E+), group II (N+E-) and group III (N +/- E+). A representative mAb from each group was analyzed for its effect on the infectivity of a group of escape mutants, selected with mAb to three sites on the H3 HA, and wild-type H3 viruses to define the relationship between neutralizing epitopes and infection-enhancing epitopes. A group I mAb (N+E+), which recognized site A on the HA, neutralized virus infection at high concentrations of antibody and enhanced virus infection at low concentrations. A group II mAb (N+E-), which recognized site B, had high neutralizing but no enhancing activity. The failure of this mAb to enhance virus uptake was a result of the inability of the Fc portion of virus-mAb complexes to bind to Fc receptor. The addition of anti-murine IgG as a second antibody to these virus-mAb complexes augmented virus uptake. A group III mAb (N +/- E+), which recognized site C, had enhancing but little neutralizing activity. This is the first definition of distinct epitopes that induce neutralizing and/or enhancing mAb.

Neuraminidase augments Fc gamma receptor II-mediated antibody-dependent enhancement of dengue virus infection

Antibody-dependent enhancement (ADE) of dengue virus infection occurs when neutralizing antibodies at sub-neutralizing concentrations or non-neutralizing antibodies form complexes with the virus. These virus-antibody complexes can then attach to a Fc gamma receptor-bearing cell, via the Fc portion of the immunoglobulin, resulting in an increased number of infected cells. ADE may be responsible in part for the most severe clinical manifestations of dengue virus infection which include haemorrhage and shock. Three classes of human Fc gamma receptors exist, Fc gamma RI, Fc gamma RII and Fc gamma RIII. In this study, we examined the effects of neuraminidase on ADE of dengue virus infection mediated by the low-affinity Fc gamma RII. K562 cells, which express only Fc gamma RII, treated with neuraminidase resulted in augmentation of ADE of dengue virus infection by human anti-dengue antibodies. This augmented ADE of infection could be blocked by anti-Fc gamma RII monoclonal antibody IV.3. Incubation of neuraminidase-treated K562 cells with IgG-coated human red blood cells resulted in an increase in the percentage of rosette formations compared with the untreated K562 cells. A bispecific antibody directed against Fc gamma RII and dengue virus (IV.3 x 2H2) enhanced virus infection. Neuraminidase also augmented ADE mediated by this antibody, but to a much lesser degree (by 50%) compared with that seen using conventional human anti-dengue antibody (by 200 to 300%). Fluorescence-activated cell sorting analysis of neuraminidase-treated K562 cells showed that the number of Fc gamma RII-specific antibodies that bind to Fc gamma RII increases by 15 to 20% after treatment with neuraminidase. These results indicate that neuraminidase augments ADE of dengue virus infection and that the augmented ADE is mediated through Fc gamma RII.

Vaccinia virus-specific CD8+ cytotoxic T lymphocytes in humans

Stimulation of human vaccinia virus immune peripheral blood mononuclear cells in vitro from vaccinia virus-immune donors with live vaccinia virus-infected autologous cells generated vaccinia virus-specific cytotoxic T lymphocytes (CTL) capable of lysing vaccinia virus-infected cells. We generated vaccinia virus-specific CD8+ clones and CD4+ CTL lines by limiting dilution from two donors by using peripheral blood mononuclear cells obtained 2 months or 4 years postrevaccination with vaccinia virus. These results demonstrate that vaccinia virus-specific CTL are generated as a result of immunization of humans with vaccinia virus and that both CD8(+)- and CD4(+)-specific T cells are maintained as memory cells.

Dengue virus protein recognition by virus-specific murine CD8+ cytotoxic T lymphocytes

The identification of the protein targets for dengue virus-specific T lymphocytes may be useful for planning the development of subunit vaccines against dengue. We studied the recognition by murine dengue virus-specific major histocompatibility complex class I-restricted, CD8+ cytotoxic T lymphocytes (CTL) of dengue virus proteins using recombinant vaccinia viruses containing segments of the dengue virus genome. CTL from H-2k mice recognized a single serotype-cross-reactive epitope on the nonstructural (NS) protein NS3. CTL from H-2b mice recognized a serotype-cross-reactive epitope that was localized to NS4a or NS4b. CTL from H-2d mice recognized at least three epitopes: a serotype-specific epitope on one of the structural proteins, a serotype-cross-reactive epitope on NS3, and a serotype-cross-reactive epitope on NS1 or NS2a. Our findings demonstrate the limited recognition of dengue virus proteins by CTL from three inbred mouse strains and the predominance of CTL epitopes on dengue virus nonstructural proteins, particularly NS3. Since human dengue virus-specific CTL show similar patterns of recognition, these findings suggest that nonstructural proteins should be considered in designing vaccines against dengue.

High levels of interferon alpha in the sera of children with dengue virus infection

We measured the levels of interferon alpha (IFN alpha) in the sera of Thai children hospitalized with dengue hemorrhagic fever (DHF) or dengue fever (DF) to examine the role of IFN alpha in dengue virus infections of humans. The percentage of patients who had detectable levels of IFN alpha (> or = 3 U/ml) was higher in patients with DHF (80%, P < 0.001) and in patients with DF (60%, P < 0.001) than in healthy Thai children (7%). The levels of IFN alpha were higher in patients with DHF and in patients with DF on the first few days after the onset of fever than in healthy Thai children. The average levels of IFN alpha in patients with DHF were high two days before defervescence, decreasing gradually until the day of defervescence. There was a subset of patients with DHF who had increasing levels of IFN alpha after defervescence. However, the levels of IFN alpha in patients with DF were not high after fever subsided. The levels of IFN alpha were not different among children with DHF grades 1, 2 and 3. Among patients with DHF, T lymphocytes were activated to a higher degree in high IFN alpha producers than in low IFN alpha producers. These results indicate that similarly high levels of IFN alpha are produced in vivo during the acute stages of DHF and DF, and that high levels of IFN alpha remain after fever subsides in some patients with DHF, but not in patients with DF.

Protective cross-reactive epitope on the nonstructural protein NS1 of influenza A virus

We reported previously that adoptive immunization with an influenza A virus NS1-specific H-2Ld-restricted, cross-reactive, CTL clone A-11 established by stimulation with A/PR/8/34 virus (H1N1) reduced lung virus titers in mice challenged with virus in vivo (Virology 178:174-179, 1990). Using a set of recombinant vaccinia virus constructs containing truncated portions of the NS gene we have localized this cross-protective CTL epitope to the N-terminal region of the NS1 protein. This region of NS1 is active in inducing CD8+ CTL in vivo because virus-stimulated BALB/c immune spleen cells in bulk cultures also recognized the N-terminal region of the NS1 protein.

Dengue virus-specific, human CD4+ cytotoxic T lymphocytes generated in short-term culture

We previously reported cytotoxic activity of dengue virus-specific CD4+ CD8- T cell clones established in long-term in vitro culture. In the present experiments we tried to determine whether dengue virus-specific CD4+ CD8- CTL3 are present in short-term bulk cultures. Peripheral blood mononuclear cells (PBMC)3 from a donor who had been immunized with an experimental live attenuated dengue 1 vaccine 8 months earlier were used. PBMC were incubated with noninfectious dengue 1 antigen (Ag)3 for 7 days, and were examined for dengue 1-specific cytotoxic activity. PBMC cultured with dengue 1 Ag lysed autologous lymphoblastoid cell line (LCL)3 pulsed with noninfectious dengue 1 Ag, but did not lyse LCL pulsed with Ag of other dengue serotype, West Nile virus, or yellow fever virus, or control Ag. Treatment of cultured PBMC with monoclonal antibody to CD3 or CD4 and complement abrogated the cytotoxic activity but treatment with a monoclonal antibody to CD8 and complement did not. A time course study showed that dengue 1 Ag-specific CTL were first detected in 5 day cultures. Lysis of target cells by these CD4+ CTL were restricted by HLA class II, and HLA DQw1 and HLA DRw52 were determined to be the restriction molecules. These results indicate that dengue virus-specific CD4+ CD8- CTL are generated in short-term bulk cultures as well as in long-term-cultured cell lines, and support the concept that CD4+ CTL may be generated in vivo during infection.

Distinction of human immunodeficiency virus type 1 neutralization and infection enhancement by human monoclonal antibodies to glycoprotein 120

There is increasing evidence that sera from HIV-1-infected individuals contain antibodies that enhance infection by HIV-1 in vitro. Previous work has demonstrated that complement receptors on T lymphoid cells and Fc receptors for IgG (Fc gamma R) on monocytic cells are required for enhanced infection by antibody-complexed HIV-1. Characterization of such infection-enhancing antibodies is essential because immunogenic epitopes which induce enhancing antibodies should be excluded from HIV-1 vaccines. This study was conducted to identify enhancing antibodies involved in Fc R-mediated enhancement of HIV-1 infection employing IgG human monoclonal antibodies (HMAbs) reactive against gp120 of HIV-1, which were produced by B cell lines derived from an HIV-1-infected individual. A potent neutralizing HMAb N70-1.5e did not enhance infection by HIV-1 (IIIB and MN strains), whereas HMAb N70-2.3a mediated enhancement of HIV-1 infection, but had little neutralizing activity. A competition radio immunoassay demonstrated that the two antibodies bind to distinct epitopes. These results indicated that enhancing and neutralizing antibodies can be induced by different epitopes on gp120, suggesting the potential for development of safe vaccines against HIV-1 by exclusion of immunogenic epitopes for enhancing antibodies. We made attempts to identify the epitope on gp120 that is recognized by the enhancing antibody N70-2.3a by using recombinant HIV-1 proteins and found that the antibody binds to a conformational site of nonvariable sequences in the carboxyl half (aa 272-509) of gp120.

Mutation of human immunodeficiency virus type 1 at amino acid 585 on gp41 results in loss of killing by CD8+ A24-restricted cytotoxic T lymphocytes

A human leukocyte antigen A24-restricted CD8+ cytotoxic T-cell clone specific for gp41 of human immunodeficiency virus type 1 was isolated from an infected individual. The epitope was localized to amino acids 584 to 591 (YLKDQQLL, NL43 env sequence) of gp41 by using a panel of recombinant vaccinia viruses that contain truncated env genes and synthetic peptides. The clone killed autologous B-lymphoblastoid cell lines pulsed with a synthetic peptide reflecting the sequence of the IIIB and MN strains. This clone, however, failed to kill target cells pulsed with the peptides that have a mutation from Lys to Arg or Gln at amino acid 585 which is present in some prototype human immunodeficiency virus type 1 strains, e.g., ADA, JFL, SC, ALA1, BAL1, SF2, VRF, SF33, and WMJ2. This finding that a mutation at amino acid 585 on gp41 results in nonrecognition by human leukocyte antigen A24-restricted CD8+ cytotoxic T lymphocytes suggests that antigenic variation at T-cell epitopes contributes to the failure of immune control of human immunodeficiency virus type 1 infections.

Vaccinia virus-specific human CD4+ cytotoxic T-lymphocyte clones

Vaccinia virus-specific cytotoxic T-lymphocyte (CTL) clones were established from a healthy donor, who had been immunized with vaccinia virus vaccine, by stimulation of peripheral blood lymphocytes with UV-inactivated vaccinia virus antigen. The phenotype of all of the clones established was CD3+ CD4+ CD8- Leu11-. We used a panel of allogenic vaccinia virus-infected B-lymphoblastoid cell lines and demonstrated that some of the clones recognized vaccinia virus epitopes presented by human leukocyte antigen (HLA) class II molecules. Monoclonal antibodies specific for either HLA-DP or HLA-DR determinant reduced the cytotoxicity of specific clones. The HLA-restricted cytotoxicity of the clones is vaccinia virus specific, because vaccinia virus-infected but not influenza virus-infected autologous target cells were lysed. Using vaccinia virus deletion mutants, we found that some of the CTL clones recognize an epitope(s) that lies within the HindIII KF regions of the vaccinia virus genome. These results indicate that heterogeneous CD4+ CTL clones specific for vaccinia virus are induced in response to infection and may be important in recovery from and protection against poxvirus infections.

Studies of antibody-dependent enhancement of human immunodeficiency virus (HIV) type 1 infection mediated by Fc receptors using sera from recipients of a recombinant gp160 experimental HIV-1 vaccine

Subneutralizing concentrations of sera from human immunodeficiency virus (HIV)-1-infected patients augment HIV infection mediated by Fc receptor uptake by human monocytes and the monocytic cell line U937. Antibody-dependent enhancement (ADE) and neutralization activity were studied in the sera of HIV-1 antibody-negative volunteers who had been immunized with three 40-micrograms doses of a recombinant gp160 (rgp160) candidate HIV vaccine. Volunteers were vaccinated with rgp160 or a hepatitis B vaccine as a control on days 0, 30, and 180. Sera were obtained before and after three doses of vaccine and were tested for ADE and neutralization activity. Serum samples collected before vaccination showed neither neutralization nor ADE activity. Thirteen sera from volunteers who received gp160 and four from placebo recipients failed to show ADE. Three sera showed low levels of neutralization of strain IIIB of HIV. Vaccination with this dose of rgp160 produced neutralizing antibodies in some subjects but did not induce detectable enhancing antibodies.