Expansion of restricted cellular immune responses to HIV-1 envelope by vaccination: IL-7 and IL-12 differentially augment cellular proliferative responses to HIV-1

The failure of immune effector mechanisms to control HIV-1 infection has important consequences for the human host. In a randomized cohort of HIV-infected patients, there was striking in vitro restriction of the proliferative response to HIV-1 envelope protein (Env), gp160; only 34% of patients recognized Env. Therapeutic vaccination with recombinant gp160 or gp120 (rgp160, rgp120) reversed the restriction in vitro, with Env recognition rising to 81%. Peripheral blood mononuclear cells (PBMC) from HIV-infected vaccine recipients, placebo recipients, and seronegative volunteers were cultured with exogenous IL-7 or IL-12 and either tetanus toxoid (TT) or gp160. IL-7 significantly augmented proliferative responses to TT and gp160, whereas IL-12 only affected proliferation to gp160. IL-7, but not IL-12, increased the number of HIV-infected placebo recipients who recognized rgp160. IL-12 had its greatest effect in the induction of rgp160-specific responses from seronegative individuals. The data suggest that these two cytokines have differential activity in the relief of restricted cellular immunity to Env; the predominant effect of IL-7 is in individuals who have been primed by exposure to antigen, while the effect of IL-12 is most evident in seronegative, unprimed individuals. Modification of restricted proliferative responses to Env by vaccination or cytokines in vitro suggests that strategies incorporating IL-7 or IL-12 as adjuvants may selectively boost cellular reactivity to HIV-1.     

Phase 2 study of an HIV-1 canarypox vaccine (vCP1452) alone and in combination with rgp120: negative results fail to trigger a phase 3 correlates trial

BACKGROUND: A goal of T-cell HIV vaccines is to define the correlation between a vaccine-induced immune response and protection from HIV infection. We conducted a phase 2 trial to determine if a canarypox vaccine candidate (vCP1452) administered with rgp120 subunit protein would "qualify" for a trial to define a correlate of efficacy. METHODS: A total of 330 healthy volunteers were enrolled into 4 groups: 120 received vCP1452 alone (0, 1, 3, and 6 months), 120 received vCP1452 with 2 different regimens of rgp120 coadministration, and 90 received placebo. HIV-specific antibody responses were measured by enzyme-linked immunoassay (ELISA) and neutralizing activity. T-cell responses were measured by chromium release and interferon-gamma (IFNgamma) enzyme-linked immunospot (ELISpot) assay. RESULTS: Significant neutralizing antibody responses to the HIV MN strain were detected in all vaccine groups, with net responses ranging from 57% (95% confidence interval [CI]: 40% to 71%) to 94% (95% CI: 85% to 99%). Net cumulative HIV-specific CD8 IFNgamma ELISpot assay responses were 13% (95% CI: -1% to 26%) for recipients of vCP1452 alone and 16% (95% CI: 2% to 29%) for recipients of vCP1452 plus rgp120. CONCLUSIONS: Overall, the HIV-specific CD8 cytotoxic T lymphocyte (CTL) response was not sufficient to qualify the regimen for a subsequent trial designed to detect an immune correlate of protection requiring a minimum CD8 CTL frequency of 30%.     

Antibody to human immunodeficiency virus type 1 (HIV-1) gp160 in mucosal specimens of asymptomatic HIV-1-infected volunteers parenterally immunized with an experimental recombinant HIV-1 IIIB gp160 vaccine. The National Institute of Allergy and Infectious Diseases-sponsored AIDS Vaccine Evaluation Group.

Twenty-two human immunodeficiency virus type 1 (HIV-1)-infected, asymptomatic volunteers with CD4 cell counts of >600 cells/mm3 who were enrolled in a phase I immunotherapy trial comparing two schedules of immunization of an HIV-1 IIIB-based recombinant gp160 (rgp160) experimental vaccine were evaluated for rgp160-specific antibodies in parotid saliva, genital secretions, and serum. When the study was unblinded, it was determined that five volunteers had received rgp160 on a month 0, 1, 2, 3, 4, and 5 immunization schedule, seven volunteers had received rgp160 on a month 0, 1, 2, and 5 schedule, five had received alum/deoxycholate placebo, and seven had received a licensed hepatitis B virus vaccine. Five volunteers consented to the donation of parotid saliva but not genital secretions. Prior to immunization, parotid saliva specimens were available for 11 of 22 volunteers, seminal plasma (SP) specimens were available for 7 of 22 volunteers, cervicovaginal lavage (CVL) specimens were available for 5 of 22 volunteers, and serum was available for 22 of 22 volunteers. These baseline specimens and specimens collected at 1 and 7 months after the final immunizations were assessed by enzyme-linked immunosorbent assay for immunoglobulin G (IgG) and IgA antibodies specific for HIV-1 LAI rgp160 or HIV-1 MN rgp160. No augmentation in HIV rgp160-specific IgG or IgA antibody production in either parotid saliva or serum specimens of vaccinees compared to that in controls was observed after immunization. There were insufficient numbers of SP or CVL specimens available for statistical comparisons between vaccinees and controls. Overall, anti-LAI rgp160 IgG antibodies were detected in the parotid saliva specimens of 20 of 22 volunteers, the seminal plasma specimens of 11 of 11 volunteers, and the CVL specimens of 6 of 6 volunteers and in 21 of 22 serum specimens. Fewer volunteers expressed anti-LAI rgp160 IgA antibodies in mucosal or serum specimens: 11 of 22 parotid saliva specimens, 3 of 11 SP specimens, 3 of 5 CVL samples, and 12 of 22 sera.     

Human immunodeficiency virus type 1 envelope-specific cytotoxic T lymphocytes response dynamics after prime-boost vaccine regimens with human immunodeficiency virus type 1 canarypox and pseudovirions

Virus-specific cytotoxic T lymphocytes (CTLs) may represent significant immune mechanisms in the control of human immunodeficiency virus (HIV) infection and, therefore, CTL induction may be a fundamental goal in the development of an efficacious acquired immunodeficiency syndrome (AIDS) vaccine. In the current study, prime-boost protocols were used to investigate the potential of noninfectious human immunodeficiency virus type 1 (HIV-1) pseudovirions (HIV PSV) in enhancing HIV-specific CTL responses in Balb/c mice primed with the recombinant canarypox vector, vCP205, encoding HIV-1 gp120 (MN strain) in addition to Gag/Protease (HIB strain). The prime-boost immunization regimens were administered intramuscularly and involved injections of vCP205 followed by boosts with HIV PSV. Previous vaccination strategies solely involving vCP205 had induced good cellular immune responses in uninfected human volunteers, despite some limitations. The use of genetically engineered HIV PSV was a logical step in the evaluation of whole noninfectious virus or inactivated virus vaccine strategies, particularly as a potential boosting agent for vCP205-primed recipients. Based on this current study, HIV PSV appeared to have the capability to effectively induce and boost cell-mediated HIV-1-specific responses. In order to observe the immune effects of HIV PSV in a prime-boost immunization strategy, both HIV vaccine immunogens required careful titration in vivo. This suggests that careful consideration should be given to the optimization of immunization protocols destined for human use.     

Fine specificity of the humoral immune response to HIV-1 GP160 in HIV-1 infected individuals from Tanzania.

A total of 160 sera from HIV-1 infected individuals from Tanzania were examined for their fine specificity characteristics relative to 9 synthetic peptides that define HIV-1 gp160 epitopes. Immunorecessive and immunodominant epitopes were identified in both gp120 and gp41 based on serologic reactivity of these HIV-1 infected sera. A significant difference in fine specificity among HIV-1 infected individuals from Tanzania and the United States was observed for an immunodominant gp41 epitope. No significant differences in reactivity among asymptomatic vs. symptomatic HIV-1 infected individuals were detected for the selected HIV-1 gp160 epitopes defined by these peptides. The majority of sera from HIV-1 infected Tanzanians contained antibodies that recognized a peptide corresponding to the V3 region of gp120 from the HIV-1 MN isolate. These data suggest that regional isolates of HIV-1 may exist in Tanzania that differ from HIV-1 isolated in the United States. However, based on serology, HIV-1 isolates exhibiting sequences with HIV-1 MN V3 similarity may also be prevalent in Tanzania. The results of this study may be useful for the design of more effective AIDS diagnostic and therapeutic products for use worldwide.     

Detection of Human Immunodeficiency Virus Type 1 Envelope Peptide- Stimulated T-helper Cell Responses and Variations in the Corresponding Regions of Viral Isolates among Vertically Infected Children

Although human immunodeficiency virus type 1 (HIV-1) specific CD4 T-helper cells are vital in mediating antiviral defence, little is known concerning the influence of HIV-1 antigenic variation on CD4 T-cell responses. In this study, the amino acid sequences of 5 synthetic HIV-1 envelope peptides used for in vitro stimulation (T2, P18 MN, P18 IIIB, T1 and TH4.1) were compared to the corresponding amino acid sequences of the gp 160 region of viruses isolated from HIV-1 infected children to determine whether variation in the envelope region of HIV-1 was associated with the ability to detect Env-specific T-helper cell responses. Although the T2 region appeared to offer some evidence as to the role antigenic variation may have played in class II-restricted CD4 T-cell responses between those children who showed a detectable Env-stimulated T-helper cell response and those who did not, the other regions studied showed no evidence of being more conserved among those children who showed detectable responses. The combined amino acid variation across the specific peptide regions studied was not associated with peripheral levels of HIV-1, nor did the degree of amino acid variation dictate the clinical category into which the children had been classified, although there was a tendency towards HIV-1 isolates from the younger children showing a greater degree of amino acid variation than isolates from the older children. These results suggest that HIV-1 specific CD4 responses may be somewhat tolerant of viral variation, although further studies are required to fully elucidate the effect of antigenic variation on immune recognition.     

Cellular immune responses in asymptomatic human immunodeficiency virus type 1 (HIV-1) infection and effects of vaccination with recombinant envelope glycoprotein of HIV-1

Effects of human immunodeficiency virus type 1 (HIV-1) recombinant envelope glycoprotein vaccines on cell-mediated immune (CMI) responses were assessed in HIV-1-infected patients. Asymptomatic, antiretroviral-treatment-na?ve, HIV-1-infected patients with CD4(+) T-cell counts greater than 400/microl received multiple intramuscular injections of HIV-1 IIIB recombinant envelope glycoprotein (rgp160) vaccine or HIV-1 MN recombinant envelope glycoprotein (rgp120) vaccine (eight patients, referred to as the HIV-1 vaccinees) or placebo or hepatitis B vaccine (three patients, referred to as the controls). Lymphocyte proliferation in response to HIV-1 envelope glycoproteins, both homologous and heterologous to the HIV-1 immunogens, was absent prior to study treatment in all patients but increased significantly during the vaccination series and after the final vaccination in HIV-1 vaccinees (P < 0.05) and remained absent in control patients. In flow cytometric analyses of intracellular cytokines, T-cell receptor stimulation with an anti-CD3 antibody induced gamma interferon (IFN-gamma) expression by activated CD4(+) and CD8(+) lymphocytes at greater frequencies than did stimulation with recombinant envelope glycoprotein and p24 of HIV-1 (P < 0.05). Mean frequencies of HIV-1 envelope glycoprotein-stimulated, activated intra-cellular IFN-gamma-producing CD4(+) and CD8(+) lymphocytes and of interleukin-2-producing CD4(+) lymphocytes did not increase after vaccination, but cytokine-producing cells were detectable in some patients. Comparing pre- to post-HIV-1 vaccination time points, changes in frequencies of activated, IFN-gamma-producing CD4(+) cells correlated inversely with changes in lymphocyte proliferation in response to recombinant envelope glycoprotein in HIV-1 vaccinees (P < 0.05). Increased CMI responses to HIV-1 envelope glycoprotein measured by lymphocyte proliferation were associated with HIV-1 recombinant envelope glycoprotein vaccines.     

Immunization with subunit human immunodeficiency virus vaccine generates stronger T helper cell immunity than natural infection.

Healthy, human immunodeficiency virus seronegative (HIV-) volunteers were multiply immunized with a recombinant gp160 (rgp160) candidate acquired immunodeficiency syndrome (AIDS) vaccine. Peripheral blood lymphocytes from volunteers immunized with 40 micrograms or with 80 micrograms (two volunteers per group) of rgp160, as well as from control donors, were tested for T helper (Th) cell function either prior to immunization, 8 to 12 months after the third immunization, or 2 to 5 months after the fourth immunization. The Th cell functional tests included antigen-induced in vitro interleukin 2 (IL 2) production and proliferation in response to influenza A virus (FLU) and to four synthetic peptides of HIV gp120 and gp160, previously demonstrated to be recognized by T cells from HIV naturally infected patients. Our results demonstrate the following: (a) immunization of HIV- individuals with rgp160 results in IL 2 production and T cell proliferation in response to HIV determinants; (b) boosting with rgp160 enhances Th function; (c) HIV-specific Th function is up to 100-fold greater in the multiply immunized volunteers than that observed in asymptomatic, HIV-infected individuals; and (d) multiple immunization with rgp160 does not impair Th function to a non-HIV antigen such as influenza A virus. These results indicate that immunization of uninfected individuals with an HIV subunit vaccine results in much stronger Th cell immunity than does natural infection and suggests that vaccination against HIV may be possible.     

Comparison of antibody reactivity to human immunodeficiency virus type 1 (HIV-1) gp160 epitopes in sera from HIV-1-infected individuals from Tanzania and from the United States.

In this study, we compared sera from 159 human immunodeficiency virus type 1 (HIV-1)-infected individuals from Tanzania and 103 infected individuals from the United States for antibodies reactive with 10 HIV-1 gp160 epitopes defined by synthetic peptides. Our data indicate that the anti-gp160 antibody fine specificity differs between infected individuals from these two geographically diverse populations. For example, 50% of the Tanzanian sera contained antibodies reactive with an immunodominant HIV-1 gp41 epitope defined by peptide 600-611, whereas 91% of the sera from the United States were reactive. Differences in serologic reactivity between HIV-1-infected individuals from Tanzania and the United States were also observed with gp160 epitopes defined by peptides 503-528 and 846-860. Included among the peptides examined were four which corresponded to the V3 region of gp120. The majority of sera from either country contained antibodies reactive with peptide RP142, whose V3 sequence is based upon that of HIV-1 isolate MN. Further characterization of serologic reactivity suggested that sera from Tanzania were more likely to neutralize HIV-1 isolate IIIB or MN in vitro than were sera from the United States. These differences in antibody fine specificity between HIV-1-infected individuals from Tanzania and the United States suggest that regional isolates of HIV-1 may exist.     

Antibody to native human immunodeficiency virus type 1 envelope glycoproteins induced by IIIB and MN recombinant gp120 vaccines. The NIAID AIDS Vaccine Evaluation Group.

The ability of antibody induced by MN and IIIB recombinant gp120 (rgp120) human immunodeficiency virus type 1 (HIV-1) vaccines the bind to oligomeric native and monomeric recombinant HIV-1 envelope glycoproteins (rgp 120) was measured in 25 uninfected, healthy adult volunteers. A major focus was to evaluate the effect of simultaneous and sequential immunization with vaccines representing different strains of HIV-1 on the ability to broaden cross-reactivity of antibodies against these and other HIV-1 strains. A flow cytometric indirect immunofluorescence assay (FIFA) to detect vaccine-induced antibody to envelope glycoprotein expressed by infected and rgp120-coated target cells was used, MN rgp120 HIV-1 vaccine given alone and coadministered with IIIB rgp120 HIV-1 vaccine elicited antibody which bound to cells infected with HIV-1MN, HIV-IIIB, HIV-1RF, and HIV-1-SF2. The presence of envelope glycoprotein-binding antibody detected by FIFA correlated to a moderate degree with functional antibody against HIV-1MN and HIV-IIIB. Priming immunization with IIIB rgp120 HIV-1 vaccine followed by booster injections of MN rgp120 HIV-1 vaccine resulted in increased cross-reactive antibody binding to these and heterologous clade B HIV-1 strains infecting cells. MN rgp120 HIV-1 vaccine given alone was better able to induce cross-reactive antibody to cells infected with heterologous HIV-1 laboratory strains than was IIIB rgp120 HIV-1 vaccine given alone. The vaccines induced binding antibody to rgp120 possessing the amino acid sequence of a clade E HIV-1 strain as measured by enzyme-linked immunosorbent assay. Levels of antibody binding to cells infected with clade B HIV-1 and cells coated with monomeric rgp120 were greater than that induced by HIV-1IIIB-based gp160 vaccines in previous studies.     

Conglutinin Binds The HIV-1 Envelope Glycoprotein gpl60 and Inhibits its Interaction with Cell Membrane CD4

The highly glycosylated envelope glycoprotein (gp 160) of human immunodeficiency virus (HIV) interacts with the CD4 molecule present on the membrane of CD4+ cells and is involved in the pathobiology of HIV infection. Lectins bind glycoproteins through non-covalent interactions with specific hexose residues. The mammalian C-type lectin bovine conglutinin was examined for its ability to interact with recombinant gp160 (rgp160) produced in vaccinia virus-infected BHK21 cells. Specific binding of conglutinin to rgp160 was demonstrated by ELISA. The interaction of bovine conglutinin with rgp160 was calcium-dependent, which is characteristic of the binding of a C-type lectin to its ligand, and the binding was inhibited in a dose-dependent manner with N-acetyl-D-glucosamine. Deglycosylation of rgp160 abrogated the conglutinin binding. In addition, conglutinin exerted a dose-dependent inhibition of the binding of rgp160 to the CD4 receptor on CEM 13 cells, as demonstrated by FACS analyses. These results indicate that conglutinin may inhibit the infection with HIV-1 through its interaction with the viral envelope glycoprotein.     

Cytotoxic T lymphocyte responses to vaccinia virus antigens but not HIV-1 subtype E envelope protein seen in HIV-1 seronegative Thais

The HIV-1 prime boost phase I/II vaccine trial using a recombinant canarypox vector, vCP1521, containing subtype E env (gp120), and subtype B env (gp41), gag and protease has started in Thailand. We have demonstrated that although 4 from 15 human immunodeficiency virus type 1 (HIV-1) seronegative Individuals showed cytotoxic T lymphocyte (CTL) responses to vaccinia virus antigens, none of them showed specific CTL responses to subtype E Env after in vitro stimulation. This preliminary study suggests that specific CTL responses to subtype E envelope detected in HIV-1 seronegative Individuals after vaccination should be considered as specific responses to the immunization.     

The HIV-1 Env protein signal sequence retards its cleavage and down-regulates the glycoprotein folding

Secretory proteins and most membrane proteins are synthesized with a signal sequence that is usually cleaved from the nascent polypeptide chain, during its transport, into the lumen of the endoplasmic reticulum (ER). We have analyzed the kinetics of the cleavage of the HIV-1 Env protein signal sequence from gp160 and gp120 in HeLa, BHK, and Jurkat cells. Furthermore, we have determined the effects of this cleavage on the association of the gp160 and gp120 glycoproteins with the ER protein calnexin and the effects of the signal sequence cleavage on protein folding. The cleavage of the HIV-1 Env protein signal sequence on both gp160 and gp120 occurred very slowly in all three cell lines with a t(1/2) of 45-60 min. The core glycosylated and signal-sequence-retained forms of gp160 and gp120 associated with calnexin while the signal-sequence-cleaved forms of gp160 and gp120 had disassociated from calnexin and correctly folded as determined by their ability to associate with the CD4 cellular receptor. Further analysis of the folding state of gp160 and gp120 in nonreducing SDS-PAGE revealed that the signal-sequence-retained and calnexin-associated forms of gp160 and gp120 migrated as broad, diffuse bands, whereas the signal-sequence-cleaved or CD4-associated forms of gp160 and gp120 migrated as single sharper bands. The cause of this retardation in the rate of folding and intracellular transport of HIV-1 glycoproteins was localized to their signal sequences by fusing the vesicular stomatitis virus G protein with the HIV-1 Env protein signal sequence and expressing this chimeric protein in mammalian cells. The HIV-1 Env protein signal sequence on the VSV-G protein also confers a reduced rate of cleavage and slow intracellular transport and folding of the chimeric G protein. These results provide direct evidence that in vivo the HIV-1 glycoprotein signal sequence inhibits the folding of HIV-1 Env protein. Our data also suggest a direct correlation between the rate of the signal sequence cleavage and protein folding.     

Patterns of antibody reactivity to selected human immunodeficiency virus type 1 (HIV-1) gp160 epitopes in infected individuals grouped according to CD4+ cell levels

We examined sera from 160 HIV-infected individuals for antibodies reactive to HIV-1 gp160 epitopes defined by seven synthetic peptides. Seropositive individuals were placed into three groups based upon levels of circulating CD4+ cells. These groups consisted of individuals with (1) more than 400 CD4+ cells, (2) 200–400 CD4+ cells, and (3) fewer than 200 CD4+ cells/mm³. The percentage of sera containing antibodies reactive with two immunodominant gp160 epitopes (a.a. 304–321 and 600–611) was unchanged between groups, regardless of CD4 cell numbers. The percentage of sera containing antibodies reactive with weakly immunogenic gp160 epitopes, such as those defined by peptides 425–448 and 846–860, declined in the groups as CD4 values decreased. Our results suggest that the patterns of antibody reactivity to gp160 epitopes change as CD4 levels decline. A narrowing of the humoral immune response to epitopes on the envelope of HIV-1 appears to occur with disease progression.     

Fine specificity of the murine antibody response to HIV-1 gp160 determined by synthetic peptides which define selected epitopes.

In this report, we assess the humoral immune response in inbred strains of mice immunized with baculovirus-derived recombinant HIV-1 gp160 (rgp160). Six inbred strains of mice were each immunized with two different concns (5 and 50 micrograms) of rgp160, and the antibody response to rgp160 and synthetic peptides which define distinct gp160 epitopes was examined. Within a given inbred strain of mice, no significant difference in antibody titers to gp160 was observed in those groups receiving either 5 or 50 micrograms of rgp160 per injection. Following three immunizations with rgp160, differences in anti-gp160 titers were observed among the various inbred strains; however, these differences became less apparent after additional injections with rgp160. In addition, each mouse strain exhibited a unique reactivity pattern to seven gp160 epitopes defined by synthetic peptides. Multiple injections with rpg160 were required to induce responses to certain gp160 epitopes. The observed differences in the fine specificity of the humoral immune response to distinct gp160 epitopes among the six inbred strains suggest a genetic basis for regulating the antibody response to these epitopes. This apparent regulation can be overcome by multiple injections with rgp160.     

Longitudinal study of antibody reactivity against HIV-1 envelope and a peptide representing a conserved site on Gp41 in HIV-1-infected patients.

This study was designed to distinguish between antibodies in HIV-1-infected patients directed against epitopes accessible on the native HIV-1 envelope (Env) complex and non-native Env epitopes. Peptide p#13 (Env. aa642-673) containing the neutralising 2F5 epitope and recombinant soluble glycoprotein 160 (rsgp160) were used in ELISA to determine the antibody (Ab) reactivity in sera of 116 HIV-1-infected individuals and 18 HIV negative controls. The reactivity of sera classified CDC stage C against p#13 was significantly decreased in comparison to stage A sera, while staying constant against rsgp160. Accordingly, in 6 out of 8 individual patients tested over time the response against p#13 was declining at later time points of infection. The reactivity of patients' sera against p#13 corresponded directly to the recognition of infected T cells and largely also to the CD4 cell count. The causal relationships of these phenomena are not clear. It is conceivable that antibodies against epitopes on HIV are lost or escape mutants arise and consequently control of HIV is lost and virus load increases as it is known for CDC stage C. Alternatively, increasing virus load may affect B cells recognising native Env epitopes and turn antibody production down by some mechanism. In this latter scenario helper T cells might have a critical role.     

Enhanced proliferative cellular responses to HIV-1 V3 peptide and gp120 following immunization with V3:Ty virus-like particles.

The induction of CD4+ T-helper (Th) cell responses is likely to be an important requirement of vaccine candidates designed to prevent or moderate human immunodeficiency virus-1 (HIV-1) infection. We have investigated the ability of hybrid Ty virus-like particles carrying the V3 loop region of the HIV-1 IIIB envelope gp120 (V3:Ty-VLP) to elicit V3-specific proliferative responses. Significant proliferation in response to stimulation in vitro with homologous IIIB V3 peptide was observed following immunization of mice with V3:Ty-VLP either as an aluminium hydroxide precipitate or without adjuvant. Responses to MN V3 peptide were also observed in certain mouse haplotypes. To assess the effect of presenting the V3 loop in this particulate form, we compared the responses induced by V3:Ty-VLP with those obtained with two non-particulate immunogens, recombinant gp120 (rgp120) and V3 peptide conjugated to albumin. V3-specific responses to V3 peptide in vitro were reproducibly higher following immunization with V3:Ty-VLP than with either rgp120 or V3-albumin coagulate (V3-alb). The data indicate that immunization with the V3 loop as a hybrid Ty-VLP results in enhanced proliferative responses to V3 peptide and recognition of rgp120 in vitro. Some cross-reactivity of Th cells for V3 sequences from different isolates was also observed.     

Immunogenicity of neutralizing epitopes on multiple-epitope vaccines against HIV-1

Based on our hypothesis that epitope vaccine may be a new strategy to induce high levels of neutralization antibodies against HIV-1, we prepared multiple-epitope vaccines using three neutralizing epitopes (GPGRAFY, RILAVERYLKD and ELDKWA) of HIV-1 gp160, and characterized their immunogenicity. Peptide 1 [C-G-(ELDKWA-GPGRAFY)(2)-K] and peptide 2 (CG-GPGRAFY-ELDKWA-G-RILAVERYLKD) were synthesized and conjugated with carrier protein bovine serum albumin (BSA). After vaccination antibody responses to these immunogens were induced and evaluated by ELISA. The C-G-(ELDKWA-GPGRAFY)(2)-K-BSA (BSA: carrier protein) multiple-epitope vaccine induced a strong antibody response to the C-G-(ELDKWA-GPGRAFY)(2)-K peptide (antibody titer: 1:25,600) and C-(ELDKWAG)(4) peptide (antibody titer: 1:12,800), but a weak antibody response to the C-(GPCGRAFY)(4) peptide. The CG-GPGRAFY-ELDKWA-G-RILAVERYLKD-K-BSA (BSA: carrier protein) multiple-epitope vaccine also induced strong antibody response to the CG-GPGRAFY-ELDKWA-G-RILAVERYLKD-K peptide (antibody titer: 1:25, 600) and C-(ELLDKWAG)(4) peptide (antibody titer: 1:6,400), a very strong response to C-(RIVALVERYLKD-G)(2)-K peptide (dilution: 1:102, 400), and a very weak response to the C-(GPGRAFY)(4) peptide (dilution: 1:400) in mice. Both antisera induced by both multiple-epitope vaccines interacted with the recombinant soluble gp41 (rgp41), but did not bind two control peptides. In comparison with both epitope vaccines, the rgp160 subunit vaccine could induce weak epitope-specific antibody response to these three epitopes on the three epitope peptides and V3, N-domain and C-domain peptides (dilution: 1:400-1:1,600). These results indicate that both multiple-epitope vaccines could induce high levels of antibodies to both neutralizing epitopes RILAVERYLKD and ELDKWA, while the GPGRAFY epitope on both vaccines appeared to have weak immunogenicity. Both multiple-epitope vaccines showed significant potency on inducing high levels of epitope-specific neutralization antibodies in comparison with rgp160 subunit vaccine.     

HIV-1 recombinant gp160 vaccine given in accelerated dose schedules

The purpose of this randomized, double-blind study was to test the safety and immunogenicity of an HIV-1_LAI recombinant gp160 (rgp160) vaccine in healthy, uninfected volunteers using accelerated dosing schedules. Thirty volunteers were randomly assigned to receive 50-μg doses of rgp160 in one of two immunization schedules. Group 1 received rgp160 at times 0, 1, 2 and 5 months; and group 2 received rgp160 at times 0, 1, 2, 3 and 4 months. The vaccine was safe and stimulated high levels of HIV-1 envelope-specific binding antibody and T cell memory. There was a trend (P < 0.10) suggesting neutralizing antibodies were better induced by the regimen incorporating a rest period before the final immunization in group 1 volunteers. Both accelerated immunization schedules induced immune responses at levels similar to or better than those achieved by four rgp160 vaccine injections given over 12-18 months in other studies.