Induction of V3-specific cytotoxic T lymphocyte responses by HIV gag particles carrying multiple immunodominant V3 epitopes of gp120

Variations in Env at amino acids 328 and 330 affect HIV-1 replicative fitness and entry inhibitor sensitivity

While the variations in the HIV-1 Env V3 loop have been the focus of much research to explore its functional effect, how specific mutations of certain amino acids in the V3 loop affect viral fitness remains unclear. In this study, we evaluated a series of natural polymorphisms at positions 328 and 330 with different combinations of adjacent glycosylation sites in the HIV-1 subtype B backbone to address their role in replicative fitness and sensitivity to entry inhibitors based on analysis of env sequence frequency at the population level. Pairwise growth competition experiment showed that wild-type virus with major consensus amino acids obviously had higher replicative fitness (P < 0.001). A change at position 328 to a less frequently occurring amino acid, K, together with a mutated N332 glycosylation site harbored lower fitness and became more sensitive to coreceptor antagonists (AMD3100), fusion inhibitors (T20) and sCD4. A change at position 330 to a less frequently occurring amino acid, Y, together with a mutated N332 glycosylation site resulted in higher fitness and less sensitivity to entry inhibitors (T20, AMD3100, and sCD4), and viruses containing both changes showed intermediate activity. It seems that the H330Y mutation compensated for the reduced replicative capacity caused by the Q328 K mutation. Moreover, viruses that showed lower replicative fitness also exhibited slower entry kinetics, lower levels of replication intermediates and protein packaging, and a lower ability to replicate in primary peripheral blood mononuclear cells (PBMCs). The findings highlight the functional effect of variations at 328 and 330 in the V3 loop on replicative fitness and may benefit HIV-1 treatment by helping predict the sensitivity to entry inhibitors.

HIV Reverse Transcriptase and Protease Genes Variability Can Be a Biomarker Associated with HIV and Hepatitis B or C Coinfection

Variability of the HIV reverse transcriptase (RT) and protease (PR) genes has been used as indicators of drug resistance and as a mean to evaluate phylogenetic relationships among circulating virus. However, these studies have been carried in HIV mono-infected populations. The goal of this study was to evaluate, for the first time, the HIV PR and RT sequences from HIV/HBV and HIV/HCV co-infected patients. HIV PR and RT genes were amplificated and sequenced to resistance analysis. The bioinformatics analysis was performed to infer about sequences clustering and molecular evolution. The results showed that the most frequent amino acid substitutions in RT were L214F (67.6%), I135T (55.9%), and in PR was V15I (41.2%). The molecular clock analysis showed that the HIV circulating in co-infected patients were separated in two clusters in the years 1999-2000. Some patients included as HIV mono-infected according patients' medical records and inside the co-infected cluster were, in fact, co-infected by PCR analysis. Analysis of the decision trees showed susceptibility to lamivudine and emtricitabine were important attribute to characterize co-infected patients. In conclusion, the results obtained in this study suggest, for the first time, that HIV RT and PR genes variability could be a genetic biomarker to coinfection.

Nanoliposomes carrying HER2/neu-derived peptide AE36 with CpG-ODN exhibit therapeutic and prophylactic activities in a mice TUBO model of breast cancer

This study was designed to prepare and characterize nanoliposomal vaccine formulation encapsulating AE36 HER2/neu-derived peptide with or without CpG and evaluate the immunologic and therapeutic responses of that in BALB/c mice model of Her2 overexpressing breast cancer. AE36 was encapsulated in liposomes composed of DOTAP, DOPE and Cholesterol (DDC) or DD with. The formulations could induce both CD8+ and CD4+ responses and stimulate production of cytokines which was detected by Enzyme-linked immunospot assay (ELISpot) kits, cytotoxicity test and intracellular cytokine assay by flow cytometry. The formulation showed both therapeutic and prophylactic effects in BALB/c mice bearing Her2⁺ breast cancer. DDC+CpG showed the best effect in prophylactic study and DD+pG showed the best effect in therapeutic study, which both of them decreased the size of tumors significantly. The engineered nanoliposomes containing AE36 could be a candidate vaccine for the treatment or prophylaxis of HER2⁺ breast cancer and merits further investigation.

Pulse HIV vaccination: feasibility for virus eradication and optimal vaccination schedule

We modify the classical virus dynamics model by incorporating an immune response with fixed or fluctuating vaccination frequencies and dosages to obtain a system of impulsive differential equations for the virus dynamics of both the wild-type and mutant strains. This model framework permits us to obtain precise conditions for the virus elimination, which are much more feasible compared with existing results, which require frequent vaccine administration with large dosage. We also consider the corresponding impulsive optimal control problem to describe when and how much of the vaccine should be administered in order to maximize levels of healthy CD4(+) T cells and immune response cells. A gradient-based optimization method is applied to obtain the optimal schedule numerically. For a case study when the CTL vaccine is administered in a period of one year, our numerical studies support the optimal vaccination schedule consisting of vaccine administration three times, with the first dosage strong (to boost the immune system), followed by a second dosage shortly after (to strengthen the immune response) and then the third and final dosage long after (to ensure the immune system can handle viruses rebound).

HIV-1 envelope subregion length variation during disease progression

The V3 loop of the HIV-1 Env protein is the primary determinant of viral coreceptor usage, whereas the V1V2 loop region is thought to influence coreceptor binding and participate in shielding of neutralization-sensitive regions of the Env glycoprotein gp120 from antibody responses. The functional properties and antigenicity of V1V2 are influenced by changes in amino acid sequence, sequence length and patterns of N-linked glycosylation. However, how these polymorphisms relate to HIV pathogenesis is not fully understood. We examined 5185 HIV-1 gp120 nucleotide sequence fragments and clinical data from 154 individuals (152 were infected with HIV-1 Subtype B). Sequences were aligned, translated, manually edited and separated into V1V2, C2, V3, C3, V4, C4 and V5 subregions. V1-V5 and subregion lengths were calculated, and potential N-linked glycosylation sites (PNLGS) counted. Loop lengths and PNLGS were examined as a function of time since infection, CD4 count, viral load, and calendar year in cross-sectional and longitudinal analyses. V1V2 length and PNLGS increased significantly through chronic infection before declining in late-stage infection. In cross-sectional analyses, V1V2 length also increased by calendar year between 1984 and 2004 in subjects with early and mid-stage illness. Our observations suggest that there is little selection for loop length at the time of transmission; following infection, HIV-1 adapts to host immune responses through increased V1V2 length and/or addition of carbohydrate moieties at N-linked glycosylation sites. V1V2 shortening during early and late-stage infection may reflect ineffective host immunity. Transmission from donors with chronic illness may have caused the modest increase in V1V2 length observed during the course of the pandemic.

The HIV envelope gene (env) encodes viral surface proteins (Env) that are vital to the basic processes used by the virus to infect and cause disease in humans. Adaptations in env determine which cells the virus can infect, and permit the virus to avoid elimination by the immune system. Env is one of the most variable genes known, and it can change dramatically over time in a single individual. However, Env-host cell interactions are complex and incompletely understood, and changes in this viral protein during infection have not yet been systematically described. We examined a large number of env sequences from 154 individuals at various stages of HIV infection but who had never received antiretroviral treatment. We found that the env V1V2 region lengthens during chronic infection and becomes more heavily glycosylated. However, these changes partially reverse during late-stage illness, possibly in response to a weakening host immune system. V1V2 lengths are also increasing over time in the epidemic at large, possibly related to the epidemiology of HIV transmission within the subtype B epidemic. These results provide fundamental insights into the biology of HIV.

Chimaeric HIV-1 subtype C Gag molecules with large in-frame C-terminal polypeptide fusions form virus-like particles

HIV-1 Pr55 Gag virus-like particles (VLPs) are strong immunogens with potential as candidate HIV vaccines. VLP immunogenicity can be broadened by making chimaeric Gag molecules: however, VLPs incorporating polypeptides longer than 200 aa fused in frame with Gag have not yet been reported. We constructed a range of gag-derived genes encoding in-frame C-terminal fusions of myristoylation-competent native Pr55Gag and p6-truncated Gag (Pr50Gag) to test the effects of polypeptide length and sequence on VLP formation and morphology, in an insect cell expression system. Fused sequences included a modified reverse transcriptase-Tat-Nef fusion polypeptide (RTTN, 778 aa), and truncated versions of RTTN ranging from 113 aa to 450 aa. Baculovirus-expressed chimaeric proteins were examined by western blot and electron microscopy. All chimaeras formed VLPs which could be purified by sucrose gradient centrifugation. VLP diameter increased with protein MW, from approximately 100 nm for Pr55Gag to approximately 250 nm for GagRTTN. The presence or absence of the Gag p6 region did not obviously affect VLP formation or appearance. GagRT chimaeric particles were successfully used in mice to boost T-cell responses to Gag and RT that were elicited by a DNA vaccine encoding a GagRTTN polypeptide, indicating the potential of such chimaeras to be used as candidate HIV vaccines.

V3 CTL epitope density in a single recombinant molecule antigen differentially affects the number and activity of primary and memory CD8+ T cells

Previous studies have found the close correlation between epitope density and epitope-specific response, which have shown that high epitope density in a single recombinant protein molecule significantly enhances the humoral response and protective immunity. However, it has not been determined whether this kind of high epitope density could also significantly influence T cell response. Based on this, a series of recombinant DNA and proteins were designed and prepared. Each molecule consists of various copy numbers of the V3 CTL epitope on HIV-1 gp120 (one, two, four and eight copies). Our results show clearly that different V3-epitope densities in just one single DNA or protein molecules have respectively different effects on the number and activity of both primary and memory T cells. Interestingly, this effect is more complex than that on the B cells: epitope density in one plasmid or protein antigen affects the number, not the cytotoxic avidity, of primary CD8+ T cells, but affects both the number and cytotoxic avidity of memory CD8+ T cells. It indicates epitope density in the antigen is an important consideration to optimize T cell response induction and may facilitate the development of effective T cell-based anti-virus vaccines.

Hydrophilicity dependent budding and secretion of chimeric HIV Gag-V3 virus-like particles

Virus-like particles (VLPs) of numerous viruses have been considered as possible candidates for vaccine development. We have constructed HIV chimeric genes by coupling the gag gene of HIV-2 with the V3 domain of the gp120 gene of either HIV-1 or HIV-2 and expressed the chimeric genes in SF21 cells using the recombinant baculovirus expression system. Although the level of expression of the chimeric HIV-2 gag gene with the V3 domain of either HIV-1 gp120 (gagC-1V3) or HIV-2 gp120 (gagC-2V3) was high, the VLP assembly and extracellular release of GagC-1V3 was very poor. In contrast, GagC-2V3 chimeric proteins formed VLPs and released efficiently. We have constructed substitution mutants to investigate the effects of the hydrophobic region of the V3 domain of HIV-1 Gp120 (1V3) in VLP assembly and release. The substitution mutant analyses revealed that in replacing the hydrophobic region of the 1V3 in GagC-1V3 with the hydrophilic sequence of the V3 domain of HIV-2 Gp120 (2V3) enhanced the extracellular VLP. We demonstrate here that disruption of the hydrophobic character of the C-terminus of the chimeric protein improves assembly and release of the VLPs. Our results suggest that the poor GagC-1V3 VLP release was attributed to the hydrophobic region in the V3 sequence of the chimeric protein, and that not only the N-terminal myristylation and positively charged domain of the Gag protein functioned as a targeting signal to direct membrane binding, but also that the C-terminal hydrophobic region affected release of chimeric VLPs.

Immunization with hepatitis C virus-like particles results in control of hepatitis C virus infection in chimpanzees

Recombinant hepatitis C virus (HCV)-like particles (HCV-LPs) containing HCV structural proteins (core, E1, and E2) produced in insect cells resemble the putative HCV virions and are capable of inducing strong and broad humoral and cellular immune responses in mice and baboons. Here, we present evidence on the immunogenicity and induction of protective immunity by HCV-LPs in chimpanzees. Chimpanzees (two in each group), were immunized with HCV-LPs or HCV-LPs plus AS01B adjuvant. After immunizations, all animals developed an HCV-specific immune response including IFN-gamma(+), IL-2(+), CD4(+), and CD8(+) T cell and proliferative lymphocyte responses against core, E1, and E2. Upon challenge with an infectious HCV inoculum, one chimpanzee developed transient viremia with low HCV RNA titers (10(3) to 10(4) copies per ml) in the third and fourth weeks after the challenge. The three other chimpanzees became infected with higher levels of viremia (10(4) to 10(5) copies per ml), but their viral levels became unquantifiable (<10(3) copies per ml) 10 weeks after the challenge. After the HCV challenge, all four chimpanzees demonstrated a significant increase in peripheral and intrahepatic T cell and proliferative responses against the HCV structural proteins. These T cell responses coincided with the fall in HCV RNA levels. Four naïve chimpanzees were infected with the same HCV inoculum, and three developed persistent infection with higher viremia in the range of 10(5) to 10(6) copies per ml. Our study suggests that HCV-LP immunization induces HCV-specific cellular immune responses that can control HCV challenge in the chimpanzee model.

Phylodynamic analysis of human immunodeficiency virus type 1 in distinct brain compartments provides a model for the neuropathogenesis of AIDS

"Phylodynamic" analysis combines various statistical procedures that can be used to correlate the epidemiological and evolutionary behavior of viral pathogens with the immune system of the host. We utilized this approach to examine human immunodeficiency virus type 1 (HIV-1) gp120 envelope DNA sequences (V1, V2, and V3) isolated from different brain compartments of a T-cell-depleted patient diagnosed with severe HIV-associated dementia at the time of death. In agreement with previous reports, phylogenetic analysis showed distinct virodemes but also revealed a significant amount of viral gene flow among different brain compartments. Local-molecular-clock analysis showed that HIV-1 meninges and temporal lobe subpopulations evolve about 30 and 100 times faster, respectively, than the other viral populations in the brain. However, maximum likelihood codon-based substitution models did not detect any site under significant positive selective pressure, and the main cause of HIV-1 genetic variation appeared to be random genetic drift. Therefore, the higher evolutionary rate in the meninges and temporal lobe could be due to an enhanced infection/expansion rate of macrophages as a consequence of the immune system failure. In conclusion, in this case study, viral infection in the brain progressed with a nonspecific genetic evolution, recurrent migration events, and an expansion of macrophage-tropic sequences. The data suggest that after immune failure newly produced viral variants, which would be rapidly cleared under normal conditions, begin to productively infect macrophages in a "self-amplifying" cycle of infection/inflammatory response that could be at the origin of HIV-associated dementia.

Expression of recombinant small hydrophobic protein for serospecific detection of avian pneumovirus subgroup C

The small hydrophobic (SH) gene of the avian pneumovirus (APV) Colorado isolate (CO), which belongs to subgroup C (APV/C), was expressed with a baculovirus vector. The recombinant SH protein was evaluated as a potential subgroup-specific diagnostic reagent in order to differentiate infections resulting from APV/C from those induced by APV/A, APV/B, and human metapneumovirus (hMPV). When the recombinant baculovirus was used to infect insect cells, a 31- to 38-kDa glycosylated form of the SH protein was produced and subsequently tested for reactivity with antibodies specific for APV/A, APV/B, APV/C, and hMPV. Western blot analysis showed that the expressed recombinant SH protein could only be recognized by APV/C-specific antibodies. This result was consistent with sequence analysis of the APV/C SH protein, which had very low (24%) amino acid identity with the corresponding protein of hMPV and no discernible identity with the SH protein of APV/A or APV/B. A recombinant SH protein-based enzyme-linked immunosorbent assay (ELISA) was developed, and it further confirmed the lack of reactivity of this protein with antisera raised to APV/A, APV/B, and hMPV and supported its designation as a subgroup-specific antigen. This finding indicated that the recombinant SH protein was a suitable antigen for ELISA-based detection of subgroup-specific antibodies in turkeys and could be used for serologically based differential diagnosis of APV and hMPV infections.

Immunization with hepatitis C virus-like particles protects mice from recombinant hepatitis C virus-vaccinia infection

We have recently demonstrated that immunization with hepatitis C virus-like particles (HCV-LPs) generated in insect cells can elicit both humoral and cellular immune responses in BALB/c mice. Here, we evaluate the immunogenicity of HCV-LPs in HLA2.1 transgenic (AAD) mice in comparison to DNA immunization. HCV-LP immunization elicited a significantly stronger humoral immune response than DNA immunization. HCV-LP-immunized mice also developed stronger HCV-specific cellular immune responses than DNA-immunized mice as determined by using quantitative enzyme-linked immunospot (ELISpot) assay and intracellular cytokine staining. In BALB/c mice, immunization with HCV-LPs resulted in a >5 log10 reduction in vaccinia titer when challenged with a recombinant vaccinia expressing the HCV structural proteins (vvHCV.S), as compared to 1 log10 decrease in DNA immunization. In HLA2.1 transgenic mice, a 1-2 log10 reduction resulted from HCV-LP immunization, whereas no reduction was seen from DNA immunization. Adoptive transfer of lymphocytes from HCV-LP-immunized mice to naive mice provided protection against vvHCV.S challenge, and this transferred immunity can be abrogated by either CD4 or CD8 depletion. Our results suggest that HCV-LPs can induce humoral and cellular immune responses that are protective in a surrogate HCV challenge model and that a strong cellular immunity provided by both CD4 and CD8 effector lymphocytes may be important for protection from HCV infection.

Budding and secretion of HIV Gag-Env virus-like particles from recombinant human adenovirus infected cells

We have characterized the assembly, budding and extra-cellular release of human immunodeficiency virus (HIV) Gag-Env virus-like particles (VLPs) from human embryonic kidney cells (293 cells expressing the E1a protein of adenovirus) infected with recombinant replication-defective human adenovirus type 5. Recombinant human adenovirus vectors expressing the chimeric Gag-Env protein were constructed by inserting the gag-env fusion gene into the E1a region of the human adenovirus type 5. Biochemical and immunological analyses of VLPs recovered from the culture supernatant revealed that these particles contain the HIV-2 Gag protein and segments of Env protein from the HIV-1 gp120. This chimeric Gag-Env protein interacted with HIV-1 positive patient sera and with HIV-2 Gag monoclonal antibody. Immunoelectron microscopy of the 293 cells infected with the recombinant adenoviruses showed that the HIV Gag-Env antigen is present in the VLPs. Thin-section electron microscopy (EM) revealed that the Gag-Env VLPs bud through the cytoplasmic membrane, as well as through membranes of intracellular vacuoles. The thin-section EM showed that the Gag-Env VLPs have a spherical morphology with an electron-dense ring. The size of VLPs range from 110 to 140 nm in diameter, which is slightly larger than that of the Gag particles without Env protein fusion. Mice immunized with recombinant adenoviruses generated antibodies that specifically reacted with Gag-Env chimeric proteins. Our results support the idea that the replication-defective adenovirus could be used to induce immune responses that might be useful in a vaccine against HIV/AIDS.

Intranasal immunization with SIV virus-like particles (VLPs) elicits systemic and mucosal immunity

By using a baculovirus expression system, we have successfully produced simian immunodeficiency virus (SIV)-like particles (VLPs) with high levels of biologically active SIV envelope (Env) incorporated on their surfaces. To study whether SIV VLPs represent effective mucosal immunogens, we immunized groups of mice with VLPs alone or VLPs plus the mucosal adjuvant cholera toxin (CT) by the intranasal (i.n.) route. High levels of serum IgG antibody production were achieved in mice immunized intranasally with SIV VLPs, and the antibody response was found to be antigen dose-dependent. The IgG1 and IgG2a ratio indicates that immune responses induced by SIV VLPs are Th1 oriented. Mice immunized with VLPs plus CT were found to exhibit higher serum antibody responses than those immunized with VLPs alone (P<0.001). Furthermore, IgA antibody production was detected in both saliva and vaginal fluid from mice mucosally immunized with SIV VLPs. Higher levels of IgA were found in vaginal fluid than in saliva in animals immunized with SIV VLPs plus CT (P<0.05). Higher neutralizing activity to SIV 1A11 was also found in serum of animals immunized with SIV VLPs plus CT. Moreover, increased numbers of MHC I-restricted peptide-specific IFN-gamma and IL-4 producing T cells were detected in both splenocytes and lymph nodes by intranasal immunization of SIV VLP plus CT. These results suggest that VLPs are effective mucosal antigens that can induce both humoral and cellular immune responses at systemic and mucosal sites.

Study of different coupling agents in the conjugation of a V3-based synthetic MAP to carrier proteins

The conjugation of synthetic peptides to carrier proteins is a widely used method for immunological studies. Different coupling agents have been described to form the conjugate with carrier proteins. In this paper, we demonstrate that the antibody response toward V3-based synthetic MAPs derived from HIV-1, JY1 isolate, conjugated to two different carrier proteins using either m-maleimidobenzoyl-N-hydroxysuccinimide ester (MBS) or beta-maleimidopropionic acid N-hydroxysuccinimide ester (MPS), or succinic anhydride (SA) show different behaviors. An excellent anti-JY1 response without a strong response to the coupling agent is observed in the case of succinic anhydride spacer. In contrast, MBS produces total abrogation of the antibody response with a high response toward the coupling agent.

Development of Th1-mediated CD8+ effector T cells by vaccination with epitope peptides encapsulated in pH-sensitive liposomes

There have been many studies for tumor therapy mediated by cytotoxic T lymphocytes (CTL) that recognize tumor-associated antigen. It is generally accepted that CTL responses are induced when antigen is delivered into the cytosol. The pH-sensitive liposomes as vehicles are well known for their capacity to deliver the antigen into the cytosol. In this work, immunization of mice with CTL epitope peptides from Hantaan nucleocapsid protein (M6) or human papilloma virus E7 encapsulated in pH-sensitive liposomes induced effective antigen-specific CTL responses. The CTL responses induced by M6 peptide encapsulated in pH-sensitive liposomes blocked the formation of tumor mass from Hantaan NP transfected B16 melanoma cells in C57BL/6 mice and delayed the growth of preinoculated melanoma cells. During the blockade of the tumor growth, the CTL response was maintained for at least approximately 6 weeks, and the mice secreted Th1 type cytokines such as IL-2 and IFN-gamma. These results suggested that the pH-sensitive liposomes might provide an effective peptide delivery system for CTL-mediated tumor therapy.

Evaluation of a lipopeptide immunogen as a therapeutic in HIV type 1-seropositive individuals

A 32-amino acid HIV-1 Gag immunogen was assessed for its ability to augment existing virus-specific CTL responses in chronically HIV-1-infected individuals. The immunogen was an HIV-1 synthetic lipopeptide conjugate composed of an N-palmitoyl-S-[2,3-bis(palmitoyloxy)-(2R)-propyl-N-(R)-cysteinyl] group covalently coupled to a synthetic 32-amino acid Gag peptide containing at least 5 CTL epitopes known to be restricted by HLA-A33, -B8, -B27, -B35, and -Bw62. This potential immunotherapeutic was first determined to be safe in six HIV-1-seropositive subjects, with no adverse clinical effects noted during a 182-day period after administration of a dose of 350 microg. The immunogenicity of this lipopeptide conjugate was then assessed in a pilot study in nine HIV-1-seropositive volunteers with peripheral blood CD4+ lymphocyte counts of >500/microl. Three groups of individuals were studied: HLA-selected subjects who received 350 microg of the immunogen on days 0, 28, and 56 (four subjects); HLA-selected subjects who received a placebo according to a similar inoculation schedule (three subjects); and HLA-mismatched subjects who received the experimental immunogen (two subjects). All subjects were monitored for 26 weeks. After treatment, PBLs from two of the four HLA-selected subjects who received the experimental immunogen showed a transient increase in Gag peptide-specific bulk CTL activity. None of the placebo-vaccinated or vaccinated HLA-mismatched subjects showed any change in bulk Gag peptide-specific CTL activity. However, no consistent decrease in plasma HIV-1 RNA levels was noted in any of the subjects. The present study illustrates that this peptide formulation may not be a sufficiently potent immunogen to significantly augment HIV-1-specific CTLs and to decrease virus load in HIV-1-seropositive individuals.

Production and characterization of simian--human immunodeficiency virus-like particles

We have produced and characterized, in a baculovirus expression system, simian-human immunodeficiency virus-like particles (SHIV VLPs) containing SIV Gag and HIV envelope (Env) proteins. Recombinant SIV gag (SIVmac239) and full-length or cytoplasmic domain-truncated HIV env from either HIV BH10 or HIV 89.6 virus were coexpressed in insect cells and Env incorporation into released SHIV VLPs was characterized. The expression level of the Env protein was found to be about 20-50% higher in both strains producing the truncated Env. Cell surface expression of the truncated Env proteins was found to be about eightfold higher than that of the full-length Env proteins. Furthermore, the truncated Env proteins exhibited higher levels of cleavage into gp120 and gp41 compared with the full-length Env. The SHIV VLPs produced by the coexpression of SIV gag and truncated HIV env contained both precursor (gp160) and gp120, while predominantly gp160 was found in the VLPs containing full-length Env. Coinfection of a recombinant virus expressing the protease furin also resulted in more efficient cleavage of gp160 to gp120. Both full-length and truncated Env were found to induce CD4+ cell fusion. Analysis of VLPs by immunoelectron microscopy demonstrated the incorporation of both full-length and truncated Env on the surface of VLPs. Truncated Env also was incorporated at higher levels on the surfaces of VLPs than full-length Env. The assembly of VLPs containing biologically active Env proteins may be useful in vaccine development and in functional studies of the HIV envelope protein.

Hepatitis C virus-like particles synthesized in insect cells as a potential vaccine candidate

BACKGROUND & AIMS

Hepatitis C virus (HCV) is a leading cause of chronic hepatitis in the world. Successful vaccine development is crucial in controlling global HCV infection. We have previously described the generation of HCV-like particles (HCV-LPs) in insect cells using a recombinant baculovirus containing the complementary DNA of the HCV structural proteins. These HCV-LPs had similar morphological and biophysical properties as the putative virions. In this study, we analyzed the structural features, antigenic composition, seroreactivity, and immunogenicity of purified HCV-LPs.

METHODS

HCV-LPs were analyzed by electron microscopy and antibody immunolabeling and precipitation. An enzyme-linked immunosorbent assay (ELISA) using HCV-LPs was developed. The humoral response to HCV-LPs in mice was studies by core and envelope ELISAs, Western immunoblotting, and immunofluorescence.

RESULTS

Structural and antigenic compositions of HCV-LPs were shown to be similar to those of putative HCV virions. Using the HCV-LP ELISA, high-titer anti-HCV antibodies were detected in individuals infected with various HCV genotypes. In vivo, HCV-LPs elicited a humoral response broadly directed against HCV structural proteins.

CONCLUSIONS

HCV-LPs resemble HCV virions and are capable of inducing a humoral response targeted against various regions of HCV structural proteins, suggesting that HCV-LPs may be promising as a potential vaccine candidate.

Antibodies from HIV-positive and AIDS patients bind to an HIV envelope multivalent vaccine

A major problem impeding development of an effective HIV vaccine is the rapid antigenic variability that is characteristic of several envelope glycoprotein epitopes. Frequent mutations alter the composition of the most immunogenic regions of the envelope glycoprotein. We have prepared a synthetic immunogen representing the evolution of the major hypervariable epitopes on the envelope glycoprotein (gp120) of HIV-1. Five synthetic constructs, representing each of the HIV-1 gp120 hypervariable epitopes were tested for recognition by antibodies from patients infected with HIV-1 from different geographic regions worldwide. An HIV-1 human plasma panel provided a representation of the antibodies recognizing subtype-specific epitope sequences prevalent at different parts of the world. The vaccine construct was recognized by antibodies from HIV-1-positive individuals infected with subtypes A, B, C, D, E, and F. Antibodies in pooled HIV-1 patient sera from San Francisco also recognized all five constructs. This complex immunogen was recognized by antibodies in sera from individual HIV-1-positive and AIDS patients from Puerto Rico and Canada, with a strong binding to the complete vaccine and the V3 component. Altogether, our results demonstrate that antibodies from seropositive patients infected with different HIV-1 clades recognize and bind to the HIV hypervariable epitope construct vaccine preparation and its individual components.

Development of HIV/AIDS vaccine using chimeric gag-env virus-like particles

We attempted to develop a candidate HIV/AIDS vaccine, by using unprocessed HIV-2 gag pr45 precursor protein. We found that a 45 kDa unprocessed HIV-2 gag precursor protein (pr45), with a deletion of a portion of the viral protease, assembles as virus-like particles (VLP). We mapped the functional domain of HIV-2 gag VLP formation in order to find the minimum length of gag protein to form VLP. A series of deletion mutants was constructed by sequentially removing the C-terminal region of HIV-2 gag precursor protein and expressed truncated genes in Spodoptera frugiperda (SF) cells by infecting recombinant baculoviruses. We found that deletion of up to 143 amino acids at the C-terminus of HIV-2 gag, leaving 376 amino acids at the N-terminus of the protein, did not affect VLP formation. There is a proline-rich region at the amino acid positions 373 to 377 of HIV-2 gag, and replacement of these proline residues by site-directed mutagenesis completely abolished VLP assembly. Our data demonstrate that the C-terminal p12 region of HIV-2 gag precursor protein, and zinc finger domains, are dispensable for gag VLP assembly, but the presence of at least one of the three prolines at amino acid positions 373, 375 or 377 of HIV-2NIH-Z is required for VLP formation. Animals immunized with these gag particles produced high titer antibodies and Western blot analyses showed that anti-gag pr45 rabbit sera react with p17, p24 and p55 gag proteins of HIV-1. We then constructed chimeric gag genes, which carry the hypervariable V3 region of HIV-1 gp120, because the V3 loop is known to interact with chemokine receptor as a coreceptor, and known to induce the major neutralizing antibodies and stimulate the cytoxic T lymphocyte responses in humans and mice. We expressed chimeric fusion protein of HIV-2 gag with 3 tandem copies of consensus V3 domain that were derived from 245 different isolates of HIV-1. In addition, we also constructed and expressed chimeric fusion protein that contains HIV-2 gag with V3 domains of HIV-1IIIB, HIV-1MN, HIV-1SF2 and HIV-1RF. The chimeric gag-env particles had a spherical morphology, and the size was slightly larger than that of a gag particle. Immunoprecipitation and Western blot analyses show that these chimeric proteins were recognized by HIV-1 positive human sera and antisera raised against V3 peptides, as well as by rabbit anti-gp120 serum. We obtained virus neutralizing antibodies in rabbits by immunizing these gag-env VLPs. In addition, we found that gag-env chimeric VLPs induce a strong CTL activity against V3 peptide-treated target cells. Our results indicate that V3 peptides from all major clades of HIV-1 carried by HIV-2 gag can be used as a potential HIV/AIDS vaccine.