Influence of glycosylation on the efficacy of an Env-based vaccine against simian immunodeficiency virus SIVmac239 in a macaque AIDS model

Plant-Expressed Receptor Binding Domain of the SARS-CoV-2 Spike Protein Elicits Humoral Immunity in Mice

The current 15-month coronavirus disease-19 (COVID-19) pandemic caused by SARS-CoV-2 has accounted for 3.77 million deaths and enormous worldwide social and economic losses. A high volume of vaccine production is urgently required to eliminate COVID-19. Inexpensive and robust production platforms will improve the distribution of vaccines to resource-limited countries. Plant species offer such platforms, particularly through the production of recombinant proteins to serve as immunogens. To achieve this goal, here we expressed the receptor binding domain (RBD) of the SARS-CoV-2 spike (S) protein in the glycoengineered-tobacco plant Nicotiana benthamiana to provide a candidate subunit vaccine. This recombinant RBD elicited humoral immunity in mice via induction of highly neutralizing antibodies. These findings provide a strong foundation to further advance the development of plant-expressed RBD antigens for use as an effective, safe, and inexpensive SARS-CoV-2 vaccine. Moreover, our study further highlights the utility of plant species for vaccine development.

Expression and purification of an engineered, yeast-expressed Leishmania donovani nucleoside hydrolase with immunogenic properties

Leishmania donovani is the major cause of visceral leishmaniasis (kala-azar), now recognized as the parasitic disease with the highest level of mortality second only to malaria. No human vaccine is currently available. A 36 kDa L. donovani nucleoside hydrolase (LdNH36) surface protein has been previously identified as a potential vaccine candidate antigen. Here we present data on the expression of LdNH36 in Pichia pastoris and its purification at the 20 L scale to establish suitability for future pilot scale manufacturing. To improve efficiency of process development and ensure reproducibility, 4 N-linked glycosylation sites shown to contribute to heterogeneous high-mannose glycosylation were mutated to glutamine residues. The mutant LdNH36 (LdNH36-dg2) was expressed and purified to homogeneity. Size exclusion chromatography and light scattering demonstrated that LdNH36-dg2 existed as a tetramer in solution, similar to the wild-type recombinant L. major nucleoside hydrolase. The amino acid mutations do not affect the tetrameric interface as confirmed by theoretical modeling, and the mutated amino acids are located outside the major immunogenic domain. Immunogenic properties of the LdNH36-dg2 recombinant protein were evaluated in BALB/c mice using formulations that included a synthetic CpG oligodeoxynucleotide, together with a microparticle delivery platform (poly(lactic-co-glycolic acid)). Mice exhibited high levels of IgG1, IgG2a, and IgG2b antibodies that were reactive to both LdNH36-dg2 and LdNH36 wild-type. While the point mutations did affect the hydrolase activity of the enzyme, the IgG antibodies elicited by LdNH36-dg2 were shown to inhibit the hydrolase activity of the wild-type LdNH36. The results indicate that LdNH36-dg2 as expressed in and purified from P. pastoris is suitable for further scale-up, manufacturing, and testing in support of future first-in-humans phase 1 clinical trials.

[Structure and Function of a Novel Class of High Mannose-binding Proteins with Anti-viral or Anti-tumor Activity]

The recently discovered high mannose (HM)-binding lectin family in lower organisms such as bacteria, cyanobacteria, and marine algae represents a novel class of anti-viral or anti-tumor compounds. This lectin family shows unique carbohydrate binding properties with exclusive high specificity for HM glycans with core trisaccharide comprising Manα(1-3)Manα(1-6)Man at the D2 arm. At low nanomolar levels, these lectins exhibit potent antiviral activity against HIV and influenza viruses through the recognition of HM glycans on virus spike glycoproteins. In addition, some of these lectins, such as bacterial PFL, show cytotoxicity for various cancer cells at low micromolar levels. Cell surface molecules to which PFL bound were identified as integrin alpha 2 and epidermal growth factor receptor (EGFR) by peptide mass finger printing with MALDI-TOF MS. Upon PFL binding, these molecules were rapidly internalized to cytoplasm. EGFR was time dependently degraded in the presence of PFL, and this process was largely responsible for autophagy. Furthermore, PFL sensitizes cancer cells to the EGFR kinase inhibitor, gefitinib. In vivo experiments showed that intratumoral injection of PFL significantly inhibited the growth of tumors in nude mice. PFL-mediated down regulation of integrin/EGFR ultimately contributed to the inhibition of tumor growth both in vitro and in vivo. Thus, the novel anti-cancer mechanism of PFL suggests that this lectin is potentially useful as an anti-cancer drug or as an adjuvant for other drugs. This class of proteins will likely have beneficial impact as a tool for biochemical and biomedical research because of its unique carbohydrate specificity and various biological activities.

Phenotypic and Functional Characterization of Monoclonal Antibodies with Specificity for Rhesus Macaque CD200, CD200R and Mincle

Lectin-like molecules and their receptors are cell surface molecules that have been shown to play a role in either facilitating infection or serving as transporters of HIV/SIV in vivo. The role of these lectin-like molecules in the pathogenesis of HIV/SIV infection continues to be defined. In efforts to gain further insight on the potential role of these lectin-like molecules, our laboratory generated monoclonal antibodies (mAb) against the human analogs of rhesus macaque CD200, CD200R and Mincle, since the rhesus macaques are accepted as the most reliable animal model to study human HIV infection. The characterization of the cell lineages from the blood and various tissues of rhesus macaques that express these lectin-like molecules are described herein. Among the mononuclear cells, the cells of the myeloid lineage of rhesus macaques are the predominant cell lineages that express readily detectable levels of CD200, CD200R and Mincle that is similar to the expression of Siglec-1 and Siglec-3 reported by our laboratory earlier. Subset analysis revealed that a higher frequency of the CD14⁺/CD16^- subset from normal rhesus macaques express CD200, CD200R and Mincle. Differences in the frequencies and density of expression of these molecules by the gated population of CD14⁺ cells from various tissues are noted with PBMC and bone marrow expressing the highest and the mononuclear cells isolated from the colon and ileum expressing the lowest levels. While a significant frequency of pDCs and mDCs express Siglec-1/Siglec-3, a much lower frequency expresses CD200, CD200R and Mincle in PBMCs from rhesus macaques. The mAb against CD200 and CD200R but not Mincle appear to inhibit the infection of macrophage tropic SIV/SHIV in vitro. We conclude that these mAbs may have potential to be used as adjunctive therapeutic agents to control/inhibit SIV/HIV infection.

The multiple roles of sGP in Ebola pathogenesis

Ebola causes severe hemorrhagic fever in humans and nonhuman primates, and there are currently no approved therapeutic countermeasures. The virulence of Ebola virus (EBOV) may be partially attributed to the secreted glycoprotein (sGP), which is the main product transcribed from its GP gene. sGP is secreted from infected cells and can be readily detected in the serum of EBOV-infected hosts. This review summarizes the multiple roles that sGP may play during infection and highlights the implications for the future design of vaccines and treatments.

Species-specific differences in the expression and regulation of α4β7 integrin in various nonhuman primates

Among nonhuman primates, SIV-infected Asian pigtailed macaques (PM) are relatively more susceptible to infection and disease progression than SIV-infected rhesus macaques (RM). In addition, SIV-infected African natural hosts such as the sooty mangabeys (SM) are resistant to disease. The mechanisms associated with such species-related variable clinical outcomes remain ill-defined but hold the potential to provide insights into the underlying mechanisms surrounding HIV pathogenesis. Recent findings indicate that the expression of the heterodimeric gut homing integrin α4β7 can influence both susceptibility and disease progression in RM. It was reasoned that differences in the frequencies/surface densities of α4β7-expressing lymphocytes might contribute to the differences in the clinical outcome of SIV infection among NHPs. In this article, we report that CD4(+) T cells from PM constitutively express significantly higher levels of α4β7 than RM or SM. Retinoic acid, a key regulator of α4β7 expression, was paradoxically found at higher levels in the plasma of SM versus RM or PM. We also observed pairing of β7 with αE (αEβ7) on CD4(+) T cells in the peripheral blood of SM, but not PM or RM. Finally, the differential mean density of expression of α4β7 in RM versus SM versus PM was predominantly dictated by species-specific sequence differences at the level of the β7 promoters, as determined by in vitro reporter/promoter construct transfection studies. We propose that differences in the regulation and expression of α4β7 may explain, in part, the differences in susceptibility and SIV disease progression in these NHP models.

The potential of Physcomitrella patens as a platform for the production of plant-based vaccines

The moss Physcomitrella patens has a number of advantages for the production of biopharmaceuticals, including: i) availability of standardized conditions for cultivation in bioreactors; ii) not being part of the food chain; iii) high biosafety; iv) availability of highly efficient transformation methods; v) a haploid, fully sequenced genome providing genetic stability and uniform expression; vi) efficient gene targeting at the nuclear level allows for the generation of mutants with specific post-translational modifications (e.g., glycosylation patterns); and vii) oral formulations are a viable approach as no toxic effects are attributed to ingestion of this moss. In the light of this panorama, this opinion paper analyzes the possibilities of using P. patens for the production of oral vaccines and presents some specific cases where its use may represent significant progress in the field of plant-based vaccine development. The advantages represented by putative adjuvant effects of endogenous secondary metabolites and producing specific glycosylation patterns are highlighted.

The comparison of genetic variation in the envelope protein between various immunodeficiency viruses and equine infectious anemia virus

The envelope protein (Env) of lentiviruses such as HIV, SIV, FIV and EIAV is larger than that of other retroviruses. The Chinese EIAV attenuated vaccine is based on Env and has helped to successfully control this virus, demonstrating that envelope is crucial for vaccine. We compared Env variation of the four kinds of lentiviruses. Phylogenetic analysis showed that the evolutionary relationship of Env between HIV and SIV was the closest and they appeared to descend from a common ancestor, and the relationship of HIV and EIAV was the furthest. EIAV had the shortest Env length and the least number of potential N-linked glycosylation sites (PNGS) as well as glycosylation density compared to various immunodeficiency viruses. However, HIV had the longest Env length and the most PNGS. Moreover, the alignment of HIV and SIV showed that PNGS were primarily distributed within extracellular membrane protein gp120 rather than transmembrane gp41. It implies that the size difference among these viruses is associated with a lentivirus specific function and also the diversity of env. There are low levels of modification of glycosylation sites of Env and selection of optimal protective epitopes might be useful for development of an effective vaccine against HIV/AIDS.

Glycosylation of simian immunodeficiency virus influences immune-tissue targeting during primary infection, leading to immunodeficiency or viral control

Glycans of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) play pivotal roles in modulating virus-target cell interactions. We have previously reported that, whereas SIVmac239 is pathogenic, its deglycosylated essentially nonpathogenic mutant (Δ5G) serves as a live-attenuated vaccine, although both replicate similarly during primary infection. These findings prompted us to determine whether such a polarized clinical outcome was due to differences in the immune tissues targeted by these viruses, where functionally and phenotypically different memory CD4(+) T cells reside. The results showed that Δ5G replicates in secondary lymphoid tissue (SLT) at 1- to 2-log-lower levels than SIVmac239, whereas SIVmac239-infected but not Δ5G-infected animals deplete CXCR3(+) CCR5(+) transitional memory (TrM) CD4(+) T cells. An early robust Δ5G replication was localized to small intestinal tissue, especially the lamina propria (effector site) rather than isolated lymphoid follicles (inductive site) and was associated with the induction and depletion of CCR6(+) CXCR3(-) CCR5(+) effector memory CD4(+) T cells. These results suggest that differential glycosylation of Env dictates the type of tissue-resident CD4(+) T cells that are targeted, which leads to pathogenic infection of TrM-Th1 cells in SLT and nonpathogenic infection of Th17 cells in the small intestine, respectively.

Incorporation of innate immune effector mechanisms in the formulation of a vaccine against HIV-1

The realization of a major role for events that occur during acute viremia that dictate the course of disease both in HIV-1 infected humans and susceptible SIV infected non-human primates has prompted an intense interest in studies of the contribution of innate immune effector mechanisms. It is reasoned that findings from such studies may be important and need to be incorporated into the design and formulation of potential candidate vaccines against HIV-1. This review serves to outline the various non-human primate models that can best serve to address this issue, a summary of our knowledge on the various subsets of NK cells (one of the major innate immune cell lineage) that have an impact on the course of disease, the potential pathways that regulate their function and the potential role of the KIRs on SIV-induced disease course. Finally, the major points from this report and the data presented on similar subjects by other investigators is utilized to provide a summary of the potential future directions that we need to take in efforts to move this field forward.

Review and hypothesis: does Graves' disease develop in non-human great apes?

BACKGROUND

Graves' disease, caused by stimulatory thyrotropin receptor (TSHR) autoantibodies, has not been observed in animals. In contrast, Hashimoto's thyroiditis develops in chickens, rats, mice, dogs, and marmosets. Attempts to induce an immune response in mice to the luteinizing-hormone receptor suggested that autoantigen glycosylation was one parameter involved in breaking self-tolerance. Over evolution, TSHR glycosylation increased from three asparagine-linked-glycans (N-glycans) in fish to six N-glycans in humans and great apes. All other placental mammals lack one N-glycan in the shed TSHR A-subunit, the primary Graves' disease autoantigen. We hypothesized that (a) lesser TSHR A-subunit glycosylation reduces immunogenicity, accounting for the absence of Graves' disease in most placental mammals; (b) due to human-like A-subunit glycosylation, Graves' disease might arise in great apes. Here, we review and analyze the literature on this subject and report the results of a survey of veterinarians at primate centers and zoos in North America.

SUMMARY

Previous experimental data from induced TSHR antibodies in mice support a role for A-subunit glycosylation in breaking self-tolerance. An extensive search of the great-ape literature revealed five reports of noncongenital thyroid dysfunction, four with hypothyroidism and one with hyperthyroidism. The latter was a gorilla who was treated with anti-thyroid drugs but is now deceased. Neither serum nor thyroid tissue from this gorilla were available for analysis. The survey of veterinarians revealed that none of the 979 chimpanzees in primate research centers had a diagnosis of noncongenital thyroid dysfunction and among ∼1100 great apes (gorillas, orangutans, and chimpanzees) in U.S. zoos, only three were hypothyroid, and none were hyperthyroid.

CONCLUSIONS

Graves' disease appears to be either very rare or does not occur in great apes based on the literature and a survey of veterinarians. Although the available data do not advance our hypothesis, there is a paucity of information regarding thyroid function tests and thyroid autoantibodies in the great apes In addition, these primates may be protected against TSHR autoimmunity by the absence of genetic polymorphisms and putative environmental triggers. Finally, larger numbers of great apes need to be followed, and tests of thyroid function and thyroid autoantibodies be performed, to confirm that spontaneous Graves' disease is restricted to humans.

Improving immunogenicity of HIV-1 envelope gp120 by glycan removal and immune complex formation

HIV-1 envelope (Env) gp120 is an important target for neutralizing antibody (Ab) responses against the virus; however, developing gp120 vaccines that elicit potent and broad neutralizing Abs has proven to be a formidable challenge. Previously, removal of an N-linked glycan at residue 448 by an N to Q mutation (N448Q) has been found to enhance the in vitro antigenicity of neutralizing epitopes in the V3 loop. In this study the mutated gp120 was first compared with wild type gp120 for immunogenicity in mice using a DNA prime and protein boost immunization regimen. The N448Q mutant did not elicit higher titers of anti-gp120 serum Abs and failed to generate anti-V3 Abs. The sera also had no virus-neutralizing activity, even though the mutant induced higher levels of lymphoproliferation and cytokine production. Subsequently, the N448Q mutant was used to construct an immune complex vaccine with the anti-CD4 binding site monoclonal antibody (mAb) 654. The N448Q/654 complex stimulated comparably high levels of serum Abs to gp120 and V3 as the wild type complex. However, Abs against the C1 and C2 regions in the gp120 core were more elevated. Importantly, the mutant complex also elicited higher titers of neutralizing Abs activity than the wild type counterpart. Similar results were achieved with a complex made with gp120 bearing an N448E mutation, confirming the importance of the N448-linked glycan in modulating gp120 immunogenicity. Neutralizing activity was directed to V3 and other undefined neutralizing epitopes. Improved immunogenicity of the immune complexes correlated with alterations in exposure of V3 and other Ab epitopes and their stability against proteases. These data demonstrate the advantage of combining site-specific N-glycan removal and immune complex formation as a novel vaccine strategy to improve immunogenicity of targeted Ab epitopes on critical regions of HIV-1 gp120.

An attempt to induce "Graves' disease of the gonads" by immunizing mice with the luteinizing hormone receptor provides insight into breaking tolerance to self-antigens

BACKGROUND

Gonadotropin receptors, unlike the thyrotropin receptor (TSHR), are not cleaved into disulfide-linked A- and B-subunits, nor do they shed A-subunits. Heavily glycosylated TSHR A-subunits initiate or amplify responses leading to stimulating TSHR-autoantibodies and Graves' hyperthyroidism.

METHODS

To investigate the possibility that mice immunized with luteinizing hormone receptor (LHR) would develop functional antibodies, we constructed adenoviruses expressing the rat-LH holoreceptor (LHR-Ad) and an LHR A-subunit equivalent (LHR-289-Ad). Female BALB/c mice were immunized with high doses (10(11) particles) of LHR-Ad, LHR-289-Ad, or control (Con)-Ad. Sera were tested using LHR-expressing eukaryotic cells for antibody binding by flow cytometry and for bioactivity by measuring cyclic adenosine monophosphate (cAMP) stimulation.

RESULTS

Elevated serum binding to LHR cells in some LHR-Ad and LHR-289-Ad immunized mice was not specific for LHR-expressing cells. Moreover, sera lacked bioactivity, consistent with unchanged serum estradiol and ovary histology. The difference between rat and mouse LHR-ectodomains is relatively small (3% at the amino-acid level). In contrast, despite amino-acid identity, immunization of mice with adenovirus expressing membrane-bound mouse thyroid peroxidase (TPO), but not soluble mouse TPO ectodomain, elicited strong TPO-specific antibodies.

CONCLUSIONS

Our investigations provide insight into antibody responses to self-antigens. First, antibodies are induced to large self-antigens like mouse-TPO when membrane bound. Second, lesser amino acid homology between the immunogen and mouse protein (91% vs. 97% for the human-TSHR and rat-LHR, respectively) favors antibody induction. Finally, from previous studies demonstrating the immunogenicity of the highly glycosylated human TSHR A-subunit versus our present data for the nonimmunogenic less glycosylated rat LHR, we suggest that the extent of glycosylation contributes to breaking self-tolerance.

Expression-system-dependent modulation of HIV-1 envelope glycoprotein antigenicity and immunogenicity

Recombinant expression systems differ in the type of glycosylation they impart on expressed antigens such as the human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins, potentially affecting their biological properties. We performed head-to-head antigenic, immunogenic and molecular profiling of two distantly related Env surface (gp120) antigens produced in different systems: (a) mammalian (293 FreeStyle cells; 293F) cells in the presence of kifunensine, which impart only high-mannose glycans; (b) insect cells (Spodoptera frugiperda, Sf9), which confer mainly paucimannosidic glycans; (c) Sf9 cells recombinant for mammalian glycosylation enzymes (Sf9 Mimic), which impart high-mannose, hybrid and complex glycans without sialic acid; and (d) 293F cells, which impart high-mannose, hybrid and complex glycans with sialic acid. Molecular models revealed a significant difference in gp120 glycan coverage between the Sf9-derived and wild-type mammalian-cell-derived material that is predicted to affect ligand binding sites proximal to glycans. Modeling of solvent-exposed surface electrostatic potentials showed that sialic acid imparts a significant negative surface charge that may influence gp120 antigenicity and immunogenicity. Gp120 expressed in systems that do not incorporate sialic acid displayed increased ligand binding to the CD4 binding and CD4-induced sites compared to those expressed in the system that do, and imparted other more subtle differences in antigenicity in a gp120 subtype-specific manner. Non-sialic-acid-containing gp120 was significantly more immunogenic than the sialylated version when administered in two different adjuvants, and induced higher titers of antibodies competing for CD4 binding site ligand-gp120 interaction. These findings suggest that non-sialic-acid-imparting systems yield gp120 immunogens with modified antigenic and immunogenic properties, considerations that should be considered when selecting expression systems for glycosylated antigens to be used for structure-function studies and for vaccine use.

Protection of macaques with diverse MHC genotypes against a heterologous SIV by vaccination with a deglycosylated live-attenuated SIV

HIV vaccine development has been hampered by issues such as undefined correlates of protection and extensive diversity of HIV. We addressed these issues using a previously established SIV-macaque model in which SIV mutants with deletions of multiple gp120 N-glycans function as potent live attenuated vaccines to induce near-sterile immunity against the parental pathogenic SIVmac239. In this study, we investigated the protective efficacy of these mutants against a highly pathogenic heterologous SIVsmE543-3 delivered intravenously to rhesus macaques with diverse MHC genotypes. All 11 vaccinated macaques contained the acute-phase infection with blood viral loads below the level of detection between 4 and 10 weeks postchallenge (pc), following a transient but marginal peak of viral replication at 2 weeks in only half of the challenged animals. In the chronic phase, seven vaccinees contained viral replication for over 80 weeks pc, while four did not. Neutralizing antibodies against challenge virus were not detected. Although overall levels of SIV specific T cell responses did not correlate with containment of acute and chronic viral replication, a critical role of cellular responses in the containment of viral replication was suggested. Emergence of viruses with altered fitness due to recombination between the vaccine and challenge viruses and increased gp120 glycosylation was linked to the failure to control SIV. These results demonstrate the induction of effective protective immune responses in a significant number of animals against heterologous virus by infection with deglycosylated attenuated SIV mutants in macaques with highly diverse MHC background. These findings suggest that broad HIV cross clade protection is possible, even in hosts with diverse genetic backgrounds. In summary, results of this study indicate that deglycosylated live-attenuated vaccines may provide a platform for the elucidation of correlates of protection needed for a successful HIV vaccine against diverse isolates.

Tonsillar application of AT-2 SIV affords partial protection against rectal challenge with SIVmac239

BACKGROUND

Although mucosal responses are important for preventing infections with HIV, the optimal strategies for inducing them remain unclear. To evaluate vaccine strategies targeting the oral mucosal lymphoid tissue inductive sites as an approach to provide immunity at distal sites, we vaccinated healthy macaques via the palatine/lingual tonsils with aldrithiol 2 (AT-2) inactivated Simian immunodeficiency virus (SIV)mac239, combined with CpG-C immunostimulatory oligonucleotide (CpG-C ISS-ODN, C274) as the adjuvant.

METHODS

Macaques received 5 doses of C274 or control ODN C661 and AT-2 SIV on the tonsillar tissues every 6 weeks before being challenged rectally with SIVmac239, 8 weeks after the last immunization.

RESULTS

Although no T-cell or B-cell responses were detected in the blood before challenge, antibody (Ab) responses were detected in the rectum. Immunization with AT-2 SIV significantly reduced the frequency of infection compared with nonimmunized controls, irrespective of adjuvant. In the vaccinated animals that became infected, peak viremias were somewhat reduced. SIV-specific responses were detected in the blood once animals became infected with no detectable differences between the differently immunized groups and the controls.

CONCLUSION

This work provides evidence that vaccine immunogens applied to the oral mucosal associated lymphoid tissues can provide benefit against rectal challenge, a finding with important implications for mucosal vaccination strategies.

Proximal glycans outside of the epitopes regulate the presentation of HIV-1 envelope gp120 helper epitopes

Glycosylation of HIV-1 envelope gp120 determines not only the proper structure, but also the immune responses against this Ag. Although glycans may be part of specific epitopes or shield other epitopes from T cells and Abs, this study provides evidence for a different immunomodulatory function of glycans associated with gp120 residues N230 and N448. These glycans are required for efficient MHC class II-restricted presentation of nearby CD4 T cell epitopes, even though they are not part of the epitopes. The glycans do not affect CD4 T cell recognition of more distant epitopes and are not essential for the proper folding and function of gp120. Data on CD4 T cell recognition of N448 mutants combined with proteolysis analyses and surface electrostatic potential calculation around residue N448 support the notion that N448 glycan near the epitope's C terminus renders the site to be surface accessible and allows its efficient processing. In contrast, the N230 glycan contributes to the nearby epitope presentation at a step other than the proteolytic processing of the epitope. Hence, N-glycans can determine CD4 T cell recognition of nearby gp120 epitopes by regulating the different steps in the MHC class II processing and presentation pathway after APCs acquire the intact gp120 Ag exogenously. Modifications of amino acids bearing glycans at the C termini of gp120 helper epitopes may prove to be a useful strategy for enhancing the immunogenicity of HIV-1 envelope gp120.

A novel CD4-conjugated ultraviolet light-activated photocatalyst inactivates HIV-1 and SIV efficiently

In this study, we found that the electric potential derived from the redox reaction of ultraviolet (UV)-illuminated CD4-conjugated titanium dioxide (TiO2) inactivated a wide range of high-titered primary HIV-1 isolates, regardless of virus co-receptor usage or genetic clade. In vitro incubation of HIV-1 isolates with CD4-conjugated TiO2 (CD4-TiO2) followed by UV illumination led to inhibition of viral infectivity in both H9 cells and peripheral blood mononuclear cells as well as to the complete inactivation of plasma virions from HIV-1-infected individuals. Treatment with a newly established extra-corporeal circulation system with the photocatalyst in rhesus macaques completely inactivated plasma virus in the system and effectively reduced the infectious plasma viral load. Furthermore, plasma viremia and infectious viral loads were controlled following a second therapeutic photocatalyst treatment during primary SIV(mac239) infection of macaques. Our findings suggest that this therapeutic immunophysical strategy may help control human immunodeficiency viral infection in vivo.

Antibodies to the CD4-binding site of HIV-1 gp120 suppress gp120-specific CD4 T cell response while enhancing antibody response

BACKGROUND

The binding of Abs to the CD4-binding site (CD4bs) of HIV-1 envelope gp120 has been shown to obstruct the processing and generation of helper epitopes from this antigen, resulting in poor presentation of various gp120 epitopes by MHC class II to CD4 T cells. However, the physiologic significance of these inhibitory anti-CD4bs Abs in vivo has remained unclear. In this study, we evaluated the immunologic effects of anti-CD4bs Abs in vivo using a murine model.

RESULTS

Animals were immunized with recombinant envelope proteins with or without CD4-binding activity (designated CD4bs+ Env and CD4bs- Env, respectively). As expected, anti-CD4bs Abs were generated only after immunization with CD4bs+ Env and not with CD4bs- Env. The presence of anti-CD4bs Abs was associated with lower levels of envelope-specific lymphoproliferation in animals immunized with CD4bs+ Env. To further determine the specific role of the anti-CD4bs Abs, we immunized mice with gp120 in the presence of an inhibitory anti-CD4bs mAb or a non-inhibitory anti-gp120 mAb. The data show that the presence of anti-CD4bs mAb reduced CD4 T cell responses to gp120. However, we also detected significantly higher titers of anti-gp120 Abs following immunization with gp120 and the anti-CD4bs mAb.

CONCLUSION

Anti-CD4bs Abs can exert discordant effects on the gp120-specific CD4 T cell and Ab responses in vivo, indicating the importance of these particular Abs in influencing both the cellular and the humoral immune responses against HIV-1.

Identification of an N-linked glycosylation in the C4 region of HIV-1 envelope gp120 that is critical for recognition of neighboring CD4 T cell epitopes

The heavy glycosylation of HIV-1 envelope gp120 shields this important Ag from recognition by neutralizing Abs and cytolytic CD8 T cells. However, very little work has been done to understand the influence of glycosylation on the generation of gp120 epitopes and their recognition by MHC class II-restricted CD4 T cells. In this study, three conserved glycans (linked to N406, N448, and N463) flanking the C4 region of gp120 that contains many known CD4 T cell epitopes were disrupted individually or in combination by asparagine-to-glutamine substitutions. The mutant proteins lacking the N448 glycan did not effectively stimulate CD4 T cells specific for the nearby C4 epitopes, although the same mutants were recognized well by CD4 T cells specific for epitopes located in the distant C1 and C2 regions. The loss of recognition was not due to amino acid substitutions introduced to the mutant proteins. Data from trypsin digestion and mass spectrometry analyses demonstrated that the N448 glycan removal impeded the proteolytic cleavage of the nearby C4 region, without affecting more distant sites. Importantly, this inhibitory effect was observed only in the digestion of the native nondenatured protein and not in that of the denatured protein. These data indicate that the loss of the N448 glycan induces structural changes in the C4 region of gp120 that make this specific region more resistant to proteolytic processing, thereby restricting the generation of CD4 T cell epitopes from this region. Hence, N-linked glycans are critical determinants that can profoundly influence CD4 T cell recognition of HIV-1 gp120.

Impact of glycosylation on antigenicity of simian immunodeficiency virus SIV239: induction of rapid V1/V2-specific non-neutralizing antibody and delayed neutralizing antibody following infection with an attenuated deglycosylated mutant

Infection of rhesus macaques with a deglycosylation mutant, Delta5G, derived from SIV239, a pathogenic clone of simian immunodeficiency virus (SIV), led to robust acute-phase viral replication followed by a chronic phase with undetectable viral load. This study examined whether humoral responses in Delta5G-infected animals played any role in the control of infection. Neutralizing antibodies (nAbs) were elicited more efficiently in Delta5G-infected animals than in SIV239-infected animals. However, functional nAb measured by 90% neutralization was prominent in only two of the five Delta5G-infected animals, and only at 8 weeks post-infection (p.i.), when viral loads were already below 10(4) copies ml(-1). These results suggest a minimal role for nAbs in the control of the primary infection. In contrast, whilst Ab responses to epitopes localized to the variable loops V1/V2 were detected in all Delta5G-infected animals at 3 weeks p.i., this response was associated with a concomitant reduction in Ab responses to epitopes in gp41 compared with those in SIV239-infected animals. These results suggest that the altered surface glycosylation and/or conformation of viral spikes induce a humoral response against SIV that is distinct from the response induced by SIV239. More interestingly, whereas V1/V2-specific Abs were induced in all animals, these Abs were associated with vigorous Delta5G-specific virion capture ability in only two Delta5G-infected animals that exhibited a functional nAb response. Thus, whereas the deglycosylation mutant infection elicited early virion capture and subsequent nAbs, the responses differed among animals, suggesting the existence of host factors that may influence the functional humoral responses against human immunodeficiency virus/SIV.

Removal of a single N-linked glycan in human immunodeficiency virus type 1 gp120 results in an enhanced ability to induce neutralizing antibody responses

Glycans on human immunodeficiency virus (HIV) envelope protein play an important role in infection and evasion from host immune responses. To examine the role of specific glycans, we introduced single or multiple mutations into potential N-linked glycosylation sites in hypervariable regions (V1 to V3) of the env gene of HIV type 1 (HIV-1) 89.6. Three mutants tested showed enhanced sensitivity to soluble CD4. Mutant N7 (N197Q) in the carboxy-terminal stem of the V2 loop showed the most pronounced increase in sensitivity to broadly neutralizing antibodies (NtAbs), including those targeting the CD4-binding site (IgG1b12) and the V3 loop (447-52D). This mutant is also sensitive to CD4-induced NtAb 17b in the absence of CD4. Unlike the wild-type (WT) Env, mutant N7 mediates CD4-independent infection in U87-CXCR4 cells. To study the immunogenicity of mutant Env, we immunized pig-tailed macaques with recombinant vaccinia viruses, one expressing SIVmac239 Gag-Pol and the other expressing HIV-1 89.6 Env gp160 in WT or mutant forms. Animals were boosted 14 to 16 months later with simian immunodeficiency virus gag DNA and the cognate gp140 protein before intrarectal challenge with SHIV89.6P-MN. Day-of-challenge sera from animals immunized with mutant N7 Env had significantly higher and broader neutralizing activities than sera from WT Env-immunized animals. Neutralizing activity was observed against SHIV89.6, SHIV89.6P-MN, HIV-1 SF162, and a panel of subtype B primary isolates. Compared to control animals, immunized animals showed significant reduction of plasma viral load and increased survival after challenge, which correlated with prechallenge NtAb titers. These results indicate the potential advantages for glycan modification in vaccine design, although the role of specific glycans requires further examination.

Reference strand-mediated conformation analysis-based typing of multiple alleles in the rhesus macaque MHC class I Mamu-A and Mamu-B loci

The rhesus macaque exhibits individual differences in susceptibility and resistance to infectious agents such as simian immunodeficiency virus (SIV) under experimental conditions, and these may be genetically determined at least in part by major histocompatibility complex (MHC) class I polymorphism. Although the importance of defining MHC class I polymorphism is well recognized, development of a generic and comprehensive molecular typing method of MHC class I alleles of the rhesus macaque has been hampered because, during the evolution of this species, multiple copies of similar DNA sequences have been generated by duplication events including the coding sequences of Mamu-A and Mamu-B loci. We report here a newly developed reference strand-mediated conformation analysis (RSCA)-based typing method of multiple Mamu-A and Mamu-B cDNAs that allowed us to estimate the number of expressed alleles. This technique detected 1-7 Mamu-A signals and 2-12 Mamu-B signals in a single sample, indicating that the number of functional alleles may vary. By comparing the data from the parents with those from the descendants in the breeding colony, several MHC class I haplotypes consisting of variable numbers of functional Mamu-A and Mamu-B alleles could be assigned.

Problems and emerging approaches in HIV/AIDS vaccine development

According to recent estimates, 39.5 million people have been infected with HIV and 2.9 million have already died. The effect of HIV infection on individuals and communities is socially and economically devastating. Although antiretroviral drugs have had a dramatically beneficial impact on HIV-infected individuals who have access to treatment, it has had a negligible impact on the global epidemic. Therefore, the need for an efficacious HIV/AIDS vaccine remains the highest priority of the world HIV/AIDS agenda. The generation of a vaccine against HIV/AIDS has turned out to be extremely challenging, as indicated by > 20 years of unsuccessful attempts. This review discusses the major challenges in the field and key experimental evidence providing a rationale for the use of non-structural HIV proteins, such as Rev, Tat and Nef, either in the native form or expressed by viral vectors such as a replicating adeno-vector. These non-structural proteins alone or in combination with modified structural HIV-1 Env proteins represent a novel strategy for both preventative and therapeutic HIV/AIDS vaccine development.

Influences of glycosylation on antigenicity, immunogenicity, and protective efficacy of ebola virus GP DNA vaccines

The Ebola virus (EBOV) envelope glycoprotein (GP) is the primary target of protective immunity. Mature GP consists of two disulfide-linked subunits, GP1 and membrane-bound GP2. GP is highly glycosylated with both N- and O-linked carbohydrates. We measured the influences of GP glycosylation on antigenicity, immunogenicity, and protection by testing DNA vaccines comprised of GP genes with deleted N-linked glycosylation sites or with deletions in the central hypervariable mucin region. We showed that mutation of one of the two N-linked GP2 glycosylation sites was highly detrimental to the antigenicity and immunogenicity of GP. Our data indicate that this is likely due to the inability of GP2 and GP1 to dimerize at the cell surface and suggest that glycosylation at this site is required for achieving the conformational integrity of GP2 and GP1. In contrast, mutation of two N-linked sites on GP1, which flank previously defined protective antibody epitopes on GP, may enhance immunogenicity, possibly by unmasking epitopes. We further showed that although deleting the mucin region apparently had no effect on antigenicity in vitro, it negatively impacted the elicitation of protective immunity in mice. In addition, we confirmed the presence of previously identified B-cell and T-cell epitopes in GP but show that when analyzed individually none of them were neither absolutely required nor sufficient for protective immunity to EBOV. Finally, we identified other potential regions of GP that may contain relevant antibody or T-cell epitopes.

Aiming to induce broadly reactive neutralizing antibody responses with HIV-1 vaccine candidates

Neutralizing antibody induction is a key feature of many effective vaccines and is the only immune response that has proven to be capable of completely blocking AIDS virus infection in animal models. Unfortunately, the extensive genetic variability and complex immune-evasion strategies of HIV-1 have thwarted all attempts to date at eliciting an effective neutralizing antibody response with candidate HIV-1 vaccine immunogens. Recent advances in our understanding of how these evasion strategies operate, coupled with growing progress in unravelling the structure and immunobiology of the viral envelope glycoproteins, are contributing to novel immunogen designs to overcome the many barriers to inducing protective antibodies against HIV-1.

Aiming to induce broadly reactive neutralizing antibody responses with HIV-1 vaccine candidates

Neutralizing antibody induction is a key feature of many effective vaccines and is the only immune response that has proven to be capable of completely blocking AIDS virus infection in animal models. Unfortunately, the extensive genetic variability and complex immune-evasion strategies of HIV-1 have thwarted all attempts to date at eliciting an effective neutralizing antibody response with candidate HIV-1 vaccine immunogens. Recent advances in our understanding of how these evasion strategies operate, coupled with growing progress in unravelling the structure and immunobiology of the viral envelope glycoproteins, are contributing to novel immunogen designs to overcome the many barriers to inducing protective antibodies against HIV-1.