Preclinical and clinical studies on immunogenicity and safety of the HIV-1 p17-based synthetic peptide AIDS vaccine--HGP-30-KLH

Head-to-Head Comparison of Soluble vs. Qβ VLP Circumsporozoite Protein Vaccines Reveals Selective Enhancement of NANP Repeat Responses

Circumsporozoite protein (CSP) of Plasmodium falciparum is a promising malaria vaccine target. RTS,S, the most advanced malaria vaccine candidate consists of the central NANP repeat and carboxy-terminal region of CSP displayed on a hepatitis B virus-like particle (VLP). To build upon the success of RTS,S, we produced a near full-length Plasmodium falciparum CSP that also includes the conserved amino-terminal region of CSP. We recently showed that this soluble CSP, combined with a synthetic Toll-like-receptor-4 (TLR4) agonist in stable oil-in-water emulsion (GLA/SE), induces a potent and protective immune response in mice against transgenic parasite challenge. Here we have investigated whether the immunogenicity of soluble CSP could be further augmented by presentation on a VLP. Bacteriophage Qβ VLPs can be readily produced in E.coli, they have a diameter of 25 nm and contain packaged E. coli RNA which serves as a built in adjuvant through the activation of TLR7/8. CSP was chemically conjugated to Qβ and the CSP-Qβ vaccine immunogenicity and efficacy were compared to adjuvanted soluble CSP in the C57Bl/6 mouse model. When formulated with adjuvants lacking a TLR4 agonist (Alum, SE and Montanide) the Qβ-CSP induced higher anti-NANP repeat titers, higher levels of cytophilic IgG2b/c antibodies and a trend towards higher protection against transgenic parasite challenge as compared to soluble CSP formulated in the same adjuvant. The VLP and soluble CSP immunogenicity difference was most pronounced at low antigen dose, and within the CSP molecule, the titers against the NANP repeats were preferentially enhanced by Qβ presentation. While a TLR4 agonist enhanced the immunogenicity of soluble CSP to levels comparable to the VLP vaccine, the TLR4 agonist did not further improve the immunogenicity of the Qβ-CSP vaccine. The data presented here pave the way for further improvement in the Qβ conjugation chemistry and evaluation of both the Qβ-CSP and soluble CSP vaccines in the non-human primate model.

Pharmacological and toxicological assessment of a potential GnRH vaccine in young-adult male pigs

Active immunization against gonadotrophin-releasing hormone (GnRH) is successfully applied to prevent boar taint in pork. In men, GnRH immunization could be an alternative to hormone therapy in patients with prostate cancer. In this study, a new GnRH vaccine formulation (a modified GnRH peptide conjugate formulated with CoVaccine adjuvant) was investigated for its pharmacological efficacy and safety in young-adult male pigs. Immunization resulted in castrate-like plasma testosterone levels in all treated pigs from week 8 until the end of the study, 30 weeks after the first immunization. Testosterone depletion retarded testes growth, reduced the relative weight of the testes and accessory sex organs, and reduced sperm counts and motility. There was no clinically relevant toxicity. Typical vaccination-related adverse reactions, such as swelling at the injection site and fever, were considered acceptable. We conclude that this GnRH vaccine efficiently and rapidly reduced serum testosterone levels, without inducing chronic toxic effects, and therefore could be applicable in both veterinary and human medicine.

Conformational states of the Rapana thomasiana hemocyanin and its substructures studied by dynamic light scattering and time-resolved fluorescence spectroscopy

Hemocyanins are dioxygen-transporting proteins freely dissolved in the hemolymph of mollusks and arthropods. Dynamic light scattering and time-resolved fluorescence measurements show that the oxygenated and apo-forms of the Rapana thomasiana hemocyanin, its structural subunits RtH1 and RtH2, and those of the functional unit RtH2e, exist in different conformations. The oxygenated respiratory proteins are less compact and more asymmetric than the respective apo-forms. Different conformational states were also observed for the R. thomasiana hemocyanin in the absence and presence of an allosteric regulator. The results are in agreement with a molecular mechanism for cooperative dioxygen binding in molluscan hemocyanins including transfer of conformational changes from one functional unit to another.

Evaluation of two carrier protein-angiotensin I conjugate vaccines to assess their future potential to control high blood pressure (hypertension) in man

AIMS

We aim to modulate the renin-angiotensin system (RAS) by active immunization against angiotensin I hormone (AI), potentially providing a novel conjugate vaccine treatment for hypertension in man.

METHODS

Immunization studies in rat and human subjects compare the effectiveness of tetanus toxoid (TT) and keyhole limpet haemocyanin (KLH) vaccines for immunotherapy following conjugation with an AI peptide analogue (AI). Cardiovascular responses were assessed in immunized rats and human subjects (two-dose trial only), following increasing i.v. infusions of either AI or angiotensin II hormone (AII).

RESULTS

The AI-TT and AI-KLH conjugate vaccines induced an equivalent immune response, and inhibition of the pressor effects to exogenous AI in rats. Single-dose clinical trials with both conjugate vaccines only resulted in an immune response to the KLH carrier protein. A two-dose clinical trial of AI-KLH conjugate vaccine resulted in a significant immune response to AI. A shift in diastolic blood pressure (DBP) dose-response was demonstrated following challenge with AI and AII for the study volunteer showing the largest anti-AI IgG induction.

CONCLUSION

KLH was shown to be a suitable alternative to TT as a carrier protein for AI, thus supporting continued evaluation of our AI-KLH conjugate vaccine for treatment of hypertension in man.

Use of gamma-inulin/liposomes/Vitamin E adjuvant combination in contraceptive vaccines

The adjuvanticity of two gamma inulin/liposomes/Vitamin E combinations was evaluated in the mouse, in contraceptive vaccines with sperm protein extracts or a synthetic HE2 peptide ("Human Epididymis gene product"; residues 15-28) as antigen. The HE2 peptide was not conjugated to a protein carrier, to ensure that the antibodies elicited were specific against the HE2 peptide. The adjuvant combinations were designed to increase adjuvanticity, as their components have complementary mechanisms, and their performance was compared to Freund's adjuvant. Antibody production against native sperm structures was determined in sera by ELISA immunoassay and immunohistology. Toxicity of adjuvants was determined by histopathological study and treated mice were monitored for signs of pain or distress. Our results show that the gamma inulin (1-2 microm particle size)/liposomes/Vitamin E combination, with sperm protein extracts, is better than Freund's adjuvant because it elicits good antibody titres without any toxicity. When the synthetic HE2 peptide is used as antigen, the gamma inulin (1-2 microm particle size)/liposomes/Vitamin E combination is less effective than Freund's adjuvant; nevertheless, the anti-HE2 antibodies elicited are highly specific and recognize native structures in sperm.

Monoclonal antibodies to molluskan hemocyanin from Concholepas concholepas demonstrate common and specific epitopes among subunits

We studied the reactivity of mouse monoclonal antibodies (MAbs) against the hemocyanin from the Chilean marine gastropod Concholepas concholepas (CCH). This protein has been successfully used as a carrier to produce antibodies to haptens and peptides. All MAbs (13) belonging to IgG subclass exhibit dissociation constants (K(d)) from 1 x 10(-7) M to 1 x 10(-9) M. MAbs were characterized by enzyme-linked immunosorbant assay (ELISA) using CCH treated with different procedures, including dissociation into CCH-A and CCH-B subunits, Western blot, enzymatic digestion, chemical deglycosylation, and thermal denaturation. MAbs were classified into three categories, according to subunit specificity by ELISA. The epitope distribution shows that CCH subunits display common epitopes (group I, 5 MAbs, 1H5, 2A8, 3A5, 3B3, and 3E3), as well as specific epitopes for CCH-A subunits (group II, 3 MAbs, 1B8, 4D8, and 8E5) and for CCH-B subunits (group III, 5 MAbs, 1A4, 1E4, 2H10, 3B7, and 7B4). The results can be summarized as follows: (1). six antibodies react with thermal denatured CCH, suggesting that they recognize linear epitopes, whereas seven recognize conformational epitopes; (2). oxidation of carbohydrate moieties does not affect the binding of the MAbs; (3). enzymatic digestion of CCH decreases the reactivity of all antibodies irrespective of the protease used (elastase or trypsin); (4). bringing together the above data, in addition to epitopic complementarity analysis, we identified 12 different epitopes on the CCH molecule recognized by these MAbs. The anti-CCH MAbs presented here can be useful tools to understand the subunit organization of the CCH and its complex structure, which can explain its immunogenic and immunostimulating properties in mammals.

Flt3 ligand and conjugation to IL-1beta peptide as adjuvants for a type 1, T-cell response to an HIV p17 gag vaccine

The adjuvant activity of Flt3 ligand (Flt3L) and conjugation to an interleukin (IL)-1beta bioactive fragment were compared, either alone or in combination, for their ability to induce T- and B-cell responses to the HGP-30 peptide sequence (amino acids 86-115 of human immunodeficiency virus (HIV) gag p17). The efficiency of HGP-30/IL-1beta conjugation, Flt3L administration or both as adjuvants was examined and all were found to augment similar levels of delayed type hypersensitivity (DTH) responses. In contrast, significant antigen (Ag)-specific types 1 and 2 T-cell ELISPOT responses were induced only by the combination of adjuvants. Further, in vitro sensitization with HGP-30 selectively increased Ag-specific, type 1 T-cell and cytotoxic T lymphocyte (CTL) responses to HGP-30-derived nonapeptide epitopes, while type 2 responses declined as measured in the ELISPOT assay. No serum antibodies to HGP-30 were induced unless HGP-30 was conjugated to keyhole-limpet hemocyanin. This suggests that a combination adjuvant strategy using Flt3L and conjugation to a biologically active IL-1beta fragment may be used to preferentially increase type 1 T-cell and CTL responses to HIV-1 gag antigenic epitopes.

Induction of cross clade reactive specific antibodies in mice by conjugates of HGP-30 (peptide analog of HIV-1(SF2) p17) and peptide segments of human beta-2-microglobulin or MHC II beta chain

HGP-30, a 30 amino acid synthetic peptide homologous to a conserved region of HIV-1(SF2) p17 (aa86-115), has previously been shown to elicit both cellular and humoral immune responses when conjugated to KLH and adsorbed to alum. However, the free HGP-30 peptide is not immunogenic in animals. In order to improve the immunogenicity of HGP-30, peptide conjugates consisting of a modified HGP-30 sequence (m-HGP-30/aa82-111) and a peptide segment, residues 38-50, of the MHC I accessory molecule, human beta-2-microglobulin (beta-2-M), referred to as Peptide J, or a peptide from the MHC II beta chain (peptide G) were evaluated in mice. The effects of carriers and adjuvants on serum antibody titers, specificities to various HIV-1 clade peptides similar to HGP-30 and isotype patterns were examined. Peptides J or especially G conjugated to modified-HGP-30 (LEAPS 102 and LEAPS 101, respectively) generated comparable or better immune responses to modified HGP-30 than KLH conjugates as judged by the induction of: (1) similar antibody titers; (2) broader HIV clade antigen binding; and (3) antibody isotype response patterns indicative of a TH1 pathway (i.e. increased amounts of IgG2a and IgG2b antibodies). The ISA 51 and MPL(R)-SE adjuvants induced higher antibody responses than alum, with the ISA 51 being more potent. Immune responses to LEAPS 102, as compared to LEAPS 101, were weaker and slower to develop as determined by antibody titers and cross clade reactivity of the antibodies induced. Compared to KLH conjugates which induced significant anti-KLH antibody titers, minimal antibody responses were observed to peptide G, the more immunogenic conjugate, and peptide J. These results suggest that modified HGP-30 L.E.A.P.S. constructs may be useful as HIV vaccine candidates for preferential induction of TH1 directed cell mediated immune responses.

Effect of peptide-carrier coupling on peptide-specific immune responses

Synthetic peptides are covalently linked to immunogenic carrier proteins to enhance the anti-peptide immune response. To investigate whether the method of conjugation influences the immune response, we evaluated two distinctly different choices of linker for a peptide-carrier construct. HPG-30, a synthetic peptide derived from the p17 gag protein of human immunodeficiency virus 1, was covalently linked to keyhole limpet hemocyanin by either glutaraldehyde or a maleimide ester. Glutaraldehyde linkage enhanced the anti-peptide antibody and native protein response compared to maleimide. The maleimide-linked conjugate was more effective at inducing a peptide-specific cellular response. Thus, manipulation of the conjugation method can modify the magnitude and character of the immune response to a synthetic peptide vaccine.

HIV vaccines for prevention of infection and disease in humans

Phase I and II studies have been carried out with several candidate HIV-1 vaccines in seronegative volunteers. Vaccines consisting of rgp 120 stimulated moderate levels of neutralizing antibodies against homologous, TCLA adapted viruses, but did not induce CD8+ CTL responses. Canarypox vectors stimulate CD8+ CTL responses, but little neutralizing activity. The latter can be increased in titer by boosting recipients of canarypox vectors with rgp120 vaccines. Large-scale placebo-controlled efficacy trials are underway with two rgp120 vaccines: AIDSVAX B/B (VaxGen, Inc.) in the United States, and AIDSVAX B/E in Thailand. The canarypox-rgp120 combined regimen has been proposed for study in an intermediate-sized, "test-of-concept" efficacy trial by the NIAID-sponsored HVTN, with an experimental design intended to provide information on the potential in vitro correlates of immunity. The results from these studies, and the methodology used in their conduct, should facilitate the refinement of conventional and novel approaches to the development of safe and effective HIV vaccines.

Flt3 ligand enhances the immunogenicity of a gag-based HIV-1 vaccine

Liposomes and Flt3 ligand (Flt3L), a ligand for the fms-like tyrosine kinase receptor Flt3/ FLK2, can augment the immune response to an HIV peptide vaccine. The HGP-30 peptide used in these studies is a synthetic peptide that corresponds to a highly conserved region of HIV-1 p17 gag (amino acids 86-115). Mice were immunized with HGP-30 or HGP-30 conjugated to keyhole limpet hemocyanin (KLH) and delayed-type hypersensitivity (DTH) responses, antibody (IgG) amount and antigen-specific proliferative responses by spleen cells were used to monitor the immune response. Daily injections of Flt3L prior to HGP-30 administration enhanced significantly an antigen-specific lymphocyte proliferation response when compared with Flt3L, HGP-30 alone or HGP-30 containing liposomes. Intravenous administration of HGP-30 was superior to intramuscular (i.m.) immunization for the induction of DTH responses. The HGP-30/KLH containing liposomes enhanced both DTH and antibody responses, while liposomes containing HGP-30 peptide elicited only T cell responses. In these studies, either Flt3L or liposomes increased DTH responses compared with the i.m. injection of the HGP-30 vaccine alone.

Keyhole limpet hemocyanin (KLH): a biomedical review

In this review we present a broad survey of fundamental scientific and medically applied studies on keyhole limpet hemocyanin (KLH). Commencing with the biochemistry of KLH, information on the biosynthesis and biological role of this copper-containing respiratory protein in the marine gastropod Megathura crenulata is provided. The established methods for the purification of the two isoforms of KLH (KLH1 and KLH2) are then covered, followed by detailed accounts of the molecular mass determination, functional unit (FU) structure, carbohydrate content, immunological analysis and recent aspects of the molecular genetics of KLH. The transmission electron microscope (TEM) has contributed significantly to the understanding of KLH structure, primarily from negatively stained images. We give a brief account of TEM studies on the native KLH oligomers, the experimental manipulation of the oligomeric states, together with immunolabelling data and studies on subunit reassociation. The field of cellular immunology has provided much relevant biomedical information on KLH and has led to the expansion of use of KLH in experimental immunology and clinically as an immunotherapeutic agent; this area is presented in some detail. The major clinical use of KLH is specifically for the treatment of bladder carcinoma, with efficacy probably due to a cross-reacting carbohydrate epitope. KLH also has considerable possibilities for the treatment of other carcinomas, in particular the epithelially derived adenocarciomas, when used as a carrier for carcinoma ganglioside and mucin-like epitopes. The widespread use of KLH as a hapten carrier and generalised vaccine component represent other major on-going aspects of KLH research, together with its use for the diagnosis of Schistosomiasis, drug assay and the treatment of drug addiction. Immune competence testing, assessment of stress and the understanding of inflammatory conditions are other areas where KLH is also making a useful contribution to medical research.

Booster immunization of HIV-1 negative volunteers with HGP-30 vaccine induces protection against HIV-1 virus challenge in SCID mice

Eleven HIV-1 seronegative subjects previously injected with an HIV-1 p17 synthetic peptide vaccine (HGP-30) were given two booster immunizations to evaluate memory cell responses and the ability to boost cellular and humoral immune responses. Five of 11 subjects showed a significant increase in their antibody titres to HGP-30 or p17 and 6/11 had T-cell proliferation responses to either HGP-30 or p17. HIV-1 virus challenge studies in SCID mice demonstrated that 39 of 50 mice (78%) receiving PBMC from 5 of the HGP-30 immunized subjects were protected from infection with a different strain of HIV-1 compared to 4 of 30 mice (13%) that received PBMC from 3 non-immunized subjects (p < 0.001). These studies show that booster immunizations with HGP-30 vaccine are safe and non-toxic and induce protective cell mediated immune responses.

Cross-clade p17 peptide recognition by antisera to HGP-30, a 30-amino acid synthetic peptide antigen from HIV type 1 p17

HGP-30, a 30-amino acid synthetic peptide analog of HIV-1SF2 p17 (aa 86-115), was used to immunize both mice and humans. Since the amino acid sequence of HGP-30 is relatively conserved among different HIV-1 strains and clades, experiments were carried out to determine if antisera obtained by immunizing animals and humans can recognize HGP-30-related peptide consensus sequences belonging to different clades. Results show that antisera from mice immunized with HGP-30 can recognize clade B and C and to a lesser degree clade A and E consensus sequences of HIV-1, in addition to recognizing HGP-30 sequence. The cross-clade recognition was higher in mouse sera obtained on day 42 than on day 14 or 28. MPL/SE and Novasomes were better adjuvants than alum in inducing antibodies that showed cross-clade recognition and IgG2a and IgG2b antibody isotypes. Similar cross-clade recognition was observed in several sera from humans immunized with an HGP-30/KLH/alum formulation. The human sera from HGP-30-immunized subjects evaluated for cross-clade recognition of HGP-30 peptides were from subjects whose cells showed significant protection from HIV infection on virus challenge in the hu-PBL-SCID mouse model. These studies suggest that HGP-30 may be useful as a candidate vaccine antigen for populations in countries with prevalence of different HIV clades.

Mass determination, subunit organization and control of oligomerization states of keyhole limpet hemocyanin (KLH)

Analytical dark-field scanning transmission electron microscopy (STEM) of freeze-dried unstained specimens of keyhole limpet hemocyanin (KLH; from Megathura crenulata, a prosobranch gastropod) gave a molecular mass of 400 kDa for the subunit of KLH1 and of 345 kDa for the subunit of KLH2, which confirms our published values from SDS/PAGE. Within the 400-kDa KLH1 subunit we identified, by limited proteolysis, isolation of fragments and N-terminal sequencing, eight distinct 45-60 kDa functional domains (termed 1a through 1h) and determined their sequential arrangement. The KLH1 domains differ biochemically and immunologically from each other and from the previously characterized seven domains of KLH2 (termed 2a through 2g). Our partial amino acid sequences suggest that a domain, equivalent to the C-terminal domain 1h, is missing in KLH2. This deficiency is believed to be genuine and not an artifact of the subunit preparation procedure, since STEM measurements of the native didecamers yielded a mass difference of about 800 kDa between KLH1 and KLH2 (8.3 MDa versus 7.5 MDa), correlating with 20 copies of a functional 1h domain. It was also shown that the KLH1 didecamer can be rapidly split (minutes) into an almost homogeneous population of stable decamers by increasing the pH of the Tris/saline stabilizing buffer (routinely pH 7.4), which contains 5 mM CaCl2 and 5 mM MgCl2, to pH 8.5. Reformation of the didecamers occurred more slowly (days) upon dialysis against the pH 7.4 stabilizing buffer. Addition of 100 mM calcium and 100 mM magnesium ions to the pH 7.4 stabilizing buffer leads to the more rapid (overnight) formation of didecamers together with a significant number of previously unobserved KLH1 multidecamers, which could be structurally distinguished from the established multidecamers of KLH2.

Structure of keyhole limpet hemocyanin type 1 (KLH1) at 15 A resolution by electron cryomicroscopy and angular reconstitution

A three-dimensional reconstruction of keyhole limpet hemocyanin type 1 (KLH1) has been obtained using electron cryomicroscopy at liquid helium temperatures and single particle image processing. The use of a high-contrast embedding medium, 1% (w/v) glucose and 2% (w/v) ammonium molybdate (pH 7.0), enables high-resolution electron micrographs to be recorded close to focus, i.e. with excellent transfer of high-resolution information, while maintaining enough image contrast to localise the individual macromolecules in the images. When low-pass filtered to approximately 45 A resolution, the new 15 A resolution reconstruction is very similar to the earlier reconstructions of gastropodan hemocyanins of specimens embedded in vitreous ice. The map shows much detail and reveals many new symmetry elements in this very large cylindrical molluscan hemocyanin. The full KLH1 didecamer has D5 pointgroup symmetry, yet within the KLH1 decameric half-molecules local 2-fold axes have emerged that make the wall of the KLH1 decamer, in spite of its having an exact C5 symmetry only, resemble the D5-symmetric wall of the decameric cephalopod hemocyanins. In fact, the outside of each tier of this six-tiered gastropodan hemocyanin was found to have an approximate D5 symmetry. Local 2-fold axes also relate the "functional units" within the dimeric "morphological units" of the wall and the collar areas of the 8 MDa KLH1 molecule. Certain local-symmetry-related surface motifs may be present up to 60 times on the outside wall of this highly symmetric cylindrical hemocyanin. Keyhole limpet hemocyanin is used clinically as an immunostimulant. The very strong immune reaction elicited by this hemocyanin may be associated with its intricate hierarchy of local-symmetry components.

An experimental chemically inactivated HIV-1 vaccine induces antibodies that neutralize homologous and heterologous viruses

We have developed a unique multiple step procedure to inactivate human immunodeficiency virus chemically with a very high safety margin while retaining antigenically active structural virion proteins, including gp120, in the final immunogen. The whole virus preparation (1-10 micrograms per dose) was highly immunogenic in a variety of small mammals and induced antibodies that recognized homologous and heterologous strains of HIV-1. Sera from immunized animals bound to peptides representing the entire sequence of the external glycoprotein gp120. Neutralizing antibodies active against the homologous immunizing strain and against heterologous HIV-1 strains were also elicited. Sera with virus neutralizing activity did not bind to MHC class I proteins derived from the human cell line used to grow the virus.

Detection of a 23 kDa human brain protein that shares epitope(s) with the 17 kDa core protein of human immunodeficiency virus (HIV)

To search for brain molecules that share epitopes with HIV (human immunodeficiency virus) proteins, we investigated non-AIDS human brains by immunohistochemical and Western blotting methods, and detected a 23 kDa protein which was immunoreactive with antibodies against HIVp17, a core protein of HIV with a molecular weight of 17 kDa. The 23 kDa protein was localized mostly in reactive astrocytes in and around pathologic areas of the brain, but some neurons also had it. We propose that any HIV vaccine must be checked up if it induces a cross-reacting antibody to a human brain or other organs.