Targeting vaccinia virus-expressed secretory beta subunit of human chorionic gonadotropin to the cell surface induces antibodies

Membrane-tethered proteins for basic research, imaging, and therapy

Secreted and intracellular proteins including antibodies, cytokines, major histocompatibility complex molecules, antigens, and enzymes can be redirected to and anchored on the surface of mammalian cells to reveal novel functions and properties such as reducing systemic toxicity, altering the in vivo distribution of drugs and extending the range of useful drugs, creating novel, specific signaling receptors and reshaping protein immunogenicity. The present review highlights progress in designing vectors to target and retain chimeric proteins on the surface of mammalian cells. Comparison of chimeric proteins indicates that selection of the proper cytoplasmic domain and introduction of oligiosaccharides near the cell surface can dramatically enhance surface expression, especially for single-chain antibodies. We also describe progress and limitations of employing surface-tethered proteins for preferential activation of prodrugs at cancer cells, imaging gene expression in living animals, performing high-throughput screening, selectively activating immune cells in tumors, producing new adhesion molecules, creating local immune privileged sites, limiting the distribution of soluble factors such as cytokines, and enhancing polypeptide immunogenicity. Surface-anchored chimeric proteins represent a rich source for developing new techniques and creating novel therapeutics.

Biological control of vertebrate pests using virally vectored immunocontraception

Species-specific viruses are being genetically engineered to produce contraceptive biological controls for pest animals such as mice, rabbits and foxes. The virus vaccines are intended to trigger an autoimmune response in the target animals that interferes with their fertility in a process termed virally vectored immunocontraception. Laboratory experiments have shown that high levels of infertility can be induced in mice infected with recombinant murine cytomegalovirus and ectromelia virus expressing reproductive antigens as well as in rabbits using myxoma virus vectors. The strategies used to produce and deliver species-specific immunocontraceptive vaccines to free-living wildlife are presented in this review. Discussion includes coverage of the likely safety of the proposed vaccines as well as the implications of the approach for fertility control in other species.

Recent advances in contraceptive vaccine development: a mini-review

Contraceptive vaccines (CV) may provide viable and valuable alternatives to the presently available methods of contraception. The molecules that are being explored for CV development either target gamete production [luteinizing hormone-releasing hormone (LHRH)/GnRH, FSH], gamete function [sperm antigens and oocyte zona pellucida (ZP)], and gamete outcome (HCG). CV targeting gamete production have shown varied degrees of efficacy; however, they either affect sex steroids causing impotency and/or show only a partial rather than a complete effect in inhibiting gametogenesis. However, vaccines based on LHRH/GnRH are being developed by several pharmaceutical companies as substitutes for castration of domestic pets, farm and wild animals, and for therapeutic anticancer purposes such as in prostatic hypertrophy and carcinoma. These vaccines may also find applications in clinical situations that require the inhibition of increased secretions of sex steroids, such as in uterine fibroids, polycystic ovary syndrome, endometriosis and precocious puberty. CV targeting molecules involved in gamete function such as sperm antigens and ZP proteins are exciting choices. Sperm constitute the most promising and exciting target for CV. Several sperm-specific antigens have been delineated in several laboratories and are being actively explored for CV development. Studies are focused on delineating appropriate sperm-specific epitopes, and increasing the immunogenicity (specifically in the local genital tract) and efficacy on the vaccines. Anti-sperm antibody (ASA)-mediated immunoinfertility provides a naturally occurring model to indicate how a vaccine might work in humans. Vaccines based on ZP proteins are quite efficacious in producing contraceptive effects, but may induce oophoritis, affecting sex steroids. They are being successfully tested to control feral populations of dogs, deer, horses and elephants, and populations of several species of zoo animals. The current research for human applicability is focused on delineating infertility-related epitopes (B-cell epitopes) from oophoritis-inducing epitopes (T-cell epitopes). Vaccines targeting gamete outcome primarily focus on the HCG molecule. The HCG vaccine is the first vaccine to undergo Phase I and II clinical trials in humans. Both efficacy and lack of immunopathology have been reasonably well demonstrated for this vaccine. At the present time, studies are focused on increasing the immunogenicity and efficacy of the birth control vaccine, and examining its clinical applications in various HCG-producing cancers. The present article will focus on the current status of the anti-sperm, anti-ZP, anti-LHRH/GnRH and anti-HCG vaccines.

Production of anti-dengue NS1 monoclonal antibodies by DNA immunization

Monoclonal antibodies against dengue NS1 protein were generated following immunization of mice with plasmid DNA encoding the transmembrane form of NS1 from dengue serotype 2 virus. A mammalian expression vector, pDisplay, was engineered to direct cell surface expression of dengue NS1 and tested for transient expression in COS cells. Two mice were immunized intramuscularly with six doses of 100 microg of plasmid at 2-week intervals; one mouse received a booster of live virus prior to the last plasmid injection. Both mice showed antibody responses against dengue antigens in dot enzyme immunoassay. Following fusion, hybridomas were screened with dot enzyme immunoassay against all four dengue serotypes. Specificity to the NS1 protein was confirmed by western blot analysis. Among five anti-dengue NS1 monoclonal antibodies generated, two clones were serotype 2 specific, two clones reacted with all four serotypes and the last also reacted with Japanese encephalitis virus. Reactivity against native or denatured forms of NS1 revealed three clones with reactivity to linear epitopes and two clones recognizing conformational epitopes. Such diverse specificity of anti-dengue NS1 monoclonal antibodies indicates that DNA immunization, especially with the combination of virus boosting, is an efficient way of producing monoclonal antibodies against viral protein. This has opened up a possibility of producing monoclonal antibodies to rare viral proteins that are difficult to isolate or purify.

Infertility in mice induced by the rhesus monkey chorionic gonadotropin beta-subunit glycoprotein (rmCGbeta) using DNA immunization

The recombinant eukaryotic expression vector pCMV4-rmCGbeta, inserted full-length cDNA of the beta-subunit of rhesus monkey chorionic gonadotropin (rmCGbeta), as DNA immuno-contraceptive against CGbeta glycoprotein, has previously demonstrated the biological expression of rmCGbeta in vitro and in vivo. The plasmid DNA of pCMV4-rmCGbeta was inoculated into BALB/c mice at different doses and routes as DNA immuno-contraceptive to understand its antifertility effect. The results of immune responses indicated that the intradermal inoculation is the optimal pCMV4-rmCGbeta DNA delivery method for BALB/c mice, and the dose of 10 microg should be enough to elicit immune response. With different doses from 10-50 microg, marked reductions in the fertility of the female mice after two intramuscular inoculations of pCMV4-rmCGbeta DNA were seen, while the similar level of humoral immune responses were induced. With the dose of 20 microg of pCMV4-rmCGbeta DNA, the mice showed reduction in fertility from intraperitoneal, and intradermal to intramuscular inoculating method. The antifertility effect of antiserum from immunized mice confirmed that the antibodies elicited by pCMV4-rmCGbeta DNA could prevent pregnancy in female mice. At the same time, the full-length cDNA of beta-subunit of mouse chorionic gonadotropin (muCGbeta) was cloned from placenta and sequenced for the first time (GenBank Accession No. AF333067). Sequence analysis showed that muCGbeta shares 99.6% homology with rmCGbeta and 90.6% with hCGbeta respectively. The results indicated that the infertility of BALB/c mice induced by pCMV4-rmCGbeta contraceptive should be further studied as a CGbeta DNA contraceptive. (Mol Cell Biochem 231: 89-96, 2002)

Absence of corpus luteum rescue by chorionic gonadotropin in women immunized with a contraceptive vaccine

OBJECTIVE

To determine whether antibodies induced by a betahCG vaccine in women are competent to neutralize the luteotropic action of hCG.

DESIGN

Prospective clinical study.

SETTING

Hospitals and a laboratory at an academic center.

PATIENT(S)

Six immunized and three control women of reproductive age, participating in a clinical testing of betahCG contraceptive vaccine.

INTERVENTION(S)

Increasing doses of hCG simulating early pregnancy.

MAIN OUTCOME MEASURE(S)

Anti-hCG antibody titers, serum progesterone and urinary hCG levels, and onset of menses.

RESULT(S)

Administration of hCG to mimic early pregnancy sustained serum progesterone concentrations and extended the luteal phase in control women. In contrast, serum progesterone levels declined and the luteal phase was not extended if prevailing antibody titers were > or =40 ng/mL in women who had been immunized with a betahCG based vaccine. No booster effect was seen in anti-hCG titers after hCG challenge.

CONCLUSION(S)

Antibodies elicited by a betahCG vaccine inactivate hCG and prevent the hormone from rescuing corpus luteum, resulting in progesterone fall and normal menses. Lack of booster in the antibody response confirms the reversibility of the approach.

Vaccines and passive immunological approaches for the control of fertility and hormone-dependent cancers

Reviewed here is the development of a vaccine against the human chorionic gonadotropin that prevents pregnancy in sexually active women without impairment of ovulation or derangement of menstrual regularity. Also reviewed are the vaccines inducing antibodies against the luteinizing hormone-releasing hormone, which have immunotherapeutic potential in prostatic hypertrophy and other sex hormone-dependent male and female cancers. The adoption of passive immunization using humanized recombinant antihormone antibodies is advocated for assured efficacy and safe, prompt therapeutic action.

Unconventional vaccine targets. Immunization for pregnancy, peptic ulcer, gastric cancer, cocaine abuse, and atherosclerosis

Vaccine technology can be applied to targets of intervention that currently have not been considered preventable by immunization. Targets include some diseases caused by, or related to, infectious agents, and other conditions clearly unassociated with disease pathogens. This article considers vaccines for pregnancy, peptic ulcer disease, gastric cancer, cocaine abuse and atherosclerosis.

Identification of novel transmembrane gene sequence and its use for cell-surface targeting of beta subunit of human chorionic gonadotropin

We identified a 685-nucleotide gene fragment that codes for the transmembrane and cytoplasmic domains of glycoprotein of the LEP strain rabies virus and carried out experiments designed to express a novel fusion protein on the cell surface. The cDNA encoding the membrane anchor sequence was fused in the correct reading frame to the 3' end of the cDNA encoding the beta subunit of human chorionic gonadotropin (beta(h)CG), a secretory glycoprotein that is used as an antigen for a contraceptive vaccine being developed in our laboratory. The fusion gene cassette was placed under the control of a vaccinia virus early promoter and cloned in a host-restricted fowlpox viral vector. The recombinants, when used to infect mammalian cells that do not allow the replication of fowlpox virus, expressed the N-terminal 135 amino acid residues of beta(h)CG anchored in the cell membrane by the 75-amino acid C-terminal sequence derived from rabies virus glycoprotein. This hybrid protein is correctly processed post-translationally and transported efficiently to the plasma membrane of non-permissive cells such that the anchored beta(h)CG molecule retains the correctly folded native antigenic epitope(s).

Oral immunization with recombinant vaccina expressing cell-surface-anchored beta hCG induces anti-hCG antibodies and T-cell proliferative response in rats

A vaccinia recombinant, VSS2, expressing cell-surface-anchored beta-subunit of human chorionic gonadotropin (beta hCG) has earlier been found to induce high titered anti-hCG antibodies in rats immunized by tail scarification. The immunogenicity of this recombinant was compared in rats which received the virus through different routes of inoculation: intradermal, intragastric, intrajejunal or by tail scarification. The recombinant virus induced high titers of anti-hCG antibodies in all instances although the titers were about one log lower when the recombinant virus was delivered orally. The recombinant was found to induce T-cell proliferative response in rats of all immunization groups.

Recombinant adenovirus synthesizing cell surface-anchored beta hCG induces bioneutralizing antibodies in rats

A recombinant adenovirus (re-Ad) has been constructed that synthesizes a cell surface-anchored form of the beta-subunit of human chorionic gonadotropin (beta hCG). This was achieved by in-frame fusion of beta hCG cDNA at its C terminus with the gene sequences coding for the vesicular stomatitis virus glycoprotein (VSVg) transmembrane domain. The fusion protein gene was placed under the control of human cytomegalovirus (hCMV) immediate early promoter and this expression cassette was inserted into the E1 region of Ad type 5 by homologous recombination. In vitro experiments using re-Ad-infected 293 cells showed that beta hCG fusion protein was made as early as 6 h post infection and the protein was anchored to the cell membrane as seen by immunofluorescence staining. The re-Ad induced bioneutralizing antibodies (Ab) to hCG when inoculated in rats through intraperitoneal or intramuscular routes. The Ab were made in a dose-dependent manner. However, orally delivered re-Ad failed to generate any significant immune response.

Vaccines for control of fertility and hormone-dependent cancers

This article traces and reviews the development of vaccines against two reproductive hormones, luteinizing hormone release hormone (LHRH) and human chorionic gonadotrophin (hCG). The heterospecies dimer (HSD)-dehydrogenase hCG vaccine is the first to have completed phase II clinical trials providing evidence for the prevention of pregnancy in humans by immunization with this vaccine. The vaccine acts without blocking ovulation or disturbance of menstrual bleeding. Its effect is fully reversible and fertility is regained with decline of the antibodies. The antibody response in humans is directed against immunodominant epitopes located in the core part of beta hCG, distinct from the C-terminal region. However, problems arising from carrier-conjugated vaccines against 'self' hormones such as carrier-induced immuno-suppression on repeated immunization are evoked and solutions discussed. The LHRH vaccine, a model semi-synthetic vaccine, can be used in both sexes and has applications in regulation of fertility of animals. It has therapeutic applications as a cost-effective approach in clinical conditions where LHRH agonists and antagonists have therapeutic action. The vaccine has undergone phase I and II clinical trials in advanced-stage carcinoma of prostate patients with encouraging results.

The HSD-hCG vaccine prevents pregnancy in women: feasibility study of a reversible safe contraceptive vaccine

PROBLEM

To develop a vaccine for reversible control of fertility in women. MATERIALS AND PROTOCOLS: Purified beta subunit of hCG annealed to purified alpha subunit of ovine LH linked chemically to tetanus toxoid (TT) and diphtheria (DT); vaccine employed at 300 micrograms gonadotropin equivalent per injection adsorbed on alhydrogel with 1 mg SPLPS added in the first injection; Phase I safety trials in 47 women with elective tubal ligation; Phase II efficacy studies in 148 proven fertile women (2 children), sexually active, desirous of family planning using IUD; IUD removed when anti-hCG titres exceed 50 ng/ml hCG bioneutralization capacity; boosters given to maintain above threshold antibody levels; post coital tests conducted in 8 volunteers; sera of protected women analysed for immuno-determinants recognized by competitive enzyme immunoassays employing a panel of monoclonal antibodies and by direct binding to synthetic peptides; recombinant vaccines expressing beta hCG as a secreted product or as a fused protein anchored on membrane.

RESULTS

Immunization was well tolerated with no significant changes in endocrine, metabolic and hematological indices. Normal ovulatory cycles were maintained as indicated by menstrual regulation. The vaccine was highly effective in preventing pregnancy (1 pregnancy in 1224 cycles ) at and above antibody titres of 50 ng/ml. Antibodies declined in course of time in absence of boosters, with conceptions occurring below 35 ng/ml titres indicating regain of fertility. Ability of antibodies to prevent pregnancy was confirmed by post coital tests. High avidity (10(10) M-1) and other characteristics of antibodies generated by the vaccine are described and compared with those induced by two other hCG vaccines having undergone Phase I trials. The antibody response of the HSD vaccine in humans is characterized predominantly to an epitope recognized by the monoclonals 206 and P3W80. The antibodies had low or no reactivity with the carboxy terminal peptide and 38-57 region peptide. Live recombinant vaccines expressing beta hCG as a membrane anchored peptide generated antibody response to hCG in all animals following a single injection.

CONCLUSIONS

Reversible fertility control is feasible with the HSD-hCG vaccine without impairment of ovulation or disturbance of menstrual regularity. Suggestions have been made for further optimization of the vaccine, which include replacement of TT and DT by a panel of T non B determinants communicating with the entire MHC spectrum and development of recombinant vaccine expressing beta hCG along with membrane anchored carrier.