Semisynthetic anti-LHRH vaccine causing atrophy of the prostate

Development of a novel recombinant LHRH fusion protein for therapy of androgen and estrogen dependent cancers

LHRH based vaccines are promising candidates for therapy of androgen and estrogen dependent cancers. We report in this communication development of a novel recombinant protein vaccine candidate against LHRH. A synthetic gene was designed in which the codon sequence in the LHRH decapeptide was modified by substituting the codon for 6-glycine with that of l-leucine. Further the LHRH(6leu) gene was linked to heat-labile enterotoxin of E. coli (LTB) as carrier. This LHRH(6leu)-LTB gene was cloned into a prokaryotic expression vector under the control of inducible and strong bacteriophage T7 promoter to over-express LHRH(leu) fused to LTB as recombinant protein in E. coli. Recombinant LHRH(leu)-LTB protein of ∼14 kDa size, was purified from inclusion bodies using in-situ refolding on the column and Ni-NTA based immobilized affinity chromatography. Western blot confirmed the immunoreactivity of purified LHRH(leu)-LTB fusion protein with anti-LHRH monoclonal antibody. The vaccine protein was further characterized by mass spectroscopy, circular dichroism and fluorescence spectroscopy. This communication reports a recombinant LHRH fusion protein with potential for blocking of sex hormones production for eventual therapy of sex hormones dependent neoplasms.

Immunotherapy of prostate cancer in a murine model using a novel GnRH based vaccine candidate

Previous studies with gonadotrophin releasing hormone (GnRH/LHRH) vaccines have shown the usefulness of immunization against this hormone in prostate cancer. To this end, we have generated a completely synthetic peptide modified at position 6 and attached to the 830-844 tetanic toxoid (TT) helper T cell sequence. Through this work we have demonstrated that the GnRHm1-TT molecule was highly immunogenic when it is formulated as an oil-based emulsion adjuvated with Montanide ISA 51. That results correlated directly with testosterone reduction and tumor growth inhibition of the Dunning R3327-H androgen responsive prostate tumor model in rats. GnRHm1-TT, proved to be safe and useful for future clinical trials.

Identification of dominant epitopes of synthetic immunocontraceptive vaccines that induce antibodies in dogs

The specificities of immunoglobulin G antibodies obtained from the sera of dogs inoculated with totally synthetic immunocontraceptive vaccine candidates based on luteinising hormone releasing hormone (LHRH: amino acid sequence HWSYGLRPG) were examined using peptides expressed in a phage display library. The three vaccine candidates each contained a different T helper-cell epitope chemically linked with the same LHRH amino acid sequence HWSYGLRPG and all of them elicited high antibody titres against the hormone. Delineation of epitopes recognised by sera from vaccinated dogs using a phage display library indicated that two of the three vaccine candidates induced antibody directed to the consensus sequence xHWSxxLxxx whereas the third vaccine candidate induced antibody against the consensus sequence xxxxxxxRPx. Two of the three vaccine candidates elicited antibodies against B cell epitopes present within the helper T-cell epitope component of the vaccine whereas the third vaccine did not. The occurrence of anti-T helper cell epitope antibodies appeared to have little or no effect on the generation of the anti-LHRH responses indicating that carrier-induced epitope suppression was not operating here. Our results also demonstrated that with animal sera of high quality, it is possible to delineate immunodominant epitopes recognised by polyclonal antibodies with high efficiency using phage display library. The approach has utility in the definition of immunodominant epitopes, which may "decoy" antibody responses away from other epitopes, which may be more useful in prophylaxis or therapy.

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.

Contraceptive vaccines

The world's population is growing at a tremendous rate, affecting growth and development. Apart from this population growth, unintended pregnancies resulting in elective abortions continue to be a major public health issue. In over half of these unintended pregnancies, the women have used some type of contraception. Thus, there is an urgent need for a better method of contraception that is acceptable, effective and available. The contraceptive choices available to women at this time include steroid contraceptives, intrauterine devices, barrier methods, spermicides, natural family planning, male and female sterilisation, and recently available emergency contraceptives. Contraceptive vaccines (CVs) may provide viable and valuable alternatives that can fulfill most, if not all, properties of an ideal contraceptive. Since both the developed and most of the developing nations have an infrastructure for mass immunisation, the development of vaccines for contraception is an exciting proposition. The molecules that are being explored for CV development either target gamete production (gonadotropin releasing hormone, follicle-stimulating hormone and luteinising hormone), gamete function (zona pellucida [ZP] proteins and sperm antigens) or gamete outcome (human chorionic gonadotropin [hCG]). Disadvantages of CVs targeting gamete production are that they affect sex steroids and/or show only a partial effect in reducing fertility. CVs targeting gamete function are better choices. Vaccines based on ZP proteins are quite efficacious in producing contraceptive effects. However, they invariably induce oophoritis affecting sex steroids. Sperm antigens constitute the most promising and exciting targets for CVs. Several sperm-specific antigens have been delineated in several laboratories and are being actively explored for CV development. Antisperm antibody-mediated immunoinfertility provides a naturally occurring model to indicate how an antisperm vaccine will work in humans. 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 the efficacy and the lack of immunotoxicity have been reasonably well demonstrated for this vaccine. The present studies focus on increasing the immunogenicity and efficacy of this birth control vaccine.

Engineering, cloning, and expression of genes encoding the multimeric luteinizing-hormone-releasing hormone linked to T cell determinants in Escherichia coli

Two synthetic genes were designed and engineered to encode for multimeric luteinizing-hormone-releasing hormone (LHRH) peptides linked to T cell determinants. These genes were cloned into the prokaryotic expression vectors under control of strong inducible promoters, to overexpress the multimeric LHRH peptides as recombinant proteins. Multimeric LHRH-T cell peptides were expressed as insoluble inclusion bodies in Escherichia coli cultures. Cell extracts containing the recombinant proteins showed immunoreactivity on Western blots with monoclonal antibody recognizing the native hormonal peptide. These gene constructs have potential applications in therapy of sex-steroid-hormone-dependent cancers.

A recombinant luteinising-hormone-releasing-hormone immunogen bioeffective in causing prostatic atrophy

Previous studies with a semi-synthetic vaccine indicated the utility of immunization against luteinising-hormone-releasing-hormone (LHRH) in prostate cancers. To overcome the limitations of the previous vaccine, which caused carrier induced suppression of antibody response on repeated immunizations and was costly to synthesize, two recombinant vaccines were designed, in which diptheria or tetanus toxoid used as carriers were replaced by 4-5 T non B peptides. The paper reports the immunogenecity, efficacy and safety of these multimer vaccines in rats, a homologous experimental animal. All animals generated anti-LHRH antibodies, which caused the decline of testosterone to castration levels at and above 0.15 OD units of antibody titres. The prostate was significantly atrophied in all animals immunized with these vaccines.

A Vaccination Strategy for the Long-Term Suppression of Androgens in Advanced Prostate Cancer

OBJECTIVES

We have previously reported the ability of D17DT (formerly GnRH-DT) vaccination to produce castrate levels of androgens in men with advanced prostate cancer. This study examines the efficacy and tolerability of 3 and 15 micrograms of D17DT in 12 patients with advanced prostate cancer to establish a dose-response relationship.

METHODS

12 patients received either 3 or 15 micrograms of D17DT as 3 deep intramuscular injections over 6 weeks. Outcome was assessed in terms of physical and biochemical evaluations of clinical progression and antibody titres.

RESULTS

Significant titres of anti-GnRH antibodies were detected in 2 out of 6 subjects who received 15 micrograms of D17DT; suppression of testosterone to castrate levels accompanied by a significant and prolonged reduction in PSA was also demonstrated. No responses were seen following treatment with 3 micrograms of D17DT.

CONCLUSION

The induction of anti-GnRH antibodies through vaccination with 15 micrograms D17DT can produce and sustain castrate levels of testosterone in men with advanced prostate cancer.

A monoclonal antibody cytolytic to androgen independent DU145 and PC3 human prostatic carcinoma cells

BACKGROUND

While a range of therapeutic products is available for androgen-dependent prostatic cancer, no specific intervention modality exists for androgen-independent prostatic cancer. The objective of this research was to explore whether epitopes exist on androgen-independent prostatic DU145 cancer cells, which could be susceptible to cytotoxic action of specific antibodies.

METHODS

Hybrid cell clones were developed by immunization of mice with DU145 cells and tested for immunoreactivity by solid phase EIA and cytotoxicity in vitro on DU145 in the presence of the complement, employing colorimetric quantitation by MTS (3- (4-, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-(4-sulfophenyl)-2H-tetrazolium). Binding and cytotoxicity studies were also carried out by flow-cytometry.

RESULTS

Of 15 stabilized clones immunoreactive with DU145 cells, one monoclonal antibody (mAb 730) manifested cytotoxicity on DU145 cells. Approximately 80% of cells in the DU145 cell line were susceptible to lysis with this antibody at saturating levels. This figure corresponded quantitatively to the number of cells binding with this antibody as determined by Flow-cytometry. Staining with ethidium monoazide bromide (EMA) showed that the cell binding the antibody was also the one killed by the antibody in the presence of the complement. MAb 730 was also cytotoxic to PC3, another androgen-independent human prostatic cancer cell line. This antibody is devoid of classical autoantibody reactivities and does not react with normal human liver, thyroid, kidney, pancreas, and adrenal tissues, as determined by immunofluorescence. Also, it shows negative immuno-reactivity to benign glandular tissue but is observed to positively react with neoplastic prostate tissue.

CONCLUSIONS

Epitopes exist on androgen-independent prostatic cancer cells that are susceptible to cytolysis by monoclonal antibodies and these could be investigated for potential immunotherapy.

Anti-GnRH antibodies can induce castrate levels of testosterone in patients with advanced prostate cancer

D17DT consists of the GnRH decapeptide linked to diphtheria toxoid. The aim of this pilot study was to assess the tolerance of D17DT and the production of anti-GnRH antibodies from two doses, 30 and 100 microg, in patients with locally advanced prostate cancer. Twelve patients with histologically proven prostate cancer in whom hormonal therapy was indicated were recruited. Patients received either 30 or 100 microg given intramuscularly on three separate occasions over six weeks. Patients were followed up and blood was taken for estimation of serum testosterone, PSA and anti-GnRH antibody titre. Overall the drug was well tolerated. In 5 patients a significant reduction in serum testosterone and PSA was seen. Castrate levels of testosterone were achieved in 4 and maintained for up to 9 months. Patients with the highest antibody titre had the best response in terms of testosterone suppression. This study shows that it is possible to immunize a patient with prostate cancer against GnRH to induce castrate levels of testosterone. This state appears to be reversible. This novel form of immunotherapy may have advantages over conventional forms of hormonal therapy and further studies are warranted in order to try and increase the proportion of responders.

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.

Induction of early and bioeffective antibody response in rodents with the luteinizing hormone-releasing hormone vaccine given as a single dose in biodegradable microspheres along with alum

BACKGROUND

Previous studies in animals and phase I/phase II clinical trials in humans have shown the suppressive effect of immunization with the luteinizing hormone-releasing hormone (LHRH) vaccine on prostatic hypertrophy and hyperplasia. A drawback of this vaccine was a delay of about 8 weeks in buildup of antibody titers to efficacy level and the requirement of three injections of the vaccine given at monthly interval for full primary immunization.

METHODS

LHRH vaccine was encapsulated in poly-lactic-co-glycolic acid (PLGA) 50:50 copolymer microspheres of reproducible physicochemical characteristics. Immunogenicity studies were carried out in rodents and prostate weights were determined at various antibody titers.

RESULTS

The vaccine entrapped in biodegradable microspheres generated high antibody response in rats, persisting for 5-7 months following a single immunization. One hundred micrograms was the optimum dose, and the intramuscular route was more immunogenic than the subcutaneous. It was further observed that coadministration of 75% of the vaccine entrapped in microspheres with 25% adsorbed on alum generated higher antibody response in rodents, exceeding the bioeffective threshold as early as day 15 postimmunization.

CONCLUSIONS

Coadministration of the LHRH vaccine in biodegradable PLGA microspheres with a quarter of the dose adsorbed on alum generates high antibody titers within 15 days, which are effective in causing atrophy of the prostate.

Biphasic testosterone delivery profile observed with two different transdermal formulations

PURPOSE

Our long-term goal is to develop formulations for pulsatile testosterone (T) delivery. T has been reported earlier to show biphasic pharmacokinetics in humans by Mazer et al, as well as biphasic permeation across excised rat skin by our group. We examined two kinds of formulations to evaluate their delivery profiles and to assess whether differences in the formulation approach affect pharmacokinetics in animal models.

METHODS

One formulation consisted of T and a polymer blend dissolved in isopropanol; administered by dispensing the solution on the skin to cast a film in situ. The other was an adhesive-dispersion patch. In vitro release from the patch was evaluated using a flow-through cell interfaced with an HPLC pump and UV detector. Single dose pharmacokinetics were evaluated in castrated Wistar rats and bonnet monkeys immunized against gonadotropin-releasing hormone to deplete endogenous T.

RESULTS

Two maximas were observed in the T release profile from the patch and in serum concentration versus time profiles in both animal models on application of either formulation. The relative magnitudes of the two maximas and the time interval separating them were different in the case of each formulation.

CONCLUSIONS

Both formulations result in biphasic pharmacokinetics of T in the animal models studied. Discrete maximas presumably correlate with "burst" and "sustained" phases of drug release.

Effect of active immunization against luteinizing hormone-releasing hormone on the androgen-sensitive Dunning R3327-PAP and androgen-independent Dunning R3327-AT2.1 prostate cancer sublines

BACKGROUND

The objective of this study was to determine the effect of active immunization against LHRH on the growth characteristics and histology of subcutaneously implanted tumors of the androgen-sensitive Dunning R3327-PAP and androgen-independent R3327-AT2.1 rat prostate adenocarcinoma sublines.

RESULTS

We herein demonstrate that 1) active immunization with an LHRH-diphtheria toxoid-conjugate (LHRH-DT) leads to the downregulation of gonadotropins and testosterone and consequently the atrophy of testosterone-dependent organs such as the testes, prostate, and androgen-sensitive Dunning R3327-PAP tumors, 2) growth inhibition of Dunning R3327-PAP tumors is caused by suppression of cell division rather than by an increase in cell death and is associated with an increase of the tumor stroma content, and 3) volume increase of the androgen-independent Dunning R3327-AT2.1 tumor is slightly but significantly reduced, indicating a local stimulatory LHRH loop within this tumor cell line.

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.

Ability of an anti-luteinizing hormone-releasing hormone vaccine to inhibit gonadotropins in postmenopausal women

OBJECTIVE

To determine the effects of immunization with an anti-LH-releasing hormone (LH-RH) vaccine in postmenopausal women.

DESIGN

Pilot clinical study.

SETTING

Normal human volunteers in a medical research-training environment.

PATIENT(S)

Three postmenopausal women with a mean age of 60 years, 5 years of amenorrhea, and severe hypoestrogenism with elevated serum LH and FSH.

INTERVENTION(S)

Intramuscular immunization with 300 micrograms LH-RH equivalent of the vaccine in two occasions 1 month apart.

MAIN OUTCOME MEASURE(S)

Patients were followed for clinical assessment and serum LH, FSH, and anti-LH-RH titers at regular monthly intervals for 7 months.

RESULTS(S)

The injection of the anti-LH-RH vaccine followed by a booster injection 1 month later resulted in a sharp decrease, 60 days after the first injection, of both serum gonadotropins, accompanied by an increase in anti-LH-RH antibody titers, which were reversible after 180 days in the absence of further booster immunization.

CONCLUSION(S)

Active immunization offer a safe option to induce antibody response, which in the present regime employed was of about 6-months duration. This procedure opens new possibilities for its use as an affordable therapeutic agent in some hormone-dependent clinical conditions.

An investigation into the immunogenicity of a GnRH analogue in male rats: a comparison of the toxicity of various adjuvants used in conjunction with GnRH-glycys

Immunization of male Copenhagen Fischer rats with a gonadotrophin releasing hormone (GnRH) analogue, conjugated to PPD resulted in high levels of antibody being produced which disrupted gonadal function in male rats. The antibody reduced serum testosterone levels and subsequently suppressed spermatogenesis. Alternatives to Freund's adjuvant were tested, namely, aluminium hydroxide and non-ionic surfactant vesicles (NISV). The study showed that aluminium hydroxide was as effective as Freund's adjuvant and less toxic, in both BCG and non-BCG primed animals. However, NISV were completely non-toxic and most effective in conjunction with BCG priming. The data obtained showed that NISV have the potential to be used as an alternative to FCA and aluminium hydroxide-based adjuvants.

Active immunization against LHRH alone or combined with LHRH-analogue treatment impedes growth of androgen-dependent prostatic carcinoma

PROBLEM

To determine whether active immunization against LHRH can serve as treatment for androgen-dependent prostatic carcinoma.

METHOD

Male rats of Copenhagen X Fisher strain, implanted with Dunning R-3327 prostatic carcinoma cells were either immunized against LHRH, treated with LHRH-antagonist, or received a combined treatment of active immunization against LHRH and LHRH-antagonist.

RESULTS

Testicular histology was consistent with infertility in all treatment groups. The rate of tumor growth was inhibited by all three treatment regimens. Tumor size increased by 3.8 +/- 1.4 cm2 in the LHRH-antagonist group, 3.2 +/- 1.1 cm2 in the immunized group, and 1.0 +/- 0.4 cm2 in the combined treatment group, as compared to 8.2 +/- 2.6 cm2 in non-treated control group.

CONCLUSION

LHRH-antagonist administration combined with immunization against LHRH appeared to exert a synergistic effect. This may be due to the blockade of prostatic LHRH-like receptors by the antagonist, while androgen depletion was rapidly achieved by LHRH-antagonist, and maintained by continued gonadotropin suppression caused by active immunization against LHRH once antagonist treatment had been discontinued.

A birth control vaccine is on the horizon for family planning

Vaccines for control of fertility are likely to have an important impact on family planning methods. They are designed to act by mobilization of an internal physiological process and do not require external medication on a continuous basis. A number of birth control vaccines are at different stages of development, the most advanced being a vaccine inducing antibodies against human chorionic gonadotrophin (hCG). This vaccine consists of a heterospecies dimer (HSD, beta hCG associated with alpha-subunit of ovine luteinizing hormone, beta hCG:alpha oLH) linked to tetanus toxoid (TT) or diphtheria toxoid (DT) as carriers. The vaccine has recently passed an important milestone; it has completed the first leg of phase II efficacy trials. Women of proven fertility leading active sexual life were protected from becoming pregnant at antibody titres > or = 50 ng of hCG bioneutralization capacity per ml. This vaccine has previously been demonstrated to be reversible in its effect. It is free from any notable side-effects on endocrine, cardiovascular and other body functions. Ovulation was not disturbed and menstrual regularity was maintained. A logistic disadvantage of the present vaccine is the requirement for multiple injections. This is expected to be overcome by encapsulation of the requisite doses of the vaccine in biodegradable microspheres, which could be given at a single contact point for sustained antibody titres lasting over a year. A live recombinant vaccine has also been made that elicits high anti-hCG titres in monkeys for nearly 2 years following primary immunization and a booster at 8-9 months.

Synthetic gonadotrophin-releasing hormone (GnRH) vaccines incorporating GnRH and synthetic T-helper epitopes

A vaccine against the gonadotrophin-releasing hormone (GnRH) is being developed as an immunological method for treatment of prostatic hypertrophy, based on the observation that active immunization against GnRH leads to the production of anti-GnRH antibodies which results in the shrinkage of the prostate gland. We have been investigating the regulation of anti-GnRH antibody responses by carrier molecules. In previous studies we showed that the use of large protein molecules as carriers limits the use of such a vaccine owing to potential problems of carrier-induced anti-haptenic suppression. In this report we show that synthetic T-helper epitopes can be used as carriers for the generation of anti-GnRH antibody responses.

Vaccines for control of fertility and hormone dependent cancers

Two vaccines, namely one inducing antibodies against hCG and the other against GnRH, are now in clinical trials. The hCG vaccine has entered Phase II clinical trials in three centres in India after successfully completing Phase I clinical studies in several centres in India and in four countries abroad. The vaccine was found to be devoid of side-effects; its effect was reversible. The available data on 179 cycles indicate that the vaccine prevents pregnancy at antibody titres above 50 ng/ml. A genetically engineered version of the vaccine has also been approved for trials in human lung cancer patients of the type which make hCG. hCG is observed to be a growth factor for such tumours. The GnRH vaccine is usable in both males and females as the deca-peptide is common to both sexes. Following suitable experimental and toxicology studies, the vaccine is currently in Phase I/Phase II clinical trials in patients of prostate carcinoma. Where antibody GnRH antibodies were induced, the LH, FSH and testosterone levels declined. This was accompanied by a reduction in prostate specific antigen. Clinical improvement was observed in many cases. The vaccine has also entered Phase I clinical studies in postpartum women, with the objective to extend the lactational amenorrhoea and extend inter-child interval.

Effect of active immunization to luteinizing-hormone-releasing hormone on the fertility and histoarchitecture of the reproductive organs of male rat

The feasibility of using a vaccine against luteinizing-hormone-releasing factor for suppression of pituitary and gonadal functions has been indicated for some time. Antibody production against this low-molecular-weight, naturally occurring decapeptide, however, requires to be coupled to a carrier protein to enhance its immunogenicity. LHRH was coupled to diphtheria toxoid (DT). Adult male Sprague-Dawley rats with a mean basal body weight of 200 g were immunized with anti-LHRH-DT (20 micrograms/injection/rat) at four-week intervals. An equal number of unexposed animals served as controls. Six animals were killed every two weeks up the end of the week 43. The vaccination schedule did not have any effect on the gain in body weight, nor was any adverse effect of vaccination observed in the course of the investigations. The pituitary, prostate, epididymis, testes, seminal vesicles, adrenal and thyroid were excised for determination of organ weight and histological examination. The adrenal, pituitary and thyroid showed no remarkable weight changes during the observation period, whereas the weights of the reproductive organs demonstrated significant reductions compared to those of the control group. The histopathology revealed marked to significant changes in the gonads and the accessory sex organs including the prostate. A progressive phase of regeneration of spermatogenesis was evident 98 days after vaccination. Total recovery of spermatogenesis was observed 300 days after vaccination. The mating studies showed the return of fertility 300 days after vaccination. The litters borne were normal. Prostate showed recovery after 154 days of vaccination. Our observations lend strong support to the hypothesis that anti-LHRH vaccine can be effectively used on the management of prostate carcinoma. If the vaccination is given together with a suitable dose of long-acting androgen, contained in an adequate delivery system, the regimen may be used for the regulation of male fertility.

Hyporesponsiveness to a GnRH vaccine in a non-responder mouse strain is T-cell mediated

Immunization of rats and monkeys with the decapeptide gonadotropin releasing hormone (GnRH) linked to carriers such as diphtheria toxoid (DT) or tetanus toxoid (TT) results in a marked atrophy of the prostate. This vaccine is now being explored for its potential in the "immunosurgery" of prostatic hypertrophy in men and is currently undergoing Phase I/II clinical trials. We have been investigating immunogenetic aspects of immune responses to this hapten-carrier conjugate, and in a recent communication we described the responses of different strains of mice to GnRH conjugated to DT (GnRH-DT). Mice of the 129 (H-2b) strain were found to be non-responders to GnRH. However, further immunization of GnRH-DT-immunized 129 mice with GnRH linked to an alternate carrier, TT, resulted in the production of high levels of anti-GnRH antibodies. This showed that 129 mice are not deficient in GnRH-specific B cells and that the lack of response to GnRH in 129 mice is possibly due to (i) the lack of appropriate helper T-cells or (ii) the presence of suppressor cells. In this report we present evidence to support the existence of suppressor cells in GnRH-DT-immunized 129 mice.

Prostatic hypoplasia in bonnet monkeys following active immunization with semisynthetic anti-LHRH vaccine

An active immunization study using semisynthetic anti-luteinizing hormone releasing hormone (LHRH) vaccine was undertaken in adult male bonnet monkeys (Macaca radiata). Four male bonnet monkeys were immunized with LHRH-DT vaccine (100 micrograms/monkey). When the elevation of serum anti-LHRH titers reached an effective concentration, a remarkable decrease in serum testosterone level was observed. The sperm counts at 12 and 20 weeks following immunization in all immunized monkeys were reduced markedly. One representative animal with high antibody titer along with an age-matched control animal was sacrificed 20 weeks following primary immunization. The prostate weight of the immunized monkey was reduced to one-third (0.027) of the control (0.085). A reduction was also observed in other reproductive organs. Remaining animals are being studied for a reversible effect of immunization. Thus the study demonstrates that the size of the prostate can be reduced significantly by inhibition of hypothalamic-pituitary-testicular axis using this anti-LHRH vaccine.

Influence of the genetic background and carrier protein on the antibody response to GnRH

A vaccine against the gonadotropin releasing hormone (GnRH) is being developed as an immunological method for the treatment of prostatic enlargement. The work described here was aimed at investigating the influence of the genetic background on immune responses to GnRH conjugated to diphtheria toxoid (DT). Mice of different strains were injected with the conjugate and the antibody levels against GnRH and DT quantitated in order to examine the effect of genetic background on immune responses to the hapten and the carrier. All immunized animals produced antibodies to DT. Anti-GnRH antibodies were generated by all strains of mice except 129. The low anti-GnRH response in the 129 strain mice did not appear to be MHC-linked, as C57BL/6 mice, which bear the same MHC haplotype as 129 mice, were able to generate a strong anti-GnRH response. The non-responsiveness to the hapten (GnRH) in 129 strain mice was overcome by the use of an 'alternate carrier' approach.

Histopathological changes in reproductive organs of male Wistar rats following active immunization against LHRH

Histopathological changes induced by immune responses generated against luteinizing hormone releasing hormone (LHRH) were studied in adult male Wistar rats. Active immunization with a semisynthetic anti-LHRH vaccine, LHRH D-Lys6, (10, 40, and 80 micrograms/animal) conjugated with diphtheria toxoid, produced bioeffective antibodies as indicated by significant reduction in circulating testosterone levels. At the 14th week after immunization the animals were sacrificed and reproductive organs were evaluated. These organs were studied for histopathological changes and compared with those of nonimmunized control rats. Marked hypoplastic changes were observed in the genital organs. Testicular changes such as arrest of spermatogenesis at the spermatocyte level and atrophic changes in the interstitial Leydig cells were noticed in treated animals. Similarly attenuation of secretory epithelial cells with substantial increase in the stromal tissues was observed in the prostate and seminal vesicles. The current observation suggests the possible usefulness of this anti-LHRH vaccine under clinical conditions where reduction in androgenic response is desired as in the case of hormone-dependent prostatic carcinoma.