Important Role of the Carrier in the Induction of Antibody Response Without Freund's Complete Adjuvant Against a “Self” Peptide Luteinizing Hormone-Releasing Hormone (LHRH)*

Immunoregulation of mammalian fertility

Fertility management is a global issue of agricultural, medical, economic, and social consequence. Although many methods have been devised to both inhibit and assist reproduction, more acceptable alternatives are needed. Regulation by immune intervention is a promising technology as applied to livestock, pets, wildlife, and human beings. Outcome is dictated by site within the reproductive axis that is targeted. Fertility is suppressed by immunization against gonadotropin-releasing hormone, gonadotropins, prostaglandin F2 alpha, oxytocin, gonadotropin receptors, and gamete/embryonic antigens. It also is possible to lyse gonadal cells with ligand-antibody hybrid molecules. Ovulation rates are enhanced by vaccination with inhibin. Antibodies to sex steroid hormones have yielded mixed results. Perhaps recombinant viral vectors can be used to deliver reproductive immunogens. A new and simple technique to generate sustained autoimmune reactions to hormones and cellular antigens entails direct gene transfer into somatic cells. Evolving advances in reproductive immunology and biotechnology should furnish us with novel nonsurgical contraceptives and profertility agents that can be efficiently and safely implemented.

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.

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.

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.

Active immunization against LHRH: I. Effects of conjugation site and dose

Active immunization against LHRH is a promising method of contraception for men. In order to be acceptable, sufficient amounts of anti-LHRH antibodies must be induced rapidly after vaccination. In previously reported animal studies, we found that it took considerable time (up to 5 months) to obtain antibody titers (AT) that were sufficiently high for complete suppression of spermatogenesis. The possibility of accelerating the immune response to LHRH by increasing the dose of immunogen was investigated in the male rat. Six doses of LHRH conjugated to tetanus toxoid (TT) in the 10 position (LHRH10-TT), ranging from 2.5 to 612 micrograms, and three doses of LHRH1-TT (50 to 612 micrograms) were tested. The magnitude of the immune response did not depend on the dose of the antigen, provided a threshold dose had been surpassed. Antigenicity of LHRH conjugated to TT at either the 1-, 6-, or 10-position was compared in rats and rabbits. In both species LHRH1-TT induced sufficient antibody concentrations to suppress pituitary gonadotropins (LH and FSH) and, subsequently, serum testosterone (T) levels faster than either the 6- or 10-conjugates. Only materials permitted for use in humans were utilized in these experiments.

CONCLUSION

Active immunization against LHRH conjugated to TT at the 1-position has potential as a fast, convenient method of male contraception.

Functional morphology of testis and its excurrent ducts in rats immunized with synthetic luteinizing hormone releasing hormone conjugated to tetanus toxoid

The effects of active immunization against luteinizing hormone releasing hormone (LHRH) on the testis and its excurrent ducts in rats were studied using a synthetic LHRH peptide conjugated to tetanus toxoid (TT), with or without an adjuvant. The study demonstrated that LHRH-TT given alone did not elicit an appreciable immune response and that its immunogenicity could be enhanced by administration with an adjuvant, such as species-specific IgG or SPLPS. The anti-LHRH antibody response showed a corresponding regressive effect on the morphology of the testis and its excurrent ducts. The functional involution of the testis was reflected in the form of a block in spermatogenesis and the lowering of testosterone production; the basic structural organization of the testicular components was, however, maintained. Epididymal ducts displayed rather drastic atrophic changes, indicating that prolonged immunization may result in irreversible damage to the excurrent ducts and could, therefore, adversely affect the restoration of fertility even after the return of testicular function following decline in the immune response against LHRH. This could be an important consideration if LHRH immunization is to be used for male contraception.

Immunization of cattle against modified peptides of gonadotropin releasing hormone conjugated to carriers: Effectiveness of Freund's and alternative adjuvants

Two gonadotropin-releasing hormone (GnRH) peptides with a cystein substitution of the first (C1-GnRH) or tenth (C10-GnRH) amino acid were conjugated to ovalbumin and equine serum albumin, respectively, via the sulfhydryl group of the introduced cysteine. Animals were immunized three times at 3-wk intervals with both conjugates in either saline (n = 5), Freund's complete adjuvant (FCA; n = 5), Havlogen (n = 6), Ribi adjuvant system (RAS; n = 5), dimethyl dioctadecyl ammonium bromide (DDA; n = 4), Alhydrogel (n = 5) or Regressin (n = 5). Animals immunized with conjugates in saline or RAS did not produce anti-GnRH titers. The highest anti-GnRH titers were produced by animals treated with FCA. The Alhydrogel and DDA treatments stimulated the production of GnRH antibodies in all animals treated, but titers were lower than in animals immunized with FCA. When vaccines were formulated with Havlogen or Regressin, anti-GnRH titers were low or absent. Serum luteinizing hormone (LH) and follicle stimulating hormone (FSH) levels were depressed in FCA and in Alhydrogel treated animals. The antisera raised were predominantly directed against either the carboxy- or the amino-terminal end of the GnRH peptide, or directed equally against both, depending on the individual animal. Results suggest that no epitope of GnRH dominates the immune response in cattle and show that the best alternative to FCA is Alhydrogel.

Immunization of sheep against modified peptides of gonadotropin releasing hormone conjugated to carriers

The efficacy of antigens based on modified GnRH peptides in stimulating the production of antibodies against GnRH in sheep was tested. In the first study cysteine-containing GnRH peptides were conjugated to keyhold limpet haemocyanin (KLH) in 3 different orientations. The 3 conjugates were prepared in an emulsion of Freund's complete adjuvant (FCA) and were injected into 3 groups of 6 castrated male lambs. The 3 vaccines efficiently induced anti-GnRH titers in all the animals treated. The specificity of the GnRH antisera raised varied depending on the orientation of the GnRH molecule in the antigen and on the individual animal. In a second trial designed to evaluate carrier molecules, a cysteine-containing GnRH peptide was conjugated to either KLH, equine serum albumin, ovalbumin or tetanus toxoid. The conjugates were prepared with FCA and injected into intact male lambs. All 4 vaccines stimulated the production of antibodies against GnRH in all the animals treated. The conjugates prepared with equine serum albumin or ovalbumin were the most effective in raising high anti-GnRH titers. In 18 of 20 lambs treated, anti-GnRH titers resulted in a marked atrophy of the testes. We conclude that: 1) the different epitopes of the GnRH molecule are equally immunogenic in sheep; 2) the GnRH antibody response is affected by the carrier used; and, 3) anti-GnRH vaccines based on cysteine-substituted GnRH analogues show potential for use in immunocastration of livestock.

Effects of long-term immunization against LHRH and androgen treatment on gonadal function

The possibility of immunological suppression of spermatogenesis while normal libido is maintained by exogenous androgen supplementation was tested in male rats. Neither short- nor long-term treatment with androgen (testosterone-17-trans-4-N-butyl-cyclohexane carboxylate) alone influenced fertility. Active immunization against LHRH administered simultaneously with exogenous androgen supplement caused infertility in 100% of the tested animals, all of which displayed normal sexual behavior. The atrophy of the testes and accessory sex organs was reversible.

Anti-fertility vaccines

Vaccines are under development for the control of fertility in males and females. This review discusses developments in anti-fertility vaccines at the National Institute of Immunology, New Delhi, India. A single injection procedure for the sterilization or castration of male animals depending on the site at which the injection is given, has passed through field testing and is expected to be on the market in the near future. Vaccines inducing antibodies against the human chorionic gonadotropin have gone through phase I trials with satisfactory results. A vaccine producing a consistently bioeffective antibody response against gonadotropin-releasing hormone is ready for phase I/II clinical trials in patients of carcinoma of prostate after due experimentation in animals and toxicology studies. Research to identify sperm antigens for incorporation into second generation vaccines is in progress.

Semisynthetic anti-LHRH vaccine causing atrophy of the prostate

A modified luteinizing hormone releasing hormone (LHRH) analog (D-lys)6 was synthesized and linked to epsilon-amino caproic acid at the 6th position. The free amino group thus generated was used for conjugation to diphtheria toxoid. Immunogenicity and bioefficacy studies of this conjugate vaccine were carried out in rodents. All immunized animals produced antibodies reactive with native LHRH. A gradual decline in testosterone levels accompanied the rise in anti-LHRH titers. On necropsy, after 10 weeks, a significant reduction in the relative weights of testes and accessory sex organs was noticed. Of particular significance was the marked atrophy of the prostate, indicating a possible therapeutic application of this vaccine in the treatment of androgen-dependent carcinoma of the prostate.

A synthetic luteinizing hormone releasing hormone vaccine II. Temporal aspects of titer development and formulation trials in BALB/c mice

Cysteine substituted analogues of luteinizing hormone releasing hormone (LHRH) were coupled to carrier molecules, and the resulting conjugates used to characterize the immune response to native LHRH generated in BALB/c mice and to formulate vaccines in an effort to maximize titer development. In an active immunization trial designed to characterize temporal aspects of anti-LHRH titer development, titers could be detected 1 week after initial immunization. No differences were observed in response between male and female mice. Booster immunizations could enhance the titers against LHRH. The titers developed against the carrier molecule were uniformly higher than the corresponding anti-LHRH titers throughout the course of the trial. In separate trials, vaccines were formulated and tested in BALB/c mice for titer development against LHRH. Adjuvants, carrier molecules, dosage and peptide to carrier ratio were considered. Dosages of 50 micrograms conjugate per immunization per mouse, at conjugation ratios of 3-12 peptides per 10(5) Da carrier molecule, were found to produce immune responses. Adjuvants including Havlogen and dimethyldioctadecylammonium bromide (DDA), and carrier molecules including keyhole limpet hemocyanin (KLH), porcine thyroglobulin (TGB) and equine gamma globulin (EGG) were all found to be effective.

Active immunization against gonadotropin-releasing hormone combined with androgen supplementation is a promising antifertility vaccine for males

Male rats and rabbits were immunized against gonadotropin-releasing hormone (GnRH) conjugated to tetanus toxoid (GnRH10-TT) using only materials approved for humans. Testosterone (T)-releasing implants or the long-lasting T ester testosterone-17-trans-4-n-butyl-cyclohexane carboxylate (TE) was used as supplemental androgen for maintaining libido. Immunization against GnRH10-TT effectively suppressed fertility (spermatogenesis) in rats and rabbits. Neither T nor TE administration restored fertility. Both androgens were effective in maintaining normal libido in rats. TE, which is not hydrolyzed in rabbits, was less effective in maintaining normal ejaculatory behavior in this species. Active immunization against GnRH could be a convenient and cost-effective method of fertility control in males.

Immunobiology of gonadotropin-releasing hormone

This article will review methods successful in inducing antibody responses against gonadotropin releasing hormone without the use of Freund's complete adjuvant (FCA), the characteristics of the antibodies produced, and will describe the dominant antigenic determinant(s) of the decapeptide and the use of monoclonal antibodies for suppression of estrus and of sex steroid production. The potential application of such immunological approaches in veterinary species, in management of precocious puberty in humans, and in hormone dependent cancers, is indicated.

The dominant role of amide group at C-terminus for recognition by antibody in primates against gonadotropin releasing hormone

A monkey and a baboon immunized with GnRH-tetanus toxoid conjugate developed high anti-GnRH antibody titres which resulted in disruption of cyclicity and low estradiol and progesterone levels indicative of the inhibition of follicular development and ovulation. Sera of both animals reacted with GnRH(NH2) but were devoid of reactivity with peptide sequences, 4-6, 7-10 and 4-10 of GnRH as well as GnRH free acid. Both sera were however reactive with GnRH-Lys-muramyl dipeptide analogue and GnRH-Ala-Ala-Thr-Lys-Pro-Arg-OH. As these compounds differ from GnRH-free acid by the presence of amide linkage at C-terminus of GnRH, these studies point to the importance of the conformation involving amide group at this position for immunoreactivity.

Characteristics and bioefficacy of monoclonal antigonadotropin releasing hormone antibody

Mouse hybrid cell clones secreting antigonadotropin releasing hormone monoclonal antibody were developed by fusion of SP2/O-Ag 1.4 myeloma cells with splenocytes of mouse immunized with gonadotropin releasing hormone (GnRH) tagged to tetanus toxoid. The product of hybrid cell clones obtained as ascites fluid from mouse peritoneal cavity had a titre of 10(6) (30-40% binding of 125I-GnRH) in radioimmunoassay. The antibody was IgG2a and Kappa. The association constant (Ka) of the product of hybrid cell clone P(8)16(62) for binding with GnRH was 1.2 X 10(9) L/mole. The monoclonal antibody (P(8)16(62)) was highly specific for the native GnRH and devoid of reactivity with thyroid releasing hormone as tested in competitive radioimmunoassay. The recognition for GnRH agonists by monoclonal was 387-fold less with D-Ser (But)6 des Gly10 GnRH ethylamide and 608-fold less with Bz1-His6 GnRH. Monoclonal anti-GnRH antibody was competent to neutralize the in vivo bioactivity of the hormone as evident by the block of estrus cycle and termination of pregnancy in mice. Termination of pregnancy in animals receiving anti-GnRH monoclonal could be prevented by administration of progesterone.

Formulation of a potential antipregnancy vaccine based on the beta-subunit of human chorionic gonadotropin (beta-hCG). I. Alternative macromolecular carriers

The antibody response obtained after vaccinating rabbits with the beta-subunit of human chorionic gonadotropin (beta-hCG) linked to several protein and polysaccharide carriers was measured. In all but one preparation, carbodiimide was used to couple the beta-hCG to the carrier. Tetanus toxoid (TT) and cholera vaccine proved the most effective carriers among those examined. TT from different manufacturers proved to be greatly different in free amino group content and differed in ability to participate in the coupling reaction. Reasonably good replication of the coupling reaction was obtained with different production lots from the same manufacturer. Inferior antigenic response was obtained with the products of coupling beta-hCG to H. pertussis, influenza vaccine, polylysine, pneumococcus polysaccharide, or E. coli polysaccharide. The findings indicate TT and cholera vaccine to be especially effective in enhancing the antigenicity of a weakly antigenic peptide but point to significant differences in the TT from different manufacturers.