Sperm surface antigens involved in mammalian fertilization: their role in contraceptive vaccine development for humans

Effects of synthetic thymosin-alpha 1 and its analogs on fertilizability of human sperm: search for a biologically active, stable epitope

Thymosin-alpha 1 (T alpha 1) and six T alpha 1 analogs were synthesized to study structure-function relationships and to search for the biologically active and stable epitope(s) that would have clinical application in the treatment of male infertility. Four of these analogs were prepared by modification/substitution of N- and C-terminal amino acids of T alpha 1 peptide, and the other two analogs were fragments having only N-16 amino acids (N-terminal) or C-14 amino acids (C-terminal), respectively, of the T alpha 1 peptide. T alpha 1 and these six analogs were tested for their effects on human sperm penetration rates in the sperm penetration assay (SPA). T alpha 1 significantly (p < .0001) increased the penetration rates in SPA, with the strongest enhancing effect at 0.5 microgram/100 microL concentration. Of the six analogs tested only two, T alpha 1-Gly-NH2 and T alpha 1-C14, retained the enhancing effects in SPA. None of the analogs decreased the penetration rates or affected sperm motility compared to control. The enhancing activity resides primarily in an epitope, the C-terminal 14 amino acids of T alpha 1. However, for maximal effect both N- and C-terminal amino acids (serine and asparagine, respectively) have to be intact and unmodified. The T alpha 1-Gly-NH2 analog that had its C-terminal protected was as potent as the intact T alpha 1 peptide. T alpha 1 and this analog may have clinical applications in treatment of male-factor-mediated infertility.

Antibodies to sperm-specific human FA-1 inhibit in vitro fertilization in rhesus monkeys: development of a simian model for testing of anti-FA-1 contraceptive vaccine

The feasibility of using the rhesus monkey as a non-human primate model for testing the efficacy of a contraceptive vaccine based on FA-1 antigen was evaluated. Affinity-purified anti-FA-1 polyclonal antibodies (Fab' fragments) and anti-FA-1 monoclonal antibody were used as probes in these studies. Anti-FA-1 antibodies (polyclonal Fab' as well as monoclonal IgG) predominantly reacted with the postacrosomal, mid-piece and tail regions of rhesus monkey sperm, as with human sperm, by an indirect immunofluorescence technique (IFT). These antibodies also specifically recognized a single protein band of 51 +/- 2 kDa, corresponding to the dimeric form of FA-1 antigen, on a Western blot of lithium diiodosalicylate (LIS)-solubilized monkey sperm. Anti-FA-1 antibodies, when present in the insemination mixture, inhibited the in vitro fertilization (IVF) of monkey oocytes. These results indicate that FA-1 antigen in rhesus monkey sperm is similar in subcellular localization, molecular identity and function to that in human sperm, and that the rhesus monkey represents a permissible non-human primate model in which the efficacy of a contraceptive vaccine based on FA-1 antigen can be tested.

The role of antisperm antibodies in infertility

OBJECTIVE

To discuss the role of antisperm antibodies (Ab) in infertility, including proposed mechanisms of antisperm Ab formation, assays for their detection, and treatments for immune-mediated infertility.

DESIGN

Major studies in the published literature and data from The University of Texas Southwestern Medical Center, Division of Reproductive Endocrinology. Reports were reviewed that investigated the development and impact of alloimmunity and autoimmunity to spermatozoa in men and alloimmunity in women and the current methods of treatment for resultant subfertility.

RESULTS

The exposure of spermatozoal antigens to the mucosal and systemic immune systems results in development of immunity to a multiplicity of spermatozoal epitopes. The evaluation of studies that examine the role of antisperm Ab in infertility is complicated by the lack of standardization of antisperm Ab assays and the difficulty in identifying those epitopes for antisperm Ab binding that are responsible for subfertility. Sperm-associated antisperm Ab and antisperm Ab in cervical mucus (CM) reduce sperm mobility and may also impair sperm-ovum interaction. The clinical significance of serum antisperm Ab in both men and women, however, is controversial. Current therapy for antisperm Ab associated infertility is empiric and largely unproven.

CONCLUSIONS

Antisperm Ab on the sperm surface and in CM are implicated in the pathogenesis of a subset of patients with infertility. Further studies that determine the clinically relevant sites of antisperm Ab interaction will aid in directing the treatment of subfertility mediated by antisperm Ab.

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.

Vaccines against fertility

The first evidence for the efficacy of a birth control vaccine in humans is now available from the Phase II trials on the human chorionic gonadotrophin vaccine in India. Several sperm antigens have been identified as potential contraceptive immunogens and zona pellucida antigens have been reported that reversibly control fertility.

Antigenic differences in human sperm samples related to various morphological abnormalities

Sperm samples were collected from male partners of fertile and infertile couples having unexplained and male factor infertility and analyzed for morphological abnormalities. After a staining procedure, sperm samples of these infertile men showed a variety of abnormalities. The sperm samples were also studied for their binding with the Abs directed against protamine (the nuclear protein), fertilization antigen (FA-1, sperm surface antigen), and the lithium diiodosalicylate- (LIS-) solubilized sperm preparation, and the binding was correlated with the percentage of morphologically abnormal sperm in the sample. Abs used in the present study were raised in female rabbits and had high titers (ELISA titers, 1:4096 to 1:8196), and recognized no band (anti-protamine), one 49,000- +/- 2000-dalton band (anti-FA-1), and at least 8 bands of various molecular identities in the 14,000- to 92,000-dalton range (anti-LIS sperm) on the Western blot of LIS-solubilized human sperm. The affinity-purified Fab' antibodies were iodinated and used in a radioimmunobindingassay for testing their binding with the sperm cells. Anti-protamine Fab's showed minimal binding and the binding activity (cpm bound/10 x 10(6) sperm cells) did not correlate (head defect, r = .12; midpiece defect, r = .07; tail defect, r = .11) significantly with percentage of abnormal cells in the sample. The binding of the anti-FA-1 Fab's also did not show a significant correlation (head defect, r = .29; midpiece defect, r = .48; tail defect, r = .23), though a positive trend (p = .05) was observed with the midpiece defect. In contrast, the binding of anti-LIS sperm Fab's demonstrated a significant correlation with the percentage of abnormal sperm cells in the sample (head defect, r = .51, p = .04; midpiece defect, r = .80, p less than .0001; tail defect, r = .23, p = .039). With an increased percentage of abnormal sperm cells, especially those with midpiece defect, there was an increased binding of anti-LIS sperm Fab's. These results suggest that with an increase in percentage of abnormal sperm, there is a change in antigenicity of the sperm cells. An increase in structural abnormality may enhance antibody binding to an abnormal sperm cell, thus causing a further decrease in its fertilizing capacity.

The fertilization antigen-1 does not have proteolytic/acrosin activity, but its monoclonal antibody inhibits sperm capacitation and acrosome reaction

OBJECTIVE

To determine if human sperm surface fertilization antigen exhibits proteolytic or acrosin activity and to investigate the mechanism(s) whereby monoclonal antibody (mAb) to fertilization antigen inhibits human sperm penetration of zona-free hamster ova.

DESIGN

Proteolytic and acrosin activities of human fertilization antigen were determined. Acrosomal status, acrosin activity, and motion characteristics were evaluated after incubation of human sperm with immunoaffinity-purified mAb to fertilization antigen.

SETTING

Academic research environment.

PARTICIPANTS

Fertile donors used as controls for infertile patients for fertility evaluation.

INTERVENTIONS

Human spermatozoa were treated with mAb to fertilization antigen and induced to undergo acrosome reaction using calcium ionophore A23187.

MAIN OUTCOME MEASURES

Proteolytic and acrosin activities of fertilization antigen. Sperm penetration assay, acrosomal status, and motion parameters.

RESULTS

Fertilization antigen does not exhibit proteolytic or acrosin activity; however, its mAb completely blocks human sperm penetration of zona-free hamster ova. The mAb to fertilization antigen inhibits ionophore-induced acrosome reaction and blocks development of the hyperactivated state of human sperm cells.

CONCLUSIONS

Monoclonal antibody to fertilization antigen blocks fertilization by inhibiting capacitation and acrosome reaction.

Effects of antibodies to sperm surface fertilization antigen-1 on human sperm-zona pellucida interaction

OBJECTIVE

To investigate the effects of antibodies to well-defined sperm surface antigens (the fertilization antigen [FA-1] and germ-cell antigen [GA-1]) and nuclear antigen (protamine) on human sperm-zona interaction.

DESIGN

Number of total and acrosome-reacted human sperm bound to the human zona pellucida and the sperm movement characteristics assessed by computer-aided sperm analysis were evaluated after incubation of sperm with the antibodies.

SETTING

Academic research environment approved by the Institute Review Board.

PATIENTS

Human oocytes were obtained from ovaries removed at surgery. Semen from fertile donors was used in all assays.

INTERVENTIONS

Human oocytes were stored in salt solution at -80 degrees C until used. Spermatozoa were treated with the antibodies to various sperm antigens.

MAIN OUTCOME MEASURES

Total and acrosome-reacted sperm bound to zona pellucida and sperm movement characteristics were evaluated after 3 to 5 hours of incubation of the antibodies with human sperm.

RESULTS

Anti-FA-1 antibodies significantly reduced human sperm fusion with zona-free hamster oocytes and sperm binding to the human zona pellucida but did not affect binding of acrosome-reacted sperm and sperm movement characteristics. Anti-GA-1 and antiprotamine antibodies did not affect sperm-oocyte interaction, acrosomal reaction, or sperm motility.

CONCLUSIONS

Antibodies to FA-1 but not to GA-1 and protamine inhibit human sperm-zona interaction.

Human cleavage signal-1 protein; cDNA cloning, transcription and immunological analysis

The cleavage signal-1 protein (CS-1), a doublet antigen comprised of approx. 14-kDa and 18-kDa proteins has been shown to be present on the surface of sperm of various mammalian species including humans. Polyclonal antibodies to CS-1 inhibit the early cleavage of fertilized eggs without apparently affecting sperm penetration and pronuclear formation. We report here the cloning of the human CS-1 cDNA and its expression in vitro to obtain the recombinant protein (reCS-1) molecule. The CS-1 cDNA clone was isolated by immunological screening of a human testis lambda gt11 cDNA library with mono-specific polyclonal antibody against CS-1. The cDNA is 1828 bp long; the start codon assigned to the first ATG (bp 98-100) encodes a protein with 249 amino acid residues terminating at TAA (bp 845-847). The cDNA isolated has a 97-bp 5' and a 984-bp 3' untranslated region. The potential polyadenylation signal (5'-AATAAA) is at bp 1803-1808. An extensive computer search of the GenBank database did not indicate any extensive homology with any known sequence, indicating that CS-1 is a unique protein. The CS-1 cDNA was cloned in the transcription vector, pGEM-11Zf, to obtain high-level in vitro transcription by SP6 and T7 RNA polymerase. The transcribed CS-1 RNA was translated in a rabbit reticulocyte in vitro translation system and produced a 33-kDa reCS-1 protein, as assessed by migration in a SDS-polyacrylamide gel.(ABSTRACT TRUNCATED AT 250 WORDS)