A male genital tract-specific carbohydrate epitope on human CD52: implications for immunocontraception

Hexavalent sperm-binding IgG antibody released from vaginal film for development of potent on-demand nonhormonal female contraception

Nearly half of all pregnancies in the United States are unintended due to millions of women avoiding available hormonal contraceptive methods as a result of real and/or perceived side effects associated with the use of exogenous hormones. Topical vaginal delivery of antisperm monoclonal antibodies that could agglutinate sperm into clusters too large to penetrate mucus and prevent sperm from reaching the egg represents a potentially safe and potent mechanism for nonhormonal contraception. We report here the engineering of a vaginal film loaded with hexavalent (i.e., 6 Fab) antisperm IgG, made using GMP manufacturing processes, that possesses significantly superior agglutination potency than the parent IgG, enabling potent on-demand nonhormonal contraception via effectively agglutinating all human sperm within minutes.

Nonhormonal products for on-demand contraception are a global health technology gap; this unmet need motivated us to pursue the use of sperm-binding monoclonal antibodies to enable effective on-demand contraception. Here, using the cGMP-compliant Nicotiana-expression system, we produced an ultrapotent sperm-binding IgG antibody possessing 6 Fab arms per molecule that bind a well-established contraceptive antigen target, CD52g. We term this hexavalent antibody “Fab-IgG-Fab” (FIF). The Nicotiana-produced FIF had at least 10-fold greater sperm-agglutination potency and kinetics than the parent IgG, while preserving Fc-mediated trapping of individual spermatozoa in mucus. We formulated the Nicotiana-produced FIF into a polyvinyl alcohol–based water-soluble contraceptive film and evaluated its potency in reducing progressively motile sperm in the sheep vagina. Two minutes after vaginal instillation of human semen, no progressively motile sperm were recovered from the vaginas of sheep receiving FIF Film. Our work supports the potential of multivalent contraceptive antibodies to provide safe, effective, on-demand nonhormonal contraception.

Preclinical contraceptive development for men and women

This manuscript endeavors to present research considerations for the preclinical development of non-hormonal contraceptives. Topics include (1) how advances in genomics and bioinformatics impact the identification of novel targets for non-hormonal contraception, (2) the importance of target validation prior to investment in a contraceptive development campaign, (3) considerations on targeting gametogenesis vs gamete maturation/function, (4) how targets from the male reproductive system are expanding women's options for 'on demand' contraception, and (5) some emerging non-hormonal methods that are not based on a specific molecular target. Also presented are ideas for developing a pipeline of non-hypothalamic-pituitary-gonadal-acting contraceptives for men and women while balancing risk and innovation, and our perspective on the pros and cons of industry and academic environments on contraceptive development. Three product development programs are highlighted that are biologically interesting, innovative, and likely to influence the field of contraceptive development in years to come.

Engineering sperm-binding IgG antibodies for the development of an effective nonhormonal female contraception

Many women risk unintended pregnancy because of medical contraindications or dissatisfaction with contraceptive methods, including real and perceived side effects associated with the use of exogenous hormones. We pursued direct vaginal delivery of sperm-binding monoclonal antibodies (mAbs) that can limit progressive sperm motility in the female reproductive tract as a strategy for effective nonhormonal contraception. Here, motivated by the greater agglutination potencies of polyvalent immunoglobulins but the bioprocessing ease and stability of immunoglobulin G (IgG), we engineered a panel of sperm-binding IgGs with 6 to 10 antigen-binding fragments (Fabs), isolated from a healthy immune-infertile woman against a unique surface antigen universally present on human sperm. These highly multivalent IgGs (HM-IgGs) were at least 10- to 16-fold more potent and faster at agglutinating sperm than the parent IgG while preserving the crystallizable fragment (Fc) of IgG that mediates trapping of individual spermatozoa in mucus. The increased potencies translated into effective (>99.9%) reduction of progressively motile sperm in the sheep vagina using as little as 33 μg of the 10-Fab HM-IgG. HM-IgGs were produced at comparable yields and had identical thermal stability to the parent IgG, with greater homogeneity. HM-IgGs represent not only promising biologics for nonhormonal contraception but also a promising platform for engineering potent multivalent mAbs for other biomedical applications.

Production and characterization of a human antisperm monoclonal antibody against CD52g for topical contraception in women

BACKGROUND

Approximately 40% of human pregnancies are unintended, indicating a need for more acceptable effective contraception methods. New antibody production systems make it possible to manufacture reagent-grade human monoclonal antibodies (mAbs) for clinical use. We used the Nicotiana platform to produce a human antisperm mAb and tested its efficacy for on-demand topical contraception.

METHODS

Heavy and light chain variable region DNA sequences of a human IgM antisperm antibody derived from an infertile woman were inserted with human IgG₁ constant region sequences into an agrobacterium and transfected into Nicotiana benthamiana. The product, an IgG₁ mAb ["Human Contraception Antibody" (HCA)], was purified on Protein A columns, and QC was performed using the LabChip GXII Touch protein characterization system and SEC-HPLC. HCA was tested for antigen specificity by immunofluorescence and western blot assays, antisperm activity by sperm agglutination and complement dependent sperm immobilization assays, and safety in a human vaginal tissue (EpiVaginal™) model.

FINDINGS

HCA was obtained at concentrations ranging from 0.4 to 4 mg/ml and consisted of > 90% IgG monomers. The mAb specifically reacted with a glycan epitope on CD52g, a glycoprotein produced in the male reproductive tract and found in abundance on sperm. HCA potently agglutinated sperm under a variety of relevant physiological conditions at concentrations ≥ 6.25 µg/ml, and mediated complement-dependent sperm immobilization at concentrations ≥ 1 µg/ml. HCA and its immune complexes did not induce inflammation in EpiVaginal™ tissue.

INTERPRETATION

HCA, an IgG1 mAb with potent sperm agglutination and immobilization activity and a good safety profile, is a promising candidate for female contraception.

FUNDING

This research was supported by grants R01 HD095630 and P50HD096957 from the National Institutes of Health.

Engineering tetravalent IgGs with enhanced agglutination potencies for trapping vigorously motile sperm in mucin matrix

Multivalent antibodies such as sIgA can crosslink motile entities such as sperm and bacteria, creating agglomerates that are too large to permeate the dense mucin matrix in mucus, a process commonly referred to as immune exclusion. Unfortunately, sIgA remains challenging to produce in large quantities, and easily aggregates, which prevented their use in clinical applications. To develop sIgA-like tetravalent antibodies that are stable and can be easily produced in large quantities, we designed two IgGs possessing 4 identical Fab domains, with the Fabs arranged either in serial or in the diametrically opposite orientation. As a proof-of-concept, we engineered these tetravalent IgG constructs to bind a ubiquitous sperm antigen using a Fab previously isolated from an immune infertile woman. Both constructs possess at least 4-fold greater agglutination potency and induced much more rapid sperm agglutination than the parent IgG, while exhibiting comparable production yields and identical thermostability as the parent IgG. These tetravalent IgGs offer promise for non-hormonal contraception and underscores the multimerization of IgG as a promising strategy to enhance antibody effector functions based on immune exclusion.

The importance of semen leukocytes in HIV-1 transmission and the development of prevention strategies

HIV-1 sexual transmission occurs mostly through contaminated semen, which is a complex mixture of soluble factors with immunoregulatory functions and cells. It is well established that semen cells from HIV-1-infected men are able to produce the virus and that are harnessed to efficiently interact with mucosal barriers exposed during sexual intercourse. Several cofactors contribute to semen infectivity and may enhance the risk of HIV-1 transmission to a partner by increasing local HIV-1 replication in the male genital tract, thereby increasing the number of HIV-1-infected cells and the local HIV-1 shedding in semen. The introduction of combination antiretroviral therapy has improved the life expectancy of HIV-1 infected individuals; however, there is evidence that systemic viral suppression does not always reflect full viral suppression in the seminal compartment. This review focus on the role semen leukocytes play in HIV-1 transmission and discusses implications of the increased resistance of cell-mediated transmission to immune-based prevention strategies.

Role of Seminal Plasma in Human Female Reproductive Failure: Immunomodulation, Inflammation, and Infections

Human seminal plasma contains factors that can regulate the female immune system and potentially promote reproductive fitness. Adverse effects on fertility and pregnancy may occur when seminal plasma provides insufficient, excessive, or altered signals or when the female partner is incapable of receiving these signals.

Application of automation and information systems to forensic genetic specimen processing

During the last 10 years, the introduction of PCR-based DNA typing technologies in forensic applications has been highly successful. This technology has become pervasive throughout forensic laboratories and it continues to grow in prevalence. For many criminal cases, it provides the most probative evidence. Criminal genotype data banking and victim identification initiatives that follow mass-fatality incidents have benefited the most from the introduction of automation for sample processing and data analysis. Attributes of offender specimens including large numbers, high quality and identical collection and processing are ideal for the application of laboratory automation. The magnitude of kinship analysis required by mass-fatality incidents necessitates the application of computing solutions to automate the task. More recently, the development activities of many forensic laboratories are focused on leveraging experience from these two applications to casework sample processing. The trend toward increased prevalence of forensic genetic analysis will continue to drive additional innovations in high-throughput laboratory automation and information systems.

Expeditious chemoenzymatic synthesis of CD52 glycopeptide antigens

CD52 is a glycosylphosphatidylinositol (GPI)-anchored glycopeptide antigen found on sperm cells and human lymphocytes. Recent structural studies indicate that sperm-associated CD52 antigen carries both a complex type N-glycan and an O-glycan on the polypeptide backbone. To facilitate functional and immunological studies of distinct CD52 glycoforms, we report in this paper the first chemoenzymatic synthesis of homogeneous CD52 glycoforms carrying both N- and O-glycans. The synthetic strategy consists of two key steps: monosaccharide primers GlcNAc and GalNAc were first installed at the pre-determined N- and O-glycosylation sites by a facile solid-phase peptide synthesis, and then the N- and O-glycans were extended by respective enzymatic glycosylations. It was found that the endoglycosidase-catalyzed transglycosylation allowed efficient attachment of an intact N-glycan in a single step at the N-glycosylation site, while the recombinant human T-synthase could independently extend the O-linked GalNAc to form the core 1 O-glycan. This chemoenzymatic approach is highly convergent and permits easy construction of various homogeneous CD52 glycoforms from a common polypeptide precursor. In addition, the introduction of a latent thiol group in the form of protected cysteamine at the C-terminus of the CD52 glycoforms will enable site-specific conjugation to a carrier protein to provide immunogens for generating CD52 glycoform-specific antibodies for functional studies.

Identification of bovine CD52-like molecule by monoclonal antibody IVA-543: distribution of CD52-like molecule in the bull genital tract

The bovine maturation-associated sperm membrane antigen CD52-like molecule has been analysed using a mouse anti-sperm monoclonal antibody developed against bull spermatozoa. The antigen recognised by monoclonal antibody IVA-543 was detected on blood mononuclear cells (including lymphocytes and monocytes) and on a minor population of polymorphonuclear leukocytes. The bovine CD52-like molecule is secreted by the epididymal epithelium and then it is inserted into the sperm membrane during the epididymal transport in the distal part of epididymis. The CD52-like molecule was absent from spermatozoa derived from testes, and the highest proportion of IVA-543-reactive sperm was observed in the cauda epididymis (91.6%). This study has shown that the new molecule identified on bovine cells has properties analogous to those previously described for CD52 molecules in man, mouse, rat, monkey, and dog.

The GPI-anchored CD52 antigen of the sperm surface interacts with semenogelin and participates in clot formation and liquefaction of human semen

CD52 is a human glycosylphosphatidylinositol (GPI)-anchored antigen exclusively expressed in leukocytes and epididymal cells. It is also present in sperm, being inserted in their plasma membrane as they pass through the epididymis. In a previous paper we identified a new CD52 form without GPI anchor by fast performance liquid chromatography (FPLC) fractionation of semen components. The form has a lower negative charge than the GPI-anchored form and occurs as the only CD52 form in prostasome-free seminal plasma. It was also found associated with the ejaculated sperm, but in contrast to the GPI-anchored one, it is lost during the capacitation process. In this paper we indicate that (1) the GPI-anchored CD52 of the sperm surface serves as receptor for semenogelin I during clot formation, (2) liquefaction involves cleavage of the GPI anchor from certain CD52 molecules, releasing sperm from the clot and the soluble antigen bound to semenogelin fragments into the seminal plasma and (3) the clot is a sponge-like structure housing sperm. Soluble CD52 was immunopurified from the soluble CD52-containing FPLC fraction using CAMPATH-1G and was found to be complexed with a semenogelin-derived peptide of the carboxyl terminal portion of semenogelin I, having the sequence SQTEKLVAGKQI and starting from amino acid 376. Immunoprecipitation and immunoblot analyses using CAMPATH-1G and anti-semenogelin as immunoprecipitating antibodies and anti-gp20 and anti-semenogelin as immunoblot detectors of the corresponding antigens, confirmed that the soluble CD52 formed a complex with semenogelin. The semenogelin-CD52 soluble form was found to be a direct consequence of the liquefaction process since only the GPI-anchored CD52 was recovered in uniquefied semen after recovering sperm and seminal plasma by urea solubilization of the clot.

The sperm agglutination antigen-1 (SAGA-1) glycoforms of CD52 are O-glycosylated

CD52 is composed of a 12 amino acid peptide with N-linked glycans bound to the single potential glycosylation site at position 3, and a glycosylphosphatidylinositol-anchor attached at the C-terminus. Some glycoforms of this molecule expressed in the male reproductive tract are recognized by complement-dependent sperm-immobilizing antibodies in infertile patients making this antigen an important target for immunocontraception and fertility studies. Although the amount of posttranslational modification is already remarkable for such a small polypeptide, O-glycosylation of CD52 has additionally been implicated by several studies, but never rigorously characterized. In this report, we show clear evidence for the presence of O-glycans in CD52 preparations immunopurified using the murine S19 monoclonal antibody generated against sperm agglutination antigen-1 (SAGA-1), a male reproductive tract specific form of CD52. The O-glycans have been characterized by MALDI-TOF and tandem mass spectrometry after reductive elimination and permethylation. The data indicate that the major SAGA-1 O-glycans are core 1 and 2 mucin-type structures, with and without sialic acid (NeuAc(0-2)Hex(1-3)HexNAc(1-2)HexNAcitol). Minor fucosy- lated O-glycans are also present including some struc- tures with putative Le(y) epitopes (NeuAc(0-1)Fuc(1-3)Hex(1-2) HexNAc(0-1)HexNAcitol). Analysis of O-glycopeptides by tandem mass spectrometry provided an additional level of support for the O-glycosylation of SAGA-1. Elucidation of the O-glycosylation of SAGA-1 adds to the complexity of this molecule and may help to explain its biological activity.

Antisperm antibodies and conception

Sperm have been known to be antigenic for more than a century. There is a strong body of evidence that in humans and in other species at least some antibodies that bind to sperm antigens can cause infertility. Therefore, these antibodies are of interest today for two practical reasons. Firstly, the association of the antibodies with infertility means that they must be detected and then the couples treated appropriately. Secondly, because these antibodies can induce infertility they have the potential to be developed for contraceptive purposes in humans and also for the control of feral animal populations.

Different glycoforms of the human GPI-anchored antigen CD52 associate differently with lipid microdomains in leukocytes and sperm membranes

CD52 is a human GPI-anchored antigen, expressed exclusively in the immune system and part of the reproductive system (epididymal cells). Sperm cells acquire the antigen from the epididymal secretions when transiting in the epididymal corpus and cauda. The peptide backbone of CD52, consisting of only 12 aminoacids, is generally considered no more than a scaffold for post-translational modifications, such as GPI-anchor and especially N-glycosylation which occur at the third asparagine. The latter modification is highly heterogeneous, especially in the reproductive system, giving rise to many different glycoforms, some of which are tissue specific. A peculiar O-glycan-containing glycoform is also found in reproductive and immune systems. We determined to locate CD52 in microdomains of leukocytes and sperm membranes using two antibodies: (1) CAMPATH-1G, the epitope of which includes the last three aminoacids and part of the GPI-anchor of glycoforms present in leukocytes and sperm cells; (2) anti-gp20, the epitope of which belongs to the unique O-glycan-bearing glycoform also present in both cell types. Using a Brij 98 solubilization protocol and sucrose gradient partition we demonstrated that the CD52 glycoforms recognized by both antibodies are markers of typical raft microdomains in leukocytes, whereas in capacitated sperm the O-glycoform is included in GM3-rich microdomains different from the cholesterol and GM1-rich lipid rafts with which CAMPATH antigen is stably associated. The importance of the association between GM3 and O-glycans for formation of specialized microdomains was confirmed by heterologous CD52 insertion experiments. When prostasomes from human seminal fluid were incubated with rat sperm from different epididymal regions, the CD52 glycoform recognized by anti-gp20 decorated rat epididymal corpus and cauda sperm, associated with the same low-cholesterol GM3-rich sperm membrane fractions as in human sperm. The glycoforms recognized by CAMPATH-1G were not found in rat sperm. The relationship between this differential insertion and differences in glycosylation of rat and human CD52 is discussed.

Expression of gp20, a human sperm antigen of epididymal origin, is reduced in spermatozoa from subfertile men

gp20, a sialylglycoprotein of human sperm homologous to CD52, is present everywhere on the surface of the freshly ejaculated sperm but is prevalently localized in the equatorial region of the head of capacitated sperm. In the present study, we confirmed this feature on large scale and correlated equatorial exposure of the antigen to the presence of serum albumin (SA) in the capacitation medium. Furthermore, we analyzed the relationship between the presence of the antigen and its equatorial exposure after capacitation and fertility, by comparing immunostaining for gp20 in the motile fraction of spermatozoa from fertile and subfertile men. A significantly higher percentage of nonimmunostained spermatozoa before capacitation (38.5% +/- 23 vs. 12% +/- 7, P < 0.0001) and a lower increase in the percentage of sperm with equatorial localization after capacitation (19.3% +/- 25 vs. 34.6% +/- 22, P = 0.039) were observed in subfertile men (n = 60) compared to fertile men (n = 15). In the whole study group, a positive correlation was also found between the percentage of spermatozoa exhibiting equatorial localization in capacitated samples and normal head forms (R = 0.50; P < 0.0001).