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. Author manuscript; available in PMC: 2010 Jan 1.
Published in final edited form as: Am J Reprod Immunol. 2009 Jan;61(1):11–18. doi: 10.1111/j.1600-0897.2008.00663.x

Status of Contraceptive Vaccines

Rajesh K Naz 1
PMCID: PMC2681263  NIHMSID: NIHMS83963  PMID: 19086987

Abstract

Problem

This is a review of antisperm contraceptive vaccines (CV), and synthesis of human scFv antibodies that can be used as immunocontraceptives.

Method of study

Various methods of proteomics and genomics, peptide synthesis, phage display technology, and antibody engineering were used to obtain multi-epitope vaccines and human scFv antibodies from immunoinfertile and vasectomized men. The present review primarily focuses on the effect of multi-epitope vaccines and Izumo on fertility and synthesis and characterization of sperm specific human scFv antibodies.

Results

The immunization with Izumo peptides causes a contraceptive effect in female mice. The efficacy is enhanced by combination vaccination, including peptides based on other sperm antigens. Using phage display technology, we were able to synthesize at least four novel scFv antibodies with unique complimentarity determining regions (CDRs) that reacted with specific fertility-related sperm antigens. These antibodies inhibited human sperm function in vitro, and their immunocontraceptive effect in vivo is currently being investigated.

Conclusions

The multi-epitope vaccines may provide an efficacious and viable approach to contraception. The human scFv antibodies, if they block fertility in vivo, may provide unique and novel immunocontraceptives, the first of its kind for human use. The multi-epitope CV and preformed engineered antibodies of defined specificity may obliterate the concern related to inter-individual variability of the immune response.

Keywords: Contraception, vaccines, infertility, sperm, scFv antibodies

Introduction

The population explosion and unintended pregnancies continue to pose major public health issues worldwide. The world population has exceeded 6.67 billion1. In the first year AD it was 250 million, which increased to 1 billion by 1830. It took the next 100 years for the population to increase by 1 billion, and at the present rate, it is increasing by 1 billion every 12 years. Ninety-five percent of this growth is in developing nations. In the USA alone, half of all pregnancies are unintended, which results in >1 million elective abortions annually 2,3. These women use some type of contraceptive. This calls for a better method of contraception that is acceptable, effective and available both in the developed and developing nations. An ideal contraceptive method should be highly effective, safe, inexpensive, have a prolonged duration of action, be reversible, require infrequent administration, and can be used privately4. Contraceptive vaccines (CV) have been proposed as valuable alternatives that can fulfill most, if not all, of the properties of an ideal contraceptive. Since the developed and most of the developing nations have an infrastructure for mass immunization, the development of vaccines for contraception is an exciting proposition. The aim of this article is to review the current status of contraceptive vaccines, with special emphasis on vaccines targeting sperm.

Discussion

Several targets are being investigated in various laboratories for the development of CVs. These can be divided into three main categories: CV targeting gamete production, gamete function and gamete outcome5. The molecules targeting gamete production include luteinizing hormone-releasing hormone (LHRH/GnRH), FSH: gamete function includes sperm antigens and oocyte zona pellucida (ZP), and the gamete outcome targets primarily HCG molecule. CV targeting gamete production have shown varied degrees of efficacy; however, they either affect sex steroids and/or show only a partial 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 an inhibition of increased secretions of sex steroids, such as in uterine fibroids, polycystic ovary syndrome, endometriosis and precocious puberty. CVs targeting gamete function such as sperm antigens and ZP proteins are exciting choices. Vaccines based on ZP proteins are quite efficacious in producing contraceptive effects, but may induce oophoritis, affecting sex steroids in many species. They have been successfully tested in controling 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 have focused on the HCG molecule. The HCG vaccine is the first vaccine to undergo Phase I and II clinical trials in humans6, and efficacy and lack of toxicity have been reasonably well demonstrated for this vaccine. At the present time, studies are focused on increasing the immunogenicity and efficacy of this birth control vaccine, and examining its clinical applications in various HCG-producing cancers.

Of all potential targets, sperm have drawn considerable attention, and a sperm vaccine represents an exciting proposition for contraception. The rationale and feasibility for the development of a sperm vaccine is strong. Sperm have both auto- and isoantigenic potentials and can therefore form antibodies in both men and women. Antisperm antibodies (ASA) affect fertilization and fertility both in vitro and in vivo by several mechanisms, including inhibition of sperm capacitation, acrosome reaction and sperm-zona interaction and penetration. Up to 70% of vasectomised men produce ASA, 7 and 2-30% of cases of infertility may be associated with the presence of ASA in the male and/or female partner of an infertile couple. 8 Deliberate immunization of male or female animals of various species,9,10,11 including humans (both women and men),12,13 with sperm antigens causes development of ASA, leading to infertility. Baskin12, injected 20 fertile women, who had at least one prior pregnancy, with their husband's semen and these women developed antibodies and no conception was reported for up to 1 year of observation. A US patent was issued for this spermatoxic vaccine in 1937 (US patent number 2103240). Thus, spermatozoa can generate an immune response that is capable of inducing a contraceptive state. However, the whole spermatozoon per se cannot be used for development of a vaccine because of the presence of several antigens that are likely to be shared with various somatic cells. 14 Only those antigens that are sperm specific can be employed for CV development. The application of a sperm antigen in CV is contingent upon its sperm specificity, surface expression, involvement in fertility, and ability to raise high titer antibodies to be capable of intercepting fertility. If an antigen is also involved in human immunoinfertility, it is an especially attractive candidate. The immunoinfertile patients who have ASA are healthy individuals without any disease concomitant with infertility. The sperm-ZP binding site constitutes the most attractive target for immunocontraception.

Several technologies of genomics and proteomics have been employed to delineate sperm antigens that play a role in fertilization/fertility and can be used for the CV development. While several sperm genes/antigens have been delineated, cloned, and sequenced, and antibodies to some of these antigens affect sperm function/fertilization in vitro, only immunization with a few of them cause a contraceptive effect in vivo in animal models. Notable among these are FA-115, YLP1216, P10G17, A9D18, and SP5619. Most of these active immunization studies were carried out in the mouse model. The findings of these studies are summarized in Table I. No study has achieved 100% reduction after immunization with any of the antigens. The maximum reduction in fertility after immunization with any antigen is up to ˜75%. It remains to be seen whether this reduction in fertility in the mouse model translates to a 100% reduction in humans. The female mouse ovulates several (approximately 20-50) eggs every cycle and a woman ovulates typically 1 egg every cycle. Therefore, there are differences between the mouse and human. It is possible that ˜75% reduction in fertility in the mouse model translates to a 100% block in humans. This may be due to an inherent nature of the mouse model that it is challenging to make mice completely infertile. However, after active immunization or deleting a single gene, one does find a few mice that are totally infertile.

Table I.

Active Immunization with Sperm Peptides on Fertility

Peptide a.a. (n) Fertility Reduction Reference
A. Mouse



rFA-1 Whole
molecule
71% Naz and Zhu15
YLP12 12 70% Naz and Chauhan16
P10G 10 >70% O'Rand et al17
A9D 9 50% Lea et al18
SP56
16
>70%
Hardy and Mobbs19
B. Primates



LDH-C4-bC5-19 15 62% O'Hern et al20
LDH-C4-bC5-19 15 0% Tollner et al21
rEppin Whole
molecule
78% O'Rand et al22

At the present time, no sperm antigen has undergone a phase I/II clinical trial in humans. Two studies have examined the effect of sperm antigen vaccination in a non-human primate model. One study reported reduced fertility of female baboons after immunization with LDH-C420. However, a study by another group found no effect on fertility in female monkeys after vaccination with LDH-C4.21. The reason for this discrepancy is unclear. In another study, male monkeys were immunized with an epididymal protein designated as epididymal protein inhibitor, (Eppin) 22. After immunization, 78% of male monkeys who developed high anti-Eppin antibody titers became infertile, and 71% of those monkeys recovered fertility after immunization ceased. To maintain high antibody titers, booster injections with Freund's adjuvant have to be administered every 3 weeks for almost an entire duration (691 days) of the study. The potential immunopathological effects of immunization were not investigated. This study indicates that anti-sperm CV can also be developed for men.

Recently, using gene knockout technology, >100 novel testis/sperm genes/proteins have been identified that have a vital role in various aspects of fertility23, 24. Some of these gene knockouts cause a defect in testis development and endocrine milieu, some in spermatogenesis, some in mating behavior, some in sperm structure/function/motility, and others in fertilization. The majority of these knockouts also showed an effect on nonreproductive organs concomitant with an effect on fertility. We performed an extensive database analysis to examine how many of these genes/proteins have the characteristics required for the CV development. The findings revealed that only a few of these genes/proteins are expressed on the surface, thus are amenable to antibody binding. Although the genes/proteins that are not expressed on the surface can provide ideal targets for pharmacological inhibition for contraception, they are not suitable for CV development. Very few, if any, knockouts of a single gene have made mice totally infertile.

The molecules involved in sperm-oocyte membrane fusion are interesting and are being actively examined. Various candidates have been proposed, including DE, cluster of differentiation (CD)4626, equatorin Sperad, sperm acrosomal membrane-associated protein (SAMP)3225, a disintegrin and Metalloprotease (ADAM1), and disintegrin domains (ADAM2 and ADAM 3)27, and CD928. Recently, knockout of a gene, designated as Izumo, was reported that is very interesting29. Izumo is named after a Japanese shrine dedicated to marriage. Izumo gene knockout rendered the mice almost totally infertile29. The male mice produce normal-appearing sperm that bind to and penetrate the ZP but are incapable of fusing with the oocyte membrane. Human sperm also express Izumo protein. Izumo protein is not detectable on ejaculated sperm but becomes detectable after sperm cell undergoes acrosome reaction. Izumo antigen seems to be an interesting molecule because it is not exposed until the sperm cell undergoes acrosome reaction, and the antibodies have to be present at the particular time and space for binding to Izumo antigen.

In order to examine whether or not: 1) proteins involved in sperm-oocyte membrane fusion can be used for CV development, and 2) immunization with multiple antigens can enhance the contraceptive efficacy, we recently conducted a trial by immunizing female mice with various peptides based upon several sperm antigens (Izumo, FA-1, YLP12, and SP56)30. The synthetic peptides were conjugated to four carrier proteins namely keyhole limpet hemocyanin (KLH), bovine serum albumin (BSA), chicken λ-globulin, and chicken ovalbumin. Female mice were immunized with various peptide vaccines and each booster injection was given with the peptide conjugated to a different carrier protein30. Two different fertility trials with different doses of the peptide vaccines were conducted to examine the contraceptive effect. Injection of 150 μg of each peptide caused a significantly higher immune response in serum as well as in the vaginal tract causing enhanced contraceptive effect than those observed after injection with 75 μg of the peptides. Immunization with the Izumo-based peptides, which are involved in sperm-egg plasma membrane fusion, caused a significant reduction in fertility (Table II). The contraceptive effect was enhanced by including peptides based upon other sperm antigens (FA-1, YLP12, and SP56), resulting in an overall 73.33% reduction in fertility. When the antibodies against all the peptides disappeared after >9-10 months from circulation and genital tract, all the animals regained fertility (Table II). These findings indicated for the first time that the immunization with Izumo and other sperm peptides namely FA-1, YLP12, and SP56 induced antibodies in serum and genital tract that cause a reversible long-term contraceptive effect in female mice. The data further indicates that the proteins involved in sperm-egg fusion can also be used for contraceptive vaccine development. The contraceptive effects are enhanced by immunizing with multi-peptide vaccines. Similar effects on enhancement of contraceptive effect after combination vaccination was observed using sperm DNA vaccines31,32. However, even after using multi-epitope vaccines, there was up to 73.3% reduction in fertility, rather than a complete block. This may be due to variability of the immune response among the immunized animals.

Table II.

Effect of Vaccination with Various Sperm Peptides on Fertility of Female Mice

Group Peptides Dose of each
peptide/animal
Pups born/animal (% fertility reduction) (mean ± SD)
92-102 daysa >9-10 monthsa
Group 1 Izumo 150 μg 2.6 ± 2.4 (56.66%)* 6.3 ± 0.8
Group 2 FA-1 and
YLP12
150 μg 3.33 ± 2.3 (45%)* 6.1 ± 1.1
Group 3 Izumo, FA-1,
and YLP12
150 μg 1.6 ± 1.7 (73.33%) 6.4 ± 0.9
Control 6.0 ± 0.4 6.2 ± 1.0
a

Days after last injection

Values with different superscripts are significantly different, P<0.0001; all others are nonsignificant (P>0.05)

The progress in CV development has been delayed due to variability of the immune response after vaccination 5. It is envisaged that this concern may be obliterated by the passive immunization approach using the preformed antibodies. The antibody therapies have been tried and proven to be successful against various infectious diseases, both in animals and humans. Several of these antibodies have become treatment modalities in the clinics 33-35. Phage display technology has been widely used to obtain a variety of engineered antibodies, including single chain variable fragments (scFv) antibodies against several antigens 36-40. ScFv is an antibody fragment that plays a major role in the antigen-binding activity, and is composed of variable heavy (VH) and variable light (VL) chains connected by a peptide linker. The most widely used peptide linker is a repeat of a 15-residue sequence of glycine and serine (Gly4Ser)3. The affinity and stability of the scFv antibodies produced in bacteria are comparable with those of the native antibodies and are maintained by a strong disulfide bond. ScFv antibodies can be produced on a large scale using specially modified bacterial hosts and have an advantage over the whole immunoglobulin (Ig) molecule. ScFv antibodies lack the Fc portion that eliminates unwanted secondary effects associated with Fc, and due to its small size can be easily absorbed into tissues and gene manipulated41. The mouse monoclonal antibody can elicit strong anti-mouse antibody reaction, chimeric antibody can cause anti-chimeric response, and xenogenic complementarity-determining regions (CDRs) of humanized antibodies can also evoke an anti-idiotypic response, when injected into humans42-44. Antibodies must be of human origin if to be used in humans. The potential poor immunogenicity and toxicity of an antigen, and ethical issues, limit immunizing humans to obtain human antibodies. However, the phage display technology can be used to obtain these antibodies against target antigens if they exist involuntarily in humans, such as ASA in immunoinfertile men and women, and vasectomized men.

We recently did a study to obtain fertility-related scFv human antibodies that can be used for CV immunoinfertility. Peripheral blood leukocytes (PBL) were obtained from antisperm antibody-positive immunoinfertile and vasectomized men, activated with human sperm antigens in vitro, and cDNA was prepared from their RNA and PCR-amplified using several primers based on all the available variable regions of VH and VL chains45. The amplified VH and VL chains were ligated and the scFv repertoire was cloned into pCANTAB5E vector to create a human scFv antibody library. Panning of the library against specific antigens yielded several clones, and the four strongest reactive (designated as AFA-1, FAB-7, YLP20, and AS16) were selected for further analysis. These clones were shown to have novel sequences with unique completmentarity determining regions (CDRs) when a search was performed in the immunogenetic database (Table III). ScFv antibodies were expressed, purified, and analyzed for human sperm reactivity and effects on human sperm function. AFA-1 and FAB-7 scFv antibodies, having IgG3 heavy and IgK3 light chains, recognized a specific single sperm protein of 50 ± 4 kD and reacted with the purified and well characterized human sperm FA-1 antigen, which is involved in human sperm function and fertilization (Table IV). These antibodies bound to post-acrosomal, mid-piece, and tail regions of human sperm and inhibited sperm capacitation/acrosome reaction. Although both of these antibodies reacted with FA-1 antigen, they were directed against different epitopes of the molecule. AFA-1 was directed against an antigenic determinant FA-1a (human FA-1200-219 aa/mouse FA-1117-136 aa) and FAB-7 was directed against the determinant FA-1b (human FA-187-97 aa/ mouse FA012-19 aa) of the FA-1 antigen. The third, YLP20 scFv antibody, reacted with a sperm protein of 48 ± 5 kD, which contains the dodecamer sequence, YLPVGGLRIGG. This sequence is present on acrosomal, mid-piece and tail regions of human sperm and is involved in human sperm function and fertilization. The fourth antibody, AS16, reacted with a 18 kD sperm protein (major band) and was found to be a human homolog of the mouse monoclonal recombinant antisperm antibody (RASA)46. RASA is directed against a sperm agglutination antigen-1 (SAGA-1), that causes agglutination of human sperm47. These antibodies inhibited human sperm capacitation/acrosome reaction in a concentration-dependent manner (Table IV). This is the first study to report the use of phage display technology to obtain human antisperm scFv antibodies of defined antigen specificities from immunoinfertile/vasectomized men. These antibodies will find clinical applications in the development of novel immunocontraceptives, and specific diagnostics for immunoinfertility in humans. The contraceptive effect of these antibodies in vivo is currently being investigated.

Table III.

Amino Acid Sequence of CDRs for scFv Antibodies

scFv
antibody
Light chain
Heavy chain
CDR1 CDR2 CDR3 CDR1 CDR2 CDR3
AFA-1 GYIFTSYD IFPGEGST ARGDYYRRYFDLW ASSSIRY DTS QEWSGYPYTF
FAB-7 GYSFTTSS IIYPGDSE ARLPESIPHYYGMDV QSVSSGY GAS QQYGSSPLT
YLP20 GFTVSSSA VVYVDGTT ARSNWHYVTAMYN QSVTMNY AAT QQYGSSPPGVTF
AS16 GYKFTGYW IYPNSGDT DSAVYFCARGDYGCPFVY QSLLHSDRSTY EVS SQSIHVPPT

Table IV.

Immunobiological Parameters of scFv Antibodies

scFv antibody Sperm antigen
recognized
Molecular mass Epitope
sequence
Acrosome-reacted
sperm
AFA-1 FA-1 ∼50 kD Human FA-1200-219 aa/
Mouse FA-1117-136 aa
36 ± 7a
FAB-7 FA-1 ∼50 kD Human FA-182-97 aa/
Mouse FA-12-19 aa
44 ± 6a
YLP20 YLP12 ∼48 kD YLPVGGLRRIGG 42 ± 3a
AS16 SAGA 18 kD (major)
37, 55, 100 kD (minor)
Unknown Unknown
CAB-3 control None None None 74 ± 5
a

Significantly different compared to control, P<0.01 to P<0.001

In conclusion, development of CV targeting sperm is an exciting proposition, and may provide a valuable alternative to the presently available methods. As limitation with other vaccines, the progress in CV development has been delayed due to variability of immune response after vaccination. The multi-epitope vaccines may enhance the efficacy and obliterate the concern of the inter-individual variability of the response. Also, this concern may be addressed by the passive immunization approach using preformed human antibodies. Several antibodies are being tried as therapeutic agents. At the present time, >100 antibodies are in clinical trials and ∼20 FDA-approved monoclonal antibodies are available in the market for various clinical conditions, including cancer and infectious diseases. Over 80% of these antibodies are genetically engineered48,49. The scFv antibodies that we have synthesized in vitro using cDNAs from antisperm antibody-positive immunoinfertile and vasectomized men may provide useful, once-a-month immunocontraceptive. These human antibodies are sperm-specific and inhibit sperm function in vitro. Their immunocontraceptive potential in vivo is presently being investigated.

Acknowledgements

This work was supported by NIH grant HD24425 to RKN. We sincerely thank Alexis R. Engle for helping to prepare the manuscript.

References

  • 1.World POPClock Projection (Accessed on June 18, 2008) US Census Bureau [online] available from URL:http://www.census.gov/main/www/popclock.html/
  • 2.Henshaw SK. Unintended pregnancy in the United States. Fam Plann Perspect. 1998;30:24–29. [PubMed] [Google Scholar]
  • 3.Grow DR, Ahmed S. New Contraceptive Methods. Obstet Gynecol Clin North Am. 2000;27:909–916. doi: 10.1016/s0889-8545(05)70176-5. [DOI] [PubMed] [Google Scholar]
  • 4.Contraception Online . Baylor College of Medicine; Houston Texas: 2004. [online] available from URL: http://contraceptiononline.org/ [Google Scholar]
  • 5.Naz RK, Gupta SK, Gupta JC, Vyas HK, Talwar GP. Recent advances in contraceptive vaccine development: a mini-review. Hum Reprod. 2005;20:3271–3283. doi: 10.1093/humrep/dei256. [DOI] [PubMed] [Google Scholar]
  • 6.Talwar GP, Singh O, Pal R, Chatterjee N, Sahai P, Dhall K, Kaur K, Das SK, Suri S, Bukshee K, Saraya L, Saxena BN. A vaccine that prevents pregnancy in women. Proc Natl Acad Sci. 1994;91:8532–8536. doi: 10.1073/pnas.91.18.8532. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 7.Liskin L, Pile JM, Quillan WF. Vasectomy safe and simple. Popul Rep. 1983;4:61–100. [PubMed] [Google Scholar]
  • 8.Olh D, Naz RK. Infertility due to antisperm antibodies. J Urol. 1995;46:591–602. doi: 10.1016/S0090-4295(99)80282-9. [DOI] [PubMed] [Google Scholar]
  • 9.Allardyce RA. Effect of ingested sperm on fecundity in the rat. J Exp Med. 1984;159:1548–1553. doi: 10.1084/jem.159.5.1548. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 10.Edwards RG. Immunological control of fertility in female mice. Nature. 1964;203:50–53. doi: 10.1038/203050a0. [DOI] [PubMed] [Google Scholar]
  • 11.Menge AC. Immune reactions and infertility. J Reprod Fertil Suppl. 1970;10:171–185. [PubMed] [Google Scholar]
  • 12.Baskin MJ. Temporary sterilization by injection of human spermatozoa: a preliminary report. Am J Obstet Gynecol. 1932;24:892–897. [Google Scholar]
  • 13.Mancini RE, Andrana JA, Saracine D, Bachmann AE, Lavieri JC, Nemirovsky M. Immunological and testicular response in men sensitized with human testicular homogenate. J Clin Endocrinol Metab. 1965;25:859–875. doi: 10.1210/jcem-25-7-859. [DOI] [PubMed] [Google Scholar]
  • 14.Naz RK. Vaccine for contraception targeting sperm. Immunol Rev. 1999;171:193–202. doi: 10.1111/j.1600-065x.1999.tb01349.x. [DOI] [PubMed] [Google Scholar]
  • 15.Zhu X. Recombinant fertilization antigen-1 causes a contraceptive effect in actively immunized mice. Biol Reprod. 1998;59:1095–1100. doi: 10.1095/biolreprod59.5.1095. [DOI] [PubMed] [Google Scholar]
  • 16.Naz RK, Chauhan S. Human sperm-specific peptide vaccine that causes long-term reversible contraception. Biol reprod. 2002;64:674–680. doi: 10.1095/biolreprod67.2.674. [DOI] [PubMed] [Google Scholar]
  • 17.O'Rand MG, Beavers J, Widgren E, Tung K. Inhibition of fertility in female mice by immunization with a B-cell epitope, the synthetic sperm peptide, P10G. Reprod Immunol. 1993;25:89–102. doi: 10.1016/0165-0378(93)90051-i. [DOI] [PubMed] [Google Scholar]
  • 18.Lea IA, van Lierop MJC, Widgren EE, Grootenhuis A, Wen Y, van Duin M, O'Rand MG. A chimeric sperm peptide induced antibodies and strain-specific reversible infertility in mice. Biol Reprod. 1998;59:527–536. doi: 10.1095/biolreprod59.3.527. [DOI] [PubMed] [Google Scholar]
  • 19.Hardy CM, Mobbs JK. Expression of recombinant mouse sperm protein sp56 and assessment of its potential for use as an antigen in an immunocontraceptive vaccine. Mol Reprod Dev. 1999;52:527–536. doi: 10.1002/(SICI)1098-2795(199902)52:2<216::AID-MRD13>3.0.CO;2-R. [DOI] [PubMed] [Google Scholar]
  • 20.O'Hearn PA, Liang ZG, Bambra CS, Goldberg E. Colinear synthesis of an antigen-specific B-cell epitope with a promiscuous tetanus toxin T-cell epitope: a synthetic peptide immunocontraceptive. Vaccine. 1997;15:1761–1766. doi: 10.1016/s0264-410x(97)00105-9. [DOI] [PubMed] [Google Scholar]
  • 21.Tollner TL, Overstreet JW, Branciforte D, Primakoff PD. Immunization of female cynomolgus macaques with a synthetic epitope of sperm-specific lactate dehydrogenase results in high antibody titers but does not reduce fertility. Mol Reprod Dev. 2002;62:257–264. doi: 10.1002/mrd.10063. [DOI] [PubMed] [Google Scholar]
  • 22.O'Rand MG, Widgren EE, Sivashanmugam P, Richardson RT, Hall SH, French FS, Vande Voort CA, Ramachandra SG, Ramesh V, Jagannadha Roa A. Reversible immunocontraception in male monkeys immunized with eppin. Science. 2004;306:1189. doi: 10.1126/science.1099743. [DOI] [PubMed] [Google Scholar]
  • 23.Naz RK, Rajesh C. Novel testis/sperm specific contraceptive targets identified using gene knockout studies. Front Biosci. 2005a;10:2430–2446. doi: 10.2741/1708. [DOI] [PubMed] [Google Scholar]
  • 24.Naz RK, Rajesh P. Gene knockouts that cause female infertility: search for novel contraceptive targets. Front Biosci. 20005b;10:2447–2459. doi: 10.2741/1709. [DOI] [PubMed] [Google Scholar]
  • 25.Stein KK, Primakoff P, Myles D. Sperm-egg fusion: events at the plasma membrane. J Cell Sci. 2004;117:6269–6274. doi: 10.1242/jcs.01598. [DOI] [PubMed] [Google Scholar]
  • 26.Inoue N, Ikawa M, Nakanishi T, Matsumoto M, Nomura M, Seya T, Okabe M. Disruption of mouse CD46 causes an accelerated spontaneous acrosome reaction in sperm. Mol Cell Biol. 2003;23:2614–2622. doi: 10.1128/MCB.23.7.2614-2622.2003. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 27.Cho C, Bunch DO, Faure JE, Goulding EH, Eddy EM, Primakoff P, Myles DG. Fertilization defects in sperm from mice lacking fertilin beta. Science. 1998;281:1857–1859. doi: 10.1126/science.281.5384.1857. [DOI] [PubMed] [Google Scholar]
  • 28.Le Naour F, Rubinstein E, Jasmin C, Prenant M, Boucheix C. Severely reduced female fertility in CD9-deficient mice. Science. 2000;287:319–321. doi: 10.1126/science.287.5451.319. [DOI] [PubMed] [Google Scholar]
  • 29.Inoue N, Ikawa M, Isotani A, Okabe M. The immunoglobin superfamily protein izumo is required for sperm to fuse with eggs. Nature. 2005;434:234–238. doi: 10.1038/nature03362. [DOI] [PubMed] [Google Scholar]
  • 30.Naz RK. Immunocontraceptive effect of Izumo and enhancement by combination vaccination. Mol Reprod Dev. 2008;75:336–344. doi: 10.1002/mrd.20783. [DOI] [PubMed] [Google Scholar]
  • 31.Naz RK. Effect of sperm DNA vaccine on fertility of female mice. Mol Reprod Dev. 2006;73:918–928. doi: 10.1002/mrd.20487. [DOI] [PubMed] [Google Scholar]
  • 32.Naz RK. Effect of fertilization antigen (FA-1) DNA vaccine on fertility of female mice. Mol Reprod Dev. 2006;73:1473–1479. doi: 10.1002/mrd.20591. [DOI] [PubMed] [Google Scholar]
  • 33.Riethmuller G, Schneider-Gadicke E, Johnson JP. Monoclonal antibodies in cancer therapy. Curr Opin Immunol. 1993;5:732–739. doi: 10.1016/0952-7915(93)90129-g. [DOI] [PubMed] [Google Scholar]
  • 34.Casadevall A. Passive antibody therapies: progress and continuing challenges. Clin Immunol. 1999;93:5–15. doi: 10.1006/clim.1999.4768. [DOI] [PubMed] [Google Scholar]
  • 35.Dunman PM, Nessin M. Passive immunization as prophylaxis: When and where will this work? Curr Opin Pharmacol. 2003;20:351–360. doi: 10.1016/j.coph.2003.05.005. [DOI] [PubMed] [Google Scholar]
  • 36.Rader C, Barbas CF. Phage display of combinatorial antibody libraries. Curr Opin Biotechnol. 1997;8:503–508. doi: 10.1016/s0958-1669(97)80075-4. [DOI] [PubMed] [Google Scholar]
  • 37.Ye Z, Hellstrom I, Hayden-Ledbetter M, Dahlin A, Ledbetter JA, Hellstrom KE. Gene therapy for cancer using single-chain Fv fragments specific for 4-1BB. Nat Med. 2002;8:343–348. doi: 10.1038/nm0402-343. [DOI] [PubMed] [Google Scholar]
  • 38.Park KJ, Lee SH, Kim TI, Lee HW, Lee CH, Kim EH, Jang JY, Choi KS, Kwon MH, Kim YS. A human scFv antibody against TRAIL receptor 2 induces autophagic cell death in both TRAIL-sensitive and TRAIL-resistant cancer cells. Cancer Res. 2007;67:7327–7334. doi: 10.1158/0008-5472.CAN-06-4766. [DOI] [PubMed] [Google Scholar]
  • 39.Zhang W, Matsumoto-Takasaki A, Kusada Y, Sakaue H, Sakai K, Nakata M, Fujita-Yamaguchi Y. Isolation and characterization of phage-displayed single chain antibodies recognizing nonreducing terminal mannose residues. 2. Expression, purification, and characterization of recombinant single chain antibodies. Biochem. 2007;46:263–270. doi: 10.1021/bi0618767. [DOI] [PubMed] [Google Scholar]
  • 40.Zhou Y, Drummond DC, Zou H, Hayes ME, Adams GP, Kirpotin DB, Marks JD. Impact of single-chain Fv antibody fragment affinity on nanoparticle targeting of epidermal growth factor receptor expressing tumor cells. J Mol Biol. 2007;371:934–947. doi: 10.1016/j.jmb.2007.05.011. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 41.Yokota T, Milenic DE, Whitlow M, Schlom J. Rapid tumor penetration of a single-chain Fv and comparison with other immunoglobulin forms. Cancer Res. 1992;52:3402–3408. [PubMed] [Google Scholar]
  • 42.Koren E, Zuckerman LA, Mire-Sluis AR. Immune response to therapeutic proteins in humans-clinical significance, assessment and prediction. Curr Pharm Biotechnol. 2002;3:349–360. doi: 10.2174/1389201023378175. [DOI] [PubMed] [Google Scholar]
  • 43.Mirick GR, Bradt BM, Denardo SJ, Denardo GL. A review of human anti-globulin antibody (HAGA, HAMA, HACA, HAHA) responses to monoclonal antibodies. Not four letter words. Q J Nucl Med Mol Imaging. 2004;48:251–257. [PubMed] [Google Scholar]
  • 44.Sidhu SS, Fellouse FA. Synthetic therapeutic antibodies. Nat Chem Biol. 2006;2:682–688. doi: 10.1038/nchembio843. [DOI] [PubMed] [Google Scholar]
  • 45.Samuel AS, Naz RK. Isolation of human single chain variable fragment antibodies against specific sperm antigens for immunocontraceptive development. Hum Reprod. 2008;23:1324–1337. doi: 10.1093/humrep/den088. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 46.Norton EJ, Diekman AB, Westbrook VA, Flickinger CJ, Herr JC. RASA, a recombinant single-chain variable fragment (scFv) antibody directed against the human sperm surface: implications for novel contraceptives. Hum Reprod. 2001;16:1854–1860. doi: 10.1093/humrep/16.9.1854. [DOI] [PubMed] [Google Scholar]
  • 47.Diekman AB, Westbrook-Case VA, Naaby-Hansen S, Klotz KL, Flickinger CJ, Herr JC. Biochemical characterization of sperm agglutination antigen-1, a human sperm specific antigen implicated in gamete interactions. Biol Reprod. 1997;57:1136–1144. doi: 10.1095/biolreprod57.5.1136. [DOI] [PubMed] [Google Scholar]
  • 48.Holliger P, Hudson PJ. Engineered antibody fragments and the rise of single domains. Nat Biotech. 2005;23:1126–1136. doi: 10.1038/nbt1142. [DOI] [PubMed] [Google Scholar]
  • 49.Marasco WA, Sui J. The growth and potential of human antiviral monoclonal antibody therapeutics. Nat Biotech. 2007;25:1421–1434. doi: 10.1038/nbt1363. [DOI] [PMC free article] [PubMed] [Google Scholar]

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