Influence of early ICSI-derived embryo sHLA-G expression on pregnancy and implantation rates: a prospective study

Molecular regulators of human blastocyst development and hatching: Their significance in implantation and pregnancy outcome

In humans, blastocyst hatching and implantation events are two sequential, critically linked and rate-limiting events for a prospective pregnancy. These events are regulated by embryo-endometrium derived molecular factors which include hormones, growth factors, cytokines, immune-modulators, cell adhesion molecules and proteases. Due to poor viability of blastocysts, they fail to hatch and implant, leading to a low 'Live Birth Rates', majorly contributing to infertility. Here, embryo-derived biomarkers analysis plays a key role to assess potential biological viability of blastocysts which are capable of implantation and prospective pregnancy. Thus far, embryo-derived biomarkers examined are mostly immune-modulators which are thought to be associated with blastocyst development-implantation and progression of pregnancy, leading to live births. There is an urgent need to develop a quantitative and a reliable non-invasive approach aiding embryo selection for elective single embryo transfer and to minimize recurrent pregnancy loss and multiple pregnancies. In this article, we provide a comprehensive review on our current knowledge and understanding of potential embryo-derived molecular regulators, that is, biomarkers, of development of human blastocysts, their hatching and implantation. We discuss their potential implications in the assessment of blastocyst implantation potential and pregnancy outcome in terms of live births in humans.

Soluble human leukocyte antigen-G is a potential embryo viability biomarker and a positive predictor of live-births in humans

PROBLEM

Human infertility affects 15-20% of reproductive-age couples and it is mitigated by assisted reproductive technology (ART) approaches. Poor biological viability of embryos contributes to implantation failure and live birth rate (LBR). This study is aimed to examine whether or not embryo-secreted soluble human leukocyte antigen-G (sHLA-G) is (i) associated with developing embryos and (ii) able to predict successful pregnancy outcome.

METHOD OF STUDY

A retrospective, multicentric study using 539 human embryo spent medium samples (E-SMs), analysed for sHLA-G levels by ELISA. Correlation analysis was performed on sHLA-G levels with developing embryonic stages, their quality scores and pregnancy outcome in terms of LBR.

RESULTS

Of 539 E-SMs analysed, 445 had detectable sHLA-G (83%) with levels varying within and across clinics and, between stages of embryonic development. Levels of sHLA-G (ng/mL) were significantly (P < .05) different in E-SMs of cleavage-stage embryos versus blastocysts. There was an insignificant correlation between the sHLA-G levels and morphology scores of embryos. But, sHLA-G levels showed a positive correlation with grades of blastocysts and importantly, its levels were significantly (P < .05) higher in live-birth vis-a-vis no-birth cases. Also, levels were higher in live-births out of blastocysts-ETs versus cleavage-stage-embryo transfers. Altered levels were observed with embryos, which resulted in miscarriages. Overall, a significant (P < .0001) association of sHLA-G with live births was observed.

CONCLUSION

Embryo-derived sHLA-G can be a valuable embryo viability, independent, biomarker, which can predict live-birth outcome and it could be useful as an adjunct to existing criteria for elective single embryo transfer.

Evaluation of Maternal Serum sHLA-G Levels for Trisomy 18 Fetuses Screening at Second Trimester

Human leukocyte antigen-G (HLA-G) has been widely acknowledged to play critical roles in fetal-maternal maintenance. However, the significance of using maternal serum sHLA-G to detect prenatal chromosomal abnormality has not been investigated. In China, prenatal screening using maternal α-fetoprotein (AFP), unconjugated estriol (uE3), and free β subunit human chorionic gonadotropin (β-hCG) in the second trimester has been widely applied. In this study, we evaluated the use of sHLA-G as a screening marker, compared with traditional second trimester prenatal screening. Serum samples from 1,019 singleton women in their second trimester were assessed. Among them, 139 infants were confirmed with trisomy 21 (T21) by karyotyping, 83 were confirmed with trisomy 18 (T18), and the remaining 797 infants had no abnormalities. The sHLA-G levels in maternal sera were significantly lower in pregnant women with T18 fetuses (median: 47.8 U/ml, range: 9.8-234.2 U/ml) and significantly higher in those with T21 fetuses (median: 125.7 U/ml, range: 28.7-831.7 U/ml), compared with the normal controls (median: 106.3 U/ml, range: 50.5-1136.4 U/ml) (p < 0.001). The risk values of the screening of T21 or T18 fetuses were assessed using mean and standard deviation log₁₀ analyte multiples of median (MoM) which showed that the predictive values of sHLA-G were the same as free β-hCG, and superior to AFP and uE3 for T18 screening. Logistic regression analysis revealed that sHLA-G MoM was the highest risk factor associated with pregnant women carrying T18 fetuses [Exp(B): 171.26, 95% CI: 36.30-807.97, p < 0.001]. Receiver operating characteristic (ROC) analysis revealed that the area under ROC curve for sHLA-G MoM was 0.915 (95% CI, 0.871-0.959, p < 0.001), for AFP MoM was 0.796 (95% CI, 0.730-0.861, p < 0.001), for free β-hCG MoM was 0.881 (95% CI, 0.829-0.934, p < 0.001), and for uE3 MoM was 0.876 (95% CI, 0.828-0.923, p < 0.001) in the T18 group. sHLA-G MoM demonstrated the best sensitivity and negative predictive value. For the first time, our findings reveal that sHLA-G is a better second trimester screening marker for the detection of T18 fetuses and the combined application of sHLA-G with AFP, free β-hCG, and uE3 could improve clinical screening for T18 fetuses.

Comparison between embryos transferred with self-spent and fresh medium on reproductive outcomes: a prospective randomized trial

As the final and critical step in in vitro fertilization (IVF), embryo transfer has always received much attention and deserves continuous optimization. In the present study, to explore the role of autocrine factors in embryo self-spent culture media, we prospectively compared embryo transfer with self-spent culture medium and fresh medium on clinical pregnancy outcomes. A total of 318 fresh IVF/intracytoplasmic sperm injection (ICSI) cycles were randomly allocated into two subgroups based on their transfer media (using a self-spent culture medium or new pre-equilibrated culture media), and the clinical outcomes were compared between groups. The implantation rates, clinical pregnancy rates and live birth rates for transfer using self-spent medium instead of new pre-equilibrated culture medium were slightly improved without statistical significance. Interestingly, however, biochemical pregnancy rate was found to be significantly decreased after transfer using self-spent medium for Day 3 embryos compared with new pre-equilibrated culture media. In short, embryo transfer with self-spent culture medium has shown some advantages, and large sample size studies are still needed to confirm these observations.

ABBREVIATIONS

ART: assisted reproductive technologies; ICSI: intracytoplasmic sperm injection; IVF: in vitro fertilization; ET: embryo transfer.

The effect of the biochemical marker soluble human leukocyte antigen G on pregnancy outcome in assisted reproductive technology--a multicenter study

OBJECTIVE

To determine whether the presence of soluble human leukocyte antigen G (sHLA-G) affects implantation and pregnancy outcomes in vitro.

DESIGN

A multicenter retrospective study.

SETTING

Six certified in vitro fertilization (IVF) units.

PATIENT(S)

Embryos obtained from 2,040 patients from six different IVF clinics.

INTERVENTION(S)

Soluble HLA-G determination on day-2 embryos after intracytoplasmic sperm injection, with embryos transferred on day 3 using the sHLA-G data.

MAIN OUTCOME MEASURE(S)

Ongoing pregnancy rate (10- to 12-week ultrasound finding).

RESULT(S)

All embryos were individually cultured, and a chemiluminescence enzyme-linked immunosorbent assay was used to detect the presence of sHLA-G in the culture medium surrounding the embryos. Embryos were selected based on a positive sHLA-G result and a graduated embryo scoring (GES) score >70, or on embryo morphology if the test was negative. In all centers, a positive sHLA-G result was associated with an increase in the odds of an ongoing pregnancy. The incidence of an ongoing pregnancy was 2.52 times greater in embryos transferred on day 3 with a positive sHLA-G test result than the incidence of an ongoing pregnancy in embryos with a negative sHLA-G test result.

CONCLUSION(S)

Data from this multicenter study confirm that sHLA-G expression is a valuable noninvasive embryo marker to assist in improving pregnancy outcomes, with the theoretical potential to reduce multiple pregnancies.

The importance of HLA-G expression in embryos, trophoblast cells, and embryonic stem cells

The nonclassical HLA-G molecule is a trophoblast-specific molecule present in almost every pregnancy. It differs from classical HLA class I molecules by the low degree of allelic variants and the high diversity of protein structures. HLA-G is reported to be a tolerogenic molecule that acts on cells of both innate and adaptive immunity. At the maternal-fetal interface HLA-G seems to be responsible largely for the reprogramming of local maternal immune response. This review will focus on the HLA-G gene expression profile in pregnancy, in preimplantation embryos, and in human embryonic stem cells with emphasis on the structural diversity of the HLA-G protein and its potential functional and diagnostic implications.

Amniotic fluid soluble human leukocyte antigen-G in term and preterm parturition, and intra-amniotic infection/inflammation

OBJECTIVE

Circulating soluble human leukocyte antigen-G (sHLA-G) has been associated with pregnancy complications, and determination of sHLA-G concentrations in amniotic fluid (AF) has been reported in normal pregnancies. Our aim was to determine if the AF concentrations of sHLA-G change with advancing gestation, spontaneous labor at term, and in patients with spontaneous preterm labor (PTL) with intact membranes, as well as in those with preterm prelabor rupture of membranes (PROM), in the presence or absence of intra-amniotic infection/inflammation (IAI).

STUDY DESIGN

This cross-sectional study included the following groups: (1) mid-trimester (n = 55); (2) normal pregnancy at term with (n = 50) and without (n = 50) labor; (3) spontaneous PTL with intact membranes divided into: (a) PTL who delivered at term (n = 153); (b) PTL who delivered preterm without IAI (n = 108); and (c) PTL with IAI (n = 84); and (4) preterm PROM with (n = 46) and without (n = 44) IAI. sHLA-G concentrations were determined by ELISA. Non-parametric statistics were used for analysis.

RESULTS

(1) Among patients with PTL, the median AF sHLA-G concentration was higher in patients with IAI than in those without IAI or women that delivered at term (p < 0.001 for both comparisons); (2) Similarly, patients with preterm PROM and IAI had higher median AF sHLA-G concentrations than those without IAI (p = 0.004); (3) Among patients with PTL and delivery, those with histologic chorioamnionitis and/or funisitis had a higher median AF sHLA-G concentration than those without histologic inflammation (p < 0.001); and (4) The median AF sHLA-G concentration did not change with advancing gestational age.

CONCLUSIONS

AF sHLA-G concentrations are elevated in preterm parturition associated to IAI as well as in histologic chorioamnionitis. We propose that sHLA-G may participate in the regulation of the host immune response against intra-amniotic infection.

Soluble HLA-G in IVF/ICSI embryo culture supernatants does not always predict implantation success: a multicentre study

Several reports have described an association between the presence of soluble human leukocyte antigen G (sHLA-G) in human embryo culture supernatants (ES) and implantation success. However, not all studies agree with these findings. To further document this debate, a multicentre blinded study was performed to investigate, on a large number of IVF ES and ICSI ES, whether sHLA-G is a useful criterion for embryo selection before transfer. A total of 1405 ES from 355 patients were collected from three assisted reproductive technique (ART) centres and evaluated for their sHLA-G content in a single laboratory, using a chemiluminescence enzyme-linked immunosorbent assay. In only one centre was a significant association between sHLA-G-positive ES and successful implantation established (P = 0.0379), whereas no such association was observed in the other centres. It was found that the percentages and concentrations of sHLA-G-positive ES varied between centres, depending on culture media and ART conditions. The percentage of sHLA-G-positive ES was significantly higher in IVF ES than ICSI ES (P < 0.001 and P < 0.01 for two centres). These data demonstrate that substantial variations of sHLA-G content in ES occur between different ART centres, highlighting the influence of several technical parameters that differ from one centre to another.

Symposium: innovative techniques in human embryo viability assessment. Soluble human leukocyte antigen-G and pregnancy success

Non-invasive methods of assessing embryo quality are critical for pregnancy success following IVF or intracytoplasmic sperm injection (ICSI). The addition of new non-invasive morphological and biochemical analyses may further improve pregnancy success, allowing the transfer of a single embryo, thereby reducing the risks involved in multiple births following IVF/ICSI. The presence of a protein, soluble human leukocyte antigen-G (sHLA-G), in embryo cultures has been suggested as a way to non-invasively predict embryo quality and pregnancy success, especially when used in conjunction with current embryo quality assessment methods. Detection of sHLA-G in embryo culture medium has been correlated with pregnancy success in 12 studies, but three studies were not able to detect sHLA-G. This is a review of the literature on sHLA-G detection in IVF/ICSI, and reasons are proposed for the reported discrepancies, as well as guidelines for reporting of data in future studies. Furthermore, it is suggested that the use of an HLA-G transgenic mouse model would advance understanding of the mechanism of action of sHLA-G in preimplantation embryos and its correlation to embryo health and viability. Research on a mouse model, combined with clinical studies, should enable the development of a fast and reliable method for utilizing sHLA-G detection to improve pregnancy success after IVF/ICSI.

Release of sICAM-1 in oocytes and in vitro fertilized human embryos

Background

During the last years, several studies have reported the significant relationship between the production of soluble HLA-G molecules (sHLA-G) by 48–72 hours early embryos and an increased implantation rate in IVF protocols. As consequence, the detection of HLA-G modulation was suggested as a marker to identify the best embryos to be transferred. On the opposite, no suitable markers are available for the oocyte selection.

Methodology/Principal Findings

The major finding of the present paper is that the release of ICAM-1 might be predictive of oocyte maturation. The results obtained are confirmed using three independent methodologies, such as ELISA, Bio-Plex assay and Western blotting. The sICAM-1 release is very high in immature oocytes, decrease in mature oocytes and become even lower in in vitro fertilized embryos. No significant differences were observed in the levels of sICAM-1 release between immature oocytes with different morphological characteristics. On the contrary, when the mature oocytes were subdivided accordingly to morphological criteria, the mean sICAM-I levels in grade 1 oocytes were significantly decreased when compared to grade 2 and 3 oocytes.

Conclusions/Significance

The reduction of the number of fertilized oocytes and transferred embryos represents the main target of assisted reproductive medicine. We propose sICAM-1 as a biochemical marker for oocyte maturation and grading, with a possible interesting rebound in assisted reproduction techniques.

HLA-G gene polymorphism in human placentas: possible association of G*0106 allele with preeclampsia and miscarriage

Definite causes for several pathologies of pregnancy remain unknown. In light of several recent studies, however, diminished or aberrant HLA-G expression may be associated with certain complication of pregnancy and be linked to HLA-G polymorphism. We analyzed DNA from 60 normal placentas (controls), 140 placentas from miscarriage, 36 placentas from preeclampsia, 76 placentas from fetal hypotrophy, and 34 placentas with hypoxia for variations in coding regions (allelic groups G*0101 to G*0107) and the 14-bp deletion/insertion into the 3'-untranslated region. No statistically significant differences were observed in the distribution of allelic group between pathological placentas and controls with the exception of G*0106 allele frequency in preeclamptic compared with control placentas (21.2% and 6.6%, respectively). A greater frequency of this allele also was observed in the two subgroups of miscarriage and hypoxia compared with that in controls. In addition, presence of the 14-bp sequence was prominent in preeclampsia compared with controls (60.8% vs. 35%, respectively), and homozygotes with deletion were not detected in the pathology. The results suggest that the G*0106 allele, which is coupled with the presence of the 14-bp sequence, contributes and/or is a relevant marker in some specific complications of pregnancy, especially preeclampsia.

Accuracy of soluble human leukocyte antigen-G for predicting pregnancy among women undergoing infertility treatment: meta-analysis

BACKGROUND

There have been concerns about validity and accuracy of the measurement of sHLA-G in embryo culture supernatants. In this systematic review, we quantified the diagnostic accuracy of sHLA-G for predicting the ability to achieve clinical pregnancy in women who are undergoing infertility treatment.

METHODS

Medline and Embase were searched up to 7 September 2007, for full English and non-English articles concerning cohort studies evaluating sHLA-G in embryo culture for predicting clinical pregnancy in women undergoing IVF and ICSI.

RESULTS

Eleven studies including 1813 patients met our inclusion criteria. In the individual studies, sensitivity ranged from 0.01 to 0.97, specificity from 0.18 to 0.98, the positive likelihood ratio from 0.34 to 3.21 and the negative likelihood ratio from 0.08 to 1.01. These values were highly heterogeneous with, in each case, I(2) values of >75%, and P-values for the Q statistic of <0.001, arguing against generating a pooled estimate for these diagnostic test properties. The diagnostic odds ratios (DORs) ranged from 0.92 to 24.82 in the individual studies with an I(2) value of 49% indicating moderate heterogeneity. Therefore, the meta-analysis combined the logs of the DORs, which are derived from sensitivity and specificity. A random-effects model yielded a summary DOR of 4.38 (95% CI, 2.93-6.55), consistent with modest diagnostic accuracy. Interestingly, an a priori defined subgroup analysis restricted to six studies with good quality embryos showed a better diagnostic performance with a DOR of 12.67 (95% CI, 3.66-43.80) to predict the ability to achieve clinical pregnancy in women undergoing infertility treatment.

CONCLUSIONS

Further research is needed with single-embryo culture, single-embryo transfer and highly sensitive detection techniques to determine the potential application of measuring sHLA-G in culture supernatant.

Synthesis of beta(2)-microglobulin-free, disulphide-linked HLA-G5 homodimers in human placental villous cytotrophoblast cells

Human leucocyte antigen-G (HLA-G) is a natural immunosuppressant produced in human placentas that binds differently to the inhibitory leucocyte immunoglobulin-like receptors LILRB1 (ILT2) and LILRB2 (ILT4) according to its biochemical structure. To predict the binding functions of the HLA-G5 soluble isoform synthesized in placental villous cytotrophoblast (vCTB) cells, we investigated structural features of this protein. Biochemical and immunological studies showed that vCTB cell HLA-G5 heavy (H)-chain proteins are disulphide-bonded homodimers unassociated with beta(2)-microglobulin (beta2m) light-chain proteins. Although comparatively low levels of beta2m messenger RNA (mRNA) were identified by real-time reverse transcription-polymerase chain reaction, immunoprecipitation studies failed to detect beta2m protein even when specific mRNA was doubled by transduction of a lentivirus-beta2m complementary DNA into vCTB cells. No abnormalities were identified in the translational start codon of vCTB cell beta2m mRNA and differentiation into syncytium did not promote beta2m synthesis. The failure of vCTB cells to exhibit beta2m in vitro was paralleled by a lack of detectable beta2m in vCTB cells in vivo. Lack of the beta2m protein could be the result of low levels of beta2m transcripts or of as yet unidentified translational defects. Experiments with recombinant ectodomains of LILRB indicate that beta2m-free HLA-G binds strongly to LILRB2, a receptor that is expressed by macrophages. This potentially immunosuppressive cell type is abundant in the pregnant uterus. Thus, our findings are consistent with the postulate that the natural beta2m-free homodimeric form of HLA-G5 synthesized in primary vCTB cells could comprise a particularly effective tolerogenic molecule at the maternal-fetal interface.

sHLA-G production by human IVF embryos: Can it be measured reliably?

A number of reports have demonstrated that sHLA-G can be detected in the culture medium of human IVF embryos and that levels correlate with the potential of an embryo to implant. This has aroused considerable interest in the IVF field. If sHLA-G can be used as a non-invasive marker of embryo quality, it will facilitate selection of the best embryos to transfer to the mother and thereby increase IVF pregnancy rates. However, there have been concerns about some aspects of these studies, including the sensitivity of the sHLA-G ELISAs used, the IVF culture conditions and the levels of sHLA-G which have been reported. A recent study by Sageshima et al. [J. Reprod. Immunol. 75, 11-22, 2007] attempts to address some of these concerns. However, despite using a sensitive ELISA, they were unable to detect sHLA-G in 111 embryo culture supernatants, or sHLA-G secretion by less than 10,000 sHLA-G transfected cells. They concluded that it is not possible to measure sHLA-G production by human embryos. This study has highlighted technical differences between IVF culture techniques and sHLA-G ELISAs that are currently confounding the system. Further collaboration between the research groups involved is required to establish robust reproducible systems that function identically in all laboratories.

Tolerogenic functions of human leukocyte antigen G: from pregnancy to organ and cell transplantation

Over the past few years, the number of publications concerning the human leukocyte antigen (HLA)-G molecule, its functions, and its pathological implications has greatly increased, largely exceeding those focusing simply on fetal-maternal activity. The role of this molecule in other situations of tolerance such as transplantation, tumor dissemination, or virus infections has also been reported. In this paper, we focus our attention on the relevance of HLA-G in transplantation in the light of recent data associating regulatory T cells and HLA-G, and which provide evidence of the role of HLA-G in improving graft acceptance.

Soluble HLA-G molecules in follicular fluid: A tool for oocyte selection in IVF?

Currently, different approaches are used to select oocytes for in vitro fertilization (IVF) procedures, but they do not assure a significant association with the pregnancy outcome. Since several studies have proposed the expression of HLA-G antigens in early embryos to be a possible marker of elevated implantation rate, we have investigated the presence of soluble HLA-G molecules in 50 follicular fluids (FFs). The results have shown soluble HLA-G antigens (sHLA-G) in 19/50 (38%) FFs. Furthermore, we have related the presence of sHLA-G molecules in FFs to detection of the soluble antigens in culture supernatants of the corresponding fertilized oocyte, evidencing a significant relationship (p=1.3 x 10(-6); Fisher exact p-test). Specific ELISA and Western blot approaches identified both HLA-G5 and soluble HLA-G1 molecules in FFs while immunocytochemical analysis indicated polymorphonuclear-like and granulosa cells as responsible for production of sHLA-G1 and HLA-G5 molecules. In contrast, only sHLA-G1 antigens were detected in culture supernatants of fertilized oocytes. Overall, these results suggest a role for sHLA-G molecules in the ovulatory process and propose the FFs analysis for sHLA-G molecule presence as a useful tool for oocyte selection in IVF.

HLA-G Expression is a Fundamental Prerequisite to Pregnancy

Human leukocyte antigen-G (HLA-G) is thought to play a key role in implantation by controlling trophoblast invasion and maintaining a local immunosuppressive state. The secretion of soluble HLA-G antigens (sHLA-G) by early embryos seems necessary for a successful implantation and could be a marker of increased pregnancy rate following in vitro fertilization. We have reviewed the results obtained during the last years (from 1987 to 2005). They overall confirmed the predictive role of sHLA-G production in pregnancy outcome. Furthermore, we have examined the technical procedures utilized, with a particular attention to the monoclonal antibodies used in the enzyme-linked immunosorbent assay (ELISA) techniques. New functional roles for HLA-G molecules in pregnancy could be suggested by the relationship observed between the presence of sHLA-G antigens in follicular fluids and sHLA-G expression in the corresponding fertilized oocyte. Furthermore, since maternal mRNA is fundamental for protein production in early embryos, the biologic role of the HLA-G 14 base pair polymorphism could be explored.

Graduated Embryo Score and soluble human leukocyte antigen-G expression improve assisted reproductive technology outcomes and suggest a basis for elective single-embryo transfer

OBJECTIVE

To evaluate assisted reproductive technology (ART) outcomes by using Graduated Embryo Score (GES) and soluble human leukocyte antigen-G (sHLA-G) expression to select embryos for transfer on day 3.

DESIGN

Prospective cohort.

SETTING

Private practice.

PATIENT(S)

Women undergoing fresh ART cycles (n = 209).

INTERVENTION(S)

In vitro fertilization using standard protocols. Embryos scoring GES of > or =70 using were selected for transfer on the basis of sHLA-G expression in the culture media on day 2.

MAIN OUTCOME MEASURE(S)

Pregnancy, implantation, and multiple-gestation rates.

RESULT(S)

Ongoing gestations increased with the number of embryos expressing sHLA-G (37%, 42%, 58%, and 56% with 0, 1, 2, or 3 sHLA-G(+), respectively). With at least two sHLA-G(+) embryos, ongoing gestation and implantation rates were higher than those with fewer than two sHLA-G(+). Differences were even higher for women aged < or =37 years. With at least two sHLA-G(+) embryos, the odds ratio (95% confidence interval) was 1.59 (1.51-1.68) for ongoing gestation compared with the case of fewer than two sHLA-G(+). Age was the most important predictor of outcome; the odds ratio (95% confidence interval) was 2.07 (1.98-2.16) for ongoing gestation in women aged < or =37 years with at least two sHLA-G(+) embryos, compared with the case of women aged 38-40 years.

CONCLUSION(S)

Day 3 embryo transfer using GES and sHLA-G improves ART outcomes by increasing predictive accuracy. High twin rates suggest that couples with at least two sHLA-G(+) embryos consider elective single-embryo transfer.

Implication of HLA-G in Human Embryo Implantation

The mechanisms underlying the processes of human embryo implantation and maternal immunotolerance to the fetus remain incompletely understood. Growing evidence indicates that one of the nonclassic human leukocyte antigen (HLA) genes, HLA-G, is expressed selectively on the surface of the extravillous throphoblast and plays an important role in the adaptations of the maternal immune system to pregnancy; however the implication of this molecule in the process of human embryo implantation is also plausible. Therefore the aim of the present article is to review the available literature specifically focused on the possible relationship between HLA-G and human embryo implantation. In particular, studies investigating HLA-G expression on human preimplantation embryos and in the endometrium, as well as its levels in embryo culture supernatants and circulating maternal blood, are discussed.

sHLA-G expression: is it really worth measuring?

HLA-G is believed to play a pivotal role in the immunoprotection of the semiallogenic embryo. Its expression during pre- and early implantation is correlated with the cleavage rate of the embryo. Studies in congenic mice have revealed that mRNA of both the maternal and paternal haplotypes are present in zygotes and in embryos at all stages of development.

Rapid evaluation of soluble HLA-G levels in supernatants of in vitro fertilized embryos

Human leukocyte antigen G (HLA-G) molecules are crucial for the maternal tolerance against the fetus during pregnancy. Thus, the presence of soluble HLA-G (sHLA-G) in embryo cultures is thought to be correlated to a successful pregnancy after assisted reproductive techniques (ART). Here, we established a rapid detection assay based on Luminex technology, which can be integrated into ART proceedings, allowing sHLA-G quantification in sample volumes of only 10 microl within 1.5 hours. Using this method, sHLA-G levels of 526 single-embryo cultures, 47 two-embryo cultures, and 15 three-embryo cultures were analyzed corresponding to 313 ART cycles. In 117 embryo cultures, sHLA-G was detectable. In single-embryo cultures, the sHLA-G levels were positively correlated to embryo quality (p = 0.048, r = 0.20, n = 100). The presence of sHLA-G in embryo cultures was significantly (p < 0.0001) associated with clinical pregnancy after intracytoplasmatic sperm injections (ICSI), especially in couples with male factor infertility, but not after in vitro fertilization (IVF) or in couples with female infertility. Importantly, in sHLA-G negative embryos, the abortion rate was increased threefold (p = 0.04). In conclusion, the results obtained by our novel method support strongly the diagnostic relevance of sHLA-G for predicting pregnancy outcome after ART. The ultimate conditions for this prediction have to be further investigated in a multicenter study.

Polymorphism in the 5′ Upstream Regulatory and 3′ Untranslated Regions of the HLA-G Gene in Relation to Soluble HLA-G and IL-10 Expression

The nonclassical human leukocyte antigen (HLA) class Ib gene HLA-G may be important for the induction and maintenance of immune tolerance between the mother and the semi-allogeneic fetus during pregnancy. Expression of HLA-G can influence cytokine and cytotoxic T-lymphocyte responses. Different HLA-G mRNA isoform expression patterns have been associated with HLA-G polymorphism, especially with a 14-bp insertion deletion polymorphism in the 3' untranslated region (3'UTR) of the HLA-G gene. A significantly high level of interleukin-10 (IL-10) secretion is observed in homozygous +14/+14-bp HLA-G peripheral blood mononuclear cells after lipopolysaccharide (LPS) stimulation. This study finds that polymorphism in the 5' upstream regulatory region (5'URR) of the HLA-G gene may also be implicated in differences in IL-10 secretion. However, this may also be due to linkage disequilibrium with the 14-bp polymorphism. A single-nucleotide polymorphism located -477 bp from the start site of exon 1 had a significant association with IL-10 concentrations but not after correction (p=0.011; pc=0.154). This polymorphism is located next to a heat shock element. Eighteen 5'-URR/3'-UTR HLA-G haplotypes were defined; one common homozygous genotype based on these haplotypes was significantly associated with a high IL-10 level after LPS stimulation compared to certain other genotypes. This study indicates that polymorphism in the 5'-URR of the HLA-G gene may have functional significance, although a new line of investigations is needed to elucidate these findings.

Secretion of soluble HLA-G by day 3 human embryos associated with higher pregnancy and implantation rates: assay of culture media using a new ELISA kit

Identification of chemical markers in human embryo culture media that relate to embryo quality and implantation potential could be an invaluable tool in embryo selection for transfer. Embryonic secretion of soluble human leukocyte antigen G (sHLA-G) has been postulated to be a marker for 'embryonic competence'. This study examines sHLA-G concentrations in day 3 culture media droplets of embryos that were selected for transfer, as well as those being cryopreserved. A total of 712 embryo culture supernatants from 83 patients were assayed. Soluble HLA-G was detected in 306 of the 712 samples tested. In the 58 transfers in which at least one embryo selected for embryo transfer was positive for sHLA-G, the pregnancy rate was 64% (37/58) and the implantation rate per embryo transferred was 38%. In contrast, patients receiving only embryos that were negative for sHLA-G had both a lower pregnancy rate of 36% (9/25; P < 0.05) and a decreased implantation rate (19%; P < 0.05). Expression of sHLA-G was also related to increasing cell stage. Concentration of sHLA-G in embryo culture media was variable and in the low range (3-10 ng/ml). These data suggest an association between implantation potential and embryonic secretion of sHLA-G. The commercial assay kit utilized allowed for same day assessment of sHLA-G secretion. Addition of sHLA-G status to traditional morphological criteria may be useful as a clinical tool for embryo selection.

Differential Expression of Alternatively Spliced Transcripts of HLA-G in Human Preimplantation Embryos and Inner Cell Masses

It has been reported that preimplantation human embryos secrete HLA-G, and the levels may be predictive of their ability to implant. However, it is not known which of the membrane-bound (HLA-G 1-4) and soluble (HLA-G 5-6) alternatively spliced forms are present, nor the developmental stage at which they appear. Therefore, we have investigated HLA-G mRNA isoform expression on single embryos at the two-, four-, six-, and eight-cell, morula, and blastocyst stages. The percentage of embryos expressing each HLA-G isoform mRNA increased with developmental stage, but contrary to expectation, HLA-G5 mRNA was not detected in single two- to eight-cell embryos and was only expressed by 20% of morulae and blastocysts. Similarly, soluble HLA-G6 mRNA was not detected until the blastocyst stage and then in only one-third of embryos. In contrast, labeling with MEM G/9 Ab (specific for HLA-G1 and -G5) was observed in 15 of 20 two- to eight-cell embryos and 5 of 5 blastocysts. This disparity between mRNA and protein may be due to HLA-G protein remaining from maternal oocyte stores produced before embryonic genome activation and brings into question the measurement of soluble HLA-G for clinical evaluation of embryo quality. Although HLA-G is expressed in the preimplantation embryo, later it is primarily expressed in the invasive trophoblast of the placenta rather than the fetus. Therefore, we have investigated whether down-regulation of HLA-G first occurs in the inner cell mass (precursor fetal cells) of the blastocyst and, in support of this concept, have shown the absence HLA-G1 and -G5 protein and mRNA.

HLA-G in human reproduction: aspects of genetics, function and pregnancy complications

The non-classical human leukocyte antigen (HLA) class Ib genes, HLA-E, -G and -F, are located on chromosome 6 in the human major histocompatibility complex (MHC). HLA class Ib antigens resemble the HLA class Ia antigens in many ways, but several major differences have been described. This review will, in particular, discuss HLA-G and its role in human reproduction and in the human MHC. HLA-G seems to be important in the modulation of the maternal immune system during pregnancy and thereby the maternal acceptance of the semiallogenic fetus. Recent findings regarding aspects of HLA-G polymorphism, the possible significance of this polymorphism in respect to HLA-G function and certain complications of pregnancy (such as pre-eclampsia and recurrent spontaneous abortions (RSA)) are discussed together with possible importance to IVF. Finally, aspects of a possible role of HLA-G in organ transplantation and in inflammatory or autoimmune disease, and of HLA-G in an evolutionary context, are also briefly examined.

A novel sandwich ELISA for alpha1 domain based detection of soluble HLA-G heavy chains

The detection of soluble human leukocyte antigen G (HLA-G) has been a technically demanding task for several years now and various enzyme linked immunosorbent assay (ELISA) formats have been designed. However, no ELISA test has been described so far which is able to detect all possible kinds of soluble HLA-G (sHLA-G) molecules that might occur in bio fluids. Here we describe a new ELISA approach able to recognize soluble alpha1 domain containing heavy chains of all HLA-G isoforms. The detection limit is shown to be at about 150 pg soluble recombinant HLA-G1 heavy chain per milliliters. Detectable HLA-G fragments are shown to occur in the supernatants of different HLA-G transfected cell lines and appear to be particularly abundant in supernatant of trophoblast derived choriocarcinoma cell lines. The novel ELISA employs the well characterized HLA-G mAbs 4H84 and MEM-G1 which ensure high HLA-G specificity. A negative control ELISA format, designed against non-existing analytes, has been established to reveal non-specific signal interference.